Symposium Organizers
Kornelius Nielsch University of Hamburg
Anna Fontcuberta i Morral Lab. des Materiaux Semiconducteurs Institut des Materiaux EPFL
Jason K. Holt NanOasis Technologies, Inc.
Carl V. Thompson Massachusetts Institute of Technology
M1: Template Based Synthesis
Session Chairs
Kornelius Nielsch
Francis M. Ross
Monday PM, November 30, 2009
Constitution B (Sheraton)
9:30 AM - M1.1
Size Control of Silicon Nano-Wires by Thermal Oxidation Processes.
Pier Francesco Fazzini 1 , Florence Gloux 2 , Caroline Bonafos 2 , A. Hubert 3 , J. p. Colonna 3 , Thomas Ernst 3 , Thierry Baron 4 , Bassem Salem 4 , Pascal Gentile 5 , Olivier Demichel 5
1 , LAAS-CNRS, Toulouse France, 2 , CEMES-CNRS, Toulouse France, 3 , CEA-LETI, Grenoble France, 4 LTM-CNRS, CEA, Grenoble France, 5 INAC, CEA, Grenoble France
Show AbstractMOS transistors based on Silicon nano-wires (Si NWs) represent an attractive candidate for the development of devices with a gate length below 22 nm. The employ of gate-all-around NW-MOS devices, for example, is an effective way to increase the current density per unit surface while reducing, at the same time, short-channels effects [1,2]. The resulting lower leakages coupled with new NW architectures (like the independent gates nanowire Phi-Fet [3]) open new power reductions perspectives for integrated circuits.In the last years, two main general strategies have been proposed to obtain a high density of ordered NWs: (a) the assembling by liquid-phase transfer of NWs obtained by vapor-liquid-solid (VLS) growth [4] and (b) the patterning of Silicon On Insulator (SOI) wafer by advanced lithography techniques or selective oxidation to obtain suspended or oxide-supported NWs. In all these cases the presence of diameter fluctuations over the whole nano-wires population is a critical issue. A variation of the nano-wire diameter can cause a variation of the electrical properties of a single MOS device and this variation must be kept as small as possible for the integration of NW-MOSFETs on a large scale. Thermal oxidation followed by oxide etch has been recently proven to be an effective tool to reduce nano-wires diameter dispersion [5]. Moreover the oxidation step can be used to reduce the NWs diameter down to sizes not attainable with high-resolution lithography techniques or to remove surface damage coming from etching process steps, in the case of top-down processes.To be able to fully exploit the advantages offered by a thermal oxidation step we have developed a simulation model for Si NWs oxidation kinetics based on a cylindrical diffusion equation and taking into account the viscous flow in the oxide layer and the effects of strain induced by the volume modification due to the Si-> SiO2 reaction at the NW surface. The comparison of the simulation results with Scansion and Transmission Electron Microscopy data obtained on nano-wires fabricated by “top-down” and “bottom-up”(VLS) techniques will show that this model can correctly reproduce the self-limiting oxidation mechanisms experimentally observed during NW oxidation. Moreover, this model will be used to study the variation of size dispersion evolution as a function of the oxidation process (dry or wet), the process thermal budget and the ambient pressure in order to identify the best suited conditions to reduce nano-wires diameter dispersion over the entire population.[1] J.P. Colinge, SOI technology: Materials to VLSI, 3rd ed., Springer, (2004).[2] N. Sing et al., IEEE Electron Device Letters 27/5, 383 (2006).[3] C. Dupre et al. in IEEE International Electron Devices Meeting, p. 749-752 (2008).[4] D. Whang et al., Nano Lett. 3, 1256 (2003).[5] P. F. Fazzini et al., MRS Fall Meeting Boston (2008).
9:45 AM - M1.2
A Novel Family of Silicon Nanowires by the Controlled Manipulation of the Isotopic Content.
Oussama Moutanabbir 1 , Stephan Senz 1 , Ulrich Goesele 1
1 , Max-Planck Institute of Microstructure Physics, Halle (Saale) Germany
Show AbstractSilicon nanowires are powerful nanotechnological building blocks providing a wide spectrum of potential applications. To date, natural silicon (NATSi) is used exclusively in the growth of SiNWs. NATSi is composed of three stable isotopes: 28Si, 29Si, and 30Si with abundances of 92.23%, 4.67%, and 3.10%, respectively. In general, several physical properties of semiconductor crystals can be significantly influenced by their isotopic composition. This is due to the following differences among the isotopes: (1) the atomic mass; (2) the nuclear spin; and (3) the nuclear transmutation induced by the capture of a thermal neutron. Combining the advances in nanofabrication with what can be achieved by stable and enriched isotopes provides a rich playground to explore the origin of some basic size-related properties in nanoscale structures. Here, we present a novel family of metal-catalyzed silicon nanowires obtained by a controlled manipulation of the isotopic composition during the VLS growth. In the growth, we used monoisotopic monosilane precursors 28SiH4, 29SiH4, and 30SiH4 have an isotopic purity of (99.994 ± 0003) %, (99.909 ± 0.019) %, and (99.944 ± 0.010) %, respectively. These precursors were synthesized from SiF4 isotopically enriched in a centrifugal setup. Micro-Raman was employed to study the Si-Si LO phonon (and its behavior under local heating) of individual isotopically controlled nanowire vertically aligned on the substrate. This increase of the complexity by the controlled manipulation of the isotopic composition during the growth creates new opportunities to enhance our theoretical understanding of the fundamental properties of SiNWs and their potential technological applications.
10:00 AM - **M1.3
Template Approaches for Ordered ZnO Nanowire Arrays, Growth Understanding and the Use of Core Shell Structures for Nanotubes.
Margit Zacharias 1
1 IMTEK, TF, University of Freiburg, Freiburg Germany
Show AbstractNanowire based devices require the controlled of nanowires ordered arranged at defined positions. We will show here the use of different template approaches and discuss advantages and disadvantages. Basic ideas for understanding the VS and VLS growth of ZnO nanowire arrays will be presented. We will show how one can change the growth from VS to VLS in a simple way and present the modeling the flow conditions within growth chambers. Core-shell wires will be shown and their transfer into nanotubes by Kirkendall diffusion under limited conditions will be analyzed.
10:30 AM - M1.4
Antimony Chalcogenide Tubes and Wires in Pulsed Growth Modes.
Julien Bachmann 1 2 , Ren Bin Yang 2 , Ulrich Goesele 2 , Kornelius Nielsch 1
1 Institute of Applied Physics, University of Hamburg, Hamburg Germany, 2 , Max Planck Institute of Microstructure Physics, Halle Germany
Show AbstractOriginal approaches are presented to the fabrication of pseudo-one-dimensional objects (wires and tubes) of antimony chalcogenides. They rely on atomic layer deposition (ALD) and its high-temperature extension to a pulsed vapor-liquid-solid (VLS) growth.Our investigations have shown that tris(dimethylamido)antimony offers an entry into the ALD of the V-VI semiconductors. At 120°C already, it reacts oxidatively with ozone to yield Sb2O5, as well as in acid-base fashion with hydrogen sulfide with the formation of Sb2S3. Both depositions show the characteristic self-limited behavior, with growth rates of 0.18 nm per cycle and 0.06 nm per cycle, respectively, as measured by spectroscopic ellipsometry. The stoichiometry and purity of the thin films are quantified by atomic absorption, X-ray spectroscopy, and mass spectroscopy, their roughness by atomic force microscopy. Adequate porous templates allow the experimentalist to create ensembles of nanotubes.At higher temperatures (350°C), the sulfide reaction can be driven in the ALD reactor into a catalytic CVD mode, that is, a pulsed vapor-liquid-solid (VLS) growth that delivers nanowires. Similar conditions are reached with diethyldiselenide for the VLS of Sb2Se3. Both the sulfide and selenide wires are highly crystalline (by X-ray diffraction), stoichiometric and pure.Since both VLS reactions occur at the same temperature, they can be combined for the preparation of segmented wires. Additionally, carrying out a VLS growth followed by ALD growth delivers core-shell structures. We will now focus on investigating the novel physical properties brought about by the presence of interfaces within those heterostructures.
11:15 AM - **M1.5
Confined Growth, Structures, and Energy Applications of TiO2 Nanotube Arrays by Atomic Layer Deposition.
Hyunjung Shin 1
1 School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Show AbstractTubular structures of oxides in nanometer length scale have attracted much attention as one of the most promising one-dimensional (1-D) materials for many applications. Unlike nanowires, the inner surfaces can add more functionalities as well as accessibilities. Several different fabricating methods of nanotubes (NTs) have been proposed and showed not good enough crystalline quality of NTs. In this talk, an example of NT material systems, high crystalline quality of TiO2 NT arrays templating by atomic layer deposition (ALD) onto anodic aluminum oxides (AAO) and subsequent annealing, will be presented. Structural characterization of the resulting materials and applications in photovoltaic cells, and rechargeable lithium ion battery will be discussed. By simply changing the thickness of NT’s wall, the optimum boosting condition of crystallization has been attained. More than half of micronmeter long anatase single grains resembling the physical properties of the original bulk materials in NTs were found, and the most defective form was able to be prepared by pinning the grain growth at the thinnest wall thickness (< 5nm in thickness). The former was utilized in the fabrication of dye-sensitized solar cells, producing reproducible photovoltaic cells exceeding overall photon-to-electricity conversion efficiency of ~4%, and the high efficiency results were ascribed to the minimization of defect sites for electron trapping. The latter was found to be using in Li-ion secondary battery application, resulting in ultra-fast charging capability up to ~2000 C. The achievement is considered to be the presence of rich grain boundary defects which are easily accessible to Li-ions. The present ALD grown TiO2 NTs should hold a position of new materials system at the interface of 1- to 3-D for function-driven novel applications.
11:45 AM - **M1.6
Fabrication of Complex Nanostructures Based on Ordered Porous Alumina.
Lifeng Liu 1 , Eckhard Pippel 1 , Roland Scholz 1 , Ulrich Goesele 1
1 , Max Planck Institute of Microstructure Physics, Halle Germany
Show AbstractAn overview will be given on the fabrication of complex nanostructures based on ordered porous anodic aluminum oxide which can either be used as a template or as a convenient mask. The state of the art of fabricating ordered porous alumina via mild, hard or pulsed anodization including the case of diametermodulated pores will be outlined. After a short discussion of complex polymeric and semiconductor nanostructures the main emphasis of the presentation will be on varius complex metallic nanostructures partly involving dealloying processes of various allos within pores in alumina. Such structures are of potential interest for electrodes in fuel cells.
12:15 PM - M1.7
Fabrication of Sub-10 nm Metallic Wires using Block Copolymer Self-Assembly.
Yeon Sik Jung 1 , Kevin Gotrik 1 , Caroline Ross 1
1 MS&E, MIT, Cambridge, Massachusetts, United States
Show AbstractTemplated self-assembly of block copolymer (BCP) films is becoming an increasingly important method for nanofabrication due to its ability to create regular arrays of 10 - 100 nm scale features. We report a wide range of metallic nanowires that can be formed with diameters less than 10 nm by the self-assembly of cylindrical phase poly(styrene-b-dimethylsiloxane) (PS-PDMS) diblock copolymer [1], which exhibits a large Flory-Huggins interaction parameter (~0.26), and explore the magnetic, structural, and electrical characteristics of the nanowires. We also explore the control that can be obtained over the dimensionality of the wires by changing the environment in which the polymer self-assembles, and discuss new BCP systems that may enable a further decrease in the diameter of nanowires. Trenches (40 nm deep) were patterned on SiO2 substrates using a Lloyd's Mirror interference lithography system (He-Cd laser with 325 nm wavelength) and treated with hydroxy-terminated PDMS homopolymer to form a 3 - 4 nm thick brush layer. BCP films were spun onto the substrate and self-assembly occurred under a variety of solvent vapors for 3 - 25 hours at room temperature. Changing the solvent vapors causes varying amounts of swelling in the different blocks of the polymer, and it can be used to control the resulting size, volume fraction or even the orientation of the cylinders in the trenches. CF4 and O2 reactive ion etching removes the PS block leaving the trenches filled with evenly spaced PDMS cylinders, typically parallel to the trenches. 60 - 70 nm thick metallic films including Ti, W, Co, Ta, Ni, and Pt were sputter coated on top of the substrate and exposed to 450W CF4 plasma. This sputter-etches the metal until the PDMS cylinders are exposed and removed, leaving a reverse image consisting of metallic nanowires. The wire period and diameter are 34 nm and 16 nm respectively when using 45.5 kg/mol PS-PDMS, and 17 nm and 8 nm for 16 kg/mol PS-PDMS. Small angle scattering confirms that the long-range uniformity of the nanowires does not degrade after pattern transfer. Ni nanowires were ferromagnetic and showed a strong in-plane anisotropy. The coercivity parallel and perpendicular to the wires was 470 Oe and 119 Oe compared with 17 Oe for an unpatterned Ni film. For Pt nanowires, conductive AFM was used to measure the electrical properties. The resistance of the nanowires scales linearly with the nanowire length with a resistance per unit length of 110 MΩ/μm. In summary, we have demonstrated that using PS-PDMS block copolymer- assisted pattern transfer can yield in-plane nanowire arrays with <10 nm dimensions and long-range order. The ultimate limit of dimensional control is determined by the degree to which a low-MW BCP can be kinetically trapped into forming useful structures and how well line edge roughness can be controlled during pattern transfer.[1] Y.S. Jung, C.A. Ross, Nano Letters, 5 (2007) 2046-2050
12:30 PM - M1.8
Templated Electrodeposition as a Versatile Tool: Metal and Oxide Nanowires.
Michiel Maas 1 , E. Rodijk 1 , J. ten Elshof 1 , D. Blank 1
1 Inorganic Materials Science, Twente University / MESA+, Enschede Netherlands
Show AbstractA nanowire has unique one-dimensional properties, which makes it an important building block for future nanotechnology based applications in a large variety of disciplines. A reliable, simple and low cost technique to produce nanowires will contribute to this importance. Amongst many, a technique which meets such demands is templated electrodeposition: nanowires are deposited from an electrolyte bath inside straight pores of a commercially available polycarbonate track-etched (PCTE) membrane. The number of materials which can be deposited is increasing, ranging from metals, semiconductors, and oxides.Here, the versatility of templated electrodeposition will be presented. By changing the composition of the electrolyte bath not only nanowires, but also nanotubes can be deposited with preferred crystal orientation. In addition, several metals and oxides can be combined to deposit axially segmented nanowires. These combinations can advance the functionality of a single nanowire dramatically. Typical dimensions of the resulting nanowires/nanotubes are 6 microns in length and 50 – 200 nanometer in diameter. Examples include Ni|Au|ZnO, Ag7NO11 nanowires and Fe2O3, Fe3O4 nanotubes.
12:45 PM - M1.9
Synthesis by Electrodeposition in Ionic Liquid of Highly Luminescent Silicon Nanowires with Controlled Diameters.
Florie Martineau 1 , Michael Molinari 1 , Jeremy Mallet 1 , Michel Troyon 1
1 physics, LMEN-Reims University (URCA), Reims France
Show AbstractSilicon nanowires were fabricated for the first time by electrochemical template synthesis at room temperature. The electrodeposition at room temperature of silicon nanowires (NWs) from the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P1,4) containing SiCl4 as Si source is investigated by cyclic voltammetry. By using nanoporous polycarbonate membranes as templates, we show that it is possible to reproducibly grow pure Silicon NWs with diameters ranging from 15 to 400 nm [1,2]. Structural characterizations were performed by scanning and transmission electron microscopies, infrared absorption measurements, energy dispersive X-Ray, and Raman spectrometries. The as-deposited NWs are composed of pure amorphous silicon. The detailed examination of single NWs gives evidence of their good quality. Their growth morphology as well as their chemical composition was analyzed by scanning transmission electron microscopy (STEM) coupled to electron energy loss spectroscopy (EELS). They are amorphous and have homogeneous cylindrical shape with a roughness of a few nanometers on the wire surface. EELS measurements confirm the purity of electrodeposited Si NWs. The nanowires’ diameters and lengths well match with the initial membrane characteristics and are very homogeneous. Thanks to annealing treatments, it is possible to crystallize the Si nanowires as shown by x-ray diffraction experiments. While the crystalline NWs only emit weakly in the near infrared range, the amorphous NWs strongly emit in the visible range at room temperature. Temperature-dependent and time-dependent photoluminescence (PL) experiments show that this emission is due to the silicon and not to possible oxide defects. Even if the NW diameters are not compatible with a quantum confinement mechanism, the PL wavelength is shifting with the NWs diameters [3]. This behavior could be explained by a spatial confinement mechanism as already observed in other amorphous silicon films of related structures. This innovative and cheap elaboration process using electrodeposition is very promising and could compete with the more expensive and constraining high vacuum techniques. Thanks to their PL properties, the as-deposited amorphous Si NWs could be envisaged for light-emitting devices.[1] Mallet J., Molinari M., Martineau F., Delavoie F., Fricoteaux P., Troyon M., “Growth of Silicon nanowires of controlled diameters by electrodeposition in ionic liquid at room temperature”, Nanoletters 8 (2008) 3468 [2] Al-Salman R., Mallet J., Molinari M, Fricoteaux P., Martineau F., Troyon M., El Abedin S.Z., Endres F., “Template assisted electrodeposition of germanium and silicon nanowires in an ionic liquid”, Physical Chemistry Chemical Physics 10 (2008) 6233[3] Martineau F., Molinari M., Mallet J., Troyon M., “Strong visible photoluminescence of Silicon nanowires prepared by electrochemical template synthesis”, submitted to Applied Physics Letters
M2: Growth Mechanisms and Crystal Structures
Session Chairs
Monday PM, November 30, 2009
Constitution B (Sheraton)
2:30 PM - **M2.1
Control and Understanding of III-V Nanowire Crystal Structure.
Kimberly Dick 1
1 Solid State Physics/Polymer & Materials Chemistry, Lund University, Lund Sweden
Show AbstractIII-V materials exhibit many interesting properties that make them attractive candidates for nanowire applications. However, they typically suffer an uncontrolled intermixing of zinc blende and wurtzite crystal structures, together with high densities of stacking faults and twin planes. These structural changes lead to variations in the optical and electronic properties of the nanowires, and if uncontrolled may be detrimental to the development of applications. Therefore, significant experimental and theoretical efforts are dedicated to controlling III-V nanowire crystal structure.In this presentation I will discuss current developments in the control and understanding of nanowire crystal structure. Most theoretical models indicate that the high surface area of nanowires is responsible for the observed variations in crystal structure – in other words, the side facets stabilize otherwise unstable structures. Nanowires are believed to grow in a layer-by-layer fashion, such that nucleation at the edge determines the structure of each individual layer. Edge energies and nucleation energies will be affected by many accessible parameters, including growth temperature and pressure, precursor molar fraction and V/III ratio, nanowire diameter and surface density, and the presence of impurity atoms. If each of these effects are understood and controlled, structural tuning should be possible.Control of nanowire crystal structure by tuning of various growth parameters will be demonstrated for arsenide, phosphide and antimonide materials. The focus here will be on nanowires grown by metal-organic vapor phase epitaxy using gold seed particles, although comparison with other systems will be discussed. Under appropriate growth conditions it is possible to achieve pure zinc blende or pure wurtzite nanowires, as well as controlled combinations of these structures. The growth results will be interpreted based on the existing theory and models, in order to give a complete overview of the current status of III-V nanowire structure control.
3:00 PM - **M2.2
Wurtzite/Zinc-blende Crystal Domains in Group IV and III-V Nanowires: Implications on the Physical Properties.
Jordi Arbiol 1 2 , Sonia Conesa-Boj 1 , Sonia Estrade 1 , Francesca Peiro 1 , Joan Ramon Morante 1 3
1 Departament d'Electronica, Universitat de Barcelona, Barcelona, CAT, Spain, 2 TEM-MAT, Serveis Cientificotecnics, Universitat de Barcelona, Barcelona, CAT, Spain, 3 , IREC, Catalonia Institute for Energy Research, Barcelona, CAT, Spain
Show AbstractSemiconductor nanowires are potential building blocks in future generations of electronic, optoelectronic, sensor and energy conversion devices. Due to their dimensionality, they are ideal objects to study fundamental quantum mechanical concepts and related phenomena. Many modern semiconductor devices rely on heterostructures such as the high electron mobility and heterobipolar transistors, some types of light-emitting diodes and lasers. This is because the properties of the charge carriers in layers that are part of heterostructures can be quite different from their bulk counterpart. Heterostructures consist of the combination of two materials, with different band gaps and electron affinities. In this way, more complex nanowire structures have been obtained by combining materials coaxially and axially along the growth direction of the nanowires [1,2]. Classically, heterostructures have been formed with chemically different semiconductors (AlGaAs/GaAs, AlGaN/GaN, etc). However, a new type of heterostructure, whose junction is formed by the same material in two crystalline phases has been presented recently and is nowadays a hot topic in materials science. These heterostructures are possible because the bandgap and electron affinity of semiconductors such as GaAs, Si, InP and GaN depend on the crystalline phase [3,4,5,6]. In the bulk state, these materials are stable in the zinc-blende (wurtzite in the case of GaN) structure. When reduced to a nanoscale volume, such as in the form of nanowire, other phases like wurtzite (zinc-blende in the case of GaN) also become stable. In this way, zinc-blende/wurtzite (ZB/WZ) “heterostructures” have become possible, and thus the possibility to obtain new devices.In the present work we fully characterize by means of transmission electron microscopy (TEM) advanced tools the structural, morphological and chemical properties of a wide variety of ZB/WZ heterostructures in group IV and III-V semiconductor nanowires (Si, GaAs and GaN). We will relate the obtained structural and chemical properties of these nanowires with their optoelectronic properties measured by means of spatially resolved photoluminescence (PL). In order to perform the necessary structural and chemical characterization at atomic scale we will use the aberration (Cs) corrected high angular annular dark field (HAADF) in combination with high resolution (HR) electron energy loss spectroscopy (HREELS) to measure compositions and bandgap variations. Those results will be conformed with ab inito simulations and HRTEM, and 3D atomic supercell modeling of the heterostructures.References[1] A. Fontcuberta i Morral et al. Small, 4, 899 (2008)[2] M. Heigoldt et al. J. Mat. Chem, 19, 840 (2009)[3] A. Fontcuberta i Morral et al., submitted, (2009)[4] A. Fontcuberta i Morral et al. Adv. Mat., 19, 1347 (2007)[5] J. Arbiol et al., J. Appl. Phys., 104, 064312 (2008)[6] J. Arbiol et al. Nanotech., 20, 145704 (2009)
3:30 PM - M2.3
Wurtzite to Zinc Blende Phase Transition in GaAs Nanowires Induced by Epitaxial Burying.
Gilles Patriarche 1 , Frank Glas 1 , Maria Tchernycheva 1 , Jean-Christophe Harmand 1 , George Cirlin 2
1 Laboratoire de Photonique et de Nanostructures, CNRS, Marcoussis France, 2 , St. Petersburg Physical Technical Centre of the Russian Academy of Sciences for Research and Education, St. Petersburg Russian Federation
Show AbstractSemiconductor nanowires (NWs) are promising building blocks for future photonic and electronic devices. Many efforts have recently been devoted to their fabrication using epitaxial growth techniques such as metal organic vapor phase epitaxy (MOVPE), chemical beam epitaxy or molecular beam epitaxy (MBE), in presence of a catalyst. Indeed, metal particles deposited on the semiconductor surface can induce unidirectional crystal growth. Nowadays, wires diameters of a few nanometers are achieved and carrier confinement effects have been reported. Gold is the metallic element most commonly used to catalyze the growth of elemental, III-V or II-VI NWs. However, the NWs resulting from such a catalyst-assisted growth very often have a peculiar crystalline structure: although the most stable crystal structure of many III-V and II-VI bulk materials is cubic sphalerite (or zinc blende, ZB), the same compounds often adopt the hexagonal wurtzite (WZ) structure when forming NWs [1]. This phenomenon has been reported for most compounds and growth techniques and several possible explanations have recently been discussed [2]. However, stacking faults (SFs), twin planes and polytypes are frequently observed and it remains very challenging to synthesize NWs of a pure crystalline phase.We have observed and explained how NWs standing vertically on their substrate and having the wurtzite crystalline structure can be buried by epitaxial overgrowth and transformed to the zinc blende structure. We examined the case of GaAs/AlGaAs core/shell NWs initially grown by VLS (Vapor-Liquid-Solid) and then buried by GaAs. The burying process is efficient in a narrow temperature range (630 – 650 °C) where VLS growth is inhibited while 2D growth persists at the substrate surface. The crystalline phase transition of the NWs was found to occur step by step. Each new ML growing by step flow at the ZB substrate surface induces a translation of the emerging part of the NW that it meets, if the corresponding NW ML is out of registry. This translation brings the NW ML in registry with the ZB position of the growing ML. This mechanism is repeated as long as overgrowth proceeds. When the burying layer is fault-free, it suppresses all the SFs pre-existing in the NW. Complete burying results in perfect ZB GaAs NWs with their AlGaAs shells embedded in the overgrown GaAs matrix.
3:45 PM - M2.4
Ordered Stacking Faults in Si Nanowires Lead to New Polytypes.
Francisco Lopez 1 , Eric Hemesath 1 , Lincoln Lauhon 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractPeriodic (111) stacking faults along the [111] direction in cubic crystals lead to polytypes with distinct and potentially useful electronic properties, and polytypes not commonly observed in bulk crystals have been produced in III-V and Si nanowires by catalyst-mediated growth processes. Hexagonal polytypes in Au-catalyzed Si nanowires have been identified based on Raman spectroscopy and electron diffraction evidence, but there are contradicting reports in the literature arising from discrepancies in the interpretation of Raman spectra and diffraction patterns. Furthermore, (111) twin planes parallel to the Si nanowire growth direction have been observed to trap Au atoms,[1] motivating a more detailed investigation of the formation and structure of planar defects. We have correlated single-nanowire Raman spectra with high-resolution transmission electron microscopy (HRTEM) and diffraction data to provide definitive evidence for the existence of polytype inclusions in Si nanowires with diameters as small as 20 nm.[2] Nanowires were grown by the vapor-liquid-solid method using Au catalysts and silane in a CVD reactor. 2H (or diamond-hexagonal silicon) and 9R polytypes were identified by HRTEM, diffraction, and polarization-dependent Raman spectroscopy. Forbidden peaks in the Raman spectra can be explained by Brillouin zone folding and experimental diffraction patterns match simulations with less than 1% error. The polytypes were found in NWs with a <112> growth direction, and thus are more common in small diameter nanowires for the growth conditions used. By studying the polarization-dependent Raman intensities of different vibrational modes, we found that polytypes can be readily distinguished from (i) a disordered array of {111} stacking faults or lamellar twins, also occurring in <112> oriented wires; and (ii) from overlapping twin crystal structures. We will illustrate the potential of Raman spectroscopy to rapidly probe the density, periodicity, orientation and disorder of stacking fault distributions in large numbers of nanowires, as we anticipate that Raman spectroscopy will be valuable in efforts to grow pure polytypes not found in bulk materials. REFERENCES: [1] Allen, J. E.; Hemesath, E. R.; Perea, D. E.; Lensch-Falk, J. L.; Li, Z. Y.; Yin, F.; Gass, M. H.; Wang, P.; Bleloch, A. L.; Palmer, R. E.; Lauhon, L. J. Nature Nanotechnology 2008, 3, 168-173. [2] Lopez, F. J.; Hemesath, E. R.; Lauhon, L. J. Nano Letters 2009 (DOI: 10.1021/nl901315s).
4:30 PM - M2.5
Diameter Dependence of the Wurtzite–Zinc Blende Transition in InAs Nanowires.
Jonas Johansson 1 , Philippe Caroff 2 , Kimberly Dick 1 , Maria Messing 1 , Jessica Bolinsson 1 , Knut Deppert 1 , Lars Samuelson 1
1 Solid State Physics, Lund University, Lund Sweden, 2 Institut d'Electronique de Microélectronique et de Nanotechnologie, University of Lille, Lille France
Show AbstractThe success of semiconductor nanowires in future electronics and optoelectronics applications relies heavily on the degree of atomic level control that can be achieved in their fabrication. One major hurdle to overcome for the technologically important III–V nanowires is their high density of twin defects and stacking faults. In the extreme case and for <111>-oriented nanowires made of materials with zinc blende crystal structure, we often get more or less random inclusions of wurtzite structure. It is of utmost importance to be able to control and predict this polytypism, since controlling the structure means controlling the bandgap, which is necessary for reproducible production of electronic and optoelectronic devices. We have recently demonstrated extraordinary polytypic control of gold seeded InAs nanowires with diameter and growth temperature as control parameters [P. Caroff et al, Nature Nanotech. 4 (2009) 50]. In this presentation, however, we will focus on the cross-over from wurtzite to zinc blende crystal structure as the nanowire diameter is increased.The nanowires were grown by metal-organic vapor phase epitaxy (MOVPE) at 10 kPa, using aerosol fabricated, size-selected gold particles with diameters between 10 and 150 nm as seed particles. Trimethyl indium (TMIn) and arsine were used as precursors. The molar fractions of the precursors were 3×10-6 for TMIn and 4×10-4 for arsine, giving a V/III ratio of 130.When increasing the nanowire diameter, a transition from pure wurtzite (thin wires) to a zinc blende dominated crystal structure (thick wires) is observed. At 420°C, the cross-over diameter for this smooth transition is about 110 nm. At the higher growth temperature of 460°C, the cross-over diameter is significantly smaller, about 80 nm. We explain these results with classical nucleation theory combined with Poissonian statistics. A new monomolecular layer can either nucleate in the ordinary ABC stacking orientation, resulting in zinc blende. Alternatively, it can nucleate in fault orientation, resulting in twinning for an isolated fault plane, or in wurtzite formation for an uninterrupted sequence of fault planes. By comparing the nucleation rates of ordinary and fault planes, we can estimate the fraction of wurtzite as a function of the chemical potential. The strong nanowire diameter dependence is, in turn, handled by including the Gibbs-Thomson effect in the chemical potential. This approach leads to much larger (almost an order of magnitude), and thus more realistic, cross-over diameters than what has previously been theoretically predicted.
4:45 PM - M2.6
The Effect of Gold Particle Type on GaAs Nanowire Growth.
Maria Messing 1 , Karla Hillerich 1 , Jessica Bolinsson 1 , Kristian Nilsson 1 , Kimberly Dick 1 , Jonas Johansson 1 , Knut Deppert 1
1 Solid State Physics, Lund University, Lund Sweden
Show AbstractFor years highly controlled particle-assisted growth of semiconductor nanowires has been performed, still several questions regarding the growth mechanism are under debate. It is well known that gold particles are excellent seeds for nanowires of almost any type of material at a wide range of growth conditions. Nanowire growths from gold particles generated and deposited with various different methods have been reported; however no comparative investigation of the effect of gold particle type on growth have been reported and therefore remains unknown. For that reason it is unclear whether direct comparisons between nanowire growth studies done in similar systems could be performed, when different types of gold particles have been used to seed the growth.In this work we report on the influence of gold particle type on GaAs nanowires grown by Metal Organic Vapor Phase Epitaxy (MOVPE). Aerosol gold particles generated by two different methods, colloidal gold particles deposited in two different ways, electron beam lithography (EBL) defined gold particles and gold particles generated by annealing of thin films were used to achieve a direct comparison between the resulting nanowires. General comparisons induced by the particle preparation method as well as comparisons of the nanowire incubation time, i.e. the time before any growth occurs, nanowire growth rate and nanowire crystal structure between nanowires seeded with the different particle types are reported. A clear difference in incubation time between the particle types could be seen. Nanowires grown from the very pure aerosol generated particles of high crystalline quality needed a much shorter incubation time compared to the nanowires seeded with EBL defined and directly deposited colloidal particles that contains residues from the generation process. No clear variation in final length of the nanowires could be found between nanowires from the various particle types which indicate that the differences in incubation time are too minor to affect the overall growth rate. Furthermore the crystal structure, investigated by high resolution transmission electron microscopy (HRTEM) was very similar between the nanowires seeded from different particle types with the exception of nanowires seeded from particles generated by annealing of thin films. However, we believe that the noticeable difference in crystal structure of these nanowires is due to the much higher surface coverage of nanowires in this case compared to the coverage for the other particle types, since it is virtually impossible to achieve a low surface coverage with this method. This investigation strongly indicates that it should be possible to directly compare nanowire growth results if similar growth systems and growth conditions have been used also when the nanowires have been seeded by different types of gold particles.
5:00 PM - M2.7
Nucleation Mechanisms in Self-Induced GaN Nanowires: What Determines Their Initial Radius?
Vincent Consonni 1 , Matthias Knelangen 1 , Lutz Geelhaar 1 , Achim Trampert 1 , Henning Riechert 1
1 , Paul Drude Institute, Berlin Germany
Show AbstractThe most famous way to induce the formation of nanowires (NWs) is the vapour-liquid-solid mechanism, for which a catalyst, such as gold droplets for instance, acts as a collector for the different species contributing to growth. Very importantly, the position and the initial radius of the catalyst-induced NWs are completely governed by the droplet position and size. Although well-organized periodic arrangements of NWs with homogeneous dimensions can be grown within the catalyst-induced approach, there is an ongoing debate that the NW contamination by the catalyst profoundly limits their structural and optical properties. Increasing efforts have thus been dedicated to the catalyst-free NW growth. In particular, the self-induced approach employed in molecular beam epitaxy (MBE) of GaN NWs has the great advantage to avoid the use of any foreign material. However, to fabricate NWs in this way, it is still unclear what determines their position and initial and final radii. Yet, the understanding of these controlling mechanisms is crucial since it represents the key point to reveal the technological potential of the self-induced approach. In this work, GaN NWs are grown by plasma-assisted MBE on Si(111) substrates with the presence of an AlN buffer layer. We study the nucleation processes occurring during the self-induced growth of GaN NWs, by combining in-situ reflection high-energy diffraction (RHEED) measurements with ex-situ high-resolution transmission electron microscopy (HRTEM) imaging. In particular, we monitor the development of the RHEED intensities related to GaN and AlN as growth proceeds and determine the evolution of the in-plane lattice parameter with high accuracy. Also, dedicated samples are grown at different durations so as to observe the distinct morphologies of GaN islands as well as their associated relaxation mode. We show that the self-induced growth of GaN NWs occurs through the nucleation of dislocation-free coherent islands. These islands develop distinct successive predominant shapes initially differing from the NW morphology, which aim at relieving elastically the lattice-mismatch-induced strain. We further show a strong correlation between the subsequent process of plastic relaxation and the final transition to the NW shape: experimental critical dimensions to form a misfit dislocation have been compared with predicted values given by existing theoretical models. Interestingly, the critical radius required to nucleate a misfit dislocation in the islands determines the initial NW radius. Correlatively, the driving force for the initial formation of self-induced GaN NWs is elucidated by thermodynamic considerations.
5:15 PM - M2.8
Alternative Catalytic Materials for the Growth of Si and Ge Nanowires.
Sonia Conesa-Boj 1 , Sonia Estrade 1 , Ilaria Zardo 2 , Ying Xiang 2 , Pere Roca i Cabarrocas 3 , Linwei Yu 3 , Linyou Cao 4 , Mark Brongersma 4 , Francesca Peiro 1 , Joan Ramon Morante 1 5 , Anna Fontcuberta i Morral 2 6 , Jordi Arbiol 1 7
1 Departament d’Electronica, Universitat de Barcelona, Barcelona, CAT, Spain, 2 Walter Schottky Institut, Technische Universitaet Muenchen, Garching Germany, 3 LPICM, Ecole Polytechnique, Palaiseau France, 4 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States, 5 , IREC, Catalonia Institute for Energy Research, Barcelona, CAT, Spain, 6 Laboratoire des Matériaux Semiconducteurs, Institut des Matériaux, Ecole Polytechnique Fédérale de Lausanne, Lausanne Switzerland, 7 TEM-MAT, Serveis Cientificotecnics, Universitat de Barcelona, Barcelona, CAT, Spain
Show AbstractMany efforts have been made in the last few years in order to avoid gold as a catalytic seed for the growth of semiconductor nanowires (NWs). Gold acts as a deep carrier trap in Si and Ge, which results in a strong suppression of the carrier mobility and decrease in the minority carrier lifetime and thus it is not desirable. As an alternative to gold, several metals have been tried as catalysts seeds for the growth of nanowires. Depending on the growth conditions and material properties different growth regimes can be reached, from vapor-liquid-solid (VLS) to vapor-solid-solid (VSS). In the present work, we show the main structural and morphological properties of the synthesized Si and Ge nanowires when using different catalysts: In, Cu and Ga in the case of Si NWs and In and Bi for the growth of Ge NWs. The morphology, structure and chemical composition of the heterostructures are characterized by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) in bright field, and high angular annular dark-field (HAADF) modes and electron energy loss spectroscopy (EELS). We will correlate the presence of crystal defects and changes in morphology to the growth properties.References:[1] Y. Xiang et al., Nanotechnology 20, 245608 (2009)[2] Y. Xiang et al., Appl. Phys. Lett. 94, 163101 (2009)[3] I. Zardo et al., Nanotechnology, 20, 155602 (2009)[4] A. Fontcuberta i Morral et al. Adv. Mat., 19, 1347 (2007)[5] J. Arbiol et al., J. Appl. Phys., 104, 064312 (2008)[6] J. Arbiol et al., Nanotechnology, 18, 305606 (2007)
5:30 PM - M2.9
Growth Mechanism and Device Applications of In-plane Solid-liquid-solid Si Nanowires.
Linwei Yu 1 , Maher Oudwan 1 , Oumkelthoum Moustapha 1 , Franck Fortuna 2 , Pere Roca i Cabarrocas 1
1 , Laboratoire de Physique des Interfaces et Couches Minces, LPICM, Ecole Polytechnique/CNRS, Palaiseau France, 2 , CSNSM, Univ. Paris-Sud, Bâtiment 108, Orsay Campus 91405, Orsay France
Show AbstractA systematic investigation of the in-plane solid-liquid-solid (IPSLS) growth mechanism for obtaining horizontal Si nanowires (SiNWs) is presented. The IPSLS growth mode [1] can be viewed as a nano-scaled liquid phase epitaxy process, where rolling forward indium drops absorb and transform hydrogenated amorphous silicon (a-Si:H) into crystalline SiNWs. During growth, the moving rate balance condition of the two solid/liquid interfaces, that is, the front a-Si:H/In absorption interface and the rear SiNW/In deposition interface, imposes different deformation states for the catalyst drops with different sizes and causes rich dynamics interplays. This unique feature enables an effective control of the morphology of the produced SiNW. The temperature and size dependence of the growth rate of SiNWs are studied. Interestingly, two distinct growth modes for the SiNWs have been identified: 1) the grounded-growth (GG) mode in which the produced SiNWs are fixed to the substrate; and 2) the suspended growth (SG) mode where the SiNWs are carried by and moved together with the catalyst drops. A comparative study of the SiNWs produced in SG and GG modes provides further insights into the IPSLS mechanism. An analytical kinetic equation model has been established to satisfactorily account for the rich dynamic and the fine corrugation structures observed on the SiNWs. Based on the effective morphology and spatial controls over the IPSLS SiNWs, in-situ growth and fabrication of SiNWs-based TFT devices have been achieved in a reacting-gas-free and low temperature fabrication process. These results provide a new design principle and an important basis for future SiNWs-based nanodevices. [1].Yu, L., et al., 2009 An in-plane solid-liquid-solid growth mode for self-avoiding lateral silicon nanowires. Phys. Rev. Lett., 102, 4.
5:45 PM - M2.10
Synthesis and Properties of VO2 Nanowires as Advanced Catalysts and Sensors.
Jeong Min Baik 4 , Myung Hwa Kim 1 , Cafer T. Yavuz 1 , Sungsik Lee 2 , Byeongdu Lee 3 , Christopher Larson 1 , Galen D. Stucky 1 , Alec M. Wodtke 1 , Martin Moskovits 1
4 School of Advanced Materials and Systems Engineering, Kumoh National Institute of Technology, Gumi Gyungbuk Korea (the Republic of), 1 Chemistry and Biochemistry, University of Santa Barbara, Santa Barbara, California, United States, 2 Chemical Science and Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 X-ray Science Division, Advanced Photonic Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractOne-dimensional metal-oxide semiconductors are currently the subject of intense research both in order to discover fundamental sciences as well as for their wide applications at the nanoscale. Of all, vanadium dioxide (VO2) is an interesting material on account of its easily accessible and sharp Mott metal-insulator transition (MIT) at ~ 68 oC in the bulk, which is of great interest in sensing and catalytic applications. In this Paper, we describe the synthesis and properties of VO2 nanowires as novel catalytic and gas sensor materials. High yields of single crystalline VO2 nanowires are synthesized by atmospheric-pressure, physical vapor deposition. Palladium-decorated VO2 nanowire sensors show extraordinary sensitivity towards hydrogen. This comes about as a result of the rapid dissociation of the diatomic hydrogen on the Palladium nanoparticles followed by the migration of the atomic hydrogen over the surface of the VO2 nanowire and its diffusion into the vanadia lattice, causing a significant downward shift in the Mott transition temperature. By biasing the nanowire judiciously so that its temperature is just below the Mott transition temperature, even trace amounts of hydrogen induce the Mott transition, producing an almost 3 order-of-magnitude increase in the current through the nanowire. Methanol oxidation by vanadium oxides is also studied, hence, serves as a good measure for catalytic activity. Highly ordered arrays of VO2 nanowires grown on r-cut sapphire prove to be unique for the in situ catalytic activity tests. Here, we present size and morphology dependent activity of Platinum-coated VO2 nanowires in methanol oxidation reactions.
Symposium Organizers
Kornelius Nielsch University of Hamburg
Anna Fontcuberta i Morral Lab. des Materiaux Semiconducteurs Institut des Materiaux EPFL
Jason K. Holt NanOasis Technologies, Inc.
Carl V. Thompson Massachusetts Institute of Technology
M7: Latest Progress in Growth Mechanisms and Methods
Session Chairs
Wednesday AM, December 02, 2009
Constitution B (Sheraton)
9:15 AM - M7.1
One-Step Synthesis of Ge-SiO2 Core-Shell Nanowires.
Peter Sutter 1 , Fernando Camino 1 , Eli Sutter 1
1 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractThe continued trend toward aggressive reduction of device feature sizes requires consideration of alternative materials and geometries for electronic devices. Semiconductor nanowires (NWs), self-assembled nanostructures that can be prepared in high-yield processes [1] could become the basis for alternative device architectures. A key concern toward NW electronics, however, is developing important device components, such as gate dielectrics and contacts. Optimal gate coupling and reduced power consumption in NW-FETs would be achieved by cylindrical gate dielectrics with wrap-around gate electrodes, but such geometries pose significant fabrication challenges.Moreover to minimize the extent and complexity of any post-growth device processing the gate dielectrics and contacts should ideally be formed during growth. Here we demonstrate a one-step growth process that yields single-crystalline Ge NWs encapsulated in dielectric SiO2 shells, which can serve as high-quality gate oxides [2]. We discuss the mechanisms of formation of the semiconductor-insulator core-shell NWs during thermal evaporation at moderate temperatures in the presence of oxygen. We show first electrical measurements of p-type Ge FET devices with cylindrical SiO2 gate that demonstrate efficient gate control and hole mobilities of 20 cm2/Vs.[1] E. Sutter, B. Ozturk, and P. Sutter, Nanotechnol. 19, 435607 (2008).[2] E. Sutter, F. Camino, and P. Sutter, Appl. Phys. Lett. 94, 083109 (2009).
9:30 AM - M7.2
Formation of Compositionally Abrupt Axial Heterojunctions in Si/Ge Nanowires Using Al-Au Alloy Catalysts and the Vapor-Solid-Solid Method.
Cheng-Yen Wen 1 , Mark Reuter 2 , John Bruley 2 , Jerry Tersoff 2 , Suneel Kodambaka 3 , Eric Stach 1 , Frances Ross 2
1 School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 2 , IBM T. J. Watson Research Center, Yorktown Heights, New York, United States, 3 Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California, United States
Show AbstractSynthetic control of junction structures in self-assembled semiconductor nanowires has received increasing interest for applications in electronic, optoelectronic and thermoelectric devices. It has proven difficult to produce compositionally abrupt interfaces in VLS-grown group IV semiconductor nanowires due to a fundamental constraint: a semiconductor material in the liquid catalyst can not be efficiently depleted before growth of the second material. The composition is therefore graded across the interface over a distance that scales with wire diameter. Here we present the formation of abrupt and defect-free interfaces in Si/Ge axial heterostructures using Al-Au alloy catalysts and the VSS growth method. The growth experiment is conducted in an UHV-TEM. We first grow Si nanowires using the VLS method and then switch to the VSS mode for growth of the junction structures. Through in-situ observations, we find that the solid Al-Au catalyst suits both Si and Ge growth and kinetic measurements are consistent with low solubility of Si and Ge in the solid catalyst. These properties reduce the inter-mixing problem upon switching the gas reactant in the growth of the heterostructures, and, therefore, allow us to form Si/Ge and Si/SiGe interfaces with a width of less than 2 nm as well as thin Ge quantum dots in Si nanowires. These abrupt interfaces lead to strong strain gradients in the wires and we further study the strain distribution near the Si/Ge interface using the geometrical phase analysis method and discuss its effect on the electronic properties.
9:45 AM - M7.3
Time Dependence of Au-free InAs Nanowire Growth.
Bernhard Mandl 2 1 , Martin Huber 3 , Julian Stangl 1 , Guenther Bauer 1 , Knut Deppert 2 , Lars Samuelson 2
2 Solid State Physics, Lunds University, Lund Sweden, 1 Semiconductor and Solid State Physics, Johannes Kepler University Linz, Linz Austria, 3 Center for Computational Engineering Science (CCES), RWTH Aachen, Aachen Germany
Show AbstractLattice mismatch and defects at boundaries between different semiconductor are limiting factors hindering the fabrication of otherwise extremely appealing heterostructures. It seems that nanowires provide a way to circumvent many of those problems due to the small contact area between substrate and wire, which leads to almost defect-free structures even if the interface region itself may contain some defects. This makes some material combinations possible, which have long been desired but very difficult to produce, like III-V on top of silicon. One such example is the growth of InAs nanowires, which are - like many other nanowire materials - usually grown in a vapor-liquid-solid growth mode with Au seed particles. InAs is of high interest to the electronic industry due to its low effective electron mass. However, in the case of growth on Si, gold is rather unwanted since it acts as a deep trap in Si, and it is crucial to develop other growth schemes without Au seed particles. We have previously achieved the controlled Au-free growth of InAs nanowires on Si, as well as on III-V substrates, using SiOx or organic layers to "nucleate" wire growth. [1,2] Further postion controlled growth of InAs on Si has also been demonstrated in the literature. [3] However, in contrast to Au-nucleated nanowire growth, so far only little is known about the details of this Au-free growth mechanism. The wires grown by this method exhibit several interesting differences to Au-nucleated InAs nanowires: wires grow continuously in length and diameter, with a rate depending on the detailed growth parameters. But strikingly the wires do not exhibit any tapering from bottom to top, even though their diameter constantly grows. The goal of this work is therefore to investigate and model the time dependence of length and diameter growth, and from this model to provide an interpretation of the physical mechanisms active during nanowire growth. To do so, we used InAs wires grown on InP (111) B substrates as a model system. We developed a diffusion model, describing the material transport from the adsorbed gas phase to the wire, and the material incorporation at different locations along the wire, especially at the wire top and the wire side facets. Using different assumptions on how this incorporation takes place, we are finally able to determine the mechanisms at work, describe the nanowire growth in detail, and explain the experimentally observer dependencies of growth rates on the growth parameters. [1] B. Mandl et al., Nano Lett., 2006, 6 (8), 1817 - 1821[2] T. Martensson et al., Advanced Materials, 2007, 19 (14), 1801 - 1806[3] K. Tomioka et al., Nano Lett., 2008, 8 (10), 3475 - 3480
10:00 AM - M7.4
Fast, Easy, Cost Efficient Fabrication of Patterned Nanowires Based on a Reusable Ultrananocrystalline Diamond Film Platform.
Daniel Dissing 1 , David Seley 1 , Anirudha Sumant 2 , Ralu Divan 2 , Christina Miller 2 , Orlando Auciello 2 3 , Eric Terrell 1 , Mike Zach 1
1 Chemistry, UWSP, Stevens Point, Wisconsin, United States, 2 Center for Nanoscale Materials , Argonne National Laboratory, Argonne, Illinois, United States, 3 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractA new method for creating large numbers of patterned nanowires of metals and semiconducting materials, using a non-sacrificial template has been demonstrated. The template consists of alternating layers of highly conductive nitrogen doped ultrananocrystalline diamond (N-UNCD) and highly resistive undoped ultrananocrystalline diamond (U-UNCD) layers grown on appropriate substrates. Each conductive N-UNCD layer is isolated from the electroplating solution, used to grow the nanowires, by the resistive U-UNCD layers and is exposed only at edges of holes or trenches produced by reactive ion etching of the U-UNCD/N-UNCD layered heterostructure. Electrodeposition occurs on the N-UNCD edge of the hole or trench patterns rather than on the flat surface of the substrate exposed at the bottom of the patterned trenches or holes, which is common in more conventional patterned platforms for growth of nanowires. To visualize this structure, think of a typical two-layer cake. The exposed edge of N-UNCD between two U-UNCD layers is similar to the edge of a layer of frosting found between two layers of cake. That center layer of frosting is exposed only where the multiple layers are cut. The N-UNCD layer is tens to hundreds of nanometers in thickness, thus forming a very thin electrode. That thickness limits the minimum achievable diameter of nanowires. Longer electrochemical deposition times on the same N-UNCD layer edge yields thicker wires. Because of low work of adhesion to the UNCD surface, the patterned nanowires can be lifted off without damage to the surface by applying a polymer coating to which the nanowires are transferred upon peeling the polymer away from the UNCD surface. The polymer-based peeling off of nanowires actually helps to restore the surface of the N-UNCD edge electrode to a pristine state which enables duplicate sets of nanowires to be synthesized outside of a clean room environment. Because the template is not sacrificial, the manufacturing cycle for making duplicate sets of nanowires is shortened to minutes, as compared to the many hours or days needed for serial methods currently used for making complex patterned nanowires, such as electron beam lithography or dip-pen lithography. Manufacturing duplicate sets of nanowires can be done in a two-step process similar to using a rubber stamp and ink to produce duplicate information. Instead of “ink and stamp,” the steps are electroplating and removal. We demonstrate electrodeposition of nanowires of various metals and semiconducting materials such as Pb, Au, Cu, Ni, Pd, Pt, Co, Te, CdTe, and CdS. The repeatable simple nanowire fabrication technique described here provides a low cost alternative to the serial nanomanufacturing processes for producing nanowires of many materials. This opens the way for large scale manufacturing of nanowires for many technological applications.
10:15 AM - M7.5
Top-to-bottom Approach to Produce Extremely Long Semiconducting Nano-ribbons and Nano-wires.
Mehmet Bayindir 1 2 , Mecit Yaman 1
1 UNAM, Bilkent University, Ankara Turkey, 2 Department of Physics, Bilkent University, Ankara Turkey
Show AbstractNano-wires and nano-fibers are 1-D materials with nanoscale cross sections that span extensive lengths in the other dimension. These unique structures can be produced using bottom-up approaches such as chemical vapor deposition, electrochemical methods or electron beam lithography yielding structures that are no more than few micrometers long and are either randomly distributed on substrates or loosely aligned normal to substrate plane. For many applications, however, these nano building blocks required to be properly aligned, positioned and integrated in order to exploit their unique properties. Inexpensive fabrication of ordered nanowires arrays at high production rates, with simultaneous control of diameter, length, position and orientation does not exist. In this paper we report a simple top-to-bottom production method to obtain kilometer long, ordered, semiconducting thin films, nano-ribbons and nano-wires with uniform diameter, homogenous distribution, and endlessly parallel orientation. Recently, composite fibers incorporating semiconducting, insulating and metallic materials are successfully co-drawn using the same drawing process, opening an altogether new research area in smart fibers [1-4]. In a similar way, we have produced uniform semiconducting nanowires using a multiple step fiber drawing process. The process involves thermal drawing of a macroscopic preform composed of a cylindrical shaped glassy semiconducting rod inside a close fitting hollow polymer mold. The materials are selected so that the thermoelastic properties of the glassy material are compatible with the polymer preform. Simultaneous control of diameter, length, position and orientation is easily achieved with a computer controlled fiber drawing tower. Semiconducting bundle of wires are drawn at ~5 mm/sec draw rate. The wire diameter can be scaled from 20 nm to 20 μm. It is possible to produce insulating and metallic wires or their more exotic combinations to mass produce functional nano materials. Composite fiber drawing seems to be a promising economical way of making extremely long nano-fibres and nano-ribbons using a variety of materials provided that the all materials can be simultaneously drawn. Nano-wires and nano-ribbons are already expected to find applications in many areas including microelectronics, composite materials, biological and chemical sensing and separation. When produced in extensive lengths these they can also find applications in large-area applications such as photovoltaics, thermoelectric applications, bioengineering such as scaffolding for tissue growth in wounds. Also the development of a robust method for integrating bundles of nano-ribbons and nano-wires in flexible plastics could enable exciting avenues in fundamental research and novel applications in nanotechnology. [1] M. Bayindir, et. al. Nature 431, 826 (2004); [2] Adv. Mat. 18, 845 (2006); [3] Nature. Mat. 4, 820 (2005); [4] IEEE J. Quantum Electron 12, 1212 (2006).
10:30 AM - **M7.6
Step Flow Kinetics during VSS Si and Ge Nanowire Growth.
Frances Ross 1 , Cheng-Yen Wen 2 , Jerry Tersoff 1 , Mark Reuter 1 , Eric Stach 2
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States, 2 School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractThe use of solid catalysts to grow group IV nanowires offers a significant advantage compared to the use of liquid catalyst droplets: solid catalysts enable the formation of compositionally abrupt interfaces within nanowires, potentially allowing applications such as tunnel field effect transistors and thermoelectric devices. It has been suggested that abrupt interfaces can form because solid catalysts have a lower solubility for the growth species, reducing the “switching time” when changing from one gas phase material source to another. In order to test this hypothesis, we examined the kinetics of group IV nanowires grown using several solid catalysts. Wire growth took place in situ in a UHV transmission electron microscope capable of delivering disilane and digermane chemical vapour deposition precursor gases to a heated specimen while it remains under observation. Si(111) substrates were used, on which Au2Al alloy catalysts were formed by depositing the elements sequentially, and Cu3Si catalysts were formed by annealing deposited Cu. Wire growth kinetics and catalyst structure were then recorded directly during growth. For both catalysts, growth movies clearly show ledge nucleation and propagation at the catalyst/wire interface, allowing us to measure the nucleation rate, incubation time, or time between completing one ledge and nucleating the next, and propagation speed. We find step flow kinetics that are strikingly different from those we see in growth from liquid AuSi catalysts, particularly with respect to the incubation time and propagation speed. By comparing with the predictions of a model, we will show that the ledge propagation kinetics are consistent with a low solubility of Si in the solid catalyst, compared to the solubility in liquid Au eutectic droplets. In agreement with this conclusion, we have used Au2Al catalysts to grow Si/Ge and Si/SiGe interfaces that are compositionally abrupt. We will discuss the practical implications of these results in designing novel electronic devices using Si/SiGe and Si/Ge/Si structures with abrupt interfaces.
M8: Properties
Session Chairs
Wednesday PM, December 02, 2009
Constitution B (Sheraton)
11:30 AM - **M8.1
Functional Imaging of Nanowires.
Lincoln Lauhon 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractNanowires are nanoscale in two dimensions and microscale in a third dimension, providing a wealth of opportunities to exploit novel nanoscale electronic, optical, magnetic, and thermal properties in devices with well-defined microscale electrical contacts. An attendant challenge is the establishment of quantitative structure-property relationships that enable rational engineering of new and/or superior function. In semiconductors, the dopant concentration determines the carrier concentration, so correlated studies of dopant distribution and local conductivity are important when intentional or unintentional inhomogeneities are present. In materials that undergo phase-changes near room temperature, such as vanadium oxide (VO2), the crystal structure determines the conductivity, so local mapping of domains is important to understanding and controlling switching behaviors. Doping in VO2 can also be used to control the phase transition temperature. The talk will describe the functional imaging of nanowires, that is, the correlation of local structure and electronic properties with the characteristics of devices by integrating scanning probe techniques with electrical transport measurements. We have used atom probe tomography to map the distribution of dopant atoms in Si and Ge nanowires [1,2], and we have used scanning photocurrent microscopy to correlate non-uniform dopant distributions with device characteristics [2]. We find that surface doping can play a useful role in the fabrication of improved nanowire transistors [3]. In VO2 nanowires, we have used temperature-dependent Raman spectroscopy to map structural domains in devices under test, revealing the key role of the Mott insulator M2 phase in the metal-insulator transition of clamped devices. We also find that charge injection can induce an electronic phase transition even in the absence of a structural phase transformation, i.e., we observe metallic monoclinic phases. These findings are particularly relevant to the development of the Mott field-effect transistor. References: [1] Perea, Hemesath, et al, Nature Nanotech. 4, 315 (2009); [2] Allen et al, Adv. Mater., DOI:10.1002/adma.200803865; [3] Allen et al, Nano Lett. 9, 1903 (2009).
12:00 PM - M8.2
Silicon Nanowires: Functionality at the Nanoscale.
Massimo Mongillo 1 , Georgios Katsaros 1 , Panayotis Spathis 1 , Pascal Gentile 2 , Celine Mouchet 3 , Emmanuelle Rouviere 3 , Silvano de Franceschi 1
1 Laboratoire de Transport Electronique, Quantique et Supraconductivité (LaTEQS), Commissariat à l'Énergie Atomique (CEA) , Grenoble France, 2 Service de Physique des Matériaux et Microstructures, Commissariat à l'Énergie Atomique (CEA) , Grenoble France, 3 Laboratoire d’Innovation pour les Technologies des Energies nouvelles et les Nanomatériaux, Commissariat à l'Énergie Atomique (CEA) , Grenoble France
Show AbstractSemiconductor nanowires have attracted wide interest during the last few years owing to their exciting properties associated with their low dimensional character. Furthermore, they are receiving attention in view of their potential for future functional nanodevices such as high-performance FETs, nanoscale photodetectors, sensors, logic circuits.A key step in the fabrication of nanowire-based devices is to obtain an efficient carrier injection into the nanowire which is hindered by the unavoidable presence of a Schottky barrier at the metal-semiconductor interface. A common approach to obtain sufficiently transparent contacts is to heavily dope the semiconductor in proximity to the metal contact. We are currently investigating an alternative approach based on the use of local electric fields acting independently on the source and drain Schottky barrier contacts.Here we present our studies on the transport properties of silicon nanowires grown from catalytic gold nanoparticles. The silicon nanowires are contacted by means of e-beam lithography followed by nickel deposition and lift-off. Through a thermal annealing process we form a nickel silicide metallic phase protruding into the nanowire from each metal contact. A pair of split gates are defined in correspondence of the two silicon-silicide interfaces in a gate-all-around geometry. These gates can independently modulate the Schottky barriers of the source and drain contacts. This offers the possibility to embed different functionalities in a single device, which can act as a bipolar field-effect transistor, a p-n junction or a Schottky diode.
12:15 PM - M8.3
Crystalline Phase Variation, Doping and Phonon Confinement Effects in Nanowires Observed by Spatially Resolved Raman Spectroscopy.
Ilaria Zardo 1 , Bernt Ketterer 2 , Sonia Conesa-Boj 3 , Emanuele Uccelli 1 2 , Francesca Peiro 3 , Ying Xiang 1 , Joan Ramon Morante 3 4 , Jordi Arbiol 3 , Anna Fontcuberta i Morral 1 2
1 Walter Schottky Institut, Technische Universität München, Garching Germany, 2 Institut des Matériaux, Ecole Polytechnique Fédérale de Lausanne, Lausanne Switzerland, 3 Departament d’Electrònica, Universitat de Barcelona, Barcelona, CAT, Spain, 4 , Institut Catala d'Energia, Barcelona, CAT, Spain
Show AbstractSemiconductor nanowires will play an important role in several areas of nanotechnology, such as electronics, sensing and energy conversion. The functional properties of nanowires are influenced by different factors, the structure being one of the most determining. On the one hand, the structure of nanowires is usually characterized by High Resolution Transmission Electron Microscopy, with which it is difficult to achieve a good statistic analysis on a high number of nanowires. On the other hand, techniques such as X-Ray diffraction give structural information on a large ensemble of nanowires, without enabling the study of structural variations along or within the nanowires. Spatially resolved Raman spectroscopy is a non-destructive technique used for the structural characterization of materials, which enables to determine the crystalline phase, presence of strain. Furthermore, spatially resolved Raman spectroscopy gives information on a single nanowire, making the analysis on a large number of samples possible in a reasonable amount of timeIn this work, the structural properties of germanium and gallium arsenide nanowires have been studied. The structural homogeneity and doping of the nanowires is studied by spatially resolved Raman spectroscopy, and the obtained results are compared with Transmission Electron Microscopy measurements. We find that the germanium nanowires are formed by a core–shell structure. The crystalline core has a diameter which varies along the nanowire, from 30 down to few nanometers, while the shell consists of amorphous Ge. The small size of the crystalline core gives rise to phonon confinement effects. GaAs nanowires presenting a mixture of zinc-blende and wurtzite structure are also studied. There, the Raman selection rules are determined and strain related effects underlined. This work shows that Raman spectroscopy of individual nanowire is a powerful technique for revealing the structural homogeneity of nanostructures such as nanowires.
12:30 PM - M8.4
Superelastic Perfect Crystal Au Nanowires.
Bongsoo Kim 1 , Youngdong Yoo 1 , Jong Hyun Seo 2 , Sol Han 1 , Hyun You Kim 3 , Sang Won Yoon 2 , Da Hye Kim 3 , Hyuck Mo Lee 3 , Jae Pyung Ahn 2
1 Chemistry, KAIST, Daejeon Korea (the Republic of), 2 Advanced Analysis Center, KIST, Seoul Korea (the Republic of), 3 Materials Science and Engineering, KAIST, Daejeon Korea (the Republic of)
Show AbstractNanowires show superb structural versatility and unique physicochemical properties. In order to fabricate advanced three-dimensional nanowire devices, aligning the nanowires in a specific orientation at selected locations of a substrate is critically important. Here we show that by forming well-oriented seed crystals on a substrate, we can grow perfect crystal Au nanowires in a selected direction. Analysis of the correlations of the geometry and orientation of seed crystals with those of as-grown nanowires reveals that vertical nanowires grow epitaxially from half-octahedral seeds.Superelastic behavior has been observed for the perfect crystal Au nanowires. The nanowires elastically recover its shape after extremely excessive bending by in situ manipulation using a nanoprobe. This exceptional mechanical property is believed to originate from perfect crystallinity of nanowires. The elastic recovery of the nanowire after extremely large deformation makes it a potential structure for nanoscale elastic energy storage.
12:45 PM - M8.5
Ion Beam Modification of Structural Properties of Epitaxial Si and Ge Nanowires Obtained by Electron Beam Evaporation.
Alessia Irrera 1 , Emanuele Francesco Pecora 1 2 , Lucia Romano 1 2 , Francesco Priolo 1 2
1 , MATIS CNR-INFM, Catania, Ct, Italy, 2 Dipartimento di fisica e astronomia, Università di Catania, Catania, Catania, Italy
Show AbstractSemiconductor nanowires NWs are attracting a huge interest for potential applications as novel devices, sensors and solar cells. We report the possibility to control structural features such as length, density and orientation of Si and Ge NWs grown by electron beam evaporation (EBE). EBE is a very simple and cheap technique, still unexploited for the growth of nanostructures, having an high throughput so to have easy industrial applications. We demonstrate the growth of epitaxial NWs and the ability to design and control which is the prevailing NWs orientation in the samples. Similarities and differences in the case of Si and Ge growth are discussed. The microscopic mechanisms of growth are also investigated.The NWs doping is still a challenging issue. It is a fundamental step before a full control of their properties; nevertheless the approaches reported in literature (as in-situ doping) are not satisfying. In fact a segregation of dopants in the NWs shell is often reported, and the active dopant concentration can hardly be determined. In the last period, some papers reported about ion implantation as the doping technique, but the effects of ion irradiation on nanowires are completely unknown. This is a very important issue because ion implantation is the most used technique to dope planar layers; it allows a precise control of the dopant concentration and position so to have a full control of the active region of the devices. Similar results could be in principle achieved in Si NWs, but a comprehension of the microscopic mechanisms of the energy loss effects on the structural properties of NWs is required.We performed a very detailed study by implanting Ge ions on the NWs obtained by EBE. We varied ions energy and fluence and we investigated the structural effects on NWs having different orientations. We observed a clear bending of a portion of the NWs in a opposite direction to the beam strongly depending on the implanted fluence. In fact the NWs curvature increases linearly with the implanted fluence. On the contrary, the unaffected fraction is not depending on this parameter. We changed the beam energy so to modify the damaged region in the NWs. Scanning electron microscopy and transmission electron microscopy images allow us to propose a bending mechanism related to the amorphization of the NWs. Finally, the possibility to recover the ion beam damage through thermal treatments is explored.
M9: Electrical Properties and Doping
Session Chairs
Wednesday PM, December 02, 2009
Constitution B (Sheraton)
2:30 PM - **M9.1
Understanding Growth and Doping in Group IV Semiconductor Nanowires.
Eli Sutter 1 , Peter Sutter 1
1 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractSemiconductor nanowires (NWs), self-assembled nanostructures that can be prepared in high-yield processes [1] based on vapor-liquid-solid (VLS) growth, could become the basis for novel electronic device architectures that avoid complex top-down processing. The successful realization of practical devices requires a fundamental understanding of NW growth and doping.Central to the VLS growth process is a liquid metal-semiconductor alloy seed drop whose equilibrium with the adjacent NW governs important aspects of the growth. For example, for a fixed amount of metal the equilibrium composition of the binary alloy defines the size of the seed drop, which in turn controls the diameter of the NW. Given the small size of the alloy drop, typically few tens of nanometers, the known binary bulk phase diagrams cannot provide a reliable basis for predicting such growth phenomena. Hence, we have developed in-situ microscopy techniques to establish the nanoscale phase diagrams of alloy seed drops used in VLS NW growth. Variable-temperature transmission electron microscopy on individual Au-Ge alloy seeds at the tips of Ge NWs was used to measure key features of the phase diagram of the nanoscale alloy [2]. To illustrate the predictive power resulting from knowledge of the true phase diagram of the nanoscale VLS seed drop, we demonstrate control over the local, position-dependent diameter of the growing NW.The phase behavior of the VLS seed will also be key to developing strategies for doping of NWs. To ensure homogeneous doping of the growing NW, rather than conformal deposition of a doped shell around it, the preferred incorporation of dopant is via the VLS drop. We demonstrate successful in-situ Sb-doping of Ge NWs during their synthesis by thermal evaporation at moderate temperatures using Ge and Sb powders [3]. We use our in-situ microscopy method to identify the mechanisms of doping during NW growth. We study the phase behavior of the catalyst alloy drops, which now include a dopant species in addition to the metal and semiconductor, and show that dopants are incorporated in the growing NW via the ternary alloy VLS drops.[1] E. Sutter, B. Ozturk, and P. Sutter, Nanotechnol. 19, 435607 (2008).[2] E. Sutter and P. Sutter, Nano Lett. 8, 411 (2008).[3] E. Sutter and P. Sutter, submitted.
3:00 PM - M9.2
Model of Nanowire Doping by the VLS Mechanism and Determination of the Partition Coefficient.
Edwin Schwalbach 1 , Daniel Perea 1 , Eric Hemesath 1 , Peter Voorhees 1 , Lincoln Lauhon 1
1 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractControlled doping of semiconductor nanowires (NWs) is necessary for the fabrication of functional NW devices. Recent progress has been made to directly synthesize doped NWs using the vapor-liquid-solid (VLS) technique, however a fundamental understanding of dopant incorporation via the liquid catalyst has been lacking. We have developed a model to describe steady-state NW growth that includes dopant and catalyst incorporation [1]. Through the local equilibrium approximation, the model predicts that the relative flux of dopant and semiconductor atoms through the liquid dictates the incorporation and concentration of both dopant and catalyst atoms in the solid. Changes in the dopant flux induce changes in the composition of the liquid droplet, thus the composition-dependent liquid chemical potentials are also functions of the dopant flux. This is significant because, for some semiconductor vapor-phase precursors, the liquid chemical potential could influence the kinetics of decomposition at the liquid-vapor interface, thereby affecting the growth rate of the NW. We also develop analytical expressions for the relevant phase boundaries in the dilute dopant limit for a general ternary semiconductor-catalyst-dopant system. In support of the model, atom probe tomography was used to measure changes in P and B dopant concentration in Si and Ge nanowires as a function of dopant precursor flux. Spatial variations in dopant concentration were used to determine the dopant partition coefficient and infer the dopant concentration in a ternary liquid droplet during steady-state growth. This combination of model and experiment provides insight into doping of semiconductor NWs that will enable increased control of the doping process and the resulting NW properties. [1] D. E. Perea, E. R. Hemesath, E. J. Schwalbach, J. L. Lensch-Falk, P. W. Voorhees, and L. J. Lauhon, Nature Nanotechnology 4, 315 (2009).
3:15 PM - M9.3
Effect of Growth Conditions and Metal-organic Precursor Selection on InAs Nanowire Resistivity.
Claes Thelander 1 , Kimberly Dick 1 , Linus Froberg 1 , Magnus Borgstrom 1 , Philippe Caroff 2 , Lars Samuelson 1
1 Solid State Physics, Lund University, Lund Sweden, 2 Institut d'Electronique de Microélectronique et de Nanotechnologie, UMR CNRS, Villeneuve d'Ascq France
Show AbstractNearly all semiconductor devices rely on control of carrier type and concentration by introduction of impurities. Similar control must also be developed in the growth and processing of semiconductor nanowires intended for device applications. An exception may be for the thinnest nanowires where the statistical distribution of impurities leads to a strong device-to-device fluctuation. In this case the carrier concentration may instead be controlled through changes in the nanowire surface potential. Carbon is an impurity of particular importance in epitaxial growth of III-V semiconductors where metal-organic precursors are used. Carbon is amphoteric, meaning that it can act as either p-type or n-type dopant depending on how it is incorporated in the material. Studies on bulk and 2D growth of III-Vs have shown that the amount of carbon incorporated depends on the precursors used, the V/III ratio, and growth temperature. We have investigated how the resistivity of n-type InAs nanowires is affected by the growth conditions and precursors used for chemical beam epitaxy and metal-organic vapor phase epitaxy. We find small but consistent changes in the resistivity as the growth temperature and V/III ratio are changed, indicative of changing levels of carbon incorporation. Moreover, we find that the choice of indium precursor can have a relatively strong effect on the resistivity, without affecting the overall InAs crystal structure.The intentional doping of InAs nanowires will also be discussed, and how electrical characterization can be used to determine whether dopants are incorporated through lateral overgrowth or assisted by the gold particle. We have tested precursors of S, Se, Si, Sn, and Zn, and in addition to electrical measurements have investigated effects of dopant incorporation on crystal structure. Finally, the application of n-doped InAs nanowires in vertical transistor structures will be presented.
3:30 PM - M9.4
P-doping of GaN and InN Nanowires: Growth and Optical Properties.
Raffaella Calarco 1 , Toma Stoica 1 , Friederich Limbach 1 , Tobias Gotschke 1 , Roberta Caterino 1 , Eike Oliver Schaefer-Nolte 1 2 , Eli Sutter 2
1 IBN 1, Research Center Juelich, Juelich Germany, 2 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractThe understanding and control of doping of GaN nanowires (NWs), is a necessary task to allow using nanowires in optoelectronic applications. The incorporation of specific doping atoms in NWs is a complex process due to possible self-purification effects. High crystal quality GaN and InN nanowires doped by Mg were obtained using plasma assisted molecular beam epitaxy growth in N-rich conditions. Here we report on the influence of the Mg-flux on the structural and optical properties of NW growth. To investigate the effect of the doping a set of samples was fabricated, in which the substrate temperature, the dopant and the Ga or In flux were varied.For InN NWs doped with Mg compared to the undoped counterpart, a reduced NW density is observed carefully increasing the substrate temperature. The great challenge of producing InN nanowires is indeed the tight window for growth parameter, due to the low decomposition temperature of InN. In HRTEM the presence of stacking faults for higher Mg-doping was revealed.The morphology of the GaN:Mg wires with respect to their undoped counterpart is not changed, however Mg increases the tendency of the wires to coalesce. The diameter of the wires is constant over their length and does not broaden or taper. The wire density increases at the beginning of the nucleation very slowly and then suddenly within few minutes reach a maximum value (after 45min). It then decreases as soon as coalescence phenomena take place. The samples have been investigated by means of photoluminescence. The near band edge peak is quenched with respect to the ultra violet (UV) luminescence band due to Mg doping. In addition the dominance of donor-acceptor-bound exciton emission of the near band edge peak is diminished and a contribution of the neutral-acceptor-bound exciton can be observed.Finally the photoluminescence properties of p-i-n junctions in nanowires are discussed with an emphasis on the Mg-doped region of the junctions and its position in the junction relative to the substrate. Especially the peak position of the near band edge peak is strongly dependent on the orientation of the p-i-n junctions.
3:45 PM - M9.5
Photoconductivity in Infrared-absorbing Semiconducting InN Nanowires.
Reui-San Chen 1 , Tsang-Ho Yang 2 3 , Hsin-Yi Chen 4 , Li-Chyong Chen 3 , Kuei-Hsien Chen 1 3 , Ying-Jay Yang 4 , Chun-Hsi Su 2 , Chii-Ruey Lin 2
1 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan, 2 Graduate Institute of Mechanical and Electrical Engineering, National Taipei University of Technology, Taipei Taiwan, 3 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 4 Graduate Institute of Electronic Engineering, National Taiwan University, Taipei Taiwan
Show AbstractWe report the first photoconductivity study of the individual infrared-absorbing indium nitride (InN) nanowires. Temperature-dependent dark conductivity measurement indicates the semiconducting transport behavior of these InN nanowires. An enhanced photosensitivity from 0.3 to 14 is observed by lowering down temperature from 300 to 10 K. A calculated ultrahigh photoconductive gain at around 8*10^7 at room temperature is obtained from the low-bandgap nitride nanowire under 808 nm band-to-band excitation. The current gain and sensitivity show further enhancements while changing the surrounding from the atmosphere to the vacuum. The physisorbed oxygen that creates deep-level electron trap compensating the native accumulated surface electron is proposed to sensitize the high-gain photoconductivity of the InN nanowires. An anomalous supralinear power dependence of photocurrent is also observed, which suggests the strong acceptor effect on changing the photocarrier recombination and probably compensating thermal carriers in these non-metallic InN nanowires. The results demonstrate the potential of InN nanostructures for new-generation high-efficiency infrared photodetectors.
M10: Optical Properties and Devices
Session Chairs
Wednesday PM, December 02, 2009
Constitution B (Sheraton)
4:30 PM - **M10.1
Quantum Optics with Nanowire Quantum Dots.
Val Zwiller 1 , Maarten van Weert 1 , Nika Akopian 1 , Maarten van Kouwen 1 , Mark den Heijer 1 , Anne Hidma 1 , Michael Reimer 1 , Reinier Heeres 1 , Sander Dorenbos 1 , Leo Kouwenhoven 1
1 Kavli Institute of Nanoscience, TU Delft, Delft Netherlands
Show AbstractNanowires grown by epitaxial methods enable the fabrication of complex semiconducting heterostructures where composition, size, position and doping can be controlled with unprecedented freedom. We study the optical properties of single nanowires containing single quantum dots with the aim of interfacing the world of quantum transport and quantum optics. We have demonstrated the operation of a single nanowire light emitting diode and performed photocurrent measurements on gated quantum dots in nanowires. Gated nanowire devices also enable control of the charge state of a single quantum dot. The polarization luminescence from nanowire quantum dots was studied along different orientations and we demonstrate that vertical nanowire devices enable the generation and readout of any exciton spin orientation.Because both zincblende and wurtzite crystal phases are stable in nanowires, a novel type of charge confinement where both quantum dot and barrier are composed of the same material are possible. We will present results obtained on InP quantum dots in InP nanowires.Superconducting nanowire detectors are well established single photon detectors, we have demonstrated the direct detection of single plasmons using superconducting detectors, paving the way towards integrated plasmonics where emission, waveguiding and detection is performed on a chip at the single plasmon level.
5:00 PM - M10.2
Fabrication of GaAs/AlGaAs Core-multishell Nanowire-based Light-emitting-diode Array on Si Substrate.
Katsuhiro Tomioka 1 , Tomotaka Tanaka 1 2 , Junichi Motohisa 1 2 , Shinjiroh Hara 1 2 , Kenji Hiruma 2 , Takashi Fukui 1 2
1 Graduate School of Information Science and Technology, Hokkaido University, Sapporo Japan, 2 Research Center for Integrated Quantum Electronics (RCIQE), Hokkaido University, Sapporo Japan
Show AbstractHeteroepitaxy of III-V semiconductor nanowires (NWs) on Si have been attracting attention for nano-optical devices and high speed electron devices on Si platforms. Recently, we have overcome difficulty in controlling growth directions of III-V NWs on Si by using selective-area MOVPE [1, 2]. Here, we report on fabrication of double hetero (DH) p/n junction AlGaAs/GaAs/AlGaAs core-multishell (CMS) NW-based light emitting diodes (LEDs) on Si(111) substrate. The CMS NW can enlarge the p/n junction area as compared to that of normal planar structure in same surface area, thus the vertical CMS NW-based optical devices such as LEDs, photodetectors, and solar cells have an advantage of their performance.Si(111) substrate (n-type, 0.02 Ωcm) was used in this experiment. Process for the selective-area MOVPE was previously reported [1]. Trimethylgallium (TMGa), trimethylalminum (TMAl) and arsine (AsH3) gas were used for CMS-NW growth. Silane (SiH4) and Diethylzinc (DEZn) was used as n-type and p-type dopants. The growth temperatures were 750°C for growth of core GaAs NWs (the core diameter and height is 100 nm and 2 µm), 700°C for lateral growth of AlGaAs and GaAs shell-layers. The Al composition was 12%. Under this growth condition, we succeeded in making p-AlGaAs(45nm)/p-GaAs(5nm)/n-AlGaAs(45nm) DH lateral structures. In addition, 10 nm-thick p-GaAs capping layer was finally grown. As for LED fabrication, semitransparent Cr /Au thin film was deposited on the top parts of the NWs for Ohmic contact. Ti/Au was used as back-side electrode on n-Si. The device area was 50 × 50 µm2, which include 104 NWs.I-V measurements showed a rectifying property with premature turn-on behavior. The threshold voltage was approximately 1.48 V and the dark current with reverse bias was 0.2 µA at - 4 V. Electroluminescence (EL) at the peak position of 1.48 eV (827 nm) was observed at room temperature. The threshold current for the EL was 0.5 mA (current density: 4.3 A/cm2). The EL intensity was super-linearly increased with inclement of the current injection, which is close to the super-luminescence property. Moreover, saturation of EL intensity resulting from the carrier overflow effect was observed from 3 mA (25.8 A/cm2). The saturated EL intensity was 2×104 counts/sec in CCD. Such bright EL can not be obtained from GaAs thin film-based LED on Si substrate without buffering techniques since dislocations due to lattice and thermal coefficient mismatches in GaAs/Si reduce their device performance. As for the CMS NW growth on Si, such dislocations were not included in the NWs without buffer layer [2]. Also, the strong emission is reflected in the geometrical advantage in the CMS NWs as we had expected. The CMS NW-based LED on Si is, therefore, superior to that of planar GaAs-based LED on Si.[1] K. Tomioka et al., Nano Lett., 8, 3475 (2008). [2] K. Tomioka et al., Nanotechnology, 20, 145302 (2009).
5:15 PM - M10.3
MBE Growth and Characterization of Nitride Nanowires Yielding Materials for High Efficiency Green Light Emitting Diodes.
Kevin Goodman 1 , Vladimir Protasenko 1 , John Simon 2 , Kejia Wang 3 , Tom Kosel 1 , Debdeep Jena 1
1 Electrical Engineering, University of Notre Dame, Notre Dame, Indiana, United States, 2 , Yale University, New Haven, Connecticut, United States, 3 , IBM, Yorktown Heights, New York, United States
Show AbstractThere exists an opportunity in alleviating the energy demand that has slowly grown to maturity over the past decades. 21% of the electricity used in the United States is solely for the purpose of artificial lighting [Zukauskas, Intro. to Solid State Lighting, John Wiley & Sons, 2002]. Solid state lighting offers a means to reduce this staggering percentage. Currently, however, solid state lighting lacks the maturity to offer solutions due to the low efficiency of green light emitting diodes. Research has shown that in the vicinity of wavelengths of 550 nm, known as the ‘green gap’ in solid state lighting, efficiencies of light emitting diodes decreases [Wetzel, RPI]. The reason for the decrease has been attributed to high numbers of threading dislocations that abound at the material interface between InGaN thin films grown which emit in the green gap and the underlying epitaxial growth substrate [Bertness, J. Defense Software, Oct. 2006]. This research focuses on molecular beam epitaxial growth of Nitride Nanowires on Silicon substrates. The nanowire growth is not dictated by the atomic lattice of the underlying Silicon which allows them to grow without strain [Bertness, as above]. This permits the growth of defect free material with high Indium concentrations near 40%, which offer a 2.5 eV band gap required for green emission. Such materials would be key in filling the ‘green gap’ that is currently plaguing solid state lighting.Results to date include growth of defect free Gallium Nitride nanowires showing PL peaks at 364 nm. Indium inclusion has permitted red shifts in emission to 550 nm, indicating a 38% Indium content in the nanowires. Efficiency measurements obtained from the wires reveal 8% optical efficiencies in the InGaN wires, over two orders of magnitude increase from c-plane thin films reported [Chichibu, Nature Materials, 5, 2006]. This value is obtained in spite of stacking faults which have been observed in TEM images of InGaN nanowires as the material shifts from Wurtzite to Zincblende construction. Electrical measurements of the nanowires have shown single wires with diameters as thin as 80 nm are capable of nearly MA/cm2 current densities. Further, Nitride nanowire/Silicon substrate heterostructures have been fabricated allowing for hole injection from the Silicon growth substrate into the Nitride nanwires. The p-type Silicon offers an inexpensive and relatively easily p-doped material as opposed to p-type Gallium Nitride. Current work in progress to be discussed includes patterned growth of nanowires along with growths carried out on Aluminum Oxide layers deposited by atomic layer deposition in efforts to produce electroluminescense from the Nitride nanowire/Silicon substrate heterostructures.
5:30 PM - M10.4
Quantitative Assessment of Wave Guiding Properties of Ga2O3 Nanowires by Cathodoluminescence.
Emilio Nogales 1 , Bianchi Mendez 1 , Javier Piqueras 1
1 Fisica de Materiales, Universidad Complutense de Madrid, Madrid Spain
Show AbstractSemiconductor oxide nanowires have attracted increasing attention for their applications in optoelectronics at the nanoscale because of their improved functionalities. Active research has been ongoing for several years in Transparent Conductive Oxides (TCO) in order to exploit their tunable optical properties and to be used as light emitters, detectors, optical sensors…. Some of the TCO have a rather high refractive index (close to 2), which makes them suitable for waveguiding purposes. Although SnO2 (1), GeO2 (2) and Ga2O3 (3) nanowires have been demonstrated as optical waveguides in the visible region, further assessment is needed to transfer this functionality to practical nanodevices. In this work, a direct observation and further analysis of the optical waveguiding properties of monoclinic Ga2O3 nanowires is presented.The nanowires have been grown by oxidation of metallic gallium in a furnace under a controlled argon flow and waveguiding properties have been studied with the aid of a scanning electron microscope (SEM) equipped with a cathodoluminescence (CL) setup. The experimental setup enables us to perform measurements with different light collection angles allowing a quantitative assessment of waveguiding behavior of nanowires. CL images of the Ga2O3 nanowires reveal that the light generated under electron beam excitation travels through the wire and an attenuation of the CL intensity is clearly observed. Light losses along Ga2O3 nanowires are observed in CL images when collecting the guided CL signal. CL spectra when exciting at different distances from the wire end show that the losses in nanowires with lateral dimensions of a few hundred nanometers depend on the CL wavelength: they are higher for lower wavelengths. Combining both CL imaging and spectroscopy in different nanowires, losses are quantified as a function of guided light wavelength and nanowire lateral dimensions.References:(1) M. Law, D. J. Sirbuly, J. C. Johnson, J. Goldberger, R. J. Saykally and P. D. Yang, Science, 305, 1269 (2004).(2) P. Hidalgo, B. Méndez and J. Piqueras, Nanotechnology, 18, 155203 (2007).(3) E. Nogales, J. A. García, B. Méndez and J. Piqueras, Appl. Phys. Lett. 91, 133108 (2007).
5:45 PM - M10.5
Optical Characterization of III-V Nitride Nanowire Heterostructures by Cathodoluminescence in Scanning Transmission Electron Microscopy.
Sung Keun Lim 1 , Megan Brewster 1 , Silvija Gradecak 1
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractDue to nano-scale dimensions and large surface-to-volume ratios, semiconductor nanowires and nanowire heterostructures have position-dependent optical properties. Direct correlation between structural and optical properties is therefore necessary for the rational synthesis of complex heterostructures for the development of nanowire opto-electronic devices. We achieved this direct correlation by employing parallel-detection mode cathodoluminescence coupled with scanning transmission electron microscopy (CL-STEM), and III-V nitride nanowires and nanowire heterostructures were characterized with sub-20 nm spatial resolution. The CL spectra of Si-doped GaN/AlGaN core-shell (CS) nanowires grown by metal-organic chemical vapor deposition (MOCVD) show strong near band edge (NBE) GaN emission at 365 nm at room temperature, but the spectra are eventually dominated by donor-acceptor pair (DAP) emission at 380 nm as the sample is cooled down to 110K, implying the existence of SiN or VGa-O acceptor in Si-doped GaN core. Furthermore, monochromatic CL images collected at the DAP emission reveal that these dopants are distributed uniformly in the CS nanowires. Monochromatic CL images of the cross-section of a single quantum well (SQW) GaN/InGaN/GaN/AlGaN nanowire grown by MOCVD show spatially-resolved emission at 380 nm (DAP) and 430 nm (InGaN SQW), as well as confirm selective growth of InGaN SQW on particular facets of GaN core. A CL linescan in parallel-detection mode along the length of a tapered SQW nanowire illustrates In segregation within the InGaN SQW, as well as a gradient in the composition or thickness of the InGaN SQW along the nanowire. Additionally, the optical properties of GaN and InGaN ternary nanowires grown by chemical vapor deposition (CVD) and MOCVD were characterized by CL-STEM. Our results demonstrate the correlation of optical properties of III-V nitride nanowire heterostructures with their structure on nano-scale, aiding the development of the photonic and opto-electronic applications.
M11: Poster Session I: Semiconductor Nanowires
Session Chairs
Anna Morral
Kornelius Nielsch
Thursday AM, December 03, 2009
Exhibit Hall D (Hynes)
9:00 PM - M11.1
Quantifying the Traction Force of a Single Cell by Aligned Silicon Nanowire Array.
Jinhui Song 1 , Zhou Li 2 1 , Giulia Mantini 3 1 , Ming-Yeh Lu 4 1 , Hao Fang 1 , Christian Falconi 3 , Lih-J. Chen 4
1 Material Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Department of Advanced Materials and Nanotechnology, Peking University, Beijing China, 3 Department of Electronic Engineering, University of Tor Vergata, Roma Italy, 4 Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractThe physical behavior of stationary cells, such as the morphology, motility, adhesion, anchorage, invasion and metastasis, are likely to be important for governing their biological characteristics. A change in the physical properties of mammalian cells could be an indication of diseases, which could be possibly developed to be a useful tool for mammalian detection. We present a silicon-nanowire-array based technique for quantifying the mechanical behavior of single cells representing three distinct groups: normal mammalian cells, benign cells (L929) and malignant cells (HeLa). By culturing the cell on the top of NW arrays, the maximum traction forces of two different tumor cells (HeLa, L929) have been measured by quantitative analyzing the force required to induce the bending to a nanowire based on the calibrated mechanical parameters provided by AFM and finite element caculation. The cancer cell exhibits a larger traction force than the normal cell by ~20% for a HeLa cell and ~50% for a L929 cell. The traction forces have been measured for the L929 cells and mechanocytes as a function of culture time. The relationship between cells extending area and their traction force has been investigated. We found that the cancer cells exhibit significantly larger CTFs in comparison to a normal cell. Discussions are given regarding the reliability of the force data and the corresponding sensitivity. Our study is likely important for studying the mechanical properties of single cells and their migration characteristics. The method and results are potentially useful for oncology, disease diagnosis, drug developing and tissue engineering.
9:00 PM - M11.10
Growth of Straight GaAs Nanowires on Si (111) Substrates Coated with Thin GaAs Buffer Layer.
Kang Jung-Hyun 1 , Gao Qiang 1 , Tan Hark-Hoe 1 , Jagadish Chennupati 1 , Kim Yong 1 2 , Guo Yanan 3 , Zou Jin 3 , Fickenscher Melodie 4 , Smith Leigh 4 , Jackson Howard 4
1 Electronic Material Engineering, The Australian National University, Canberra, Australian Capital Territory, Australia, 2 Department of Physics, Dong-A University, Busan Korea (the Republic of), 3 Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, Queensland, Australia, 4 Department of Physics, University of Cincinneti, Cincinneti, Ohio, United States
Show AbstractGaAs nanowires (NWs) were grown on the Si (111) substrates by horizontal flow low pressure - metal organic chemical vapor deposition (MOCVD) using Au particles as catalysts via vapor-liquid-solid mechanism. Prior to the growth of GaAs NWs, thin GaAs layer (40~80 nm thickness) was deposited on the Si surface as a buffer layer. The growth conditions including growth temperature, V/III flow ratio, and annealing effect of the GaAs buffer layers were studied. The reactor pressure was fixed at 100 mbar and Trimethylgallium (TMGa) and Arsine (AsH3) were used as III- and V-source materials, respectively. The Si substrates coated with GaAs buffer layer were treated firstly by Poly-L-lysine solution to attach Au particles onto the surface. The substrate was then loaded into the reactor and annealed under AsH3 ambient to remove contamination and make the eutectic alloys. GaAs NWs were grown at 450°C for 30 min. They were then characterized by field emission scanning electron microscopy (FE SEM), transmission electron microscopy (TEM) and micro-photoluminescence (PL) measurement.1. GaAs nanowires on Si substrates coated with GaAs buffer layersThe NWs grew straight along the [111] direction on Si (111) substrates coated with thin GaAs layers. This is in contrast to GaAs NWs grown directly on Si (111) substrates which are usually kinked. Results indicate the use of GaAs buffer layers may avoid some factors that prevent epitaxial growth of GaAs NWs on Si such as lattice mismatch, different thermal coefficient, and native oxide layers. GaAs NWs have tapered, truncated cross-sectional shape, with twin stacking faults. The GaAs buffer layer bears no crystallographic relation with these defects. It does, however, affect the growth morphology of the NWs, such as growth direction. PL spectra show only one emission peak at 1.515 eV from those GaAs NWs and same quality as those grown directly on GaAs substrates. 2. Improvement for the morphology of GaAs nanowiresImprovement in the quality of the buffer layer can be achieved by using a double layer structure. The initial GaAs layer directly deposited on the surface of Si substrates was grown under low V/III ratio (15.4) and low temperature (400°C). It can play a role as the buffer to reduce mismatch properties between GaAs NWs and Si substrates. The subsequent GaAs layer grown under high V/III ratio (154.3) and high temperature (700°C) has high structural quality, which improves the morphology of GaAs NWs. In addition, an annealing step for buffer layers at high temperature (750°C) improves its crystalline quality. As a result, the morphology and density of subsequent GaAs NWs deposited improves dramatically.
9:00 PM - M11.11
Phase Transition of Se Nanowires Confined in Mesoporous Silica: Effect of Host Doping.
Kuangmin Li 1 , Congshang Wan 1 , Arianne Saunders 1 , Gang Chen 1
1 Physics and Astronomy, Ohio University, Athens, Ohio, United States
Show AbstractPhase-change memory materials (PCMM) are based on semiconducting chalcogenides that exhibit rapid phase transitions under thermal excitation, thus are promising candidates for use in next-generation non-volatile memory devices. A key challenge remains as current PCMM demand high-power consumption caused by the phase transitions. A potential solution is to utilize nanoscale confinement to lower the phase transition temperatures. To understand the effect of 1D confinement on the phase transition properties of chalcogenide nanowires, we select Se as a testing material. Se nanowires were grown inside mesoporous silica that was doped with copper, iron, or silver ions. The purpose of ion doping is to investigate the feasibility of tuning the host-guest interaction by host doping. Small-angle and wide-angle x-ray scattering were used to characterize the medium-range and nanoscale structures of doped mesoporous silica. Phase transition temperatures of Se nanowires under 1D confinement were measured by differential scanning calorimetry. Correlation between the host structure and phase-transition temperature of the guest is explored. Our study stands to provide structural insights into the effect of host doping on the phase transition properties of Se nanowires under 1D confinement.
9:00 PM - M11.12
Electronic Properties of One-Dimensional Gd Silicide Nanowires Studied by STM.
Shengyong Qin 1 , Tae-Hwan Kim 1 , Wen-Jie Ouyang 2 , Ru-Qian Wu 2 , Chih-Kang Shih 3 , An-Ping Li 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Physics & Astronomy, University of California Irvine, Irvine, California, United States, 3 Department of Physics, University of Texas at Austin, Austin, Texas, United States
Show AbstractMetallic nanowires have attracted great interest for understanding the electronic interactions and conductivity in one dimension [1]. Well-ordered and uniformly oriented array of GdSi2 nanowires with dimensions of the order of 0.4 nm x1.9 nm x1000 nm are fabricated on Si (100) through self-assembly by carefully choosing the growth conditions. Scanning tunneling microscopy measurements reveal two different types of nanowire structures: nanowire bundles and single nanowires. Scanning tunneling spectroscopy indicates that single wires are metallic at 80 K but they appear to be insulating with a small energy gap at 4.5 K, while the bundles composed of four or more unit wires show clear metallic behavior with finite tunneling conductance down to 4.5 K. Furthermore, adatom-like structures are resolved on single wires with a spacing quantized in odd integers of Si lattice constant, while on bundles they appear along the edge of wires with random spacing. This suggests the interactions between nanowires in the bundle may play a role. Density function theory calculations are performed to understand the growth mechanism through metal atoms at different sites and formation energies of nanowires in different geometries. For example, we have found that Y (in lieu of rare earth) prefers to take the side of nanowires whereas Au tends to adsorb on top of the nanowire. STM images are emulated for direct comparison with the experimental results. The electrical transport properties are probed along the individual nanowires and bundles to examine the conductance of the nanowires with a cryogenic four-probe STM. These nanowires not only represent an interesting model system for exploring one-dimensional quantum transport, but they can also be used as electrodes or interconnects in nanoscale electronic devices on a silicon platform. This research at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.[1] C. Zeng, P.R.C. Kent, T.-H. Kim, A.P. Li, and H. H. Weitering, Nature Materials 7, 539 (2008).
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Radial Active Dopant Distribution in Silicon Nanowires Measured by Kelvin Probe Force Microscopy.
Yossi Rosenwaks 1 , Elad Koren 1 , Noel Berkovich 1 , Jhon Allen 2 , Lincoln Lauhon 2
1 , Tel-Aviv University, Tel-Aviv Israel, 2 , Northwestern University, Chicago, Illinois, United States
Show AbstractSemiconductor nanowires are one of the most promising building blocks for near future nano-electronics because they provide a new route to continuing miniaturization as well as a wealth of opportunities in nanoscale science and technology. However, the concentration and distribution of the active dopants are generally unknown, which poses a major challenge towards the realization of high quality electrical devices. We have directly measured the radial distribution of active dopant atoms in individual nanowires grown by the vapor-liquid-solid approach. Our method is based on surface etching of a portion of a contacted nanowire, followed by measurement of the potential difference between the etched and the unetched areas using Kelvin probe force microscopy (KPFM). This process is repeated several times to gradually remove material, and the surface potential difference (between the etched and unetched parts) is measured for a number of nanowire radii. The radial dopant distribution is obtained by fitting the extracted potentials with a 3D solution of Poisson equation. We find that the radial active dopant distribution within a single n-type silicon nanowire decreases by almost two orders of magnitude from the wire surface to its core. The dopant profile is consistent with enhanced surface doping during growth and an enhanced diffusion coefficient of phosphorous in the silicon nanowires of D~1x10-19 m2 s-1. This result suggests that P diffusion during VLS growth and subsequent thermal processing should be considered when correlating synthesis conditions with the electrical characteristics of devices.
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Fabricating Conductive Nanowires using Dislocations in GaN Thin Films.
Shin-ichi Amma 1 , Nobuaki Takahashi 1 , Tsubasa Nakagawa 2 , Isao Sakaguchi 2 , Rie Takenaka 3 , Keiichi Edagawa 3 , Naoya Shibata 1 , Teruyasu Mizoguchi 1 , Yuki Tokumoto 4 , Takahisa Yamamoto 4 5 , Yuichi Ikuhara 1 5 6
1 The University of Tokyo, Institute of Engineering Innovation, Tokyo Japan, 2 , National Institute for Materials Science, Ibaraki Japan, 3 The University of Tokyo, Institute of Industrial Science, Tokyo Japan, 4 The University of Tokyo, Department of Advanced Materials Science, Tokyo Japan, 5 Japan Fine Ceramic Center, Nanostructures Research Laboratory, Nagoya Japan, 6 Tohoku Univercity, WPI Advanced Institute for Materials Research, Sendai Japan
Show Abstract It is well known that dislocation in crystals is an atomic-scale line defect that exhibits unique properties that are quite different from those in the bulk. It has been reported that dislocation can be used to fabricate conducting nanowires inside an insulating sapphire single crystal by doping foreign atoms along the dislocations [1]. In the present study, we use high-density threading dislocations in GaN thin films grown on sapphire in order to form high-density conductive nanowires along the GaN dislocations. Experimental procedures are as follows. GaN films were grown on (0001) sapphire by metal-organic chemical vapor deposition. 4 metals(Al,Mn,Nb,Ti) were respectively deposited on the GaN films, and these sample were annealed at 1073K in N295%+H25% gas for 120 hours in order to enhance pipe diffusion of metals along the dislocations. Diffusion behaviors (both bulk diffusion and pipe diffusion) of 4 metals were investigated using secondary ion mass spectroscopy (SIMS). Diffusion tails, which are attributed to rapid pipe diffusion, appeared in concentration profiles for Al and Nb doped sample, but those were not found for Mn and Ti doped samples. These results indicate that Al and Nb atoms can diffuse rapidly along the dislocations. For Al deposited sample, Al segregation was investigated using nano-probe TEM-EDS analysis. EDS analysis showed that Al atoms were actually localized in the vicinity of dislocation cores. This indicates that Al atoms are indeed infiltrated along the dislocations, and that ‘Al-enriched nanowires” are formed inside GaN films. In order to evaluate electric properties of the nanowires, the electric conductivities of dislocations were investigated by the contact current mode of scanning probe microscopy (SPM) using conductive diamond-coated Si cantilever under the applied voltage of 10 V at room temperature. It was found that many conductive spots are observed in the current-mapping images, which are comparable to the density of the nanowires. It is thus considered that Al nanowires formed along the dislocations are conductive. [1] A. Nakamura, K. Matsunaga, J. Tohma, T. Yamamoto, Y.Ikuhara, Nat. Mater. 2 (2003) 453.
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Structural and Luminescent Study of Er-doped SnO2 Microtubes and Nanowires.
Elena Hernandez 1 , David Maestre 1 , Ana Cremades 1 , Javier Piqueras 1
1 , Universidad Complutense de Madrid, Madrid Spain
Show AbstractDoping with rare earth (RE) ions has attracted an increasing interest during the last years due to the wide range of applications based on their characteristic luminescence. The use of wide band gap materials as host could overcome the thermal quenching of RE emission at room temperature, spreading the potential applications of these materials. A transparent conductive oxide such as SnO2, with a 3.6 eV direct bandgap, good transparency in the visible and high reflectivity in the IR, could be considered as a promising candidate to host the Er doping, leading to the development of applications in many different fields such as optical communications, amplifiers, waveguides, electroluminescent displays or building blocks in nanotechnology.In this work, we report on the growth and characterization of Er doped SnO2 elongated micro- and nanostructures grown by a vapor-solid method. During the last years, some works referred to SnO2 thin films doped with RE ions, however less has been done in the study of Er doped SnO2 elongated micro- and nanostructures, as those presented in this work. The analyzed structures have been grown by a vapor-solid process which avoids the use of a catalyst or external substrates [1]. This method has been previously used in our group to grow different semiconducting elongated structures including SnO2 micro and nanotubes [1], as well as Er doped Ga2O3 wires [2]. In this work, an initial mixture of SnO2 and Er2O3 powders with different weight ratios has been used as starting material. Thermal treatments carried out at temperatures between 1400 °C and 1500 °C are needed to generate the growth of microtubes, as well as other elongated micro- and nanostructures. The characteristic morphology of these structures, which depends on the growth conditions, could favour the development of some specific applications. Moreover the presence of Er2Sn2O7 has been also observed in the treated samples. EDS spectra and mappings have been performed in order to investigate the incorporation of Er into the elongated structures. A small concentration of Er, not higher than 2 %, has been detected in the tubes.The luminescence properties of these doped samples have been analyzed in the visible and the near infrared range by means of the CL in the SEM. The characteristic Er3+ sharp lines arising from intra shell transitions have been observed in the tubes, thus confirming the presence of Er. These intra-emissions appear as sharp lines grouped in the visible and IR region of the spectrum. A detailed study of the band centered at 1540 nm has been performed as its energy lies at the region of minimum losses for silica-based waveguides used in telecommunications.[1] D. Maestre, A. Cremades and J. Piqueras. J. Appl. Phys. 97, 044316 (2005)[2] E. Nogales, B. Méndez and J. Piqueras. Nanotechnology 19, 035713 (2008)
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Growth and Characterization of Indium Oxide Nanoneedles Codoped with Manganese and Europium.
Manuel Herrera 1 2 , David Maestre 1 , Ana Cremades 1 , Javier Piqueras 1
1 , Universidad Complutense de Madrid, Madrid Spain, 2 , Universidad Autónoma de mexico, Ensenada Mexico
Show AbstractDoping of semiconductor nanostructures in order to modulate their physical properties is an active field of research.In particular, incorporation of Mn into In2O3 has attracted interest because their influence on the magnetic behaviour of nanocrystalline and bulk material (1), whereas doping wide band gap semiconductors with rare earth ions improves the luminescence emission (2). In the present work, Mn-Eu codoped In2O3 nanoneedles have been grown by a thermal evaporation-deposition method, previously reported for the growth of pure In2O3 elongated structures (3,4). Structural, compositional and optical characterization of the doped structures was carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) in SEM, cathodoluminescence (CL) in SEM and X ray photoelectron spectroscopy (XPS) and microscopy carried out at the Esca beamline of the Elettra Sinchrotron laboratory in Triest (Italy).The samples were grown from a precursor formed by 95 % wt In2O3 powder and 5 % wt of Mn2O3, including traces of Eu2O3 powders. The precursor sample was annealed at 1400 C for 10 hours. The needles grow on the surface of a second sample located in a region opposite to the gas inlet, at 900 C. The longer needles give rise to nanowires with lengths of hundreds of microns and parallel arrays of wires are observed in some regions. Th larger needles show a stepped surface that indicates that the growth takes place by formation of terraces of decreasing cross section terminating in micro- or nanowires. The content of Mn as measured by EDS is about 0.1 at % or in some regions seemed to be in the detection limit of the technique. This is also the case for Eu although the characteristic emission of Eu ions is resolved in the CL spectrum. CL images recorded in regions with needles, have shown alternating bright and dark stripes perpendicular to growth direction. A similar contrast is observed in the images recorded by selecting the kinetic energy of characteristic emitted photoelectrons of indium and oxygen. A combined CL - XPS study enables us to associate the observed luminescence contrast with a defective local stequiometry at the terraces.1.D. Berardan, E. Guilmeau and D. Pelloquin, J. Magn. Magn. Mat. 320, 983 (2008)2.E. Nogales, B. Méndez and J. Piqueras. Nanotechnology 19, 035713 (2008)3.D.A. Magdas, A.Cremades and J.Piqueras, Appl. Phys. Lett. 88, 113107 (2006)4.D.A. Magdas, a.Cremades and J.Piqueras, J. Appl. Phys. 100, 094320 (2006)
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Thermal Stability Characterization of ZnS Nanowires Using in-situ Heating X-ray Diffraction.
Hee Suk Chung 1 , Seul Cham Kim 1 , Hyun Chul Roh 1 , Ji Woo Kim 1 , Kyu Hwan Oh 1
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractThe thermal stability of ZnS nanowires grown by Au/Pd-mediated vapor-liquid-solid manner was studied by X-ray diffraction equipped with in-situ heating system. Using in-situ heating X-ray system, We have monitored the structural degradation of ZnS nanowires in the temperature range from 25°C to 900°C. From X-ray diffraction data recorded from 25°C to 900°C, the As-synthesized ZnS nanowires were identified with sphalerite structure and preserved initial structure up to 400°C. Above the 500°C, a distinct sphalerite structure degradation was revealed, which is related to be disappeared (111) and (200) peaks. Through the extended temperature region up to 900°C, we found continuous reduction of (111) and (200) peaks. Especially, pure Zn peak showed up at the 700°C, which can be considered phase decomposition of partial ZnS nanowires. Further, we employed electron microscopes to observe morphological and structural changes corresponding to the initial and final states of ZnS nanowire products.
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A Universal Growth Process for Various Functional Nanowire Architectures Without Using Metal Catalysts.
Paresh Shimpi 1 , Pu-Xian GaO 1
1 Material Science and Engineering, CMBE, IMS, University of Connecticut, Storrs, Connecticut, United States
Show AbstractNanowire arrays and nanodendrite film of SiOx, ZnO, and ZnS have been successfully grown by heating silicon substrates coated with SiO2, ZnO, and ZnS nanoparticle films. Different nanowire architectures with varying density were achieved by changing the duration period. The influences of gas flow rate, temperature (≤1200 °C), coating thickness, and duration time on these nanostructures have been studied in detail using a wide array of electron microscopy and spectroscopy. A carbon assisted and lattice mismatch strain driven growth process was proposed as a common growth mode for enabling these nanowire architectures without using metal catalysts. This simple growth process might be universal for enabling the rational synthesis of a large family of ultra-pure nanowire architectures based on thin films of pure metal oxides, sulfides and nitrides without involving metal catalyst-based vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) processes.
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ZnO-based Single Wire Generator and Its Application for Biomechanical Energy Conversion.
Rusen Yang 1 , Yong Qin 1 , Cheng Li 1 , Guang Zhu 1 , Liming Dai 2 , Zhong Lin Wang 1
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Department of Chemical and Materials Engineering, University of Dayton, Dayton, Ohio, United States
Show AbstractZinc oxide is a smart material that exhibits semiconducting, piezoelectric, and pyroelectric multifunctionalities. The unique coupling effect of piezoelectric and semiconducting properties of ZnO is the fundamental principle of nano-piezotronics [1], a new field using the piezoelectric effect for fabricating electronic devices and components. The study of nano-piezotronics has resulted in the important discovery of single wire generator (SWG) [2], which can convert mechanical energy, including biomechanical energy, into electricity. Converting mechanical energy into electricity has unique applications in sensing, medical science, defense technology and personal electronics. The flexible SWG is based on cyclic stretching-releasing of a piezoelectric fine-wire, which is firmly contacted at two ends with metal electrodes, laterally bonded and packaged on a flexible substrate. When the ZnO wire is stretched as driven by substrate bending, a piezoelectric-potential-drop is created along the wire, which acts as a “capacitor” and “charge pump” that drives the back and forth flow of electrons in the external circuit to achieve a charging and discharging process when the wire is stretched and released, respectively. Various mechanical disturbances can serve as the source for energy conversion. The reported work demonstrates a new approach towards robust, no sliding-contact technology for mechanical energy harvesting. For instance, muscle stretching results in the back and forth stretching of the substrate and the nanowire, and a tapping finger and a running hamster has successfully driven a SWG for electricity output [3]. The output voltage has been increased by integrating multiple SWGs. A series connection of four SWGs produced an output voltage of up to ~0.1- 0.15 V. The success of energy harvesting from biomotion reveals the potential of using the nanogenerators for scavenging low-frequency energy from regular and irregular mechanic energies. [1] http://www.nanoscience.gatech.edu/zlwang/[2] R.S. Yang, Y. Qin, L.M. Dai, and Z.L. Wang, Nature Nanotechnology, 4 (2009), 34-39[3] R.S. Yang, Y. Qin, C. Li, G. Zhu, and Z.L. Wang, Nano Letters., 9(2009), 1201-1205
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Kinetically-induced Hexagonality in Chemically Grown Silicon Nanowires.
Xiaohua Liu 1 , Dunwei Wang 1
1 Chemistry, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractBulk silicon is known to have the diamond crystal structure. However, various silicon polymorphs with different atomic arrangements are observed in the silicon nanowires (SiNWs) chemically synthesized via the widely used vapor-liquid-solid (VLS) method. Instead of viewing them as stacking defects, we define the concept of hexagonality, which is thought to be a better parameter to illustrate the real structure of a SiNW. The small transverse dimensions of a nanowire make this approach meaningful. Unique among the polymorphs are cubic symmetry diamond and hexagonal symmetry wurtzite structures, with hexagonality of 0% and 100%, respectively. Our TEM and Raman spectroscopy characterizations confirm the existence of the hexagonal symmetry SiNWs. Rather than NWs with random stacking faults, localized ordered polymorphs such as 9R segments are also frequently observed. Our cohesive energy calculations suggest that the wurtzite polymorph is the least stable and the diamond polymorph is the most stable. Cohesive energies of intermediate polymorphs follow a linear trend with respect to their structural hexagonality. We identify the driving force in the polymorph formations as the growth kinetics. Fast longitudinal elongation during the growth freezes stacking mismatches and thus leads to a variety of Si polymorphs. The results are expected to shed new light on the importance of growth kinetics in nanomaterial syntheses and may open up ways to produce structures that are uncommon in bulk materials.
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Monitoring and Controlling Electrically Induced InP Nanowire Growth from Solution.
August Dorn 1 , Peter Allen 1 , Moungi Bawendi 1
1 Chemistry, MIT, Cambridge, Massachusetts, United States
Show AbstractEfficient placement and integration of nanowires into devices remains a major challenge to a wider use of these technologically interesting materials. Here we extend the technique of electrically induced catalytic nanowire growth from solution (EC SLS) [1], to indium phosphide. We are able to control the amount of wire growth by varying the bias voltage between the electrodes in solution, and to monitor nanowire bridging by recording the conductivity as a function of growth time. In addition, issues related to in situ nanowire doping will be discussed. These are valuable tools for controllably fabricating nanowire devices with the EC-SLS process. Structures of this type could find applications in nanoelectronics and as electrodes in solar cells and batteries.[1] August Dorn, Cliff R. Wong, and Moungi G. Bawendi, Electrically Controlled Catalytic Nanowire Growth from Solution. Advanced Materials, 2009. 21(1-4).
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Arsenic-Doped Indium Oxide Nanowires for Transparent Thin Film Transistors and Active Matrix Organic Light-Emitting Diode Displays.
PoChiang Chen 2 1 , Guozhen Shen 2 , Saowalak Sukcharoenchoke 2 , Haitian Chen 2 , Yue Fu 2 , Young-geun Ha 3 , Chao Wu 4 1 , Jun Liu 3 , Antonio Facchetti 3 , Tobin Marks 3 , Mark Thompson 4 1 , Chongwu Zhou 2 4
2 Ming-Hsieh Department of Electrical Eng., University of Southern California, Los Angeles, California, United States, 1 The Mork Family Department of Chemical Engineering and Materials Scienceng., USC, Los Angeles, California, United States, 3 Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, Illinois, United States, 4 Department of Chemistry, University of Southern California, Los Angeles, California, United States
Show AbstractDue to the attraction of optical transparency and, in principle, low temperature processing, there have been numerous research efforts on transparent electronics. The core technology to realize the transparent electronics requires the development of high-performance transparent thin film transistors (TTFTs), with high device mobilities, moderate carrier concentrations, low threshold voltages, and steep subthreshold slopes. Currently, TTFTs fabricated with amorphous or polycrystalline transparent conducting oxide thin films have been widely studied. However, TTFTs made from these materials usually exhibit rather low mobilities (0.2~120 cm2V-1sec-1) and high threshold voltages (Vth: 10~20 V).We present high-performance arsenic (As) -doped indium oxide (In2O3) nanowires for transparent electronics, including their implementation in transparent thin-film transistors (TTFTs) and transparent active-matrix organic light-emitting diodes (AMOLED) displays. The As-doped In2O3 nanowires were synthesized using a laser ablation process, and then fabricated into TTFTs with indium-tin-oxide (ITO) as the source, drain and gate electrodes. The nanowire TTFTs on glass substrates exhibit very high device mobilities (~1,490 cm2V-1s-1), on/off ratios (5.7 × 106), steep subthreshold slopes (88 mV/dec), and a saturation current of 60 μA for a single nanowire. By using a self-assembled nanodielectric (SAND) as gate dielectric, the device mobilities and saturation current can be further improved up to 2,560 cm2V-1s-1 and 160μA, respectively. All devices exhibit good optical transparency (~81% on average) in the visible spectral range. In addition, the nanowire TTFTs were utilized to control green OLEDs with varied intensities. Furthermore, a fully integrated seven-segment AMOLED display was fabricated with a good transparency and with each pixel controlled by two nanowire transistors. This display successfully showed different digital numbers. Our results suggest that As-doped In2O3 nanowires have promise as building blocks for future transparent electronics and display electronics.
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Zn1-xMgxO Nanowire Arrays with Controllable Structure and Conductivity Type.
Shisheng Lin 1 2 , Jung-Il Hong 1 , Jinhui Song 1 , Ying Zhu 2 , Haiping He 2 , Zheng Xu 2 , Yaguang Wei 1 , Yong Ding 1 , Robert Snyder 1 , Zhizhen Ye 2 , Zhonglin Wang 1
1 , School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , State Key Labratory of Silicon Materials, Hangzhou China
Show Abstractp-type Zn1-xMgxO NWs can allow fabrication of LEDs emitting shorter wavelength compared to p-type ZnO NWs. Moreover, band-gap engineering in ZnO NWs is also highly desirable since heterostructure or quantum wells should be incorporated into the LEDs structure to further enhance the internal quantum efficiency. Up to now, there is no report of growth of p-type Zn1-xMgxO NWs. Using pulsed laser deposition (PLD), we demonstrate controlled growth of Zn1-xMgxO nanowire (NW) array not only in the aspect ratio and density, but also in tuned electronic structure through alloying and doping. Fabrication of p-type Zn0.92Mg0.08O NWs array has been demonstrated by phosphorous doping for the first time. The dependence of the conductivity type of the Zn1-xMgxO NWs on the growth pressure is investigated. Valence band (VB) XPS reveals the Fermi level is ~0.9 eV close to VB maximum compared to that of 3.1 eV for ZnO NWs, confirming the p-type conductivity of Zn0.92Mg0.08O:P NWs. Rectified electrical properties between the Zn0.92Mg0.08O:P NWs and the underlying pure ZnO film demonstrate gives further strong evidence of p-type conductivity in Zn0.92Mg0.08O:P NWs. The p-type conductivity is also consistent with the dominating donor-acceptor pair in the photoluminescence (PL) spectra and a shallow acceptor level of ~110 meV is identified by the temperature-dependent PL measurements. A piezoelectric output of 60 mV on average has been received using the phosphorous doped NWs. The Zn1-xMgxO NWs with controllable conductivity type has potential application in high-efficiency all-ZnO NWs based LED, high-output ZnO nanogenerator and other optical or electrical devices.[1]. S. S. Lin, J.-I. Hong, J. H. Song, Y. Zhu, H. P. He, Z. Xu, Y. G. Wei, Y. Ding, R. L. Snyder, Z. Z. Ye and Z. L. Wang, submitted.[2]. Z. L. Wang, J. H. Song, Science, 312, 242 (2006). [3]. For more information: http://www.nanoscience.gatech.edu/zlwang/
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Raman Spectroscopic Study of the Interface between the Directly Grown Silicon Nanowires and the Growth Seedbed.
Youngsik Song 1 , Jaewu Choi 2
1 Electrical and Computer Engineering, Wayne State University, Detroit, Michigan, United States, 2 Information Display, Kyung Hee University, Seoul Korea (the Republic of)
Show AbstractWe studied the interface between the directly grown silicon nanowires and the seedbed for the silicon nanowire. The stress developed during the growth of the silicon nanowires plays the important role to determine the growth behavior. The residual stress was measured from the Raman peak shift of the silicon transverse optical mode.
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Vertically Well-Aligned Epitaxial Ni2Si Nanowire Arrays with Excellent Field Emission Properties.
Chung-Yang Lee 1 , Ming-Pei Lu 2 , Chi-Te Huang 1 , Chen-Ho Lai 1 , Lih-Juann Chen 1
1 Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan, 2 , National Nano Device Laboratories, Hsicchu Taiwan
Show AbstractVertically well-aligned single crystal Ni2Si nanowire (NW) arrays were successfully grown at 850 °C for the first time. The growth of highly oriented and large area arrays of NWs were epitaxially grown on Ni2Si films preferentially formed on Ni foil substrates with a simple vapor transport and condensation method in one step. The Ni2Si NWs are 7-9 μm in length and 20-50 nm in diameter, respectively. By four-terminal I-V measurement, the resistivities of the Ni2Si NWs were measured to be 21 μΩ-cm. The Ni2Si NWs can endure very high current densities and possess excellent field emission properties. The growth of vertically well-aligned Ni2Si NWs arrays provides a significant advantages for building vertical Si nanodevices.
9:00 PM - M11.26
Random Lasing from Nanowires Network and Individual Nanowire Laser.
Chuanwei Cheng 1 , Huiying Yang 2 , Siu Fung Yu 2 , Hongjin Fan 1
1 Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore Singapore, 2 Division of Microelectronics, School of Electrical & Electronic Engineering, Nanyang Technological University, Singapore Singapore
Show AbstractMetal-oxide nanowires possess a wide range of applications due to their large surface area, rich surface chemistry, and generally high crystalline quality (compared to their bulk counterparts). For branched nanowire networks, most of the demonstrated functions are gas sensing and photocatalytic properties. In this paper, we will show the fabrication and lasing properties of a SnO2-ZnO hybrid nanostructure with a morphology resembling the leaves of a pine tree. The morphology can be facilely controlled (in a way similar as different growth stages of a tree) by changing the baking condition. Interestingly this type of structure emits evident lasing peaks which are stronger than that from the pristine nanowires. Through characterizing different samples, it is identified as multi-mode random lasing which is correlated with the random alignment of the nanowires. The lasing has an unusual temperature stability and can occur up to 700 K. In addition, lasing through guided modes in individual nanowires will also bee shown. For such waveguiding laser, the main concern is the mode intensity loss (at both edges and mirror ends), for which a larger diameter and a metal capping layer between the nanowire and the substrate are shown to be helpful.
9:00 PM - M11.27
Position-controlled ZnO/MgZnO Coaxial Nanotube Heterostructure Arrays.
Jinkyoung Yoo 1 , Young Joon Hong 1 , Hye Seong Jung 1 , Yong-Jin Kim 1 , Chul-Ho Lee 1 , Gyu-Chul Yi 2
1 National CRI Center for Semiconductor Nanorods, Department of Materials Sci. and Eng., POSTECH, Pohang Korea (the Republic of), 2 National CRI Center for Semiconductor Nanorods, Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of)
Show AbstractSemiconductor nanotubes with a hollow geometry are particularly interesting because of their high porosity and low mass density due to their extremely large surface-to-weight ratios. In particular, coaxial nanotube heterostructures that are fabricated with composition modulation along the circumferences of nanotubes can efficiently confine both carriers and emitted photons. This can make their optical and electrical characteristics much more useful for various device applications such as electron emitters, light-emitting devices, and waveguides than those of homogeneous nanostructures, However, during nanodevice integration, extremely precise control of the nanostructure position and dimensions is required. Here, the position-controlled growth and structural and optical characteristics of ZnO nanotubes and their coaxial heterostructures are presented. To control both the shape and position of ZnO nanotubes, hole-patterned SiO2 growth mask layers on Si(111) substrates with GaN/AlN intermediate layers using conventional lithography are prepared. ZnO nanotubes are grown only on the hole patterns by catalyst-free metal-organic vapor-phase epitaxy. Furthermore, the position-controlled nanotube growth method allows the fabrication of artificial arrays of ZnO-based coaxial nanotube single-quantum-well structures (SQWs) on Si substrates. In situ heteroepitaxial growth of ZnO and MgZnO layers along the circumference of the ZnO nanotube enable an artificial formation of quantum-well arrays in a designed fashion. The structural and optical characteristics of the ZnO nanotubes and SQW arrays are also investigated using synchrotron radiation X-ray diffractometry and photoluminescence and cathodoluminescence spectroscopy.
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Surface Dangling Bond Dependent Enhancement on Raman Scattering and Si-O-Si Stretching Mode Absorption of Si Nano-rods.
Yung-Hsiang Lin 1 , Yi-Hao Pai 1 , Gong-Ru Lin 1
1 Graduate Institute of Photonics and Optoelectronics, National Taiwan University , Taipei Taiwan
Show AbstractThe electrical and optical properties of Si nano-structural materials such as nano-crystals, nano-wires and nano-rods have attracted much attention due to their versatile photonic applications. However, structural defects such as surface dangling bonds are always accompanied with the Si nano-roughened surface to degrade the surface reflection/absorption and carrier transport dynamics. In the work, the surface dangling bonds enhanced Raman scattering and Si-O-Si stretching mode absorption of the vertically aligned Si nano-rods obtained by etching the (100)-oriented Si substrates are demonstrated. In experiment, the Si nano-rod sample was obtained by wet-etching the Si substrate in aqueous solution of HF and AgNO3 mixture with same concentration. Ag nucleuses are self-assembled into nano-particles and deposited at the etching pores randomly distributed on Si surface. The randomized pores on Si substrate eventually form Si nano-rods by dissolving its surface with increasing etching time. The area density of Si nano-rods with diameter of about 50 nm on each sample is nearly identical. The nano-rod length is exponentially increased from 0.19 to 2.7 μm with the etching time lengthening from 2 to 20 min. The surface area which correlates well with the quantity of the surface dangling bonds is a linear function of the nano-rod length and can be precisely controlled by increasing etching time. The quantity of dangling bonds is linearly proportional to the surface area, therefore the increment of surface dangling bond is also proportional to A1/A0=1+(Nπd/A0)h, where A0 and A1 denote the surface areas of smooth and nano-rod covered Si substrates, respectively, N denotes the total quantity of Si nano-rods with diameter d and length h on Si substrate.A green laser with 532 nm wavelength is used as the pumping light source. The Stoke Raman scattering intensity is linearly increased with Si nano-rod length, which is assumed to be proportional to the quantity of surface dangling bonds. FTIR of Si-O-Si stretching mode related absorption is employed to quantitatively analyze the etching-time dependent variation on number of dangling bonds on the as-etched and oxidized Si nano-rod surface. The Si-O-Si mode related FTIR peak wave-number shifts from 1010 cm-1 to 1097 cm-1 with its spectral linewidth broadened to reveal the formation of the standard SiO2 due to the saturation of oxygen atoms accumulated on Si nano-rod surface. Samples with longer Si nano-rod reveal higher peak wave-number and broader absorption spectrum, indicating that the sample surface has fewer dangling bonds but exhibits complicated SiOx phases with changing O/Si composition ratios. After annealing at 1050oC for 30 minute to heavily oxidize the Si nano-rod surface, the surface dangling bonds are completely passivated to cause the Raman scattering intensity dramatically decreased. Weak Raman scattering intensity further confirms the Si-O-Si based surface dangling bond dependency.
9:00 PM - M11.29
Impurity Doping in Silicon Nanowires During and After Synthesis by Ion Implantation.
Naoki Fukata 1 2 , Naoyuki Saito 3 , Shinya Ishida 3 , Shigeki Yokono 3 , Keisuke Sato 1 , Jun Chen 4 , Takashi Sekiguchi 4 , Kouichi Murakami 3
1 International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Sciences, Tsukuba Japan, 2 , PRESTO, JST, Saitama Japan, 3 Institute of Applied Physics, University of Tsukuba, Tsukuba Japan, 4 Advanced Electronic Materials Center, NIMS, Tsukuba Japan
Show AbstractSilicon nanowires (SiNWs) are of great interest in the fields of both fundamental and application research. In order to realize nanoscale silicon devices using SiNWs, it is important to investigate the impurity doping. SiNWs were synthesized by laser ablation of a Si target with nickel as a metal catalyst and boron (B) and phosphorus (P) as dopants which were placed in a quartz tube heated at 1473 K in a flowing Ar gas. A frequency-doubled NdYAG laser (532 nm, 7ns pulse width, 10 Hz, 150 mJ/pulse) was used to ablate the targets. Micro-Raman scattering measurements were performed at room temperature with a 532-nm excitation light. Electron spin resonance (ESR) measurements were carried out at 4.2 K using an X-band ESR spectrometer to investigate the state of P donors in SiNWs. A Raman peak was observed at about 618 cm-1 for SiNWs doped with B during synthesis. The peak frequency is in good agreement with that of a local vibrational mode of B in Si crystal. The Fano broadening due to a coupling between the discrete optical phonon and a continuum of interband hole excitations was also observed in the optical phonon peak, which indicates heavily B doping. These results prove that B atoms were doped in substitutional sites of the crystalline Si core of SiNWs [1]. ESR measurements were also performed to investigate defects and P donor/conduction electrons in SiNWs. An ESR signal due to conduction electrons were observed for SiNWs doped with with P during synthesis, showing that P atoms were clearly doped in substitutional sites of the crystalline Si core of SiNWs [2]. B and P doping were also carried out by ion implantation. The local vibrational peaks of B, Fano interference, and the ESR signal of conduction electrons were clearly observed, showing the formation of p-type and n-type SiNWs.[1] N. Fukata et al., APL. 89, 203109 (2006). [2] N. Fukata et al., APL. 90, 153117 (2007).
9:00 PM - M11.3
Critical Parametres of Quasi-one-dimensional Growth of Nanowires According to the Scheme Vapor-Dropping-Liquid Crystal.
Valeriy Nebolsin 1
1 Laboratoire Nanowires, Voronezh State Technical University, Voronezh Russian Federation
Show AbstractIt was revealed that physics of the nanowhisker growth mechanism in the system vapor- liquid drop-crystal encloses facilitation of crystal layer initiation at the expense of the drop surface energy release in the process of its balling on top of the growing nanowire and leads to the considerable decrease of supersaturation necessary for the growth of crystallization front singular face at the specified speed. A driving force for the drop motion is an excess of free energy, a source of which is the outer surface of the drop. With all this going on steps of growth on the crystallization front face are formed on the closed border of three phases along the perimeter of the drop moistening. Limiting values of the biggest and the least semi-conductor nanowire radius, exceeding which quasi-one-dimensional crystal growth according to the scheme vapor-liquid drop-rystal is absent, were experimentally determined. It was revealed that the maximum critical radius of nanowires, grown according to the scheme vapor-dropping liquid-crystal, is determined by the correlation of capillary and gravitational forces, influencing the catalyst drop in the process of crystal growth, and the minimum possible nanowire radius is determined by the influence of the three-phase contact border line tension vapor-liquid drop-crystal on the balance conditions of the nanoscopic size drop. The impact effect of the line tension causes the increase of the nanodrop moistening contact angle and the decrease of thermodynamic stimuli for nanowire growth. The condition for the catalyst drop rupture into smaller drops, leading to the subsequent nanowire branching and the multiple crystal growth, is the exceeding of some critical quantity values of the phase division border crystal-gas free surface energy in respect of the border liquid-gas free energy value.
9:00 PM - M11.30
Hysteresis in Silicon Nanowire Field Effect Transistors.
Tae-Eon Park 1 , Myongha Kim 1 , Hwangyou Oh 1 , Ilsoo Kim 1 , Joonyoen Chang 2 , Suk-Hee Han 2 , Heon-Jin Choi 1
1 Department of Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of), 2 Center for Spintronics Research, Korea Institute of Science and Technology, seoul Korea (the Republic of)
Show AbstractCurrent planar metal oxide field-effect transistor (MOSFET) structures fabricated by top-down approach have limitation in the development of nano devices. In this regard, bottom up approach based on one-dimensional nanostructures such as nanotubes and nanowires have been interested in the development of nano devices. In particular, silicon nanowires (SiNWs) have been interested because of the dominance of Si in semiconductor industry, easy integration into CMOS process, and easy manipulation of shape, composition and their electrical properties. Meanwhile, unprecedented transport behavior appears in SiNW devices due to their “nano” characteristics. Hysteresis in SiNW field effect transistors (FETs) is one example that has to be understood clearly for enhanced performance and reliability of SiNW FET. In this study, we systematically investigated the hysteresis in SiNW FETs. We prepared SiNWs by vapor-liquid-solid (VLS) method in a chemical vapor deposition (CVD) furnace. We then fabricated SiNW FETs by disperse SiNWs on a SiO2 doped-Si substrate with Si substrate serving as the back gate, and deposited by metal electrodes (source and drain) through standard e-beam and/or photolithography. We observed peculiar hysteresis in SiNW FETs under ambient conditions. It, however, disappeared under vacuum (10-2 Torr) or N2 or O2 atmosphere. Moreover, it disappeared when the FETs were annealed at a temperature 550-600 °C. The hysteresis is ascribed to the combination of a large surface area to active channel volume ratio of NW FETs with surface induced dipole moments. It implies that the electrical transport in SiNW FETs is dominated by their large surface area. Based on the experimental results, an approach to improve the performance and reliability of SiNW FETs will be discussed.
9:00 PM - M11.31
Structural Properties of Axial Nanodiscs in GaN/AlGaN Nanowires.
Sonia Conesa-Boj 1 , Sonia Estrade 1 , Florian Furtmayr 2 , Martin Stutzmann 2 , Martin Eickhoff 2 3 , Francesca Peiro 1 , Joan Ramon Morante 1 4 , Jordi Arbiol 1 5
1 Departament d’Electronica, Universitat de Barcelona, Barcelona, CAT, Spain, 2 Walter-Schottky-Institut, Technische Universität München, Garching Germany, 3 I. Physikalisches Institut, Justus-Liebig-Universität, Giessen Germany, 4 , IREC, Catalonia Institute for Energy Research, Barcelona, CAT, Spain, 5 TEM-MAT, Serveis Cientificotecnics, Universitat de Barcelona, Barcelona, CAT, Spain
Show AbstractThe group III-nitride system is known for remarkable optical properties. With direct bandgaps ranging from 0.7 eV (InN) to 3.4 eV (GaN) and 6.0 eV (AlN), these materials are well suited for low-voltage and short wavelength (ultraviolet and blue) optoelectronic devices such as light emitting diodes and laser diodes. Semiconductor nanowires (NWs) are emerging as a powerful class of nanostructures that, through controlled growth and organization, are opening up substantial opportunities for novel nanoscale photonic and electronic devices. The integration of device function at the nanoscale can also be carried out during NW synthesis by varying the composition and/or doping during axial growth.The optical properties of complex heterostructures such as multi quantum wells (MQWs) are still a topic of current discussions. Due to the presence of polarization-induced electric fields, the emission properties of typical nitride QWs are strongly influenced by the Quantum Confined Stark effect, leading to a redshift of the emission energy and a decrease in luminescence intensity. As the impact of piezoelectric polarization strongly depenbdes on strain and relexation in the QWs, many recent works have been dealing with QWs growth on semiconductor NWs in the last decade. These QWs can be grown as axial nanodiscs (along the growth axis) or as coaxial/prismatic, those created as a shell of the central NW core [1, 2]. In the present work we report a detailed structural investigation of GaN/AlN and GaN/AlGaN nanowire heterostructures with different Al concentrations. These NWs exhibit the presence of GaN multi quantum wells.They have been grown by Plasma-Assisted Molecular Beam Epitaxy (PAMBE) as described in Ref. [3]. To obtain a complete characterization of the GaN/AlGaN MQW nanowires, their morphology, structure and chemical composition are studied by means of high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) in bright field, and high angular annular dark-field (HAADF) modes, and electron energy loss spectroscopy (EELS), respectively. In addition to the structural analysis, the optical properties of these nanowires are studied by means of Photoluminiscence (PL) techniques. These optical properties for NWs with MQWs of different widths, are compared with the results from the HRTEM and HAADF measurements.References[1]A. Fontcuberta i Morral et al. Small, 4, 899 (2008)[2]M. Heigoldt et al. J. Mat. Chem, 19, 840 (2009)[3]F. Furtmayr et al. J. Appl. Phys., 104, 034309 (2008)
9:00 PM - M11.32
Influence of Zinc Blende Phase on the Preferred Growth Directions of GaN Nanorods Non-catalytically Grown on Si (111) Substrates.
Sanghwa Lee 1 , Taegeon Oh 1 , Boa Shin 1 , Chinkyo Kim 1
1 Physics, Kyunghee University, Seoul Korea (the Republic of)
Show Abstract GaN is a wide-band-gap semiconductor with two possible phases, a wurtzite and a zincblende structure. Due to its wide and direct-bandgap characteristics, it has drawn much attention for short-wavelength light-emitting devices, such as white light emitting diodes, blue and UV laser diodes for high-density storage media, and high-power and high-temperature devices. However, because of large mismatch in thermal expansion coefficients and lattice constants between GaN and its substrates, a very high dislocation density is commonly observed in GaN layers heteroepitaxially grown on sapphire or other substrates. If the dislocation density and strain of GaN thin films are to be reduced, lower dimensional structures, such as nanograins, nanorods, and nanowires composed of GaN and related III-nitrides, are thought to be promising candidates. Due to the confinement effect in 1D and reduced defect density, the 1D GaN structure in optoelectronic devices shows a relatively high efficiency compared to that of broad-area GaN films. Light-emitting-diode (LED) structures utilizing GaN nanorods grown by using hydride vapor phase epitaxy (HVPE) were previously reported to show superior optical properties compared to LEDs made of broad area films. On the other hand, the vapor-solid growth mechanism can give rise to diversity in the formation of nanorods with various structures. Branched multipods of ZnO or CdSe have been broadly investigated, and tetrapod-nanostructure-based photovoltaic devices showed improved electron extraction compared with one-dimensional nanorod structures or bulk materials. In addition, optically-pumped lasing has been demonstrated in ZnO multipod structures by a number of groups. According to these results, the GaN multipod nanorod structure may have exploitable advantages as an optical device. Therefore, selective synthesis of either vertically-aligned GaN nanorods or multipod structures may be necessary in order to fabricate more efficient nano-scale devices, but the research in this area on GaN has been very limited. In this work, GaN nanorods were grown on Si(111) substrates by using hydride vapor phase epitaxy, and crystallographic characteristics associated with their preferred growth directions were investigated by utilizing synchrotron x-ray reciprocal space mapping in a grazing incidence geometry and scanning electron microscopy. Crystallographic analysis reveals that the nanorods containing both wurtzite and zinc blende phase tend to be more vertically aligned than those containing only wurtzite phase. The subtle roles of zinc blende phase on the preferred growth directions of GaN nanorods grown on Si(111) is discussed. This work was supported in part by the Seoul Research and Business Development Program-Grant No.10583.
9:00 PM - M11.33
Gas-phase, Catalytic Growth of Si Nanowires with Sub-5 nm Ni Nanoparticles Synthesized in an Atmospheric-pressure Microplasma.
Pin Lin 1 , R. Mohan Sankaran 1
1 Chemical Engineering, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractThe interesting electronic and optical properties of silicon (Si) nanowires are uniquely determined by their atomic-scale structure and composition. A critical challenge for emerging applications in electronics, photonics, and photovoltaics is the growth of high-purity nanowires with controlled diameters and lengths. While there have been previous reports of diameter-controlled Si nanowire growth [1], the most commonly used catalyst material, Au, is a deep-level impurity that has been found to detrimentally affect the optical properties [2]. We have recently developed a two-step, gas-phase process to study and grow well-defined Si nanowires with alternative catalyst materials such as Ni and Fe and produce optically-active material. In the first step, narrow distributions of nanometer-sized nanoparticles tunable between 1 and 5 nm mean diameter are synthesized in a continuous-flow, atmospheric-pressure microplasma. We have previously shown that vapor-phase precursors such as nickelocene can be non-thermally dissociated in the microplasma to homogenously nucleate nanoparticles [3]. Particle growth and agglomeration is limited by the microreactor geometer (< 1 nanoliter) to obtain narrowly-dispersed nanoparticles. The aerosol flow is then injected directly into a tubular flow furnace with hydrogen (H2) and silicon tetrachloride (SiCl4) gas to catalyze the growth of Si nanowires. In this talk, we will show that the Si nanowire nucleation and growth discretely depends on the catalyst material, catalyst diameter, furnace temperature, and gas composition. Characterization of the Si nanowires by high-resolution transmission electron micrscopy (HRTEM), micro Raman spectroscopy, and photoluminescence (PL) spectroscopy will be discussed.1. M.S. Gudiksen, J. Wang, and C.M. Lieber, J. Phys. Chem. B 105, 4062-4064 (2001).2. R. H. Hopkins and A. Rohatgi, J. Crystal Growth 75, 67 (1986).3. Wei-Hung Chiang and R. Mohan Sankaran, Appl. Phys. Lett. 91, 121503 (2007).
9:00 PM - M11.36
On the Luminescence of VLS-grown GaAs-AlGaAs Core-shell Nanowires and its Dependence on MOVPE Growth Conditions.
Paola Prete 1 , Nico Lovergine 2 , Ilio Miccoli 2 , Jonadan Ando Burger 2 , Giancarlo Salviati 3 , Laura Lazzarini 3 , Takashi Sekiguchi 4
1 IMM, CNR , Lecce Italy, 2 Dept. of Innovation Engineering, University of Salento, Lecce Italy, 3 IMEM, CNR, Parma Italy, 4 Nanomaterials Laboratory, National Institute for Materials Science, Tsukuba Japan
Show AbstractWe report on the luminescence of free-standing GaAs/AlGaAs core-shell nanowires grown by Au-catalysed MOVPE on (111)B-GaAs and (00.1)-sapphire substrates using tertiarybutylarsine, trimethylgallium, and trimethylaluminium (TMAl). Colloidal Au nanoparticles were used as catalyst for the VLS growth of nanowires. Cylindrically-shaped (111)B-aligned and kink-free GaAs nanowires were grown at 400°C [1], with average diameters in the 50÷70 nm range and lengths up to ~10 µm. AlGaAs shells with thickness ranging in the 70÷160 nm interval were then grown at 650°C by conventional MOVPE. Compositional analysis by Energy Dispersion X-ray spectroscopy (EDS) were performed on single core-shell nanowires in a transmission electron microscope using high angle annular dark field (Z-contrast) imaging mode. The Al composition in the shell alloy turned out to be x(Al)=0.32±0.02; a high carbon signal was also detected within the nanowire core and ascribed to unintentional carbon doping during VLS growth. Photoluminescence (PL) spectra recorded from dense arrays of GaAs-AlGaAs core-shell nanowires showed similar emissions for samples grown on GaAs or sapphire, the nanowire core emission being dominated by a broad band in the 1.49-1.51 eV energy range. Comparison with high resolution cathodoluminescence spectra recorded from single core-shell nanowires demonstrated that each nanowire has a core emission slightly (within few tens of meV) shifted in energy [2], an effect ascribed to a varying built-in electric field at the core–shell hetero-interface. Notably, decreasing the V:III ratio among precursors from 30:1 to 4:1 during either GaAs core or AlGaAs shell growth leads to a broadening and red-shift of the GaAs core PL emission, along with the appearance of a weak broad emission band at around 1.67 eV, ascribed to a spatially indirect transition between electrons in the core and holes in the shell. Both these effects are consistent with the build-up of a space-charge induced electric field at the core-shell hetero-interface, the latter associated to the unintentional incorporation of C in GaAs and Si in AlGaAs, assumed as dominant acceptors and donors in the core and shell materials, respectively. Si doping of the AlGaAs shell was indeed proved in our samples as a result of residual background contamination of the TMAl source.[1] P. Paiano et al., J. Appl. Phys. 100 (2006) 094395.[2] P. Prete et al., J. Cryst. Growth 310 (2008) 5114.
9:00 PM - M11.39
Crystal Structure and Orientation of Nanowires.
Dominik Kriegner 1 , Mario Keplinger 1 , Aaron Maxwell Andrews 2 , Julian Stangl 1 , Gottfried Strasser 2 , Guenther Bauer 1
1 Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz Austria, 2 Institut fuer Festkoerperelektronik, Technical University of Vienna, Vienna Austria
Show AbstractMaking semiconductor nanowires exploitable for applications, requires precise control of their structural properties. For this purpose we use x-ray diffraction to investigate semiconductor nanowires with respect to their epitaxial relationship to the substrate and their orientation distribution. Due to defects, such as stacking faults, the crystal lattice orientation may change in nanowires rather easily. We present a method for the determination of the crystal orientation of nanowires using x-ray diffraction pole figures. Our method is based on diffraction measurements using monochromatic x-rays from which we directly obtain the distribution of lattice directions. This is done by looking at Bragg diffraction from certain lattice planes while changing the orientation of the sample. The method allows for separate determination of the crystal orientation of the constituents of nanowire heterostructures. Analyzing such pole figures we find that stacking faults leading to 60 degree rotation of the lattice appear in Si and III-V nanowires. We also apply this method to a system of branched GaAs nanowires on Si nanowire trunks grown by a combination of MOVPE and MBE. The crystal orientation of GaAs and Si is determined from pole figure measurements on various Bragg reflections. We determine the relative orientation of the initial Si nanowires and the GaAs "branches", and find that stacking faults leading to a 60 degree rotation of the lattice appear not only perpendicular to the growth direction but also in several tilted directions.
9:00 PM - M11.42
Catalyst-Free GaN Nanowire Nucleation.
Kaylee McElroy 1 , Jon Callahan 1 , Benjamin Jacobs 2 1 , Martin Crimp 1 , Thomas Bieler 1 , Virginia Ayres 1
1 , Michigan State University, East Lansing , Michigan, United States, 2 , Sandia National Labs, Livermore, California, United States
Show AbstractExtensive research on nanowire devices and applications has unleashed exciting possibilities in a quest for smaller, faster electronic equipment, more sensitive detectors, and new devices that take advantage of the quantum mechanical world. One of the roadblocks to new nanowire technologies is a clear understanding of how nanowires are formed and how to control their growth. Nanowire growths can be grouped in two broad categories: catalytic growths and catalyst free growths. Catalyst free nanowire growths are useful in applications where catalyst particles are not desirable. GaN nanowires are of particular interest because of their unique optical and electronic properties. The formation mechanisms of catalyst-free GaN nanowire growth are studied through investigations of the matrix from which the nanowires grow by high resolution electron microscopy (HRTEM), selected area electron diffraction (SAED), X-ray diffraction (XRD) and scanning electron microscopy (SEM), and through novel use of the nanowires themselves as a diagnostic of their own growth mechanism. This work shows that nanowire orientation changes as a function of growth temperature and investigates this orientation change in terms of availability of nucleation sites and constituent adatom materials. A model consistent with evolving supersaturation conditions is proposed. [1] Jacobs, BW, Crimp, MA, McElroy, K, Ayres, VM, 2008. Nanopipes in gallium nitride nanowires and rods. Nano Lett, 8: 4354-4358[2] Jacobs, BW, Ayres, VM, Crimp, MA, McElroy, K, 2008. Internal structure of multiphase zinc-blende wurtzite gallium nitride nanowires”, Nanotech.19: 405706 (6 pp)[3] Jacobs, BW, Ayres, VM, Petkov, MP, Halpern, JB, He, MQ, Baczewski, AD, McElroy, K, Crimp, MA, Zhang, J, Shaw, HC, 2007. Electronic and structural characteristics of zinc-blende wurtzite biphasic homostructure GaN nanowires, Nano Lett. 7: 1435-1438[4] Jacobs, BW, Ayres, VM, Stallcup, RE, Hartman, A, Tupta, MA, Baczewski, AD, Crimp, MA, Halpern, JB, He, M, Shaw, HC, 2007. Electron transport in zinc-blende wurtzite biphasic gallium nitride nanowires and GaNFETs”, Nanotech.18: 475710 (6 pp)
9:00 PM - M11.43
Si-TiSi2 Hetero-structure for High Capacity and Stability Li Ion Battery Anode.
Sa Zhou 1 , Xiaohua Liu 1 , Yongjing Lin 1 , Dunwei Wang 1
1 Chemistry, Boston College, Chestnut hill, Massachusetts, United States
Show AbstractRecent years enormous efforts have been attracted to search new materials and/or novel structures for Li ion batteries with high stability and capacity. Among studied materials, Si stands for its high theoretical capacity (4200mAh/g). However, just like most other anode materials (eg, Sn and TiO2¬), Si exhibits large volumetric expansion during lithiation and poor conductivity. The first deficiency results in short cycling life time and the second one strongly limits the charge transfer efficiency in battery. Here we present a chemically synthesized Si-TiSi2 core-shell nanostructure to tackle these challenges. As one of the most conductive silicides, TiSi2 has been widely used in microelectronics as a contacting material. Here Si nanoparticles (NPs) were epitaxially deposited on the surface of two-dimensional TiSi2 nanonets (NNs). Besides maximizing Si/electrolyte interface area, this design also decreases electrode cracking degree because sufficient space is offered for the volumetric expansion of Si particles, which are bond together by TiSi2 NNs. Furthermore, because of the highly conductive core, the charge transport efficiency is significantly improved, which promises the device can be used at high charge/discharge rate. This design can be applied to other materials too. For example, TiO2-TiSi2 heterostructure exhibits excellent cycle stability and capacity at high charge-discharge rate too.
9:00 PM - M11.44
Mechanism of Cu2S Nanowire Array Growth at Ambient Temperature and Pressure.
Matthew Mayer 1 , Xiaohua Liu 1 , Dunwei Wang 1
1 Chemistry, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractOne-dimensional nanoscale semiconductor materials, such as nanowire arrays, have generated recent interest because of their favorable properties for use in photovoltaic devices. Namely, nanowire devices have shown improvements over thin-films in both light absorption and charge separation and transport. However, common methods of nanowire formation require the use of high temperatures, hazardous precursors, expensive catalyst materials, and/or sophisticated instrumentation, all of which make the processes costly and complicated. In contrast, we herein report the interesting growth mechanism of copper (I) sulfide (Cu2S) vertical nanowire arrays by a simple and well-controlled gas-solid reaction on copper metal. The nanowire growth occurs spontaneously at room temperature and pressure and requires no template or catalyst, producing vertical nanowire arrays of controllable length. Nanowire growth is controlled by the transport of Cu from the substrate to the tip, resulting from Cu vacancy diffusion through the crystal. Importantly, rapid growth and vertical nanowire orientation is best achieved when the copper substrates are subjected to electropolishing, or electrochemical planarization, prior to growth.Cu2S is a promising material for photovoltaics due to its narrow bandgap (1.2 eV) and high absorption coefficient, and the facile synthesis of Cu2S nanowire arrays makes the material a promising candidate for use in photovoltaic cells. Furthermore, the uncommon yet simple growth mechanism can likely be applied to the fabrication of a host of other semiconductor nanostructures.
9:00 PM - M11.46
Zigzag Sphalerite ZnS Nanowires: Large Scale Synthesis and Their Structure Evolution Induced by Electron-irradiation.
Daesoo Kim 1 , Paresh Shimpi 1 , Pu-Xian Gao 1
1 , University of Connecticut, Storrs, Connecticut, United States
Show AbstractLarge scale zigzag zinc-blend single crystal ZnS nanowires have been successfully synthesized during a vapor phase growth process with a small yield of straight wurtzite single crystal ZnS nanowires. AuPd alloy nanoparticles were utilized to catalyze a vapor-solid-solid growth process of both types of ZnS nanowires, instead of the vapor-liquid-solid growth process. Surprisingly, the vapor-phase grown zigzag zinc-blend ZnS nanowires are metastable under high energy electron irradiation in transmission electron microscope (TEM), with straight wurtzite nanowires to be much more stable. Upon exposure to electron irradiation, wurtzite ZnO nanoparticle layer formed on the zigzag zinc-blend ZnS nanowire surface with displacement damage occurred simultaneously. The electron inelastic scattering and surface oxidation as a result of electron-beam heating take effect in this structure evolution process. When prolonged higher voltage electron irradiation was applied, local zinc blend ZnS nanowire bodies could evolve into ZnS-ZnO nanocables, ZnS-ZnO nanotubes, and dispersed ZnS-ZnO nanoparticle networks. Random AuPd nanoparticles were observed distributed on zigzag ZnS nanowire surface, which might impose a catalytic oxidation effect to speed up the surface oxidation induced structure evolution.
9:00 PM - M11.48
Controlling Mechano-electronic Superlattices in Hybrid Nanowire Ribbon/Quantum Dot Structures.
Clark Ritz 1 , Ming-Huang Huang 2 , Bozidar Novakovic 3 , Hyun-Joon Kim-Lee 2 , Narayana Appathurai 5 , Rebecca Metzler 2 , Pupa Gilbert 2 , Kevin Turner 4 , Irena Knezevic 3 , Max Lagally 2 1
1 Physics Department, University of Wisconsin, Madison, Wisconsin, United States, 2 Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States, 3 Electrical and Computer Engineering, University of Wisconsin, Madison, Wisconsin, United States, 5 Synchrotron Radiation Center, University of Wisconsin, Madison, Wisconsin, United States, 4 Mechanical Engineering, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractNanowire ribbons fabricated from ultra-thin Si membranes are a useful platform for the creation of hierarchical self-assembled hybrid nanoribbon/quantum dot structures. We combine the lithographic patterning of Si nanoribbons with mechanically-controlled self ordering of epitaxial Ge and SiGe quantum dots (QDs) to produce a narrow Si ribbon with alternating strain fields along its length [1]. Strained Si has a different band structure from unstrained Si, therefore an electronic superlattice exists along the length of the ribbon which could create minibands and alter the ribbon’s density of states [2]. Combining photoemission electron microscopy (PEEM) and x-ray absorption spectroscopy [3], we have observed the influence of local strain on the Si bandstructure in such strained ribbons.We pattern nanoribbons between ~100 nm and ~1 micron wide on ultrathin silicon on insulator (SOI) substrates with a thick (3 micron) buried oxide whose Si template layers have been thinned to a thickness of ~20 nm. The ribbons are tethered at the ends and are suspended above the substrate after partially etching away the buried SiO2 layer with hydrofluoric acid. After this release step the ribbons, still attached to the original host wafer, are subject to an epitaxial overgrowth of self assembled SiGe or Ge QDs by ultra-high vacuum chemical vapor deposition. The interaction of the strain field created by an initial QD with the elastic anisotropy of the Si ribbon creates nearby nucleation sites on the opposite surface of the ribbon for QDs, which in turn reach back through the thin membrane to influence the nucleation of QDs on the top surface. This process leads to a self assembled and self ordered network of nanostressors on the surfaces of the ribbon and a network of strained and unstrained regions within the ribbon itself.One-dimensional modified Kronig-Penney calculations based on the electronic response of Si to strain, the size and spacing of QDs, and the amount of strain induced by each QD predict the formation and structure of minibands under different conditions (e.g., for different QD compositions and Si membrane thicknesses). Such a periodic nanowire exhibiting a tunable electronic miniband could have a sharply peaked density of states, particularly useful in a thermoelectric material. Si nanowires have been shown to have greatly enhanced thermoelectric properties over bulk Si due to a lowering of thermal conductivity. Because of the sharpening of the density of states by the minibands, our ribbon/QD structure could have an improved Seebeck coefficient as well. PEEM measurements have observed local shifts of approximately 100 meV with a spatial resolution better than 100 nm.[1] H. J. Kim-Lee, et al., Physical Review Letters 102, 226103 (2009).[2] M. H. Huang, et al., ACS Nano 3, 721 (2009).[3] C. Euaruksakul et al., Physical Review Letters 101, 147403 (2008).
9:00 PM - M11.49
Self-assembled Crystalline Silicon Carbide Y Junctions and Heterostructures.
Zhenyu Liu 1 , Vesna Srot 2 , Judith C. Yang 1
1 Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 , Max-Planck-Institute for Metals Research, Stuttgart Germany
Show AbstractHere we show that the coalescence of the nucleated iron catalysts can lead to crystalline SiC Y junctions, where the SiC branches are either parallel or inclined with respect to each other. The resulting crystalline SiC Y junctions have been observed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The microstructure of the resulting products is analyzed by various techniques, including X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) as well as high resolution transmission electron microscopy (HRTEM). Intriguingly, the nucleated metal catalyst droplets could coalesce and the merged catalyst would remain catalytic activity and assist the growth related to the original branches, ultimately, crystalline SiC Y junctions have been successfully synthesized. The Y junction with two parallel branches of various diameters suggests that the Y junction can be induced by the growth kinetics attributed to the diameter dependence, such as by the Gibbs-Thomson or surface tension effect. The crystalline SiC Y junction formed by coalescence of two parallel branches follows the original growth direction and the merged catalyst yields a shared interface due to the same growth directions of two parallel branches and creates a single crystal stem. Whilst the crystalline SiC Y-junction formed by coalescence of two inclined branches, the merged catalyst creates a bicrystal stem with a planar grain boundary along the center of the stem and with two crystal orientations reflecting the orientation of each inclined branch. The coalescence of already nucleated catalyst droplets will open the solution for straightforward crystalline nanowire junction and heterostructure formations. These understanding may provide a lead to a novel modulation approach of nanowire by tailoring solid-liquid interface between the catalyst droplet and solid precipitated nanowire, the growth front of nanowire development, which might be extended to other systems in terms of various nanojunction formations.
9:00 PM - M11.5
β-Ga2O3 Nanowires and Nanobelts Synthesized by Using GaAs Powder Evaporation.
Hee Suk Chung 1 , Do Hyun Kim 1 , Eu Sun Yu 1 , Jung Han Kim 1 , Tae Jun Ko 1 , Kyu Hwan Oh 1
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe report the synthesis and characterization of β(monoclinic)-Ga2O3 nanowires and nanobelts prepared by using GaAs powder evaporation under a low vacuum condition (300Torr). As-grown -Ga2O3 nanostructures were synthesized based on the well-known vapor-liquid-solid (VLS) mech-anism by employing a Au thin film and vapor-solid (VS) reaction. Dense and uniform Ga2O3 nanowires with a diameter of ~80 nm were synthesized at a higher temperature (800°C), while various nanostructures including nanowires and nanobelts were found around 650° C. The crystalline structures and the chemical compositions of the as-synthesized β-Ga2O3 nanostructures were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmissionelectron microscopy (TEM), and energy dispersive X-ray spectrometry (EDS).
9:00 PM - M11.50
Writing Si Nanowires on Si(100) with an STM Tip: Surface Preparation and Initial Results.
Joshua Smith 1 , Weihua Hu 3 , Ying Yi Dang 1 , Onur Ozcan 4 , Metin Sitti 4 , James Bain 2 , Robert Davis 1 , David Ricketts 2
1 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 3 Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 4 Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractA persistent problem in nanotechnology has been the fabrication of nanoscale features in deliberate patterns. One approach for writing such patterns employs the current emitted from the probe tip of a scanning tunneling microscope (STM) to decompose molecules adsorbed on a cleaned and reconstructed surface. One objective of the present research is the “writing” of silicon nanowires on a clean, reconstructed Si(100) surface via the cracking of a monolayer of chemically adsorbed disilane. The probe tip of the STM is rastered over the surface to create an arbitrary pattern of Si nanowires. The cleaning and other surface preparation procedures will be presented for obtaining an oxide- and hydrocarbon-free (2x1) Si(100) surface. The results of characterization of the cleaned and reconstructed surface using x-ray photoemission spectroscopy, Auger electron spectroscopy, and scanning tunneling microscopy will be presented. Initial results concerned with disilane adsorption and the nanoscale writing experiments will also be detailed.
9:00 PM - M11.52
Dopant Incorporation in VLS-grown Semiconductor Nanowires Studied Using Atom Probe Tomography.
Eric Hemesath 1 , Daniel Perea 1 , Lincoln Lauhon 1
1 Materials Science & Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractThe vapor-liquid-solid (VLS) growth mechanism has been widely used to synthesize semiconductor nanowires with excellent control of ‘bulk’ composition. While many groups have demonstrated that doping during VLS growth can be used to control nanowire conductivity, quantitative dopant concentrations are generally not reported, despite their value for comparison with electrical properties. Recently we have shown that laser-assisted atom probe tomography (APT) can be used to determine three-dimensional dopant distributions in nanowires with sub-nm resolution.[1] Here we focus on the characterization of Si nanowire homojunctions to provide new insights into doping efficiency of the VLS growth. Silicon nanowires were grown in a hot-walled chemical vapor deposition (CVD) reactor using silane as a precursor. Diborane and phosphine were introduced sequentially to define a p-type segment followed by an n-type segment. Immediately following the Si nanowire growth, a Ge shell was deposited to encase the entire nanowire and provide a radial marker for APT experiments. Several aspects of the dopant distribution were analyzed. First, we found that boron doping of the nanowire core continued for some time after the diborane precursor source was evacuated from the growth chamber. By fitting the B concentration along the nanowire axis, the B segregation coefficient was determined and the amount of B dissolved in the Au-Si catalyst was estimated. Second, surface doping with P was observed, as we reported previously.[2] The P diffusion coefficients in the Ge shell and Si core were determined by fitting the concentration profiles. Finally, the influence of different background gases on surface doping was investigated, enabling a comprehensive understanding of distinct incorporation pathways that contribute to nanowire doping during CVD growth. [1] Perea, Hemesath, et al, Nature Nanotech. 4, 315 (2009).[2] Allen et al, Adv. Mater. 21, 1-6 (2009).
9:00 PM - M11.53
Selective Fabrication of Multifunctional ZnO Nano-heterostructures.
Nilima Hullavarad 1 , Shiva Hullavarad 1
1 Office of Electronic Miniaturization, University of Alaska Fairbanks, Fairbanks, Alaska, United States
Show AbstractAs miniaturization of electronic devices progresses, there is a need for innovation in materials, processes, systems and circuit designs that are robust, operate at low power and have multifunctionality. Large surface areas and quantum confinement effects in small dimensional nanoscale materials lead to unique properties (electronic, optical, chemical and thermal etc.) and their coexistence in one material that is not normally observed in bulk materials. These unique properties can be exploited to make devices that allow extreme miniaturization and enhanced functionality. In this paper, we demonstrate the selective area growth of ZnO nanowires using various catalysts. Some of the catalysts are so chosen as to inhibit the growth of nanowires. Nanomaterials based on ZnO are extremely attractive due a direct optical band-gap (Eg = 3.37 eV) material with a large exciton binding energy (60 meV), exhibiting near UV emission, and tunable for transparent conductivity and piezoelectricity. The ZnO nanowires are grown on p-Si and NiO (inherently p-type) to form the heterostructures. The nano-heterostructures are used to fabricate multifunctional sensors. The heterostructures exhibit excellent signal-to-noise properties of the order of >10E4. Application of our approach combined with growth of variety of nano materials with controlled organization will be discussed. We will present the results on the optical properties of ZnO nanowires and correlate with the heterostructure electrical properties.
9:00 PM - M11.54
Processing and Characterization of Atomic Force Microscope-Induced Direct Deposition of Semiconductor Nanostructures.
Jessica Torrey 1 , Stephanie Vasko 2 , Peter Morse 1 , Marco Rolandi 1
1 Materials Science and Engineering, University of Washington, Seattle, Washington, United States, 2 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractCurrent nanostructure synthesis offers detailed structural control, but precise positioning is still being pursued. Direct deposition of materials merges lithography and synthesis in one step to overcome this issue. Recent work has proven atomic force microscope (AFM)-induced direct deposition as a viable means of writing semiconducting nanofeatures in complex geometries. By applying a potential difference between the probe of the AFM and a conducting surface, reactions are triggered that afford the deposition of inorganic nanowires from a designated liquid precursor. Results will be presented on the characterization of two direct-deposited systems, carbon and germanium, including phase and microstructural analysis and preliminary electronic conductivity investigations.
9:00 PM - M11.55
Carrier Transport in MOVPE-Grown GaAs and Core-Shell GaAs/AlGaAs Nanowires.
Eric Gallo 1 , Guannan Chen 2 , Jonadan Ando Burger 2 , Ilio Miccoli 3 , Michael Coster 2 , Stephanie Johnson 2 , Craig Johnson 2 , Adriano Cola 4 , Paola Prete 4 , Nico Lovergine 3 , Jonathan Spanier 2 1
1 Electrical & Computer Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 3 Innovation Engineering, University of Salento, Lecce Italy, 4 Institute for Microelectronics and Microsystems, National Research Council, Lecce Italy
Show AbstractWe present the results of experimental investigations of the electronic transport within GaAs and GaAs/AlxGa1-xAs (x = 0.33) core-shell nanowires (NWs) grown on (111)B-GaAs via Au nanoparticle-catalyzed metallorganic vapor phase epitaxy using trimethylgallium (Me3Ga), trimethylaluminium (Me3Al), and tertiarybutylarsine (tBuAsH2). High-resolution TEM and electron diffraction analysis of the co-axial NWs confirms that their axes are aligned along <111>. Two- and three-terminal electron transport measurements of Schottky-contacted GaAs and GaAs/GaAs/AlxGa1-xAs core-shell NWs were collected in the range of 4K < T < 450K and in selected contact configurations. The data exhibit temperature-dependent transport that is consistent with a metal-semiconductor-metal (MSM)-based model description. Our model incorporates contributions from the blocking contact(s) and the GaAs/GaAs/AlxGa1-xAs heterojunction(s), accounting also for thermal activation of background C doping in the NW core and Si doping in the shell.* *Work supported in part by the US Army Research Office under W911NF-08-1-0067 and by the NSF under DMR-0907381, DMR-0722845, and ECCS-0702716.
9:00 PM - M11.56
Magnetic Anisotropy in Room Temperature Ferromagnetic GaN:Cu Nanowires.
Sojung Shim 1 , Ungkil Kim 1 , Ilsoo Kim 1 , Tae-Eon Park 1 , Ju-Jin Kim 2 , Joonyeon Chang 3 , Han-Kyu Seong 1 , Heon-Jin Choi 1
1 , Yonsei University , Seoul Korea (the Republic of), 2 , Chonbuk National University, Jeonju Korea (the Republic of), 3 , Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractDiluted magnetic semiconductors (DMSs) are the promising candidates for spintronics. DMSs can be prepared by doping of semiconductors with transition metals (Mn, Fe, Co) that have partially filled d states. It transforms spin-frustrated semiconductors to ferromagnetic one. Meanwhile, room temperature (RT) ferromagnetism and magnetic anisotropy in DMSs are important to realize DMS-based spintronic devices. It has shown that room temperature ferromagnetism can be achieved in transition metal doped wide band gap semiconductors. However, the origin of ferromagnetism in these DMSs is still controversial, due to the possibility of magnetic secondary phases and uncertainty of magnetic interactions. Furthermore, magnetic anisotropy has been rarely realized in DMSs. We studied magnetic anisotropy in Ga1-xCuxN nanowires by the magnetoresistance (MR) measurement. The nanowires were ferromagnetic at room temperature, as confirmed by SQUID and XMCD characterization. For 4-probe resistance measurements of Ga1-xCuxN nanowires, metal electrodes (Ti/Au and/or Co) to a single nanowire were contacted using e-beam lithography techniques. A magnetic field up to H = ± 1 T was applied to the sample in the parallel and perpendicular directions with respect to the long axis of the GaN:Cu nanowire, respectively. The resistance exhibited hysteretic behaviour with two resistance minima at the switching fields for both parallel and perpendicular directions of the applied magnetic field with respect to the nanowire axis. We observed MR in both parallel and perpendicular direction, however, the MR signal is much larger in the parallel direction. We also observed negative and positive MR for the two different magnetic fields. It indicates that the magnetization in the remanent state lies mostly along the axis of the Ga1-xCuxN nanowires. At a switching field of H = ± 200 Gauss, the resistance sharply increased in both sweeping directions. Observations of hysteretic MR and switching fields demonstrate magnetic anisotropy in the room temperature ferromagnetic Ga1-xCuxN nanowires. It would helpful for realizing DMS based spintronics.
9:00 PM - M11.57
New Strategy for Biofunctionalization of ZnO Nanowires for Biosensor Applications.
Rizwan Khan 1 , Hyun-Wook Ra 1 , Jin Tae Kim 1 , Bo Ra Kang 1 , Yeon Ho Im 1
1 Chemical Engineering, Chonbuk National University, Jenju Korea (the Republic of)
Show AbstractZinc oxide (ZnO) nanowires have attracted considerable research attention on account of their superior properties, such as large piezoelectric constant, wide band gap energy (3.37 eV), large exciton binding energy (60 meV), high thermal and mechanical stability. Therefore, it is suitable for the fabrication of variety of devices which includes transparent transistors, optoelectronic devices, chemical and biological sensing. Although ZnO nanowires are one of the promising candidates for various applications, robust surface functionalization methods for biomolecules immobilization have not established yet for biosensor applications. In this work, we developed novel biofunctionalization methods of ZnO nanowires including covalent bonding of the silane based modifier, and surface polymerization using plasma for the immobilization of biomolecules on the ZnO nanowire surface. The chemical stability and solubility of the functionalized ZnO nanowires were evaluated under various pH conditions. Based on the optimized biofunctionalization method, the ZnO nanowires with biomolecules immobilized on the surface were evaluated using fluorescence microscopy and field effect transistor (FET) with electrolyte gate configuration for biosensor applications.
9:00 PM - M11.58
Theoretical Investigation on the Facet Formation Processes in InP Nanowires.
Tomoki Yamashita 1 , Toru Akiyama 1 , Kohji Nakamura 1 , Tomonori Ito 1
1 , Mie University, Tsu Japan
Show AbstractSemiconductor nanowires (NWs) are expected to play a key role in future nanotechnology due to their potential application as building blocks in electronics and optoelectronics. In particular, NWs consisting of group III-V materials (III-V NWs) have attracted much attention because of their specific electronic and optical properties. In order to control the NW growth, many experimental and theoretical studies have been carried out. So far, it has been found that the crystal structure of InP NWs is the wurtzite (W) structure, different from that in bulk form [1]. Besides, InP NWs grown by selective-area metalorganic vapor phase epitaxy exhibit two different types of facets, such as {1-100} and {11-20} facets, depending on the growth conditions [2]. InP NWs with {1-100} facets are formed for low V/III ratio and high temperature, while InP NWs with {11-20} facets are fabricated for high V/III ratio and low temperature. In spite of these findings, the facet formation processes in InP NWs still remain unclear. In this work, in order to clarify the relationship between the growth conditions and the formation of these facets, the adsorption-desorption behaviors of In and P atoms on InP{1-100} and InP{11-20} surfaces are investigated using ab initio-based approach in which surface phase diagram depending on temperature and pressure is described by comparing the calculated adsorption energy to chemical potential estimated by quantum statistical mechanics.Our calculated results show that both In and P adsorption energies are larger than the chemical potentials of In and P in vapor phase, respectively, i.e., adsorption probability of each adatom is negligible under the typical growth conditions. Subsequently, we investigated the adsorption-desorption behaviors of In atom on P-adsorbed InP{1-100} and InP{11-20} surfaces. The results suggest that In adsorption energies on these surfaces become smaller than the chemical potential of In atom in the vapor phase. Furthermore, the In adsorption energy on P-adsorbed InP{11-20} surface is found to be smaller than that on P-adsorbed InP{1-100} surface. From these calculated results, we can classify the growth conditions into two different types of regions. One is the region where In atom adsorbs on the these surfaces for low temperature and high pressure condition. In this region, lateral growth of InP NWs progresses as In adsorbs on the both surfaces. On the other hand, In atom adsorbs only on the {11-20} surface for high temperature and low pressure condition in the other region. In this region, side facets of InP NWs are terminated by {1-100} facets since the growth on the {1-100} surface is not predominant. These results are qualitatively consistent with experimental results in which InP NWs with {1-100} facets are formed at high temperature and InP NWs with {11-20} are fabricated at low temperature [2].[1] P. Mohan, J. Motohisa and T. Fukui, Nanotech. 16 (2005) 2903.[2] J. Motohisa, private communication.
9:00 PM - M11.59
Comparison of Silane and Disilane as Source Gases for Vapor-Liquid-Solid Growth of Silicon Nanowires.
Sharis Minassian 1 , Joan Redwing 1 2 3
1 Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractSilicon nanowires (SiNWs) have received increasing attention as potential building blocks for nanoscale devices. Development of such devices requires a better understanding of the synthesis process and the mechanism of wire growth. SiNWs are commonly grown by a vapor-liquid-solid mechanism utilizing different techniques such as chemical vapor deposition (CVD) and molecular beam epitaxy. Silicon tetrachloride (SiCl4) is typically used as the silicon precursor for high temperature, atmospheric pressure CVD while silane (SiH4) and disilane (Si2H6) have been used for lower temperature, low pressure CVD (LPCVD). The majority of studies have focused on SiNW growth using SiCl4 and SiH4 sources. Disilane is of interest since it is more reactive than silane and therefore may enable higher nanowire growth rates at lower temperatures and partial pressures. The lower thermal stability of disilane could also be an advantage to enable the growth of SiGe nanowires over the entire composition range at lower temperatures (275°C to 375°C) which are more compatible with the range of conditions typically used for Ge nanowire growth. Hence, in this study, the effect of growth parameters on the growth rate of SiNWs using disilane has been investigated and the results have been compared to that of silane.The growths were carried out in a hot wall LPCVD reactor at 13 Torr using 1% Si2H6 in H2 and 10% SiH4 in H2 as the gas sources. Oxidized silicon wafers coated with 3nm Au thin film were used as substrates. Higher SiNW growth rates at lower partial pressures were obtained using Si2H6 compared to that of silane, due to the greater reactivity of disilane gas. At T=500°C and PSi2H6=0.065 Torr a growth rate of 7 um/min was obtained which was ten times higher than that of silane (0.7 um/min at PSiH4=0.65 Torr). To investigate the effect of temperature, a series of experiments was performed using growth temperatures ranging from 425°C to 525°C. The growth rate was observed to increase exponentially with increasing temperature up to 490°C which is indicative of a kinetically-limited process. Above this temperature, the growth rate increased more slowly with temperature suggesting that the nanowire growth is mass transport limited in this range. The Arrehnius behavior at lower temperatures resulted in an activation energy of 31 ± 2 kcal/mol. Similar experiments with silane gave an activation energy of 30 ± 3 kcal/mol which is interestingly comparable to that of disilane. This result suggests that the rate-limiting step may be identical for nanowire growth with SiH4 and Si2H6. Silane, which is more stable, does not decompose homogeneously but rather is assumed to decompose via a surface reaction. However, pyrolysis of disilane in the gas phase readily occurs due to its lower stability producing SiH4 and silylene (SiH2). Hence the same molecule (SiH4) could be responsible for the surface reaction and nanowire growth in both cases.
9:00 PM - M11.6
Doped GeO2 Nanowires for Photonic Applications.
Pedro Hidalgo 1 , Emanuela Liberti 1 , Yamilet Rodriguez-Lazcano 1 , Bianchi Mendez 1 , Javier Piqueras 1
1 Fisica de Materiales, Universidad Complutense de Madrid, Madrid Spain
Show AbstractGermanium dioxide is a transparent conductive oxide with a high potential in optoelectronics mainly due to its wide band gap (5 eV), which makes this oxide attractive as host for optical dopants. By suitable doping of GeO2, luminescence devices from the ultraviolet-blue range to the near infrared may be developed. Doping of semiconductor oxide nanowires is an expanding field with unresolved problems, such as the interplay between native defects with impurities or the difficulty to achieve efficient impurity solubility in crystalline nanowires. A few works have been reported about doping of semiconductor oxide nanostructures with luminescent sensitive ions, as for instance Er in SnO2 (1) or Eu in Ga2O3 (2). In this work, luminescence properties of GeO2 nanowires doped with rare earth ions (Er and Eu) and metal impurities (Sn and Mn) are investigated. The nanowires have been obtained from compacted germanium powder by a vapor-solid process. This method enables to grow doped GeO2 nanowires in a single step process by the addition of doping elements into the initial powder. Morphology and luminescence properties have been evaluated by means of a scanning electron microscope (SEM) complemented with a cathodoluminescence (CL) setup. Light waveguiding experiments have been performed with the aid of an optical microscope. Spatially resolved X-ray photoelectron spectroscopy (XPS) measurements were also performed at the ESCA microscopy beamline of the Elettra synchrotron facility in Trieste. CL measurements reveal a complex blue-green visible band from GeO2 nanowires and their components have been discussed in relation with the presence of impurities and native defects. XPS shows that a germanium sub-oxide phase is present at the surface of some wires and may influence the optical properties. Rare earth doped wires show the characteristic emission lines of rare earth ions with a rather high efficiency, even at room temperature, which is useful for practical applications, and Mn impurities originate a luminescence band at 1.75 eV not observed in other doped wires. Sn codoping affects mainly to the morphology of the wires, avoiding the formation of sharp bends, and makes the nanowires more useful for waveguiding applications. Optical coupling of Er doped GeO2 nanowires for green laser light has been demonstrated.References:(1) J. Wu, J. L. Coffer, Y. Wang and R. Schulze, J. Phys. Chem. B 113, 12 (2009)(2) E. Nogales, J. A. García, B. Méndez and J. Piqueras, Appl. Phys. Lett. 91, 133108 (2007)
9:00 PM - M11.60
Threshold Switching in Wet-Chemically Synthesized Sb2Se3 Nanowires.
Karthik Chinnathambi 1 2 , Wei Jiang 1 , Rutvik Mehta 1 , Ramanath Ganapathiraman 1 , Theodorian Borca-Tasciuc 2
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractNanostructured chalcogenide semiconductor materials, especially nanorods and nanowires have been the subject of extensive research especially in the thermoelectric and memory switching arena. In this paper we report the electrical characteristics of wet-chemically synthesized nanowires of a wide band gap (Ea ~1eV) semiconductor, Sb2Se3. Nanorods (80 to 100 nm in diameter and 5-6 micron length) of Sb2Se3 were synthesized via a “rapid microwave route”. The nanorods were characterized for their structure and microstructure by X-ray diffraction and electron microscopic techniques. For electrical measurements, nanowires were dispersed on a Si/SiO2 substrate and the gold electrode contacts were fabricated in a four-probe configuration using photo and e-beam lithography. The I-V characteristics were measured in the range of 150–310 K. At low applied voltages the measured I–V curves show an Ohmic behavior, whereas at higher voltages the I–V characteristics become strongly nonlinear. Beyond a critical threshold voltage VT, the current increases drastically and the voltage snaps back towards lower voltages and the slope of the I–V curves becomes negative (Negative Differential Resistance, NDR). The experiments showed that the I-V traces are completely reversible without any significant hysteresis. The S-shaped I-V characteristics, where the sample goes from a high resistance state to a low resistance state known as “threshold switching” has been observed before in amorphous chalcogenide semiconductors including nanowires. Semiconductors exhibit this behavior, provided that a carrier generation driven by field and carrier concentration competes with a strong Shockley–Hall–Read (SHR) recombination via localized states. Amorphous chalcogenides are ideal systems to exhibit this behavior with their high level of defects which leads to the high concentration of donor as well as acceptor trap states. We report this behavior in a crystalline semiconductor nanowire which has not been observed before. The main reason responsible for the observed nonlinear transport in the present case might be the high surface area leading to the presence of high concentration of surface defect states. The surface states dominated transport was confirmed in our case through ambient dependent conductivity measurements (in vacuum verses air). The present results make these nanowires potential candidates for thermoelectric, memory switching and gas sensing applications.
9:00 PM - M11.61
Incoherent Transport in Nanowire - The Effect of Electron-phonon Interaction.
Hideyuki Nishizawa 1 , Satoshi Itoh 1
1 Advanced Functional Materials Lab. , Toshiba Corporate R&D Center, Kawasaki Japan
Show AbstractThe incoherent transport model based on electron-phonon interaction was introduced for calculating the current-voltage characteristics of the one-dimensional conductor (nanowire). The current-voltage characteristics of the nano silicon wire calculated based on this model was discussed. The charge transport process was described by the rate equation that contains the coherent (tunneling) rates and the incoherent (energy dissipation) rates, and the incoherent rate was calculated from the Hamiltonian in which the electron-phonon interaction was incorporated. The coherent transition corresponds to the electronic transition between electrode state and conductor state where the total energy of two states is conserved. On the other hand, the incoherent transition corresponds to the electronic transition between electrode state and conductor state where the energy difference between two states is equal to the dissipated phonon energy. Therefore, to execute the calculation by the rate equation, the density of states (DOS) of the electrode and the conductor and the special distribution of the phonon of the conductor are needed. The current-voltage characteristics was calculated by using the DOS of one-dimensional N-type semiconductor for the electrode and the DOS of one-dimensional intrinsic semiconductor for the conductor. In addition, the calculation was used the special distribution of the one-dimensional silicon phonon (1). The calculated results will be discussed in detail.(1) Y. Zhang, J. X. Cao, Y. Xiao, and X. H. Yan, J. App. Phys. 102, 104303 (2007).
9:00 PM - M11.62
Width-Dependent Electron Mobility of Silicon Nanowire.
Min-Hyun Lee 1 , Sung-Wook Nam 1 , Hyun-Mi Kim 1 , Wanjun Park 2 , Ki-Bum Kim 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Electronics and Computer Engineering, Hanyang University, Seoul Korea (the Republic of)
Show Abstract As the dimension of nanoelectronic circuits continue to shrink, it is important that the carrier mobility does not degrade and, if possible, improves. Moreover silicon nanowires are the most candidates due to its familiar materials system and properties. But electron mobilities of silicon nanowire field effect transistors (FET) are quite different from fabrication method and size of nanowire/metal contact. Silicon nanowires used in this study were fabricated with the conventional CMOS process with SOI wafer. The nanowire had been defined by 100kV electron beam lithography and chlorine reactive ion etching with hydrogen silsesquioxane negative resist. And the nanowires were oxidized for thinning the nanowires and recovering the etching damage from reactive ion etching. The widths of patterned nanowires were ranged from 5nm to 2000nm to investigate the electrical properties as nanowire scaling. Additionally, the nanowires were fabricated with two types, with micro size pad and without pad, to show the effect of nanowire/metal contact. The electrical properties of nanowire were investigated by using back gate FETs with Ti electrode. Electron was flown to 5nm width device with pad structure. Without pad structure, electron cannot flow under 50nm nanowire. From the transfer characteristic of FETs, on/off ratio and subthreshold swing were improved as nanowire miniaturization. And the electron mobility was continuously improved to 1275cm2/Vs at 20nm. but under 20nm, the electron mobility was extremely degraded by surface scattering effect. In this presentation, I will discuss about the fabrication method of sub-10nm silicon nanowire FETs and the electron mobility enhancement with nanowire miniaturization. Additionally, I will show on/off ratio improvement and effect of nanowire/metal contact as width decreasing for the silicon nanowire FETs.
9:00 PM - M11.63
Threshold Defect Production in 〈111〉-oriented Si Nanowire.
Eero Holmstroem 1 , Arkady Krasheninnikov 1 , Kai Nordlund 1
1 , University of Helsinki and Helsinki Institute of Physics, Helsinki Finland
Show AbstractSemiconductor nanowires represent an interesting possibility for new nanotechnological applications, and they are expected to play a crucial role in the future of electronic and optoelectronic devices. Silicon nanowires in particular have attracted much attention due to their successful application in sensor technology and in themanufacturing of transistors.The threshold displacement energy and threshold energy for sputtering are crucial quantities for understanding radiation damage in any solid state system. In silicon, understanding the behavior of the material under irradiation is especially important. This is due to theextensive use of the material under ion implantation and inapplications in harsh radiation environments, such as detectors inside particle accelerators or devices in space applications.We studied the threshold displacement energy and sputtering threshold energy of a silicon nanowire using classical molecular dynamics simulations with the Stillinger-Weber interatomic many-body potential. The wire was studied both in the completely relaxed state as well as with applied longitudal strain. The system was hexagonal in its cross section, with a diameter of 43 Å and a length of 103 Å inthe unstrained state, with the bulk core oriented in the <111> direction.The average threshold energy for creating a Frenkel pair within the bulk core of the wire was determined as a function of relative longitudal strain and was found to decrease linearly from 29.5 +- 0.3 eV to 19.3 +- 0.1 eV as strain on the wire was increased from 0.00 to 0.10. Also the minimum threshold energy for creating a Frenkel pairdecreased almost linearly, from 17.5 +- 0.5 eV to 12.5 +- 0.5 eV as a function of strain from 0.00 to 0.10. Remarkably, the average threshold energy for sputtering an atom from the reconstructed surface of the wire wasfound to remain practically constant as the strain wasincreased. Similarly, the minimum threshold energy for sputtering remained nearly constant. The formation energies of the relevant point defects were also studied as a function of strain, and these results were found to be in agreement with the results from the dynamic simulations.
9:00 PM - M11.64
Size-dependent Persistent Photoconductivity and Surface Band Bending in m-axial GaN Nanowires.
Hsin-Yi Chen 1 2 , Reui-San Chen 2 , Fu-Chieh Chang 1 , Li-Chyong Chen 3 , Kuei-Hsien Chen 2 3 , Ying-Jay Yang 1
1 Graduate Institude of Electronics Engineering, National Taiwan University , Taipei Taiwan, 2 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan, 3 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan
Show AbstractDifferent from the traditional films and bulks, nanowires, having large surface sensing area while maintaining a continuous transport path in the same time, show much higher photocurrent gain and responsivity as a light sensing material.[1,2] Accordingly, understandings of the size and/or surface effects on the transport properties of this one-dimensional nanostructure are crucial. Persistent photoconductivity (PPC) in GaN nanowires (NWs) induced by the absence of direct recombination is the most different PC characterization from their thin film contourparts. The PPC phenomenon will lead to different rise time (τr) and decay time (τd) in PC measurement. We propose the PPC is induced by surface band bending (SBB). Upon UV-light illumination, the electron-hole pairs (EHP) will be generated and suppress surface band bending. After the UV-light is turned off, the SBB will be recovered to the thermal equilibrium status. The EHP will be separated by SBB and brings out prolonged recombination lifetime. That is why rise time was typically ten times of magnitude longer than decay time. Here, we report the size-dependent PPC measurement. We found that the decay time will decrease with diameter reducing. It shows an obvious drop from 780s-150s while the diameter ranges from 120nm-20nm. As the photoconductivity of the m-axial GaN nanowires has been proved of being dominated by charge separation induced by surface electric field,[1,2] the strong diameter-dependent decay time result actually implies the lower surface band bending in smaller nanowires. On the other hand, we cannot find similar size-dependence from the rise time result. It also implies that SBB will be flattened under UV-light illumination so the rise time didn’t reveal obvious size-dependent phenomenon. In addition, power-dependent measurement was performed in order to verify the SBB in different size of GaN nanowires. We found all samples show that the fitting indices for different size of nanowires are around 0.85-0.89. The fitting indices values ranging from 0.8-0.9 represent that PC mechanism of GaN NWs is dominant by surface band bending other than bulk trap effect. However, the degree of surface band bending/electrical field cannot be distinguished from the power-dependent measurement. The probable cause to bring about the different result between τr and τd, as well as the relationship between persistent photoconductivity and surface band bending, are also proposed and discussed.
9:00 PM - M11.65
Effect of Growth-interruption on Structural and Optical Properties of GaAs/GaAsSb Axial Heterostructured Nanowires.
Dheeraj Dasa L 1 , ATJ van Helvoort 2 , Fervin Moses 1 , Hailong Zhou 1 , Thang Ba Hoang 1 , Bjorn-Ove Fimland 1 , Weman Helge 1
1 Institute of Electronics and Telecommunications, Norwegian University of Science and Technology, Trondheim, Sør-Trondelag, Norway, 2 Department of Physics, Norwegian University of Science and Technology, Trondheim, Sør-Trondelag, Norway
Show Abstract Recently it has been shown that band-structure can be engineered in nanowires (NWs) not only by modulating the crystal material but also the crystal phase [1]. Homomaterial (heterocrystalline) NW quantum dot confinement is possible by introducing either a twin plane in the zinc-blende (ZB) phase or a stacking fault (SF) in wurtzite the (WZ) phase. The growth of binary ZB GaP [2] and ZB InP [3] NWs with periodic twins is recently demonstrated by metal organic chemical vapor deposition (MOCVD) making also homomaterial NW quantum dot superlattices possible. However such controlled growth of either ternary NWs or NWs grown by molecular beam epitaxy (MBE) is still a challenging task. On the other hand, controlled growth of periodic SFs in WZ phase is still far from achievable.In this study we demonstrate the growth of ZB GaAsSb NWs with nearly-periodic twins by MBE, where the twinning frequency is varied by changing either the Sb mole fraction or the diameter of the NWs. This means that the Sb mole fraction in GaAsSb NWs can be estimated by measuring the twinning frequency. We employ this technique to check the effect of growth-interruption (GI) on the interfaces of GaAs NWs with GaAsSb inserts. These results are corroborated with state-of-the-art Cs-corrected transmission electron microscope. We find that a GI at the bottom interface of the GaAsSb insert deteriorates the uniformity of the Sb mole-fraction in the GaAsSb insert, while a GI above the GaAsSb insert enables us to control the crystal phase of GaAs barrier above the insert. Micro-photoluminescence measurements on these NWs show that the ZB GaAsSb insert with either ZB or WZ GaAs barrier at the upper GaAs barrier exhibit type II or type I band-alignment, respectively. Further, we demonstrate the techniques to eliminate the formation of SFs in WZ GaAs NWs [4] and their effect on the optical properties. The NW heterostructures with type I and type II band-alignment are interesting for different applications such as light-emitting devices, and photovoltaic devices respectively.References:1. D.L. Dheeraj, G. Patriarche, H. Zhou, T.B. Hoang, A.F. Moses, S. Grønsberg, A.T.J. van Helvoort, B.-O. Fimland, and H. Weman, Nano Lett. 8 (2008) 4459.2. J. Johansson, L.S. Karlsson, C.P.T. Svensson, T. Mårtensson, B.A. Wacaser, K. Deppert, L. Samuelson, and W. Seifert, Nat. Mat. 5 (2006) 574.3. R.E. Algra, M.A. Verheijen, M.T. Borgström, L.F. Feiner, G. Immink W.J.P. van Enckevort, E. Vlieg, and E.PA.M. Bakkers, Nature 456 (2008) 369.4. D.L. Dheeraj, G. Patriarche, H. Zhou, J.C. Harmand, H. Weman, and B.O. Fimland, J. Crystal Growth 311 (2009) 1847.*E-mail:
[email protected]9:00 PM - M11.66
Experimental Determination of Single Nanowire Absorption Cross-sections through Photothermal Heterodyne Imaging.
Jay Giblin 1 , Masaru Kuno 1
1 Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana, United States
Show Abstract Semiconductor nanowire (NW) absorption cross-sections (σabs) are important physical parameters that enable one to quantify NW concentrations, emission quantum yields, photocurrent conversion efficiencies, as well as the number of photogenerated carriers in optical experiments. However, despite the usefulness of σabs, such numbers are not common and to the best of our knowledge only two ensemble studies exist on the subject for NWs. As such, we present a method for determining single CdSe NW cross-sections using photothermal heterodyne imaging (PHI). NWs employed in this study were synthesized via solution-liquid-solid (SLS) methods yielding highly crystalline wires, possessing straight, v-shaped, y-shaped, and tripod morphologies. Wire ensemble radii were tunable between 3-15 nm with lengths readily exceeding 1μm. The distinct branching angles of the v-shaped, y-shaped, and tripod NWs made it possible to identify single wires during optical experiments. CdSe NW σabs values were determined by comparing their photothermal signal to the photothermal signal of gold nanoparticles (NPs) with known radii and absorption cross-sections. Specifically, Au NPs (rensemble=20.9 nm) with σabs = 5.47x10-11cm2 (determined via Mie theory at 532 nm) were compared to CdSe NWs (rensemble=9.65 nm) excited at 532 nm. The data revealed that on average, the NWs’ photothermal signal was 1.29 times larger per micron then the corresponding Au NPs’. Based on this 1.29x increase we obtain single CdSe NW cross-sections of ~7.08x10-11cm2μm-1 at 532 nm for circularly polarized excitation. These experimental values agree well with theoretical cross-sections for the same average NW radius derived from a Poynting vector analysis we have developed. The NWs studied also exhibited significant sensitivity to the polarization of excitation consistent with previous polarization anisotropy studies our group and others have conducted. In addition, single CdSe NW absorption and emission were found to be linear with respect to excitation power from ~180 kWcm-2 to ~7 MWcm-2 as determined by PHI in parallel with photoluminescence measurements. These studies add to the growing knowledge of single NW optical properties and compliment the efforts made by others to implement NWs into real world applications.
9:00 PM - M11.67
Controlled Growth of Disordered Si Nanowire Arrays at Room Temperature for Self-cleaning and Anti-reflection Applications.
Yu-An Dai 1 , Hung-Chiz Chang 1 , Chin-An Lin 1 , Jr-Hau He 1
1 , Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, Taipei Taiwan
Show AbstractVarious methods to synthesize Si nanowire arrays (Si NWAs) have been developed [1-3]. Very recently, Si NWAs have been widely utilized for the device applications, such as antireflection (AR) or self-cleaning [4, 5]. The reduction of surface reflection and the super-hydrophobic effect are desirable to apply for solar cells. To the best of our knowledge, there are no reports on the AR and super-hydrophobic effect on the structural properties, such as morphology and density of Si NWAs.In this work, the galvanic wet etching was adopted to fabricate disordered single-crystalline Si NWAs at room temperature in HF/AgNO3 solution. The length of Si NWAs could be controlled by adjusting the etching time, and the growth rate is estimated to be ~50 nm/min. An average total reflectance ~1% over a wide range of wavelength showed the broadband AR characteristics of Si NWAs. Angular dependent of spectral measurements of the Si NWAs are insensitive to TE and TM polarization, demonstrating omnidirectional AR characteristics. Excellent AR behavior is due to the gradient refractive index profile of Si NWAs. The effective index of Si NWAs was calculated by the effective medium theory. Morphology-dependent Brewster angle (i.e., the angle of incidence at which no reflection occurred for TM polarization) was observed. Moreover, the self-cleaning effect was examined by the basic contact angle and hysteresis theories. According to the Cassie’s theory, the calculation results agree well with the measured data, showing super-hydrophobic effect. Building self-cleaning feature into a broadband and omnidirectional AR coating can keep contamination to a minimum so that long-term performance of optoelectronic device can be maintained.References[1] Z. Z., X. H. Fan, L. Xu, C. S. Lee, and S. T. Lee, 2001, J. Cryst. Growth, 337, 18.[2] Y. Y. Wu and P. D. Yang, 2001, J. Am. Chem. Soc., 123, 3165.[3] S. P. Ge, K. L. Jiang, X. X. Lu, Y. F. Chen, R. M. Wang, and S. S. Fan, 2005, Adv.Mater., 17, 56.[4] W. L. Min, B. Jiang, and P. Jiang, 2008, Adv. Mater., 20, 3914–3918[5] Y. Li, J. Z., S. Z., H. D., Z. W., Z. S., J. Guo and B. Yang, J. Mater. Chem., 2009, 19, 1806–1810
9:00 PM - M11.68
Self-cleaning Si Nanorod Arrays for Broadband and Omnidirectional Antireflection.
Yi-Jui Lin 1 , Hsin-ping Wang 1 , Jr-Hau He 1
1 Graduate Institute of Photonics and Optoelectronics, National Taiwan University, TaiPei Taiwan
Show AbstractThe antireflection (AR) coatings are utilized to suppress undesired reflection between different optical media for various optical applications. For example, Multilayered coatings are widely used on the surface of optical and optoelectronic devices. However, it is suffered from the problems, such as poor adhesion, thermal instability, and lattice mismatch. An alternative to multilayered coatings is to pattern the surface with a periodically structured array with the periodicity smaller than the wavelength of the incident light. Compared with multilayered AR coatings, subwavelength structure (SWS) surfaces show several advantages over the conventional dielectric AR coating, including broad spectral and angular response, hydrophobicity, and durable, because the AR structures are directly etched in the surface and there are no other materials involved. So far SWSs has been fabricated on silicon have been fabricated by various methods. Moreover, enhance-hydrophobic effect on surfaces of optoelectronic devices have attracted attention because of their self-cleaning effect.In the present work, the SWSs combining AR and enhanced hydrophobic effects was reported. A simple method, which combines sub-wavelength-scale monolayer spheres with a reactive ion etching process, to fabricate AR structures of Si nanorod arrays (NRAs) was used. Spectral reflectance measurements of Si substrates with NRA SWSs showed drastic reduction in reflection over a broad range of wavelengths and a wide range of angle of incidence, demonstrating its ability to broadband and omnidirectional antireflection. The reflectivity and the wettability as a function of diameter, height, slope of Si NWAs were discussed.
9:00 PM - M11.69
Transport Mechanism of Si NWs.
Tz-Chen Kei 1 , Jr-Hau He 1
1 , Graduate Institute of Photonics and Optoelectronics, & Department of Electrical Engineering, National Taiwan University, Taipei, 10617 Taiwan, ROC, Taipei Taiwan
Show AbstractNanowires (NWs) are one of promising candidates for next generation electronics, such as vertical field-effect transistors, 1D solar cells, and two-dimensional photonic crystals. Understanding the transport across NWs is a key issue to fabricating high performance NW-based devices.In this work, the focused-Ion-beam-deposited Pt (FIB-Pt) contact with Si NWs is studied in details for the first time. The galvanic wet etching was adopted to fabricate single-crystalline Si nanowires (NWs) at room temperature in HF/AgNO3 solution. The temperature-dependent four-probe measurements indicate that the electrical conductivity of the Si NWs exhibits two regimes. Thermal activated transport with activation energy of ~0.045 eV attributed to the shallow donor states dominates at a temperature range of 390-325K. The Mott’s variable range hopping (VRH) model is applied to the conduction at a temperature range of 325-110K due to disorder effect cause by FIB-Pt deposition. Mott’s parameters of Si NWs, such as hopping energy, hopping distance and density of states have been estimated.
9:00 PM - M11.7
Epitaxial Growth and Ordering of GeTe Nanowires on Microcrystals Determined by Surface Energy Minimization.
Hee Suk Chung 1 2 , Yeonwoong Jung 2 , Do Hyun Kim 1 , Kyu Hwan Oh 1 , Ritesh Agarwal 2
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractHighly-aligned GeTe nanowires self-assemble epitaxially in two well-defined directions on octahedral GeTe microcrystals in a one step vapor transport growth process. The epitaxial relationship of nanowires with underlying microcrystals along with the growth orientations of nanowires were investigated in detail by using electron microscopy techniques combined with atomic unit cell simulations. We demonstrate that maximizing atomic planar density to minimize energy of the exposed surfaces is the determining factor that governs the unique growth characteristics of micro/nanostructures which evolve from three-dimensional octahedral microcrystals to tetrahedral bases to one-dimensional nanowires. The crystallographic understanding obtained from this study will be critical to understand, predict and control the growth orientation of nanostructures in three-dimensions.
9:00 PM - M11.70
Heterojunction Nanodevice based on CuPC/GaN Single Nanowire.
Chun-Chiang Kuo 1 3 , Wei-Chao Chen 1 3 , Shih-Chang Chen 2 , Kuei-Hsien Chen 1 3 , Li-Chyong Chen 3
1 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan, 3 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 2 Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung Taiwan
Show AbstractOrganic-inorganic hybrid systems have been investigated widely in the field of renewable energy because of a potential unification of the solution processability and large-area scalability of organic system with the high electron mobility, stability, and robustness of inorganic semiconductors. For the application of photodiode and photovoltaic devices, the unique geometry of 1-Dimensional nanostructure, with large surface to volume ratio, is considered to be able to improve the charge separation and collection efficiencies. Since it is most important to explore and improve the pure interface properties between organic molecules and inorganic materials, the design of single inorganic semiconducting nanowire/organic heterojunction device is presented in this work based on GaN nanowire (GaNNW) and copper phthalocyanine (CuPC), which have merits of high electron and hole mobility, and strong photo-absorption with proper energy band alignment.The nanodevice was fabricated by depositing CuPC and Au thin film on a dispersed single GaNNW via electron beam lithography process, and then followed by metal contacts deposition on both Au/CuPC and GaNNW with focus ion beam technique. Current-voltage (I-V) measurements exhibited typical diode behavior but with an unexpected high/low turn-on voltage, which should be attributed to the poor interface condition and the intrinsic surface band bending of GaNNW. By means of surface passivation with different surface-modification of GaNNW, the I-V characteristics were observed to be improved reflecting better contact between CuPC and NW. The wavelength-dependent photoconductivity and photoluminescence measurements were performed to characterize the involved charge transfer phenomena. In summary, the interface properties of CuPC/GaNNW heterojunction are studied based on a single nanowire device, which provide direct observations, evidences, and most importantly, better realization regarding to the photovoltaic application of organic-inorganic hybrid nanostructured system.
9:00 PM - M11.8
Silicon Nanowire Growth by Plasma Sputtering Method.
Kenkichi Nishimura 1 , Takumi Saegusa 1 , Yoshinori Takao 1 , Koji Eriguchi 1 , Kouichi Ono 1
1 Department of Aeronautics and Astronautics, Kyoto University, Kyoto Japan
Show AbstractNanowires have been attracting a great research interest all over the world for the last several years, because they are expected to exhibit novel electrical, optical, and mechanical properties owing to their unique one-dimensional structures [1]. Among nanowire synthesizing methods, the VLS (vapor-liquid-solid) originally developed by R.S.Wagner and L.C.Ellis in 1960s [2] is now the most widespread and successful method [3]. However, the VLS method employing high-temperature furnaces seems not suitable for synthesis of nanowires on large-diameter substrates, because of a difficulty to scale up the system [4]. In this paper, we demonstrate a new method with plasmas (PLS: plasma-liquid-solid) to synthesize nanowires, which employs plasma sputtering to supply source gases. The process of PLS is: a) A silicon substrate was cleaned in de-ionized water, and then etched in 1.0 % hydrofluoric acid to remove native oxides from the surface. b) A thin catalytic Au film (~ 10 nm thick) was deposited on the substrate by plasma sputtering. c) The substrate was annealed at temperatures higher than the Si / Au eutectic point (above 363°C), thus creating Au / Si liquid alloy nano-droplets on the surface (the droplets become smaller with thinner Au films). d) Si atoms were supplied onto the substrate at temperatures above 363°C by magnetron plasma sputtering, being diffused and dissolved into liquid alloy droplets. e) Supersaturated Si atoms were separated out at interfaces between liquid alloy droplets and substrates, which in turn result in growth of crystalline silicon nanowires. By using this method, we can synthesize nanowires at low temperatures as compared to the VLS method, and also we can scale up the substrates by applying semiconductor manufacturing processes. We will show detailed experimental results at the conference.[1] Z.L.Wang, Nanowires and Nanobelts: Materials, Properties and Devices, Volume 1, Metal and Semiconductor Nanowires, Springer (2006).[2] R.S.Wagner and W.C.Ellis, Appl. Phys. Lett. 4, 89–90 (1964).[3] N. Wang, Y.H. Tang, Y.F. Zhang, C.S. Lee, I. Bello, and S.T. Lee, Chem. Phys. Lett. 299, 237–242 (1999).[4] M. Law, J. Goldberger, and P. Yang, Ann. Rev. Materials Res. 34, 83–122 (2004).
9:00 PM - M11.9
Homogeneous Nucleation of Epitaxial CoSi2 and NiSi in Si Nanowires.
Yi-Chia Chou 1 , King-Ning Tu 1 , Lih-Juann Chen 2 , Wen-Wei Wu 3
1 , UCLA, Los Angeles, California, United States, 2 , National Tsing Hua University, Hsinchu Taiwan, 3 , National Chiao Tung University, Hsinchu Taiwan
Show AbstractHomogeneous nucleation is rare except in theory. We observed repeating events of homogeneous nucleation in epitaxial growth of CoSi2 and NiSi silicides in nanowires of silicon by using high resolution TEM. The growth of every single atomic layer requires nucleation. Heterogeneous nucleation is prevented because of non-micro reversibility between the oxide/Si and oxide/silicide interfaces. We determined the incubation time of homogeneous nucleation. The calculated and the measured nucleation rates are in good agreement. We used Zeldovich factor to estimate the number of molecules in the critical nucleus; it is about 10 and reasonable. A very high super-saturation is found for the homogeneous nucleation.
Symposium Organizers
Kornelius Nielsch University of Hamburg
Anna Fontcuberta i Morral Lab. des Materiaux Semiconducteurs Institut des Materiaux EPFL
Jason K. Holt NanOasis Technologies, Inc.
Carl V. Thompson Massachusetts Institute of Technology
M12: New Fabrication Methods
Session Chairs
Thursday AM, December 03, 2009
Constitution B (Sheraton)
9:30 AM - M12.1
Direct Growth of High Aspect Ratio Titania Nanowires on Transparent Conductive Oxide Surface using a Polymeric Nanotemplate.
Ying Chen 1 , Sang-Min Park 2 , Ho-Cheol Kim 2 , Jim McVittie 1 , Chiu Ting 1 , Yoshio Nishi 1
1 Electrical Engineering, Stanford University, Stanford, California, United States, 2 Almaden Research Center, IBM Research Division, San Jose, California, United States
Show AbstractTitanium dioxide (TiO2), an abundant, low-cost and non-toxic wide band gap semiconductor material, has found a variety of applications in optoelectric, electrochemical, and photoelectrochemical areas. In particular, anatase TiO2 has been used as the most suitable photoanode material in the fabrication of dye-sensitized solar cells (DSSCs) [1] due to its unique electronic energy band structure. Morphology of titania has been known as a critical factor determining the performance: for example, 1D single crystalline anatase TiO2 nanowire/nanotube arrays synthesized directly on a transparent electrode substrate are highly desirable to provide direct pathways for carriers, to minimize recombinations [2], and to increase surface area. In this paper, we report the formation of high aspect ratio TiO2 nanowires on top of fluorine doped tin-oxide (FTO) coated glasses. We used a sacrificial polymeric template containing cylindrical pores wherein titania was deposited by a cathodic electro-deposition. To achieve high-aspect ratio of pores in polymer template, we adopted a multi-level anisotropic reactive ion etching (RIE) using a self-assembled etch mask. Different from templated sol-gel process using porous anodic alumina [3] reported previously, the approach used in this study makes it possible to synthesize the nanowires directly on top of FTO substrates with simpler process scheme. Our results demonstrate the formation of titania nanowires of 20 nm in diameter, 25 in aspect ratio and 1.3x1011 cm-2 in areal density. Details on the crystal structure of nanowires and the effect of substrate nature on the growth will be presented along with potential applications of these high aspect ratio titania nanowires.[1] M. Gratzel, Inorg. Chem. 2005, 44, 6841-6851[2] P. Yang et al, Inorg. Chem. Vol. 45, No. 19, 2006[3] Z. Miao et al, Nano Lett. Vol. 2, No. 7, 2002
9:45 AM - M12.2
Precisely Controlled Silicon Nanowire Branch Fabrication via a Focused Ion Beam Based Process.
Kimin Jun 1 2 , Joseph Jacobson 1
1 Media Laboratory, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractNanowire branching has been explored by several researchers since it can create complex networked structures which have the potential to form the building blocks for nanoscale circuits. One of the most widely adopted approaches is to use the vapor-liquid-solid(VLS) mechanism, in which, after a backbone nanowire is grown, a secondary catalyst is deposited on the sidewall of the backbone nanowire followed by subsequent repeated nanowire growth. However, in most results to date, the location of the secondary catalyst is purely random which significantly hinders the usefulness of the resulting branched structure. In this research, we demonstrate that nanowire branched structures can be synthesized such that the branching position is precisely defined with the assistance of focused ion beam(FIB). The key of our approach lies in the patterned opening of a core-shell nanowire followed by subsequent gold deposition via galvanic displacement. In this approach backbone silicon nanowires were first grown, followed by gold catalyst removal. The resulting pure silicon nanowires were oxidized in a dry oxygen environment and then transferred to the FIB chamber where precise oxide etching was conducted, making a small hole through which silicon was exposed. Since gold has a higher redox potential than silicon, a secondary gold catalyst could be selectively deposited in this silicon opening through ionic exchange process(galvanic displacement). Silicon nanowire branches were then successfully grown from these catalyst positions. These initial results indicate that this approach should be successively repeatable over a number of cycles thus enabling the hierarchical deterministic formation of highly complex nanowire structures.
10:00 AM - M12.3
Novel Method for Metal Oxide Nanowire Growth.
Simas Rackauskas 1 , Albert Nasibulin 1 , Hua Jiang 1 , Ying Tian 1 , Victor Klesch 2 3 , Jani Sainio 4 , Elena Obraztsova 2 , Alexander Obraztsov 3 6 , Esko Kauppinen 1 5
1 Department of Applied Physics, Helsinki University of Technology, Espoo Finland, 2 , A.M. Prokhorov General Physics Institute of Russian Academy of Sciences, Moscow Russian Federation, 3 , Physics Department of M.V. Lomonosov Moscow State University, Moscow Russian Federation, 4 Laboratory of Physics, Helsinki University of Technology, Espoo Finland, 6 , University of Joensuu, Joensuu Finland, 5 , VTT Biotechnology, Espoo Finland
Show AbstractMetal oxide nanowires (NWs) have received broad attention due to their distinguished performance in electronics, optics and photonics. Common metal oxide nanowire synthesis methods include metal organic chemical vapor deposition, vapor synthesis, hydrothermal, chemical solution route. Typically, the NW growth has been explained by vapor-liquid-solid or vapor-solid mechanisms, not taking into account electrochemical nature of metal oxidation.Here we propose a novel non-catalytic one-step process method for an efficient and rapid synthesis of NWs by direct resistive heating of metals. This method does not necessarily require controlled atmosphere, since the synthesis can be carried out at ambient conditions; the process of NW formation is very rapid, with a typical growth time of a few seconds, and consuming very little energy compared to traditional methods. The simplicity of the method and possibility to rapidly heat up the substrate allowed us to investigate and discuss the mechanism of the NW formation from different metals.As a result, Fe2O3, CuO, V2O5 and ZnO NWs were synthesized and thoroughly characterized. The possibility of growth of metal oxide NWs was also demonstrated with Al, W and Mo. The mechanism of the NW growth is based on the faster diffusion of metal ions to the surface of wire through grain boundaries and to the tip of the growing NW through defect diffusion and by surface diffusion. The produced metal oxide NWs were characterized by means of SEM, TEM, EDX, XPS and Raman techniques. Finally, based on photoluminescence and field emission measurements application of as-produced wires for optoelectronic or field emission devices is shown.
10:15 AM - M12.4
Cation Assisted Morphology Control of ZnO Nanowire Synthesis with Optimized Chemical Reaction Parameters.
Jaebum Joo 1 2 , Joseph Jacobson 2
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Media Laboratory, MIT, Cambridge, Massachusetts, United States
Show Abstract Crystalline shape control in semiconductor nanowire synthesis would enable the tuning of electrical and optical properties that are highly influenced by size and morphology of crystals. In this work, we report on the controlled synthesis of ZnO nanowires using various cations as crystal growth modifiers using a low temperature hydrothermal technique. We examined the morphology changes induced by growing nanowires in the presence of additional divalent and trivalent cations at various concentrations by SEM and TEM. We found that certain ions suppress ZnO nanowire growth in the lateral direction (with respect to the surface), thereby creating high aspect ratio nanowires, while others suppress top-face growth, thereby promoting synthesis of low aspect ratio nanoplates. We developed a thermodynamic model in which changes in the supersaturation condition and ion concentration by the addition of competing, yet unincorporated ions (as determined by EDAX), alter the crystal growth behavior. Since direct bandgap ZnO (3.37eV) is one of the most important functional materials used for field emitters, UV lasers, piezoelectric energy generators, photodetectors, gas sensors, and solar cells, this fundamental study on ZnO nanostructure growth may lead to the development of new nanoelectronics and optical device with highly tunable electrical and optical properties.
10:30 AM - M12.5
Decoupled Axial versus Radial Nanowire Growth by In-situ Etching.
Jesper Wallentin 1 , Magnus Borgstrom 1 , Johanna Tragardh 1 , Peter Ramvall 1 , Martin Ek 2 , Reine Wallenberg 2 , Lars Samuelson 1 , Knut Deppert 1
1 Solid State Physics, Lund University, Lund Sweden, 2 Polymer & Materials Chemistry/nCHREM, Lund University, Lund Sweden
Show AbstractRecently nanowires (NWs) have attracted attention as one of the most promising ways of combining high performance III/V materials with existing Si technology. The NWs are usually grown by the vapour–liquid–solid (VLS) mechanism[1], showing promising characteristics for devices such as field-effect transistors and solar cells. However, there is a strong need to take control of radial growth. For instance, a radial NW shell leading to short circuiting of an axially designed component will effectively destroy device functionality. So far, the radial growth rate has been controlled by growth parameters like temperature and precursor molar fractions. For III-V semiconductor NWs however, only a relatively narrow V/III parameter space results in growth of morphologically non-tapered NWs[2]. We report the decoupling of radial versus axial growth by use of an In-Situ etching agent. The molar fraction of the etching agent can be tuned to control the radial growth rate. This opens up a wide field for optimization of NW growth parameters for devices, previously inaccessible due to induced tapering.InP nanowires were grown using the VLS mechanism, with varying concentrations of the etching agent HCl. SEM and TEM investigations of the NWs show that the radial growth can be regulated and fully impeded, allowing controlled design of axially defined NW structures. Etching experiments reveal that HCl etches preferentially beneath the gold particle. Despite this, the axial growth rate with low HCl concentrations is higher than for the unetched nanowires. The nanowires were also studied using photoluminescence (PL), in which the etched NWs show enhanced crystal and optical quality. This is attributed to a removal of carbon defects originating in the radial growth.To demonstrate the usefulness of these results, we have fabricated Light Emitting Diodes (LEDs) based on axial p-n-junctions. The in-situ etching prevents growth of a conductive shell, which would have short-circuited the devices. The p-n junctions show typical diode I-V-characteristics with an ideality factor of 2.9, while electroluminescense measurements display a spectrum centered around 1.33 eV.1.Wagner, R.S., Ellis, W.C., Vapor-Liquid-Solid Mechanism of Single Crystal Growth (New method growth catalysis from impurity whisker epitaxial + large crystal SI E). Applied Physics Letters, 1964. 4(5): p. 89-90.2.Dick, K.A., et al., InAs nanowires grown by MOVPE. Journal of Crystal Growth, 2007. 298: p. 631-634.
10:45 AM - M12.6
Direct Comparison of Catalyst-induced and Catalyst-free GaN Nanowires.
Caroline Cheze 1 , Lutz Geelhaar 1 , Oliver Brandt 1 , Henning Riechert 1 , Steffen Muench 2 , Ralph Rothemund 2 , Stephan Reitzenstein 2 , Alfred Forchel 2 , Thomas Kehagias 3 , Philomela Komninou 3 , George Dimitrakopulos 3 , Theodoros Karakostas 3
1 , Paul-Drude-Institut für Festkörperelektronik, Berlin Germany, 2 Technische Physik, Universität Würzburg, Würzburg Germany, 3 Physics Department, Aristotle University, Thessaloniki Greece
Show AbstractThe most popular approach for the self-organized growth of nanowires (NWs) is based on the effect of catalyst seeds, frequently tiny gold droplets. However, the use of a catalyst raises concerns about contamination of the nanowire material and possible consequences for device performance. Thus, approaches that do not require any foreign material for NW growth are studied intensively. Obviously, an assessment of the respective advantages and drawbacks is crucial for the employment in devices. Here, we study GaN NWs induced by Ni seeds on sapphire substrates and GaN NWs that formed without the help of any foreign material on silicon substrates. Both types of NWs were grown by molecular beam epitaxy (MBE) at the same temperature and fluxes, thus excluding any possible effects of different growth conditions. This allows us to directly compare the respective crystal quality, growth mechanisms, and luminescence properties. The investigation by transmission electron microscopy shows that both approaches yield single crystalline NWs that have the wurtzite structure and are Ga-polar. The difference in the microstructure is that the catalyst-induced NWs contain many basal plane stacking faults (SFs) while the self-induced NWs are free of any extended defects. There are several mechanisms how the seed, the only distinguishing factor during growth, may cause SFs: First, the cubic structure of the actually solid seed, second, the triple phase line at the edge of the seed, and third, impurities in GaN like from the seed material may favor the zincblende bonding configuration associated with SFs. The growth mechanisms were studied by comparing the influence of the Ga- and N-fluxes. The catalyst-induced NWs grow faster, and their rate is governed by the N-flux. Thus, there are locally Ga-rich conditions at the NW tip. In contrast, the catalyst-free NWs grow faster than the rate of impinging Ga but slower than that of N. Hence, in this case there are N-rich conditions at the NW tip. Essentially, the catalyst seeds collect all the Ga diffusing to the NW tip along the sidewalls, while the axial growth rate of the self-induced GaN NWs is governed by the ratio of the intrinsic incorporation rates at the different NW top and sidewall facets. Last, the luminescence properties of the NWs were investigated by photoluminescence (PL) spectroscopy. Both types of NWs exhibit clear exciton emission and no yellow luminescence. The main difference is that the PL intensity of the catalyst-free NWs is more than one order of magnitude larger. The most likely explanation is an additional non-radiative recombination center in the catalyst-induced NWs. As both types of NWs were grown in the same MBE chamber under the same conditions, these measurements strongly suggest Ni contamination from the catalyst seeds. In conclusion, the use of catalyst seeds may offer additional control over NW growth, but both the structural and the optical quality are inferior to self-induced NWs.
M13: Quantum Properties and Devices
Session Chairs
Harry Atwater
Anna Morral
Thursday PM, December 03, 2009
Constitution B (Sheraton)
11:30 AM - **M13.1
Single Electron and Spin Transport in Semiconductor Nanowire Quantum Dots.
Renaud Leturcq 1 2 , Andreas Pfund 2 , Ivan Shorubalko 2 , Klaus Ensslin 2
1 ISEN, IEMN - CNRS UMR 8520, Villeneuve d'Ascq France, 2 Laboratory for Solid State Physics, ETH Zurich, Zurich Switzerland
Show AbstractSemiconductor quantum dots have been the subject of many studies in the last few years, in particular due to the possibility to manipulate single electronic states and single spins. Most of the transport experiments have been performed on quantum dots defined by lithography in GaAs heterostructures. Recently, using semiconductor nanowires, high quality quantum dots have been fabricated in other semiconductor materials, opening new opportunities for applications and fundamental studies.Among these new materials, InAs is of great interest. Its large effective mass gives rise to quantum effect at larger temperature than in GaAs. Its large g-factor and strong spin-orbit interaction make it a good candidate for spin manipulation. Based on experiments done in single and double quantum dots in InAs nanowires, I will show how these enhanced properties affect single electron and single spin transport.The nanowire geometry also opens new device concepts. By combining a nanowire quantum dot and a quantum point contact etched in a GaAs heterostructure, we show the effective integration of two technological approaches in the field of electron counting. Another interest is the possibility to build high quality suspended quantum dots. Based on an experiment on a suspended carbon nanotube, I will discuss the new opportunities opened by such a nano-electro-mechanical system.
12:00 PM - M13.2
Nanoscale Effects on Heterojunction Electron Gases in Core/Shell Nanowires.
Bryan Wong 1 , Francois Leonard 2
1 Materials Chemistry Department, Sandia National Laboratories, Livermore, California, United States, 2 Materials Physics Department, Sandia National Laboratories, Livermore, California, United States
Show AbstractThe unique properties of semiconducting heterostructure nanowires hold great promise for their incorporation in next-generation transistors, circuits, and nanoscale devices. The reduction in dimensionality produced by confining electrons in these heterostructure nanowires results in a dramatic change in their electronic structure, leading to novel properties such as ballistic transport and conductance quantization. One area of particular interest is in the formation of heterojunction electron gases in III-nitride core/shell nanowires which may provide a route towards quasi-one-dimensional electron gases.In order to tailor these nanostructures with the desired physical properties, we must first understand their electronic properties as a function of size and material composition. To this end, we developed a self-consistent Poisson-Schrodinger approach to calculate the properties of heterojunction electron gases in polar and non-polar AlGaN/GaN core-shell nanowires. We find that the nanoscale size of these wires leads to the appearance of quasi-one-dimensional electron gases at the corners of the hexagonal and triangular cross-sections, in contrast to what would be expected from analogy with bulk heterojunctions. Our results allow a guided understanding of low-dimensional electron gas formation in freestanding semiconductor heterostructure nanowires.
12:15 PM - M13.3
Novel UV Photodetector with High Sensitivity and Square Response by Bridging ZnO Nanowires.
Yanbo Li 1 , Alexander Paulsen 1 , Ryohei Uchino 1 , Takero Tokizono 1 , Masaki Shuzo 1 , Ichiro Yamada 1 , Jean-Jacques Delaunay 1
1 , The University of Tokyo, Tokyo Japan
Show AbstractDue to their wide bandgap and large surface-to-volume ratio, ZnO nanowires are promising materials for highly sensitive UV photodetection. Recently, different types of photodetector using ZnO nanowires have been demonstrated, including photoconductive detector and Schottky barrier detector. The photoconductive detectors made with ZnO nanowires have a slow response time which is attributed to surface reaction with air molecules, band bending near the surface, and electron-hole separation in the nanowires. Although the Schottky barrier detectors have much faster response time, there is an apparent trade-off between the response time and the signal-to-noise ratio. In this report, we propose a new type of UV photodetector by bridging ZnO nanowires. The device exhibits a high sensitivity to UV illumination with a square response. The photocurrent decay upon switching off UV is much faster than that of the photoconductive detectors. The sensitivity and signal-to-noise ratio are improved compared with Schottky barrier detectors. Furthermore, our device is fabricated in one step in a chemical vapor deposition process, which makes this device suitable for mass production. The mechanism of UV detection is also studied and a model is presented.
12:30 PM - **M13.4
Electronic and Photonic Devices Enabled by Nanowires.
Lars Samuelson 1
1 Solid State Physics/the Nanometer Structure Consortium, Lund University, Lund Sweden
Show AbstractIn the general trend towards the use of self-assembly for realization of ultra-small devices on the 10nm-scale, semiconductor nanowires (NWs) have emerged as one of the most interesting candidates. In this talk I will first describe different materials science aspects of NW growth, with a focus on III-V NWs grown epitaxially on a single-crystalline substrate as a top-down guided bottom-up growth of NWs in which lithography is used to define location and dimension and where compatibility with silicon wafer technology is of particular importance. I will then describe the controlled formation of axial and radial heterostructures, which is of great importance for the use of NWs for basic physics studies as well as for applications in electronics and photonics. As examples of recent physics studies of NWs I will describe transport via single and multiple quantum dots and optical studies of radiative recombination in single quantum dots positioned in NWs. Finally, I will give more details on the efforts to realize electronic as well as photonic devices using NWs. Specifically I will describe the development of state-of-the-art wrap-gate field-effect transistors, which we have developed within a framework of the EU-funded Integrated Project NODE (“Nanowire-based One-Dimensional Electronics”). I will also report recent progress in the realization of nanowire-based light-emitting diodes and nanowire-based solar-cells and I will conclude with visions for where I think NW-based science and technology may be heading in the future.I want to thank the many colleagues and students that have been and that are involved in this research. Most of the research results reported here has been created within the PhD-student thesis projects of my students: Jonas Ohlsson (2002), Claes Thelander (2003), Magnus Borgström (2003), Mikael Björk (2004), Nikolay Panev (2004), Tomas Bryllert (2005), Ann Persson (2005), Kimberly Dick (2007), Carina Fasth (2007), Brent Wacaser (2007), Johanna Trägårdh (2008), Niklas Sköld (2008), Thomas Mårtensson (2008) and Linus Fröberg (2008). I also want to acknowledge the crucial support from our funding agencies, the Swedish Research Council (VR), the Swedish Foundation for Strategic Research (SSF), the Knut and Alice Wallenberg Foundation (KAW), the Office of Naval Research (ONR) and the European Union in the project NODE 015783.
M14: Nanowire Sensors
Session Chairs
Thursday PM, December 03, 2009
Constitution B (Sheraton)
2:30 PM - **M14.1
Hydrogen Gas Sensing Using a Palladium Nanowire.
Reginald Penner 1
1 Chemistry, UCI, Irvine, California, United States
Show AbstractNoble metal nanowires have attributes including strength, ductility, and chemical stability that make them attractive candidates for chemical sensing applications. We have developed a new method for preparing and patterning noble metal nanowires that involves the electrodeposition of metals (palladium, silver, platinum and gold) onto lithographically patterned glass surfaces. Under the conditions employed for nanowire growth, metal is deposited within this patterned photoresist layer on a sacrificial nickel electrode leading to the formation of polycrystalline nanowires that are up to 1 cm in length and 5-200 nm in lateral dimension. The palladium nanowires prepared using this method, called lithographically patterned nanowire electrodeposition can form the basis for chemical sensors in which the resistance of the nanowire array is modulated by molecules that chemisorb at the surfaces of these metals. One particularly interesting example involves palladium nanowires in the presence of hydrogen. For this system, Pd nanowires respond to H2 exposure by becoming either more resistive or more conductive, depending on the details of nanowire and sensor fabrication. What is the origin of these resistance changes? In this talk, we focus attention on this issue and we discuss the prospects for developing practical hydrogen sensors based on these novel mechanisms.
3:00 PM - M14.2
Label-Free, Electrical Detection of the SARS Virus N-Protein with Nanowire Biosensors Utilizing Antibody Mimics as Capture Probes.
Fumiaki Ishikawa 1 , Hsiao-kang Chang 1 , Marco Curreli 1 , Hsiang-I Liao 2 , C. Anders Olson 1 , Po-Chiang Chen 1 , Rui Zhang 1 , Richard Roberts 1 , Ren Sun 2 , Richard Cote 1 , Mark Thompson 1 , Chongwu Zhou 1
1 , USC, Los Angeles, California, United States, 2 , UCLA, Los Angeles, California, United States
Show AbstractBiosensors based on nanowire/carbon nanotube transistors have shown their tremendous potential as highly selective, ultra sensitive devices capable of detecting specific proteins and DNA sequences. These devices utilize a capture agent on the sensor surface to selectively bind the target biomolecules and those commonly used include antibodies, oligonucleotides, and small ligands (e.g. biotin). Antibody mimic proteins (AMPs) can is a class of affinity binding agents, which can be evolved/engineered to improve recognition properties such as selectivity and binding affinity, and they further offer advantages such as small size, stability in a wide range of pH, and possibly production in large quantity at relatively low cost. These imply that AMPs may be an ideal probe molecule in nanowire/nanotube biosensors. In this report, we introduce evolved AMPs as a new class of capture agents for nanowire/nanotube biosensors, and demonstrate selective detection of a protein related to severe acute respiratory syndrome (SARS), using devices based on In2O3 nanowires. A fibronectin-based protein (Fn) was employed as an example of AMP capture agent to selectively recognize and bind the nucleocapsid (N) protein. The N protein is a biomarker associated with the SARS coronavirus. Our platform is capable of specifically detecting the N protein at sub-nanomolar concentrations, in the presence of 44 uM bovine serum albumin (BSA) as a background. This sensitivity, while comparable to current immunological detection methods, can be obtained in a relatively short time and without the aid of any signal amplifier, such as fluorescence labeled reagents. Ultimately, we show that our platform can also be used to accurately determine the dissociation constant of the N protein and Fn by applying a conventional Langumir model to the concentration-dependent sensing response.
3:15 PM - M14.3
Gigantic Enhancement in Response and Reset Time of ZnO UV Nanosensor by Utilizing Schottky Contact and Surface Functionalization.
Youfan Hu 1 , Jun Zhou 1 , Zhong Lin Wang 1
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractUltraviolet (UV) photon detectors have a wide range of applications from environmental monitoring, missile launching detection, space research, high temperature flame detection to optical communications. Due to large surface-to-volume ratio and reduced dimensionality of the active area, ZnO nanostructures are expected to have high photon conductance. In our former work [1], by functionalizing the surface of ZnO nanobelts using polymers that have a high absorption at the UV range, the sensitivity of the ZnO NW UV nanosensor (NS) have been improved for five orders of magnitude. However, little attention has been paid on improving the response and recovery time. In this report [2], we demonstrate effective ways for improving both the sensitivity and reset time (defined as the time need to recovery to 1/e of the maximum photocurrent) of ZnO NW NSs. By utilizing Schottky contact instead of Ohmic contact, the photocurrent of the nanosensors has been increased by four orders of magnitude, and the reset time has been dramatically reduced from ~417 s to 0.8 s. The working principle is discussed, and the excellent performance of the nanosensor is considered related to the modification of Schottky barrier height and width under UV irradiation. By further surface coating with positive charged poly(diallydimethylammonium chloride) (PDADMAC) and negative charged poly(sodium 4-styrenesulfonate) (PSS), the reset time has been decreased to ~20 ms even without correcting the electronic response of the measurement system. These results demonstrate an effective approach for building high response and fast reset UV detectors. Beside the UV sensors, we believe that the performance of gas sensors, strain sensors and biosensors can also be improved dramatically by the Schottky contacts introduced in device fabrication, which is distinctly different from the conventionally designed devices with Ohmic contacts.[1] Changshi Lao, Myung-Chul Park, Qin Kuang, Yulin Deng, Ashok K. Sood, Dennis L. Polla, and Zhong Lin Wang, “Giant Enhancement in UV Response of ZnO Nanobelts by Polymer Surface-Functionalization”, J. Am. Chem. Soc. 2007, 129, 12096-12097.[2] Jun Zhou, Yudong Gu, Youfan Hu, Wenjie Mai, Ping-Hung Yeh, Gang Bao, Ashok K. Sood, Dennis L. Polla, and Zhong Lin Wang, “Gigantic enhancement in response and reset time of ZnO UV nanosensor by utilizing Schottky contact and surface functionalization”, Appl. Phys. Lett. 2009, 94, 191103.[3] Research supported by DARPA, DOE and NIH.[4] For more information: http://www.nanoscience.gatech.edu/zlwang/
3:30 PM - M14.4
pH Sensitivity of Single Crystal Silicon Nanowires.
Songyue Chen 1 2 , Johan Bomer 1 , Wilfred van der Wiel 2 , Edwin Carlen 1 , Albert van den Berg 1
1 , BIOS Lab on a Chip Group, MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands, 2 , Strategic Research Orientation NanoElectronics, MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractOver the past decade there has been keen interest in semiconductor nanowires due to their unique properties, especially for label-free biosensing. It is important to understand the solution/sensor interface behavior in order to optimize the detection sensitivity of nanowires. We present an in-depth study of the pH sensitivity and behavior of silicon nanowires (Si-NWs). Extensive electrical and electrochemical testing of fabricated Si-NWs has been conducted including conventional current-voltage characteristics, gating behavior (both back-gate with substrate and front-gate with reference electrode), and pH behavior. The site-binding model, previously applied to ISFETs (ion-selective field-effect transistors), has been used to describe the pH behavior of oxidized Si-NWs, which gives sinh(v-y0)=y0/β, where v=2.303(pHpzc-pH), y0=qφ0/kT, φ0 is the interface potential, β is a dimensionless sensitivity parameter and pHpzc is the pH at the point-of-zero charge on the oxide surface [1]. Si-NWs have been fabricated with a robust and low-cost method consisting of conventional microlithography, wet anisotropic etching and size reduction, as previously reported [2]. Si-NW devices were encapsulated with an epoxy and the oxide surfaces were cleaned with UV ozone. Packaged Si-NWs were immersed in 0.1 M NaCl, or 0.01 M UBM (universal buffer mixture), solution at pH 2.1 for more than 2 hours to stabilize the oxide/electrolyte interface prior to measurements. All pH measurements were realized by titrating to supporting electrolyte with HCl/NaOH to change the pH. The measured pH behavior of oxidized Si-NWs fits very well to the site-binding model for pH 2.1 to pH 5 with β=0.29 and pHpzc=2.1. Surface modifications of the oxide Si-NW gate with HMDS (hexamethyldisilazane) and APTES (3-aminopropyl triethoxysilane) monolayers have also been performed to show the control over the pH response. With HMDS, the methyl groups reduce the active sites and result in a lower pH response, while the APTES monolayer introduces more active sites to the surface, and thus increases the pH response. Detailed experimental and modeling results will be presented. References[1] L. Bousse, N.F. de Rooij, P. Bergveld: IEEE Trans. Electr. Dev., 1983, ED-30, 1263-1270. [2] S. Chen, J.G. Bomer, W.G. van der Wiel, E.T. Carlen, A. van den Berg, Materials Research Society (MRS2009), Spring Meeting, San Francisco, CA, U.S.A, 2009.
3:45 PM - M14.5
Manipulation and Alignment of Nanowires and Their Integration in Sensing Devices.
Roman Jimenez-Diaz 1 , J Daniel Prades 2 , Francisco Hernandez-Ramirez 2 3 , Jun Pan 5 , Sven Barth 4 , Joan Ramon Morante 2 7 , Albert Romano-Rodriguez 1 , Albert Cornet 1 , Sanjay Mathur 5 6
1 MIND/IN2UB, University of Barcelona, Barcelona Spain, 2 IREC, Institut de Recerca en Energia de Catalunya, Barcelona, Barcelona, Spain, 3 , Electronic Nanosystems S.L., Barcelona Spain, 5 Institute of Inorganic Chemistry, University of Cologne, Cologne Germany, 4 Department of Chemistry, University College Cork, Cork Ireland, 7 M2E/XaRMAE/IN2UB Department of Electronics, University of Barcelona, Barcelona Spain, 6 Nanocrystaline Materials and Thin Films Systems, Leibniz Institute of New Materials, Saarbruecken Germany
Show AbstractMonocrystalline SnO2 nanowires were positioned in a controlled way by using Dielectrophoretic (DEP) alignment techniques. First of all, nanowires were dispersed on ethanol, making solutions with different concentrations. Afterwards, their manipulation was carried out by spreading a droplet of the solution (~10 µl) onto a SiO2 / Si wafer with pre-patterned microelectrodes, while an AC voltage of controlled frequency between these microelectrodes was applied. These experimental conditions were kept constant until the complete evaporation of the suspension was reached. Efficiency of DEP alignment process with different nanowire concentrations and frequency of the AC voltage applied was analyzed by means of SEM inspection. This step allowed determining the optimal experimental conditions to perform the DEP alignment process with SnO2 nanowires. To guarantee the formation of good electrical contacts between pre-patterned microelectrodes and nanowires, Electron Beam Assisted Deposition and Ion Beam Assisted Deposition processes were performed. These nanowires were electrically contacted using a FEI Strata 235 dual beam instrument equipped with an injector to deposit Pt. The details of this fabrication method were explained in detail elsewhere [1]. Finally, two- and four-probe dc electrical measurements were done using a Keithley 2602 Source Measure Unit, enabling the estimation of the key-parameters of these nanowires. On the other hand, some of these nanowires were also tested as gas sensors, using well-controlled environmental conditions. The obtained results demonstrated the huge potential of nanowires as building-blocks of a new generation of devices with improved performances. It is noteworthy that DEP-aligned nanowires did not exhibit any significant difference in their electrical response than those reported with non-aligned nanowires [1]. For this reason DEP-based technologies are a promising approach for the fabrication of nanosensors in a scalable process which fulfill the requirements to become industrialized.[1] F. Hernandez-Ramirez, J. Rodriguez, O. Casals, E. Russinyol, A. Vila, A. Romano-Rodriguez, J.R. Morante, M. Abid, Characterization of metal-oxide nanosensors fabricated with focused ion beam (FIB), Sens. Actuators, B, Chem 118 (2006) 198–203.
M15: Nanowires for Biotechnology
Session Chairs
Jason Holt
Reginald Penner
Thursday PM, December 03, 2009
Constitution B (Sheraton)
4:15 PM - **M15.1
Heterogeneous Integration of Bioprobe-coated Nanowires.
Christine Keating 1 , Theresa Mayer 2
1 Chemistry, Penn State University, University Park, Pennsylvania, United States, 2 Electrical Engineering, Penn State University, University Park, Pennsylvania, United States
Show AbstractCombining biomolecular function with integrated circuit technology could usher in a new era of biologically enabled electronics. A key challenge has been coupling different molecular functions to specific chip locations for communication with the circuit. We are developing directed assembly methods based on spatially confined electric fields to assemble different populations of DNA-coated nanowires to desired positions on a patterned Si wafer. This combination of off-chip synthesis and biofunctionalization with high-density, heterogeneous assembly and integration at the individual nanowire level points to new ways of incorporating biological functionality with silicon electronics.
4:45 PM - M15.2
Design of Multifunctional Virus-based Fibers for Antibacterial Applications.
Joan Mao 1 , Angela Belcher 1 2 , Krystyn Van Vliet 1 2
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractMultifunctionality can be imparted to protein-based fibers and coatings via either synthetic or biological approaches. Here, we demonstrate potent antimicrobial functionality of genetically engineered, phage-based fibers and fiber coatings, processed at room temperature. The bacteriophage or viruses are nanoscale, genetically modifiable objects that can be conjugated to form nanofibrils, which can then be further crosslinked to form nano- to microscale fibers that maintain this genetically engineered functionality. In the present work, facile genetic engineering of the M13 bacteriophage genome leverages the well-known antibacterial properties of silver ions to kill bacteria. Predominant expression of negatively-charged glutamic acid (E3) peptides on the pVIII major coat proteins of M13 bacteriophage enables solution-based, electrostatic binding of silver ions and subsequent reduction to metallic silver along the phage length. We demonstrate assembly of antibacterial fibers of up to micrometer-scale diameters and comprised of E3-modified phage, via wet-spinning and glutaraldehyde-crosslinking of the E3-modified phage. We then confirm silverization of the free-standing phage-fibers via energy-dispersive spectroscopy and inductively-coupled plasma atomic emission spectroscopy, showing 0.61 µg/cm of silver on E3-Ag fibers. This degree of silverization is threefold greater than that attainable for the unmodified M13-Ag fibers. Conferred bactericidal functionality is determined via live-dead staining and a modified disk-diffusion (Kirby-Bauer) measure of zone of inhibition (ZoI) against Staphylococcus epidermidis and Escherichia coli bacterial strains. Live-dead staining and ZoI distance measurements indicate increased bactericidal activity in the genetically engineered, silverized phage-fibers. Coating of Kevlar fibers with the nanoscale E3 phage also exhibits antibacterial effects, with relatively smaller ZoIs attributable to the lower degree of silver loading attainable in these coatings. Such antimicrobial functionality is amenable to rapid incorporation within multifunctional, fiber-based textiles to reduce risks of infection, biofilm formation, or odor-based detection, with the clear potential to exploit the additional electronic and thermal conductivity of fully silverized fibers and coatings.
5:00 PM - M15.3
Precision Transport of Nanowires for Drug Delivery to a Single Cell.
Donglei Fan 1 2 4 , Zhizhong Yin 3 , Frank Zhu 2 5 , Robert Cammarata 1 , Andre Levchenko 3 , Chia-Ling Chien 2 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland, United States, 4 Mechanical Engineering, University of Texas at Austin, Austin, Texas, United States, 3 Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 5 , Current address: Hitachi Global Storage Technology, San Jose, California, United States
Show AbstractWe report the precision transport of drug conjugated nanowires onto the membrane of a single mammalian cell for stimulation of cellular responses. The Au nanowires (6 µm in length and 150 nm in radius) are conjugated with Tumor Necrosis Factor-alpha (TNF-α) by hydrophobic absorption. The nanowires can be precisely transported onto a selected cell following any prescribed trajectory using a combination of dielectrophoretic (DEP) force and electrophoretic (EP) force. We found that one or two TNF-α conjugated nanowires are sufficient to stimulate the cell, revealed by the translocation of nuclear factor-kappa B (NF-κB) from cytoplasm to the nucleus. This method will be useful for targeted cell signaling studies on the single-cell level.
5:15 PM - M15.4
Nanowire Transistor Arrays for High Spatiotemporal Resolution Recording in Acute Brain Slices.
Quan Qing 1 , Sumon Pal 2 , Bozhi Tian 1 , Xiaojie Duan 1 , Brian Timko 1 , Tzahi Cohen-Karni 3 , Venkatesh Murthy 2 , Charles Lieber 1 3
1 Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 Melecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, United States, 3 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractNeurons organize through synaptic connections into hierarchical networks operating on spatial and temporal scales that span many orders of magnitude. To elucidate the underlying neural circuits, electrical measurements using multi-electrode array (MEA) and optical approaches with voltage- and calcium-sensitive dyes have been developed. However, electrode diameter and spacing of traditional MEAs are intrinsically limited in the order of 10 and 100 micrometers, respectively, by passive detection limits and signal-to-noise ratio. In alternative designs with close-packed planar field-effect transistor (FET) arrays, the active gate area is still larger than 3.6 square micrometers in best cases. Moreover, reasonable temporal resolution with optical dyes for resolving single action potentials can only be achieved with reduced recording sites or compromised spatial resolution, among other limitations. Here we show that one- and two-dimensional arrays of nanowire FETs (NWFET) with flexible spatial configurations can be fabricated on optically-transparent substrates, and reliably interfaced with specific regions of acute brain slices to detect localized potential changes due to neuron activities simultaneously across many length scales with high temporal resolution. The active junction area of ~0.06 square micrometers provides reproducible signals of high spatiotemporal resolution, and the nanostructured surface can promote enhanced interactions with cells and tissue, which opens up opportunity for sub-cellular scale detection. A variety of experimental results will be presented, including signal propagation speed in the lateral olfactory tract (LOT) recorded using multiplexed measurements, and illumination of ensembles of active cells in the piriform cortex after stimulation of subsets of LOT axons using two-dimensional arrays of NWFETs. These results demonstrate potential of directly probing networks over many spatial length scales with high temporal resolution, and thus suggest potential of NWFET arrays as a powerful new platform tool that can be combined with conventional intracellular and optical methods for studying neural circuits in brain slices.
5:30 PM - M15.5
Inorganic Nanowires for Improved Water Filtration.
David Schoen 1 , Alia Schoen 1 , Sarah Heilshorn 1 , Yi Cui 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractAn important step in many filtration systems is the exclusion based filtration of bacteria and other living material. One of the biggest challenges for this step is biofouling, a process in which cells grow on and inside the filter, ultimately clogging or contaminating it to the point where it can no longer be used. Many strategies have been explored to attempt to avoid this process, and one particularly simple approach is the addition of silver nanoparticles, which are a well known bactericide. Nanoparticles do have a downside though, in that they are much smaller than the pore size in these filters so it is difficult to robustly incorporate them. We here report the application of Ag nanowires for this purpose. Nanowires have many advantages. They are simple to incorporate in filters since they become physically entangled in them, and like nanoparticles they have a potent bactericidal effect. In addition, silver nanowire networks can be used as large porous electrodes, enabling the use of electrochemical techniques to attract charged biological species and ultimately to clean the filters.
5:45 PM - M15.6
Strengthening Manganese Oxide Nanowire Membranes for Separation and Filtration Applications.
Karen Stewart 1 , Jin-Mi Jung 1 , Ozge Akbulut 1 , Francesco Stellacci 1 , Krystyn Van Vliet 1
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract Manganese oxide-based nanowire membranes are an attractive multifunctional material component for diverse separation and filtration applications due to several reasons: these nanowires are straightforward to synthesize in large quantities, require inexpensive starting materials, can be recycled, and exhibit high surface area and nanoscale porosity which confer high capillary forces. It has been demonstrated previously that vapor coating of these nanowire membranes with polydimethylsiloxane (PDMS) converts this hydrophilic porous membrane to a superoleophilic, superabsorbent material that selectively removes organics in mixed water/organic systems.1 However, industrial applications of these nanowire membranes, which are processed similarly to nonwoven paper, would be facilitated significantly by a dramatic increase in the tensile strength and fracture toughness of free-standing nanowire membranes. Here we demonstrate significant increases in the mechanical strength and toughness of such nanofiber-based manganese oxide papers (nanoMOPs). We discuss several different strategies that were designed to improve the strength to failure without reducing the functional properties of such materials for either oil absorption or other advanced separation and filtration applications, and show how each of these processing schemes modulates both the microstructure and mechanical properties of these nonwoven membranes. We find that both tensile strength and fracture toughness of the nanoMOPs were affected chiefly by duration of sonication of the nanofiber pulp, properties of the dispersion aid added to this pulp, and chemical crosslinking of the nanowires at the pulp stage. Through these approaches, we increased the tensile strength of nanoMOPs by approximately a factor of 20 and the modulus of tensile fracture by a factor of 250, while maintaining selective absorption of organic solvents. This controlled processing also enabled exploration of new functional applications of these nanoMOPs, including enhanced absorption strategies and selective filtration of small molecules and particles. Importantly, our processing-structure-properties analysis of this class of nanofibers is expected to extend to other types of nanofiber-based, nonwoven functional materials that require predictable mechanical strength for practical engineering applications. References: 1. J Yuan, X Liu, O Akbulut, J Hu, SL Suib, J Kong, F Stellacci. Superwetting nanowire membranes for selective absorption. Nature Nanotechnology 3: 332 (2008).
M16: Poster Session II: Metallic, Organic and Oxide Nanowires
Session Chairs
Anna Morral
Kornelius Nielsch
Friday AM, December 04, 2009
Exhibit Hall D (Hynes)
9:00 PM - M16.10
Spectrophotometric Investigation on the Growth Mechanism of a Single Tapered CuO Nanowire.
Anindita Chatterjee 1 , C. Huang 1 , S. Liu 1 , S. Wu 1 , C. Cheng 1
1 Department of Physics, National Dong Hwa University, Hualien Taiwan
Show AbstractUnderstanding the growth mechanism of the tapered semiconducting nanowires is essential for the synthesis of nanowires of desired physical and optical properties. Cupric oxide (CuO), a p-type semiconductor is currently considered to be the key structural components of future electronic, optoelectronic, bio and gas sensing devices. CuO exhibits an interesting monoclinic structure with narrow band gap (1.2 eV) has emerging to be an exciting subject to study the growth mechanism in one-dimensional confinement regime. A well separated array of CuO nanowires have been successfully synthesized by thermal oxidation of a copper grid in static air. It has been explored that growth of these nanowires occurs under controlled oxidation when lattice diffusion of atoms or ions from the surface of the metal takes place at high temperature under parabolic kinetics. Our studies (HRTEM, XRD, EDS mapping) reveal, it is likely, that nanowire formation proceeds through nucleation of Cu, Cu2O, CuO and a boundary transition during the growth process. The formation of a single cupric oxide nanowire is attributed to crystallization from Cu/Cu2O mixed phase to form CuO structure. A phonon confinement effect has been observed by Raman spectroscopic studies. The nanowire shows photoluminescence emission in the visible range which has a steady blue shift along the length of the nanowire. As the diameter of the single tapered CuO nanowire decreases, the photoluminescence peak of the nanowire gradually shifts towards the higher energy side. A steady blue shift of 20 nm of the photoluminescence (PL) peak has been attributed to nanosize effect. As the diameter decreases the surface roughness also increases due to increase in the surface effect for smaller nanowires. Till now, there are some reports about photoluminescence properties of CuO nanoparticles and bulk CuO while there are a few relative experimental direct observations to investigate the optical properties of a single cupric oxide nanowire by mapping along the length of the nanowire. A through investigation of the photoluminescence behavior has been done to get contemplation about the surface properties of the nanowire during the growth. A phase transformation during crystallization process from Cu/Cu2O mixed phase to form pure CuO structure along the length of the nanowire may also have some role in observed shift in the PL peak. This study is valuable to understand the surface structural properties (defects) of single CuO nanowire, and can have applications in future development of optical and sensing devices.
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Flexible Nanowire Arrays with Broadband and Tunable Plasmonic Response.
Francesco Buatier de Mongeot 1 , Daniele Chiappe 1 , Andrea Toma 1 , Corrado Boragno 1 , Ugo Valbusa 1
1 Dipartimento di Fisica, Universita di Genova, Genova Italy
Show AbstractNanostructures endowed with controlled shapes and reduced dimensionality show novel physical properties in fields ranging from catalysis, spintronics , to plasmonics. In the last context, the excitation of localised plasmon modes supported on metal nanoparticles opens up the possibility of exploiting their unconventional optical properties originated by localization and enhancement of the electromagnetic field [1].Here we report on the self-organised physical synthesis of laterally ordered arrays of noble metal nanowires/nanorods which grow supported on flexible polymeric and dielectric templates. Direct ion beam sputtering (IBS) [2,3] of polycrystalline metal films induces the formation of regular nanoscale modulations at the vacuum-metal interface as a consequence of the competition between ion beam induced erosion with kinetically controlled diffusive relaxation of the dislocated mobile atoms. At higher ion doses, when the bottom of the troughs reaches the substrate, the ripple pattern decomposes into an array of nanowires. Far-field optical characterisation demonstrates that the nanowire/nanorod arrays exhibit non-conventional optical properties in the visible range (e.g. spectrally selective dichroic absorption) due to the excitation of localised plasmon oscillations of the conduction electrons supported on the nanoparticles. The possibility to tailor the optical and plasmonic properties of the nanowires in the visible range, has been demonstrated by finely tuning the morphological parameters of the nanoparticles [4]. A strong correlation between the morphlogical anisotropy and the polarization dependence of the plasmonic response has been quantitatively assessed bothe in the linear regime, as well as in the nonlinear regime, showing e.g. a strong polarization dependent second harmonic generation (SHG) [5]. [1] E.Ozbay, Science, 311, 189 (2006)[2] A. Toma, D. Chiappe, B. Šetina Batič, M. Godec, M. Jenko, F. Buatier de Mongeot, Physical Review B 78, 153406 (2008) [3] A. Toma, D. Chiappe, B. Šetina Batič, M. Godec, C.Boragno, U.Valbusa, M. Jenko, F. Buatier de Mongeot, Journal of Applied Physics, 104, 104313 (2008) [4] A. Toma, D. Chiappe, D. Massabò, C. Boragno, and F. Buatier de Mongeot, Appl. Phys. Lett. 93, 163104 (2008)[5] A. Belardini, M.C. Larciprete, M. Centini, E. Fazio, C. Sibilia, M. Bertolotti, A. Toma, D. Chiappe, and F. Buatier de Mongeot, Optics Express 17, 3603 (2009)
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Synthesis of Magnetic Nanoparticle Chains on Alpha Synuclein Protein Template in the Absence of a Catalyst.
Sonal Padalkar 1 2 , Yu-Ho Won 1 , Lia Stanciu 1 2
1 Material Science and Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractMagnetic nanoparticle chains and nanowires are of great interest due to their unique properties they exhibit. These nanostructures find several applications such as memory devices, magnetic biosensors, magnetically guided drug delivery systems etc. In the present work magnetic nanoparticle chains, such as nickel and iron oxide, have been synthesized for the first time on the alpha synuclein protein template. The synthesis techniques were simple and carried out at room temperature without the use of a catalyst. The diameter of the nanoparticle chains was varied, from ~25 nm to ~250 nm, by varying the process parameters. The nanoparticles chains were characterized by FESEM, TEM, HRTEM, EELS, elemental mapping. The magnetic properties of the nanoparticles chains were explored by AFM.
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Synthesis of Silica Nanowires and Silver – Silica Core Shell Structures on Alpha Synuclein Protein Template.
Sonal Padalkar 1 2 , Yu-Ho Won 1 , Lia Stanciu 1 2
1 Material Science and Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractSilica nanostructures are of interest due to their unique properties they exhibit. The porous network of the silica nanowires can be exploited for several applications. In the present study silica nanowires have been synthesized on protein template, alpha synuclein, by exploiting the surface charge on the template. The synthesis technique is simple and does not require a precise control of process variables. The diameter of the nanowire can be varied, from 50 nm to 250 nm, by varying the silica precursor concentration. The effect of reaction time on the morphology of nanowires was also studied. Further, silver nanorods prepared by using alpha synuclein template were coated with a silica shell. These nanostructures were characterized by FESEM, TEM, HRTEM, EELS and elemental mapping.
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Electrochemical Conversion of Ag(I)CN Nanowires: A Quick and Soft Route to Make Metallic Nanowires on Surfaces.
Gilles Bourret 1 , Theo G. M. van de Ven 1 , Thomas Lazzara 1 , R. Bruce Lennox 1
1 Chemistry, McGill University, Montreal, Quebec, Canada
Show AbstractFabrication of one-dimensional metallic nanostructures is an important activity within nanoscience. Their fabrication usually involves the reduction of a metal precursor, involving an electron transfer between the metal ions and their surroundings. Surprisingly, the use of electrochemistry to make metallic nanostructures has been generally restricted to the electrochemical growth of metals in alumina templated materials. We present here the use of solid state electrochemistry and self-assembled metal complexes to make metallic nanostructures on surfaces. We recently found a high yield route to produce silver cyanide (AgCN) nanowires with very high aspect ratios (5 to 100 nm wide, > 50 μm long) using self-assembled polymeric nanotubes made of poly(styrene-alt-maleic anhydride; SMA). The electrochemical reduction of the AgCN to Ag is demonstrated as a proof of concept. A solid state electrochemical study of AgCN-SMA formed nanowires was performed on several conductive substrates (graphite, HOPG, ITO, glassy carbon electrodes), using cyclic voltammetry. A systematic comparison of pure, insoluble AgCN crystals, AgCN-SMA nanowires, and water soluble KAgCN2 salt was performed. The solids (AgCN-SMA nanowires and AgCN crystals) were physically adsorbed on the corresponding working electrode prior cyclic voltammetry (CV). As expected, the three compounds have almost identical CV. Electron diffraction shows that the reduced wires are pure polycrystalline silver. AgCN-SMA nanowires were also deposited on gold interdigitated microelectrodes, immersed in the electrolyte solution and used as working electrodes. IV curves between the microelectrodes of the dried samples were recorded before and after the electroreduction of the wires. Prior to the electrochemical reduction the materials are highly resistive. After the reduction, excellent electric contact is made between the electrodes. Three aspects of this work are notable. (i) The shape of the original nanowires is well preserved during their electrochemical conversion, suggesting that this technique may be applicable to a wide range of self assembled coordination compounds. (ii) The ability to create electrical contact in the gap spanning 2 electrodes is promising for use of these wires. (iii) Electrochemical reduction is readily scalable and does not require a strong reducing agent nor high heat, and is compatible with printing techniques or the use of flexible substrates.
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Synthesis of Tetra(4-pyridyl) Porphyrin Rectangular Nanotubes in the Vapor Phase.
Seok Min Yoon 1 , Hee Cheul Choi 1
1 department of chemistry and division of advanced materials science, pohang university of science and technology, Pohang Korea (the Republic of)
Show AbstractOne-dimensional single crystalline rectangular nanotubes (RNTs) of 5,10,15,20-tetra (4-pyridyl) porphyrin (H2TPyP) were fabricated by a vaporization–condensation–recryatallization (VCR) process [1,2,3] on carbon-coated Si(100) substrates. The single crystal X-ray diffraction and selected area electron diffraction (SAED) pattern data revealed that the H2TPyP-RNTs were formed by self-stacking of H2TPyP unit molecules via hydrogen bonding, hydrogen-π and π-π intermolecular interactions, with growth axis along [010], relatively broader phase on (100) and narrower phase on (001). The size of porphyrin nanotubes in terms of length, width, height and wall thickness was controllable by modulating the growth factors, for example, the flow rate of Ar carrier gas. [3] The confocal scanning microscope (CSM)-coupled photoluminescence (PL) spectroscopic studies demonstrated that the single H2TPyP-RNT show waveguide and amplified spontaneous emission (ASE) properties, based on observations exhibiting the threshold pump energy and the narrowed 0-2 emission peak at the optically flat bright tip faces of H2TPyP-RNT. These results suggest that H2TPyP-RNTs will be a promising nanomaterial for future submicron-sized organic optoelectronic devices. Reference[1] S. M. Yoon, I. C. Hwang, N. Shin, D. Ahn, S. J. Lee, J. Y. Lee and H. C. Choi, Langmuir, (2007), 23, 11875.[2] H. S. Shin, S. M. Yoon, Q. Tang, B. Chon, T. Joo and H. C. Choi, Angew. Chem. Int. Ed. (2008), 47, 693.[3] S. M. Yoon, I. C. Hwang, K. S. Kim and H. C. Choi, Angew, Chem. Int. Ed. (2009), 48, 2506.
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Fabrication of Chemical Sensor Array Using Single Metallic and Conducting Polymer Nanowires Synthesized via Electrochemical Deposition.
Yushi Hu 1 , Innam Lee 1 , Minhee Yun 1 2 3
1 Electrical and Computer Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3 Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractChemical sensors based on bundled nanowires made of the same material greatly suffer from a limited sensing range due to material properties. However, nanowire arrays composed of multiple single nanowires made of different materials are able to combine the sensing properties of each element and expand the sensing range. Moreover, sensing signals collected from single nanowire arrays can be utilized to differentiate multiple chemicals by using proper data analysis method, such as principal component analysis (PCA). We report a simple controllable and reproducible fabrication method based on electrochemically deposited single nanowire arrays on a chip. Single nanowires made from different materials, including palladium (Pd), polypyrrole (Ppy) and polyaniline (PANI), were grown inside Poly(methyl methacrylate) (PMMA) channels between Au electrodes with diameters down to 30 nm and lengths up to 7 micron. These single nanowires were synthesized with 130 micron away from each other on a single chip and functioned as a chemical sensor array in this report. We also investigated the relationship between the sensing behavior and different nanowire structures to further understand nanowire sensing mechanisms. Three different Pd nanowire structures, including grainy, plain, and hairy structures, were grown in a controlled way and hydrogen gas was used as the analyte gas in the sensing investigation. Those different structures showed two different sensing mechanisms (increased or decreased resistance) with different behaviors. Presence of hydrogen gas tended to increase the resistance of plain structured nanowires and decrease that of grainy ones, while both scenarios happen in hairy structured nanowire. Possible explanations are proposed to address the difference in sensing mechanisms in this report.Furthermore, the feasibility of biomedical sensor application based on single nanowire structures is also demonstrated. Single polymer nanowires such as PANI or Ppy nanowire were functionalized by antibodies and crosslink layer. Functionalization on PANI was carried out by covalent bonding between PANI and antibody of target via a crosslink layer of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) / N-hydroxysuccinimide (NHS). The fluorescent labeled antibodies were successfully stabilized on PANI thin film and sub-micro wire. The successful functionalization of PANI and Ppy promises to realize the multi-target biomedical sensing. Therefore, single nanowire arrays are perfect building blocks for multi-target chemical and biomedical sensing applications.
9:00 PM - M16.18
Nanoscale Interconnect for High Current Delivery.
Joondong Kim 1 , Chang-Soo Han 1
1 Nano-Mechanical Systems Research Center, Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of)
Show AbstractITRS (International Technology Road Map For Semiconductors) has declared the need of high conductors, which may alternate the Cu line bearing a limit of current delivery above 106 A/cm2 besides the electromigration. Carbon nanotubes and nanowires have been indicated to be substitutes of the Cu line. Chemically grown Ni silicide nanowires were aligned by dielectrophoresis, which control the nanowire numbers and position onto Pt-metal electrodes. Focused ion beam (FIB) process was performed to deposit Pt metal to give an ohmic contact between the Pt-metal electrode and the nanowire. The current density of single crystalline Ni silicide nanowire was reached to be around 107 A/cm2 level and single nanowire interconnect showed the uniform current delivery performances. We discuss various nanomaterials, such as carbon nanotubes and metallic nanowires for high current delivery systems. It also cover the impedance characteristics of the nanoscale interconnect with high frequency responses.
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Fabrication and Surface Characterization of Porous Gold Nanowires for Molecular Sensor.
Hyunung Yu 1 , Weon-Sik Chae 2 , Hee-Ok Lee 2
1 , Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 2 , Korea Basic Science Institute, Gangneung Korea (the Republic of)
Show AbstractThe fabrication and surface characterization of porous materials with well-ordered structures has been intensively studied for their novel physical properties. Porous gold nanowires with different diameters were fabricated using templated electrochemical deposition techniques. The technique allows dimension-controlled material for highly-active, stable, tunable substrates for molecular sensors. First, gold-silver alloy were electrochemically deposited within the porous alumina membrane with cylindrical channels of various diameters and only a silver phase was chemically dissolved using strong acid. Field-emission scanning electron microscopy image of the resulting nanowire show a highly-ordered nanoporous network. Also, a large surface-enhanced Raman scattering (SERS) were measured for the characterization of porous gold nanowires. To identify hot spots, SERS image was taken for a single porous gold fiber.
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Growth of Tungsten Oxide Nanobelts in Tetragonal Phase.
Wei Wu 1 , Qingkai Yu 1 , Jie Lian 2 , Jiming Bao 3 , Zhihong Liu 3 , Shin-Shem Pei 1
1 Center for Advanced Materials, Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, United States, 2 Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, United States
Show AbstractOne-dimensional (1D) semiconductor oxide nanostructures, such as nanobelts (NBs) and nanowires (NWs), have attracted a great research attention due to their potential in nanoelectronics and optoelectronics. With salient electrochromic, optochromic, gaschromic and catalytic properties, tungsten oxides (WOx) are of great interest, being promising in applications such as flat panel displays, 'smart windows', semiconductor gas sensors, and photocatalysts. In the past few years, diverse forms of WOx NWs have been synthesized. However, WOx NBs are less observed and studied. Here, we demonstrate the synthesis of WO3 NBs on Si substrate by hot-wall chemical vapor deposition without using any foreign catalyst. The as-synthesized products were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and photoluminescence spectrum. The width of the NBs is in the range of 50-100 nm with width-to-thickness ratios of 5-10 and lengths of up to tens μm with aspect ratios higher than 100. These NBs grew along [001] direction in the tetragonal WO3 structures with the lattice spacing measured to be 0.388 nm and 0.739 nm along the two orthonormal directions [001] and [200]. The tetragonal phase of WO3 is a high-temperature equilibrium structure, which normally presents above 770°C. To date, only a few results have been reported on the presence of tetragonal WO3 at room temperature. Raman spectrum of the NBs is very close to, but not exactly identical with any Raman spectra of tungsten oxides reported in literature. A weak ultraviolet emission at 376 nm from the NBs was observed on the room-temperature photoluminescence spectrum. The vapor-solid growth model was proposed to illustrate the formation of WO3 NBs in our experiment.
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Synthesize of Metal-semiconductor Segmented Nanowire by Electrodeposition.
Hyeon-Jin Eom 1 , Bong-Young Yoo 1 2
1 Department of Bio Nano Engineering , Hanyang University , Ansan, Kyeonggi-do Korea (the Republic of), 2 Department of Materials and Chemical Engineering, Hanyang University , Ansan, Kyeonggi-do Korea (the Republic of)
Show Abstract Recently, thermoelectric (TE) is ignited by enhancement of nano-science and engineering that uncovers the possibility of increasing of figure of merit (ZT). As a candidate for thermoelectric materials, metal could not be considered because of their high thermal conductivity. However, according to other research, it is feasible to decrease thermal conductivity of also metal without much degradation of the electrical conductivity, which strongly implies that nanoscale metal can be utilized to improve thermoelectric properties of devices, especially power factor. Semiconductor-semiconductor superlattice nanowire structure has been studied as one of the best candidates for thermoelectric devices, because of their photon scattering characteristics at the interfaces. In this research, instead of semiconductor-semiconductor superlattice structure, metal-semiconductor superlattice structure was synthesized, and its microstructure and electrical properties are investigated. With this structure, improvement of electrical conductivity as well as degradation of thermal conductivity with phonon scattering would be anticipated. Metal-semiconductor superlattice nanowires were acquired with electrochemical displacement method, which can exchange the material which has low reduction potential with more noble materials in aqueous electrolyte. To achieve this, Ni-Ag superlattice structure was firstly prepared as metal-metal superlattice structure. The electrolyte for the electrodeposition of Ni-Ag segmented nanowries was consisted of 0.3 mol/L C6 H5Na3O7, 0.7mol/L NiSO4 and AgNO3. Electrodeposition was performed galvanostatically in two electrode cell configuration with anodized aluminum oxide(AAO) template. Cu layer was deposited at the one side of AAO template as a working electrode, platinum coated titanium stripe as counter electrode. The composition of electrodeposits could be controlled by applied potential which is directly related the applied current density. Ni-rich phase could be obtained when the applied current density was over 10mA/cm2 and Ag-rich phase at 0.5mA/cm2. After acquiring Ni-Ag segmented nanowire structure, we synthesized the metal-semiconductor segemented nanowries (Ag-BiTe segmented nanowire) by using galvanic-displacement method. Because standard reduction potential energy of nickel is more negative (-0.25V) than that of BiTe in Bi ion and Te ion contained bath, it is possible to make displacement of Ni with BiTe using galvanic displacement. The morphology was investigated by SEM and composition profile was observed by EDS. In conclusion, nanoscale metal-semiconductor segmented nanowires were synthesized by electrodeposition and electrochemical displacement method. Their structural characteristics and electrical properties were investigated to understand the possibility of this segmented nanowires as a thermelectrical materials.
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Melamine Mediated Synthesis of Silver/Organic Nano-needle and its Application.
Keum-hwan Park 1 , Sang Hyuk Im 2 , O Ok Park 1
1 , KAIST, Daejoen Korea (the Republic of), 2 , Korea reserch institute of chemical technology, Daejeon Korea (the Republic of)
Show AbstractWe have investigated the generation of silver nanoparticles embedded organic nano-needle particles firstly by introducing melamine. Melamine and silver nitrate can be made linear chain with forming 1:1 complex[1], and this phenomenon might be the reason for being generated linear particles. This study shows that the shape of synthesized particles can be affected by the structure of organo-metal complex. Surprisingly, the melamine plays curial role to form nano-needle in early reaction stage but the organic frame disappeared in final reaction stage leaving only silver nanoparticles. This disappearing organic part seems to be imine and amide mixture and we confirmed that by IR spectrum. This simple synthetic route will be one protocol to make one dimensional metal-organic nanocomposite. In addition we found that these particles could be use for Nonvolatile memory. Reported studies about polymer/metal nonvolatile memory [2],[3] have been using conductive polymer such as polyaniline[4] decorated with metal nanoparticles. While these methods need two steps for fabrication of materials, our process needs only one step because the synthesized particles have the character for nonvolatile memory. Not only far easier process, but smaller size is another merit for fabrication of device. Without any process, we could fabricate nano-scaled nonvolatile memory device and confirmed write-read-erase-rewrite cycle.[1] K. Sivashankar, A. Ranganathan, V.R. Pedireddi, C.N.R. Rao, Journal of Molecular Structure, 2001, 559, 41–48[2] J. Ouyang, C. Chu, C.R. Szmada, L. Ma, Y. Yang, Nature materials, 2004, 3, 918-922[3] B. Mukherjee, M. Mukherjee, Applied physics letter, 2009, 94, 173510[4] R.J. Tseng, J. Huang, J. Ouyang, R.B. Kaner, Y. Yang, Nanoletter, 2005, 5, 1077-1080
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Tuning of the Electrical Hysteresis in the Aligned SnO2 Nanowire FETs on the Flexible Substrates.
SahngKi Hong 1 , DaeIl Kim 1 , Gyu-Tae Kim 2 , Jeong Sook Ha 1
1 Department of Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of), 2 School of Electrical Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractUnderstanding the origin of the hysteresis in the device characteristics is essential for controlling and obtaining the reproducible and the stable performances in nanowire electronic devices. There have been several reports on the electrical hysteresis in SWCNTs and various nanowire FETs. In the nanowire FETs with a SiO2 gate insulator, the existence of polar water molecules adsorbed on the surface was mainly attributed to cause the hysteresis, which can be tuned by vacuum operation, ozone treatments, or surface passivations. However, it was not easy to clarify the nature of the charge traps quantitatively residing at the interface between nanowires and dielectric layers or the nanowire itself. Furthermore, it will be harder to control the hysteresis in the flexible electronics owing to the defect-rich surfaces than the rigid substrates. Here, we report on the controllability of electrical hysteresis in aligned SnO2 nanowire FETs on the flexible substrates by changing the surface passivation with self-assembled monolayers (SAMs). N-type SnO2 nanowires with an average diameter of ~70 nm and a length of ~ μm were grown by chemical vapor deposition technique. The aligned SnO2 nanowire channel with a width of 50 μm and a length of 3 μm was prepared via a sliding transfer method on the flexible substrate, composed of two layers of polyimide (PI) films with a sandwiched bottom gate of Ti(10nm)/Au(50nm) film. A large hysteresis in a counter-clockwise direction with a hysteresis width of 18 V at a sweep rate of 1 V/sec was observed in such formed SnO2 nanowire FETs during the gate voltage sweep from -20V to 20V and again back to -20V. The large on/off ratio reaching 105 maintained above 4 hrs for both “ON” or “OFF” state. With the increase of the sweep rate (V/s), the hysteresis width increased but the “ON” current decreased, attributed to the charge traps on the PI film formed during the sliding transfer of SnO2 nanowires. When the flexible FETs were treated by 3-aminoprophylmethoxylane SAM, the hysteresis width decreased from 18 V to 7 V, but almost no change was observed with octadecyltrichlorosilane SAM treatment. The differences of the hysteresis behavior by the SAM treatments suggest the possible tuning of the hysterical device characteristics by the polar or non-polar surface treatments depending on the nature of the charge traps of the flexible electronic devices.
9:00 PM - M16.24
Light Harvesting and Highly Polarised Emission in Single Conjugated Polymer Nanowires by Polarising Excitonic Energy Transfer.
Gareth Redmond 1
1 School of Physics, University College Dublin, Dublin Ireland
Show AbstractWe demonstrate polarising excitonic energy transfer in single conjugated polymer nanowires. Polydioctylfluorene is used as the nanowire active material since its well-characterised structural polymorphism permits tailoring of its photophysical properties by creation of a specific molecular architecture without the need for chemical modification. Nanowire synthesis by solution-assisted template wetting ensures that a significant fraction of axially aligned beta-phase polymer chains, dispersed throughout a disordered glassy-phase host polymer matrix, is formed in each wire. In this manner, both nanowire shape and external dimensions, as well as internal polymer chain morphology, are controlled using a convenient, practically reagent-less, one-step synthesis method. Polarisation-resolved imaging and spectroscopy data show that individual wires exhibit strongly anisotropic emission with remarkable insensitivity to excitation polarisation. Each wire behaves as an isotropic-to-polarised light converter in which, at wavelengths of preferred optical absorption by the glassy-phase, excitations generated on these more randomly oriented chains undergo polarising energy transfer to the aligned beta-phase chains, which subsequently emit light with a high degree of linear polarisation. This optical functionality is further illustrated by undertaking measurements on more complex 2-D multi-nanowire microstructures, assembled using a novel probe-based ‘moveable-meniscus’ manipulation method.
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Direct Observation of the Gas-Surface Interaction Kinetics in Nanowires Using Pulsed Self-Heating Assisted Conductometric Measurements.
J Daniel Prades 1 , Roman Jimenez-Diaz 2 , Francisco Hernandez-Ramirez 1 3 , Albert Romano-Rodriguez 2 , Joan R Morante 1 2
1 , IREC, Institut de Recerca en Energia de Catalunya, Barcelona, Barcelona, Spain, 2 EME/XaRMAE/IN2UB, Departament d’Electrònica, Universitat de Barcelona, Barcelona, Barcelona, Spain, 3 , Electronic Nanosystems S.L., Barcelona Spain
Show AbstractDynamics of gas-surface interactions determine the limits of the fastest response times of sensors based on metal oxides. In this contribution, the kinetics of adsorption and desorption of gaseous molecules onto the surface of metal oxide nanowires are analyzed through pulsed self-heating assisted conductometric measurements. To perform these measurements, we have exploited the dissipated power at individual nanowires by Joule effect due to the bias current applied in conductometric measurements (self-heating), which enables heating the tiny mass of these wires up to the optimum temperatures for gas sensing applications with power values as low as few tens of microW. This interesting feature is exploited here to develop a sensor system that only requires few mW to bias, heat and measure the sensors, which can be supplied by state-of-the-art energy harvesting technologies, like thermoelectric microgenerators. In combination with pulsed operation mode, this single-nanowire-based approach overcomes gas diffusion, which is typical of conventional porous film based devices, and provides thermal response times fast enough to evaluate the fundamental gas-surface reactions kinetics. Experimental response and recovery times of individual SnO2 nanowires towards oxidizing and reducing gases obtained with the here-proposed methodology are faster than the values obtained with conventional approaches (i.e.: microhotplates) and can be directly related to the reaction barriers predicted by theoretical models and other experimental techniques.
9:00 PM - M16.26
Large-Scale Magnetic Assembly of Multi-segmented Nanowires into Three-Dimensional (3-D) Soldered Nanowire Networks.
Fan Gao 1 , Zhiyong Gu 1
1 Chemical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractIt is extremely challenging to fabricate 2D or 3D integrated and hybrid nanoelectronic devices or nanosystems. In this presentation, we show a recent strategy that we have developed in the assembly and soldering of nanowires into ordered 3D and electrically-active nanowire networks. Multi-segmented nanowires with nanosolder material such as tin (Sn) were self-assembled into very large scale and ordered 3D network structures by magnetic field assisted assembly in a liquid medium. Nanosolders were fabricated on both sides of the multi-segmented nanowires by template assisted electrodeposition method. The formation of junctions between nanowires and the scale of nanowire networks were dependent on nanosolder reflow temperature and controlled magnetic field. The size of the nanowire networks ranged from tens of microns to millimeters. The electrical characteristics of the 3D nanowire networks were measured using a probe station with micropositioners. Nanosolders, when combined with assembling techniques, can be used to efficiently connect and join nanowires (or other nanoelectronic components) with low contact resistance, which are very well suited for sensor integration as well as nanoelectronic device fabrications.
9:00 PM - M16.27
Effect of Flux on Lead-free Nanosolder Reflow from Nanowires and Nanorods for Nanoelectronics Assembly Applications.
Fan Gao 1 , Irene NkengforAcha 1 , Subhadeep Mukherjee 1 , Karunaharan Rajathurai 1 , Qingzhou Cui 1 , Zhiyong Gu 1
1 Chemical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractLead-free nano-solders have shown promise in the assembly and integration of nanowires and carbon nanotubes for nanoelectronics and nanosystem applications (Cui, Gao, Mukherjee, and Gu. Small 2009, 5, 1246-1257). In microelectronics industry, flux is widely used in the assembly and packaging processes. In this presentation, the effect of flux on nanosolder reflow has been investigated on two types of promising lead-free nano-solders: tin-based and indium-based nanosolders. Nano-solders (tin, indium, and tin/silver alloy) in the form of nanowires and nanorods were synthesized by using electrodeposition and chemical reduction methods, respectively. The effect of three different rosin based fluxes, rosin (R), mildly activated rosin (RMA) and activated rosin (RA) were investigated during the nanosolder reflow process, either purged with or without nitrogen at different temperatures. Compared with the reflow process without flux, the wetting performance of the lead-free nanosolders was dramatically enhanced by using a flux. It was found that similar reflow behavior was exhibited for the solder nanowires and nanorods from different synthesis methods. The morphology of nanosolders before and after reflow was analyzed by scanning electron microscopy (SEM) along with energy-dispersive X-way spectroscopy (EDS). An interesting Oswald-ripping phenomenon was observed for nano-solder reflow; solder nanowires/nanorods turned into small liquid droplets upon heating, merged into larger solder droplets, and then solidified into solder balls upon cooling.
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Self Assembled Oxide Nano Wires Through Termination Control.
Gertjan Koster 1 , Jeroen Blok 1 , Bouwe Kuiper 1 , Guus Rijnders 1 , Dave Blank 1
1 , University of Twente, Enschede Netherlands
Show AbstractThe perovskite class of oxides, with the general compositional formula ABO3 provides a unique toolset of materials to study the structure-composition to property relationship in correlated electronic systems. By using thin film deposition techniques that allow for atomic control, one can essentially build artificial crystal structures bottom up, for example by the deposition of superlattices and heterostructures, where either A or B periodically is varied (or both). Examples of such experiments are the BaCuO2/(Sr,Ca)CuO2 system, which becomes bulk superconducting when fabricated in superlattice form [1], and the LaAlO3/SrTiO3, where the interfaces between the two perovskite blocks seem to dominate the observed electronic behavior [2]. An important observation is that the starting point for these experiments is a single terminated substrate template; typically TiO2 terminated SrTiO3, which can be obtained through well-established chemical etching procedures [3]. On the other hand, in literature, there are examples of spontaneous self-organization of deposited material, with the starting template of the mixed variant [4]. A new approach would be to consider of such a template, where the termination is controlled in such a way that regions of the two possible terminations are well-defined.This paper discusses the results obtained using controlled mixed terminated substrates in combination with SrRuO3 deposition. Probably through a difference in surface diffusion on the two possible terminations, enhanced growth is observed on one of these terminations. An example is a case, where the regions of mixed termination are defined by lines parallel to the vicinal steps. SrRuO3 appears to grow selectively on one termination in wires of tens of nanometers wide and a few nanometers tall. We have characterized these nano wires by in situ SPM and PES and also provide evidence for a possible growth mechanism by Monte Carlo solid-on-solid simulations. 1.G. Koster, K. Verbist, G. Rijnders, D.H.A. Blank, H. Rogalla and G. van Tendeloo, Physica C 353 (2001) 167-1832.A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004)3.G. Koster, B.L. Kropman, G. Rijnders, D.H.A. Blank and H. Rogalla, Appl. Phys. Lett. 73 (1998) 2920-29224.F. Sanchez, G. Herranz, J. Fontcuberta, M. Garcia-Cuenca, C. Ferrater, and M. Varela, PHYSICAL REVIEW B 73, 1 (2006).
9:00 PM - M16.29
Synthesis and Structural Characterization of Ultra-thin Flexible Au Nanowires.
Alexandre Kisner 1 , Marc Heggen 1 , Karsten Tillmann 1 , Yulia Mourzina 1 , Andreas Offenhaeusser 1
1 IBN-2, Forschungszentrum Jülich, Jülich Germany
Show AbstractAu nanowires (NWs) are one of the most prominent one-dimensional nanomaterials to be employed as building blocks in the fabrication of nanodevices. In the bendable electronics the nanowires’ elastic limits are driven by the tendency of surface to reduce surface energies. Although extensive researches have been carried out on mechanical properties and reconstruction of {110} bulk surfaces of Au, very limited experimental reports concerning the synthesis of flexible Au nanowires with diameter smaller than 10 nm and their atomic arrangement on the narrow surface are available and most of the mechanisms rely on computer simulations only. Here we show that micrometer long flexible ultra-thin Au nanowires with diameter tunable between 1.6 nm and 8 nm can be produced by electroless reduction of HAuCl4 in a micellar structure formed by oleylamine. High-resolution transmission electron microscopy (HRTEM) analysis revealed the nanowires were single-crystalline with lattice spacing of 0.25 – 0.26 nm along the long direction of the wires, which corresponds to (111) lattice spacing of face centered cubic (fcc) Au. In addition, at the extremities of the wires particles with similar dimensions of nanowires, but with multiple-twinned structure were found. Although twin defects were observed in the particles structure, the same was not seen in the atomic arrangement of the nanowires. Larger defects such as dislocations were also not observed in both particles and wires. Only in some regions at the surface of the nanowires, rows of atoms are missing along [111] and the surface can be described to be an irregular saw-tooth, with concave and convex structures. The atomic arrangements and these defects observed were associated with the absence of stabilizing in such points by the micellar structure of oleylamine. A direct consequence of that microstructures is a reduction of both surface energy and surface tension due to the surface attachment that is constrained only in two dimensions of the interface. These observations can help to explain the uncommon flexibility of metal nanowires besides their small curvature radius.
9:00 PM - M16.3
Formation of Single Crystal Salt Whiskers on Solution Saturated Nanoporous Coating.
Lorraine Francis 1 , Heng Zhang 1
1 Department of chemical engineering and materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show Abstract Single crystal whiskers, high aspect ratio crystals, with diameters on the order of microns were investigated intensely about 40 years ago. In some respects, whiskers are the predecessors to modern nanowires. For example, the vapor-liquid-solid method was first used to make silicon whiskers and later adapted to nanowires. Another synthesis method, growth of whiskers from solution-saturated porous materials, was also widely studied in that era, but has yet to be revisited as a potential route to nanowires. In this research, salt whiskers (e.g., KCl, NaCl) were grown on nanoporous coatings under controlled conditions in an attempt to better understand their growth mechanism and control their dimensions. Nanoporous coatings were prepared by dip coating glass substrates in aqueous silica nanoparticle dispersions. After drying, coated substrates were partially immersed in aqueous salt solutions and set into a controlled humidity box for growth. The standard growth time was two days. Visualization studies revealed that the salt solution is wicked into the coating by capillary action and then reaches a steady position as evaporation balances the convective flow. After several hours, crystals with whisker morphologies, typically ranging from 500 nm to 50 µm in lateral dimension and up to ~3 cm in length, emerged from the coating surface at a position above the original liquid level. The effects of solution concentration, relative humidity and porous coating structure were studied, and used to explore the transport phenomena and growth mechanism. Evaporation, convection and diffusion combine to create a “whisker growth zone” on the coating surface. Visualization during growth and examination of crystal morphologies support a base growth mechanism in which ions are added to the surface of the whisker in contact with the porous coating. Most revealing were sheet-like crystals that grew from whiskers that had fallen flat onto the coating surface. Achieving finer whiskers (< 500 nm) is possible when measures are taken to avoid disturbances, which dislodge smaller whiskers from the coating. In addition, adding small crystal seeds to the coating surfaces tended to create smaller diameter whiskers. Possible applications for these fine salt whiskers will be discussed.
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Structural and Morphological Control of Manganese Oxide Nanoparticles by Aqueous Precipitation.
David Portehault 1 2 , Sophie Cassaignon 1 2 , Emmanuel Baudrin 3 , Jean-Pierre Jolivet 1 2
1 Lab. Chimie de la Matiere Condensee de Paris, UPMC, PARIS Cedex 05 France, 2 Lab Chimie de la Matiere Condensee de Paris, CNRS, UMR 7574, PARIS France, 3 Lab de Réactivité et Chimie des Solides, Université de Picardie-Jules Verne, UMR 6007, Amiens France
Show AbstractDuring the last years, research on lithium batteries has evolved toward nanoscaled electrode materials. Among them different oxides were reported to present new reactinities and/or improved electrochemical behavior upon Li reaction in terms of rate capabilities and reversibility when the surface area is high and the crystallite size is sufficiently decreased.Within this context, manganese oxide nanomaterials are of particular interest from a fundamental point of view to investigate structure and size effect on the electrochemical behavior owing to the richness of this family. Nevertheless, tailoring the electrode materials structure/texture remains a significant challenge. Our group develops the synthesis of manganese oxide nanoparticles by precipitation in aqueous medium at low temperature. This soft chemistry route is well known to provide a versatile control of the solid formation.This presentation is focused on a low temperature aqueous route for precipitation of Mn(IV), Mn(III) or mixed valence Mn(III)-Mn(IV) manganese (oxyhydr)oxides using MnO4- and/or Mn2+ precursors. Soft conditions permit fine tuning of the reaction path and different pure phases are obtained depending on the synthesis conditions (i.e. acidity, oxidation state, temperature and aging). In particular, nanowires of cryptomelane K0.11MnO1.85.(H2O)0.75, manganite γ-MnOOH and pyrolusite β-MnO2 are formed through self-assembly or topotactic processes, while γ-MnO2 hollow nanocones originate from heterogeneous oriented attachment. In parallel, heterogeneous nucleation or heteroepitaxy can be controlled in order to obtain hierarchical nanoheterostructures such as core-corona architectures of lamellar birnessite K0.19MnO1,77(H2O)0.30 or cryptomelane-birnessite nanocomposites. Soft chemistry is therefore a valuable tool to investigate and to control nucleation-growth processes, as well as the resulting morphological characteristics.Using these well defined structures, shapes, sizes and hierarchical orders, some effects of the nanoscale on the electrochemical properties versus lithium are emphasized.
9:00 PM - M16.31
The Growth and Characterization of Copper (II) Oxide Nanowires with Single Nanowire Electrical, Gas Sensing, and Photoconduction Measurements.
Benjamin Hansen 1 , Ganhua Lu 2 , I-Kuan Lin 1 , Nikolai Kouklin 3 , Junhong Chen 2 , Xin Zhang 1
1 Mechanical Engineering, Boston University, Atlanta, Georgia, United States, 2 Mechanical Engineering, University of Wisconsin Milwaukee, Milwaukee, Wisconsin, United States, 3 Electrical Engineering, University of Wisconsin Milwaukee, Milwaukee, Wisconsin, United States
Show AbstractEverywhere from integrated circuits in the personal computer to the charge-coupled device in digital cameras - microelectronic devices have found their way into nearly every aspect of our daily lives. With increasing demand for faster and better products, the microelectronic industry is reaching fundamental physical limits, and is becoming extremely costly. In response, tremendous ongoing efforts have been devoted to exploring the fabrication and characterization of novel nanostructures for next-generation solid-state devices. In particular, semiconductor nanowires (NWs) and carbon nanotubes (CNTs) have emerged as promising multifunctional materials that can be utilized as both wiring and device elements, providing an easy pathway to building a variety of hybrid nanoelectronic, nano-optoelectronic, nanomechanical, and electro-chemical devices. As a result there has been a sustained effort to produce semiconducting NWs of different material with new functionalities to meet the demands of the 21st century.To realize the full potential of these novel NW components for device applications, new methods enabling a systematic and controlled modification of their intrinsic characteristics are needed. This thesis explores the large scale growth of p-type semiconducting copper (II) oxide (CuO) NWs by a cheap and simple method of direct oxidation of copper substrates. The composition, morphology and crystal structure of the CuO NWs and the growth substrate are investigated to better understand the growth process.In addition to developing methods for the controlled growth of semiconducting NWs, there is high demand for easy and effective ways of manufacturing single NW devices for fundamental research and for technological development. Many of the current methods used are limited to the laboratory and include e-beam lithography and/or focused ion beam deposition. By using standard, cheaper photolithography techniques, single CuO NW devices are realized. The method can be broadly applied to most one-dimensional nanostructures and reduces the time and cost needed to fabricate single NW devices. Lastly, the multifunctional characteristics of single CuO NWs are explored. Room temperature sensing of low concentration gases, such as 100 ppm NO2 and 1% NH3 in dry air is demonstrated. White light sensing and the operation as a field effect transistor (FET) are also demonstrated. The possibility of increasing the device sensitivity and response, in addition to other high potential applications for CuO, may result in exciting new devices based on CuO NWs.
9:00 PM - M16.32
Synthesis of Au Nanowires and Nanoparticles in Water-soluble Chitosan Modified SBA-15.
Hangning Chen 1 2 , Ben Estes 1 , Andrew Lupini 3 , John Larese 1 3
1 Chemistry, University of Tennessee, Knoxville, Tennessee, United States, 2 Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, GanSu, China, 3 , Oak Ridge Nation Laboratory, Oak Ridge, Tennessee, United States
Show AbstractA new procedure for the preparation of Au nanostructured materials in SBA-15 mesoporous silica is reported. Au ions can be easily adsorbed within the channels of water-soluble chitosan modified SBA-15 (as Au3+-Chi-SBA-15). Highly dispersed Au nanoparticles of ~2-3 nm in size are obtained by reducing Au3+-Chi-SBA-15 with NaBH4. Au nanowires with ~6 nm diameter, several hundred nanometers long can be formed by a carefully controlled thermal regime of the Au3+-Chi-SBA-15. X-ray diffraction and High resolution TEM measurements are used to demonstrate the microscopic habitat of the metal clusters and the Au nanowires which appear to have substantial crystallinity. This work was supported by U.S. DOE Basic Energy Science, with contract no. DE-AC05-00OR22725 with ORNL.
9:00 PM - M16.33
Finite Curvature-Mediated Ferroelectricity in Co-Axial Nanowires.
Stephen Nonnenmann 1 , Oren Leaffer 1 , Eric Gallo 2 1 , Michael Coster 1 , Craig Johnson 1 , Gregory Soja 1 , Rahul Joseph 1 , Jonathan Spanier 1 2
1 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Electrical & Computer Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractWe report on the synthesis and characterization of co-axial functional nanowires of selected diameters and shell thicknesses prepared via a combined electrochemical and sol-gel process, each nanowire consisting of a noble-metal core and a ferroelectric oxide perovskite shell. X-ray diffraction, electron microscopy, Raman scattering, and Fourier transform infrared reflection spectroscopy was used to characterize the structure and composition of the Au core and Pb0.52Zr0.48TiO3 shell nanowire product. Significantly, using scanning probe microscopy of individual, electrically-addressed nano-shells we demonstrate that ferroelectric polarizations oriented along the finite thickness direction in ultra-thin films are enhanced by the introduction of extreme curvature, thereby suppressing the finite size-driven evolution of the ferroelectric phase transition temperature TC. The measured responses within individual nano-shells possess magnitudes nearly three times that for their planar counterparts while exhibiting finite curvature-dependent offsets in FE switching hystereses. In stark contrast to the expected scaling of a depression of TC with inverse thickness, results based on modified Landau-Ginzburg model calculations indicate geometric curvature-driven polarization gradients in ultra-thin films result in significant increases in TC.**Work supported by the US Army Research Office under W911NF-08-1-0067.
9:00 PM - M16.34
Copper / Copper Oxide Coreshell Nanowire Assemblies Integrated on CMOS for Sensor Applications.
Sam MacNaughton 1 , Sameer Sonkusale 1
1 Electrical and Computer Engineering, Tufts University, Medford, Massachusetts, United States
Show AbstractDue to conductance changes in the presence of light and some gases, copper oxide is an attractive material for the use in electronic gas and light sensors. We present a method for the fabrication and assembly of amorphous copper / copper oxide coreshell nanowires on CMOS substrates for sensing applications. Copper nanowires were grown electrochemically through anodized aluminum oxide templates and were oxidized chemically and thermally in an alkaline bath. The ratio of the diameters of the copper core to the oxide shell can be adjusted by changing the temperature and time in the bath. Likewise, the ratio of copper (I) oxide to copper (II) oxide can be modified with the temperature of the oxidizing bath. The nanowires had an average diameter of less than 150nm and nominal lengths of 5μm. The structure and composition of the nanowires was analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Additional insight into the oxide layers was gained through X-ray photoelectron spectroscopy.The nanowires were assembled out of an aqueous dispersion by dielectrophoresis (DEP) on the topmost metal layer of a CMOS circuit. Depending on dispersion concentration and assembly time, the degree of assembly can be tuned from a single nanowire to several nanowires aligned between the electrodes. Photoelectric and electric characteristics of the nanowire assemblies were measured in varying gas environments using on-chip circuitry. Because copper oxides display photoelectric, photoconductive, and gas sorption properties, this integrated nanowire on CMOS assembly provides for a fully miniaturized and multifunctional sensor system-on-chip.
9:00 PM - M16.35
Single LaB6 Nanowire Point Electron Source: Synthesis, Assembling and Property Measurements.
Han Zhang 1 , Jie Tang 1 , Jun Ma 1 , Benjamin Wang 3 , Luchang Qin 2 3
1 1 D Nanomaterials Group, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 3 Physics and Astronomy, University of North Caralina, Chapel Hill, North Carolina, United States, 2 Curriculum in Applied and Materials Science, University of North Carolina, Chapel Hill, North Carolina, United States
Show AbstractSingle crystalline LaB6 nanowires are featured with excellent properties such as low work function, high electric conductivity, high melting point and high mechanical strength. A new generation cold field electron point source with high brightness, good stability and low energy spread can be realized by this material. In our work, we have developed a CVD based approach to controllably synthesize single crystalline LaB6 nanowires with desired dimensions and crystallographic orientations. Measurements on single LaB6 nanowires were performed to characterize their Young’s modulus, tensile strength, resistivity, current carrying capability and high temperature stability. With our home-built nano-manipulator, we were able to pick up, transport and fix individual nanowires onto the tip of metal needles to assemble into electron emitters. By the use of a delicate UHV field emission measurement system, we were able to characterize the clean surface of LaB6 nanowire emitters after surface cleaning. Field emission IV curve and stability measurement were also performed to evaluate its merits to be used as a point electron source.
9:00 PM - M16.36
A Generic Approach for Embedded Catalyst-Supported Vertically-Aligned Nanowire Growth.
Hee Suk Chung 1 2 , Yeonwoong Jung 2 , Jung Han Kim 1 , Seoung-Bum Son 1 , Kyu Hwan Oh 1 , Ritesh Agarwal 2
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractOne-dimensional nanostructures such as nanowires and nanotubes are being researched extensively owing to their novel properties resulting from their unique geometry, which enables them to function as active device elements and passive interconnects simultaneously. Specifically, vertically-aligned architectures have been considered to utilize their potential owing to their sub-lithographic dimensions critical for high-density device assembly. Achievement of single-crystalline vertically-aligned nanowires is typically obtained by epitaxial growth on lattice-matched crystalline substrates. More significantly, vertical alignment of nanowires on amorphous substrates is severely limited since amorphous substrates do not “guide” nanowire directions due to lack of crystallographic relationship with the nanowires, therefore rendering conventional epitaxial growth schemes ineffective. Therefore, it is desirable to develop techniques that allow single-crystalline vertically-aligned growth of nanowires on arbitrary substrate for high-performance devices. Here, we demonstrate that annealed plasma-sputtered Au/Pd thin-film catalyst can be a general technique to produce vertically-aligned single-crystalline nanowires on arbitrary substrates over large areas through the vapor-liquid-solid (VLS) growth mechanism, which presents new opportunities for assembling large-scale nanowire-based devices.
9:00 PM - M16.37
Synthesis, Characterization, and Electronic Structure of Single-Crystalline V2O5 and β′- CuxV2O5 Nanowires and Nanowire Arrays.
Jesus Velazquez 1 , Christopher Patridge 1 , Cherno Jaye 2 , Daniel Fischer 2 , Sarbajit Banerjee 1
1 Department of Chemistry, State University of New York at Buffalo, Buffalo, New York, United States, 2 Material Science and Engineering Laboratory, National Institute of Standards and Technology , Gaithersburg, Maryland, United States
Show AbstractSingle-crystalline vanadium oxide (V2O5) and copper vanadium oxide bronze β′-CuxV2O5(x~0.60) nanowires have been synthesized by chemical vapor transport and hydrothermal methods, respectively. These nanowire arrays are expected to be ideal building blocks for electrochromics, sensing platforms, and novel cathode architectures of Li-ion batteries wherein the power rates are controlled by the charging/discharging of individual nanowires. Vanadium oxide, V2O5, has a layered structure based on sheets of [VO5] square pyramids sharing edges and corners. Despite possessing these optimal structural characteristics, the practical implementation of bulk V2O5 as a cathode material in battery architectures has been hindered by the sluggish kinetics of Li-ion insertion/extraction. Scaling V2O5 to nanoscale dimensions offers the potential for much improved Li-ion insertion/extraction kinetics because of shorter solid-state diffusion path lengths, improved interfacial contact with the electrolyte, and the operation of Li-ion storage mechanisms not accessible in the bulk. These single-crystalline V2O5 nanowires are fabricated by a catalyst-assisted vapor transport process on Si/SiO2 substrate. This non-template assisted method grows arrays of highly oriented V2O5 nanowires with precise control of nanowire dimensions, substrate coverage, and crystal growth direction.1 Intercalation compounds based on the incorporation of either alkali or transition metals within the interstitial spaces of the V2O5 tunnel framework have been extensively studied in recent years. These vanadium bronzes show very remarkable transport and magnetic properties some of which have only recently been discovered including metal—insulator transitions, charge and spin ordering, paramagnetism, gapless states, and superconductivity. Copper vanadium bronze nanowires have been synthesized by the hydrothermal reduction of CuV2O6 precursor by aliphatic alcohols in a hydrothermal bomb reactor.2 The recent discovery of superconductivity and charge disproportionation in bulk β′-CuxV2O5 has lead to renewed interest in these 1D metallic systems. Techniques including X-ray and electron diffraction, high-resolution scanning and transmission electron microscopy, provide evidence for the crystal structure and the morphology of these materials. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to precisely probe the alignment, uniformity in crystal growth direction, and electronic structure of single-crystalline V2O5 and β′-CuxV2O5 nanowire arrays.2,3 This work was primarily supported by the National Science Foundation under award No. DMR-0847169.References1. Velazquez, J. M.; Banerjee, S., Small 2009, 5 (9), 1025-1029.2. Patridge, C. J.; Jaye, C.; Zhang, H.; Marschilok, A. C.; Fischer, D. A.; Takeuchi, E. S.; Banerjee, S., Inorg. Chem. 2009, 48 (7), 3145-3152.3. Velazquez, J. M.; Jaye, C.; Fischer, D. A.; Banerjee, S., J. Phys. Chem. C 2009, 113 (18), 7639-7645.
9:00 PM - M16.38
Template-free Growth of NiO Nanowire Array by a Metal-etching-oxidation Method.
Tom Wu 1 , Zhipeng Wei 1
1 , Nanyang Technological University, Singapore Singapore
Show AbstractNickel oxide (NiO) is a technologically important semiconductor material, and has been extensively studied due to its potential use as a nonvolatile memory devices, gas sensors, battery material, and so on. Construction of well-ordered, specifically oriented ensembles of metal oxide material nanostructures may advance more potential applications. For the growth of well-ordered NiO nanowire array, several typical methods can be investigated, such as the template assisted method, the template-free vapor-liquid-solid growth, and the hotplate method, however, none of the current synthesis methods are not very effective. In this study, we employ a metal-etching-oxidation (MEO) method which utilizes metal etching and concurrent oxidation process to synthesize NiO nanowire array. The growth of NiO nanostructures was carried out in a home-built tube-furnace based vapor transport system. Nickel (Ni) foil was used as both the substrate and the nickel source. Nickel chloride (NiCl2) powder serves as additional Ni source and generates Cl2 etching. NiO nanostructure was synthesized by simultaneous Cl2-assisted etching and gentle oxidation. The as-grown nanowires are single crystal and show very uniform diameters (between 80 and 100 nm) and length (~2 μm). The growth axis is along the [200] direction. The diameter (from 80 to 500 nm) and the length (from 1 to 10 μm) can be controlled by the growth temperature and O2 content, respectively. This method gives a new route for synthesize metal oxide nanostructure, and may be adapted to the synthesis of other nanomaterials.
9:00 PM - M16.39
Nanosecond Pulsed Laser Fabrication of SnO2 Nanowire Arrays for Hydrogen Gas Sensing.
Nozomi Shirato 1 , Abhilash Vincent 2 , Peng Zhang 2 , Amit Kumar 2 , Hyoung-Jin Cho 2 , Sudipta Seal 2 , Ramki Kalyanaraman 1 3
1 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, Florida, United States, 3 Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractFast, sensitive and discriminating detection of hydrogen at room temperature is crucial for storage, transportation, and distribution of hydrogen as an energy source. One dimensional nanowires of In2O3-doped SnO2 are potential candidates for improved H2 sensor performance. The continuous nanowires can decrease electrical noise, and their large active surface area could improve the response time and recovery time of the sensor. In this work we discuss fabrication and characterization of nanowire arrays using nanosecond laser interference processing of ultrathin SnO2 and In2O3-doped SnO2 films on SiO2 substrates. The nanowires are formed by thermocapillary effects under the laser-interference irradiation. Our results show that fabrication of large nanowire arrays is critically dependent on thin film and laser processing conditions, including laser energy and interference angle and film thickness. We will also present results of the thermal stability of nanowires against break-up and surface composition of the oxide before and after laser processing. This laser processing approach is a cost-effective, simple and robust technique to fabricate large arrays of parallel nanowires.
9:00 PM - M16.4
Synthesis, Electronic Structure, and Depressed Phase Transitions in Single–Crystalline Vanadium(IV) Oxide Nanostructures.
Luisa Whittaker 1 , Cherno Jaye 2 , Daniel Fischer 2 , Sarbajit Banerjee 1
1 Department of Chemistry, University at Buffalo, Amherst, New York, United States, 2 Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Upton, New York, United States
Show AbstractBulk vanadium(IV) oxide exhibits a first-order metal-insulator phase transition near room temperature (68°C). Associated with the phase transition are changes in the electrical conductivity, optical properties of VO2 at all wavelengths, and a structural transition from an insulating, low–temperature monoclinic phase to a metallic, high–temperature tetragonal phase. Such properties make VO2 a suitable material for Mott field-effect transistors, optical switching devices, and thermochromic coatings. However, the properties of this phase transition are strongly dependant on its morphology, crystallinity, interfacial strain, and stoichiometry. Herein, we report two distinct hydrothermal approaches for preparing 1D single-crystalline VO2 nanostructures exhibiting sharp metal-insulator phase transitions based on a)the hydrothermal reduction of V2O5 using different alcohols as reducing and structure directing agents followed by an annealing process and b)the hydrothermal hydration, exfoliation, and recrystallization of bulk VO2. The crystal structure and morphologies of the products are strongly influenced by the reaction time and concentration of structure–directing agents. The morphologies, structure and electrical properties of the prepared nanostructures have been characterized by scanning electron microscopy, high–resolution transmission electron microscopy, X–ray powder diffraction, electrical transport measurements, thermal analysis, and near–edge X–ray absorption fine structure (NEXAFS) spectroscopy. VO2 nanosheets prepared by the hydrothermal reduction of V2O5 exhibit a crisp and well–defined phase transition at 67°C hithertho unseen for VO2 nanostrucutres grown by solution–based methods. The as-synthesized VO2 nanosheets range in dimension from 0.8–5µm in length and 50-200nm in diameter. In contrast, the second approach based on the hydration/exfoliation of VO2 yields anisotropic free–standing single–crystalline VO2 nanostructures with a considerably depressed phase transition. This phase transition has been depressed to as low as 32°C for VO2 nanobelts prepared by the 1,3 butanediol–induced exfoliation of bulk VO2. NEXAFS measurements across the phase transition temperature provide insight into changes in the VO2 band structure. The results obtained provide insights into the importance of carefully controlling the stoichiometry and dimensions of VO2 nanostructures in solution. This synthetic route provides a relatively inexpensive method of producing 1-D nanostructured metal oxides under mild conditions for device applications. This work was supported primarily by the National Science Foundation under Award No. DMR 0847169.References1. Whittaker, L.; Zhang, H.; Banerjee, S., VO2 nanosheets exhibiting a well-defined metal–insulator phase transition. J. Mater. Chem. 2009, 19, 2968.2. Whittaker, L.; Jaye, C.; Fischer, D. A.; Banerjee, S., Depressed Phase Transition in Solution-Grown VO2 Nanostructures. J.Am.Chem. Soc. 2009. ASAP
9:00 PM - M16.40
Monte Carlo Simulation to Magnetic Properties of Amorphous Co Nanowires.
S. Liu 1 , A. Soh 1 , L. Hong 1
1 Mechanical Engineering, The University of Hong Kong, Hong Kong China
Show Abstract The magnetic properties of ferromagnetic nanomaterials composed of transition metals, such as Fe, Co and Ni, have been one of the most interesting research topics in the last two decades. The amorphous nanomaterials have also drawn much attention of the researchers as the crucial materials for their excellent soft magnetic properties and potential applications as ultrahigh density storages. It is not an easy task to characterize the magnetic properties of single nanowire through experimentsespecially nanowires with their diameters lower than ten nanometers. Hence, at this stage a good alternative is to carry out simulation studies. The amorphous Co nanowires with their diameters lower than 5 nm have been studied using Monte Carlo method. The amorphous structure has been constructed by exploring serially deposited close packing spheres method and simple sampling Monte Carlo technology, and the cylindrical structure with lower aspect ratio has been built through free boundary conditions and our proposed random periodic boundary conditions respectively. The initial simulation results show that the homogeneous axial surface anisotropy has strong influence on magnetization of nanowires with diameters smaller than 5 nm, there is a unique transformation from a homogeneous magnetic state to a spin wave extension leading to non-uniform precession by increasing the temperature, and moreover, the surface anisotropy has little effect on the hysteresis loop when the applied magnetic field is parallel to the longitudinal axis of the nanowire; whereas, for applied radial magnetic field, the influence is larger. Further study of the magnetic properties of Co nanowires, where the effect of unique local random anisotropy of amorphous magnets on the magnetic properties of nanowires is investigated, is in process.
9:00 PM - M16.41
Synthesis and Characterization of Lithium Aluminate Nanowires.
Aurellis Nascimento 1 , Nelcy Mohallem 1
1 , UFMG, Belo Horizonte Brazil
Show AbstractLithium aluminate (γ-LiAlO2) has gained attention for its potential use as irradiation blanket for nuclear fusion reactors and as ceramic matrix for molten carbonate fuel cells. In this work, LiAlO2 was prepared from a precursor solution of aluminum and lithium nitrates dissolved in water, and coprecipited by addition of NaOH. The white precipitate was washed with distilled water and ethanol, dried at 110 °C and calcined at various temperatures up to 1150 °C. The samples were characterized by X-ray diffraction, infrared spectroscopy, atomic absorption, TGA-DTA analysis and scanning electron microscopy. The density, specific surface area and porosity were determined by helium pycnometry and gas adsorption, respectively. The nanowires obtained showed high specific surface area between 42 and 23 m2.g-1 in the heating temperature ranging of 550-1150 °C, respectively. The samples presented the γ-LiAlO2, LiAl5O8 and Li2Al2O4.xH2O.crystalline phases.
9:00 PM - M16.42
Synthesis and Characterization of Tungsten Oxide Nanobushes.
Rong Hu 1 , Huasheng Wu 1 , Kunquan Hong 2
1 Department of Physics, University of Hong Kong, Hong Kong China, 2 Department of Physics, Southeast University, Nanjing China
Show AbstractHighly oriented tungsten oxide nanobushes were synthesized by heating tungsten plates with potassium hydrate as catalyst at a specific temperature. The structure and morphology were characterized by various techniques. It was found that the nanobushes have a W17O47 structure with length up to hundreds of microns, and they are compacted of well aligned nanowires with diameters of tens of nanometers. Based on characterization results, secondary root growth mechanism was proposed to explain the growth process.
9:00 PM - M16.43
Novel Nanostructures by Anodization of Al Nanowires.
Maria Kokonou 1 , Zhiyong Gu 2 , Ibrahim Gunduz 1 , Konrad Fadenberger 1 , Charalabos Doumanidis 1 , Claus Rebholz 1
1 Mechanical and Manufacturing Engineering, University of Cyprus, Nicosia Cyprus, 2 Chemical Engineering, University of Massachusetts, Lowell, Massachusetts, United States
Show AbstractPorous anodic alumina is broadly used as a template due to its unique structure resembling a honeycomb. It consists of vertical cylindrical pores, homogeneously distributed in hexagonal close packed arrays, whose geometrical characteristics are accurately controlled and tuned by the anodization conditions. Their diameters are in the range from 5 to 200 nm, while their height can range from a few tenths of nanometers to several hundreds of micrometers, depending on the duration of the anodization. Therefore, an important characteristic of these templates is their very high aspect-ratio of pore diameter to height, which can reach several thousands and is very difficult to achieve with lithographic techniques. For this reason, porous alumina introduces an exceptional template for the formation of very long nanowires of a wide range of materials by electrodeposition, electroless deposition or sol-gel techniques on various substrates. So far, all of the reported work concerning anodization refers to flat Al surfaces, either Al foils or Al films deposited on other substrates. In this work, the anodization of cylindrical Al wires will be presented, which results in porous structures with pores developing radially from the cylindrical surface of the wires towards its axis. Al wires of various diameters in the range from 5 mm to 125 μm have been anodized under the conditions that result in the most homogeneous pore distributions in the case of flat Al, i.e. in oxalic acid 0.3 M under constant voltage of 40 Volts. Anodization can be done until the whole Al wire has been consumed, or it can be interrupted to leave an Al core of the desired diameter at the central axis of the wire, which can serve as a contact for the electrodeposition of metals inside the pores. Then the porous alumina template can either be dissolved, leading to tree-like structures of nanowires or nanorods protruding around the metal axis, or it can be left as anodized, offering insulation to the metal nanowires. Furthermore, the core material is not limited to Al, since Al deposited on a wire of any material can be anodized. In this work the focus is on the formation of Ni nanowires by electrodeposition, attached on the central Al axis, to form nanoheater nanostructures. Bimetallic heterostructures of Al/Ni, Al/Ti, etc. form reactive pairs with high exothermic formation enthalpies of their intermetallic compounds. Self-propagating exothermic reactions in multilayer films/foils of nickel and aluminum are of great interest for thermal processes in nanoscale engineering. Novel applications on nanoscale that enable fine local selectivity and time-exposure control in thermal processing can be derived by other forms of nanostructures, such as bimetallic nanorods, or tree-like bimetallic nanostructures.
9:00 PM - M16.44
Passivation Induced Charge Modulation in SnO2 Nanowire Transistors.
Junhong Na 1 , Junghwan Huh 1 , Gyu Tae Kim 1 , Sung Chan Park 2 , DaeIl Kim 2 , Jeong Sook Ha 2
1 School of Electrical Engineering, Korea University, Seoul Korea (the Republic of), 2 Department of Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of)
Show Abstract We have compared the effects of the passivation on the characteristics of SnO2 nanowire field effect transistors (FETs) by fabricating the three differently passivated regimes on a single SnO2 nanowire, consisting of the unpassivated, the Al2O3 passivated, and the PMMA passivated portions, respectively. Passivation with PMMA induced a positive shift of the threshold voltage while Al2O3 passivation showed almost no shift. The degradation of the currents in a FET configuration was recorded for 54 days. It took only 5 days for the current to decrease from the initial to the 90% level for the unpassivated portion. However, in the case of Al2O3 or PMMA passivated portion, it took over 45 days, indicating the role of the protection layer on the degradation. The changes of the mobility and the carrier concentration in each portion for 54 days were analyzed, showing the different behaviors depending on the Al2O3 or PMMA passivation. By using the selective functionalization, the threshold voltage of the FET can be modified intentionally, maintaining the current level of the FET.
9:00 PM - M16.45
Assembly of Nanowires by Coffee-Ring Deposition.
Mei Zhang 1 2 , Zach McDargh 1 , Farag Abdelslam 1 2 , Chuck Zhang 1 2 , Ben Wang 1 2
1 High Performance Materials Institute, Florida State University, Tallahassee, Florida, United States, 2 Industrial Engineering, FAMU-FSU College of Engineering, Tallahassee, Florida, United States
Show AbstractNanowires are normally synthesized and produced in solution. A few methods have been developed to make aligned nanowire arrays on a substrate, such as Langmuir-Blodgett, microfluidic, electric-field-assisted assembly, and optical trapping. We develop a method to assemble aligned nanowires on substrate by using coffee-ring effect. The coffee-ring effect is the name given to a well known observation where the evaporative drying of a drop of coffee leaves behind a ring of dark materials at the edge of the original drop. When the colloidal solution is dried on a substrate, the dispersed materials can be carried to the solvent-substrate contact line as a result of evaporation-induced capillary flow and lead to highly selective deposition along the perimeter of the droplet. The deposition of nanowires on substrate by coffee-ring effect is more complicated than that of nanoparticles due to their anisotropic structure. In this work, we observed different nanowires during and after drying on substrate by confocal microscope, AFM, and SEM. We show how to direct the assembly of nanowires into aligned structure by coffee-ring deposition.
9:00 PM - M16.46
Effect of Thermal Annealing on the Characteristics of Core-shell Nanowires.
Hyoun Woo Kim 2 , Hyo Sung Kim 2 , Ju Chan Yang 2 , Han Gil Na 2
2 , Inha Univ, Incheon Korea (the Republic of)
Show AbstractIn recent years, core-shell nanowires have begun to attract interest as their functions can be further enhanced by fabricating the core and shell from different materials. It is well known that the composite materials exhibit excellent physical and chemical properties that are superior to their individual materials. The present study describes the synthesis and characterization of various core-shell structures, including ZnO-coated SnO2 nanowires. Furthermore, samples before and after the thermal annealing are investigated for comparison.
9:00 PM - M16.5
Titania Coated Silica Nanowires.
Avi Shalav 1 , Dinesh Venkatachalam 1 , Fabian Reichardt 1 , Frederic Fischer 1 , Robert Elliman 1
1 Department of Electronic Materials Engineering, The Australian National University, Canberra, Australian Capital Territory, Australia
Show AbstractTitania, or Titanium dioxide (TiO2) is a non-toxic semiconductor that can be directly excited by ultra-violet radiation, with device applications ranging from photocatalysis to solar cells. Nanostructured TiO2 materials are of particular interest for these applications since high surface to volume ratios can be obtained resulting in enhanced conversion efficiencies. Unfortunately, nanowires of the more reactive anatase phase of TiO2 best suited for these applications is particularly difficult to grow using traditional nanowire growth mechanisms. However, silica nanowires can be grown under very simple conditions. At high temperatures and low oxygen partial pressures, silicon decomposes and volatile SiO vapour is produced. Utilizing the vapour-liquid-solid growth mechanism, silica nanowires can be easily grown on top of a Si substrate, where the substrate itself provides the necessary vapor precursors. The resulting silica nanowire substrates provide an ideal ‘backbone’ or supporting substrate for new highly efficient optical based devices. Recent studies have shown that Ti-alkoxides adhere well to nanostructured silica, and it is believed that strong Si-O-Ti chemical bonding at the interface is likely to reduce crystalline growth retarding the growth of the more stable, but less reactive, rutile phase. Our preliminary results of the coating of silica nanowires using different deposition techniques, including wet chemistry (Ti-alkoxides) and atomic layer deposition will be discussed. Both rutile and anatase TiO2 coatings have been produced, with the final phase dependent on post-annealing temperature conditions.
9:00 PM - M16.6
Synthesis of Noble Metal Nanowires and Their Applications in Flexible Nanoelectronic Devices.
Yujie Xiong 1
1 School of Engineering and Applied Science, Washington University in St. Louis, St. Louis, Missouri, United States
Show AbstractNanowires of noble metals with controllable sizes represent a class of particularly interesting nanostructures to synthesize and investigate because they are promising building blocks for fabricating nanoelectronic devices, such as hydrogen sensors and interconnects in electronic and optoelectronic devices. However, it is very challenging to grow nanowires of face-centered cubic (fcc) metals with high quality in a solution phase. These metals have no intrinsic driving force for the growth of anisotropic structures when the seeds are surrounded by an isotropic medium. As dictated by thermodynamics, metal atoms are expected to nucleate and grow into cubooctahedrons (with a nearly spherical shape) enclosed by a mix of {111} and {100} facets in order to minimize the total surface energy. In this presentation, I will demonstrate a universal approach to fcc metal nanowires. We have been able to manipulate the anisotropic growth by controlling a variety of parameters, including oxidative etching, capping agents, and nucleation rate. In the end, I will show a few applications of these metal nanowires in flexible nanoelectronic devices. It is expected that the present work will enable us to manipulate the anisotropic growth of metal nanostructures and open the door to new applications in sensing, electronics and optoelectronics.
9:00 PM - M16.8
FIB-based Fabrication of Subwavelength Nanocoaxial Optical Waveguides.
Pashupati Dhakal 1 , Gregory McMahon 1 , Yun Peng 1 , Krzysztof Kempa 1 , Michael Naughton 1
1 Department of Physics, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractRybczynski et al. [1] recently demonstrated that visible light can be transmitted through coaxial waveguides having subwavelength transverse dimensions. We have fabricated vertically-aligned nanocoax waveguides using focused ion beam-assisted (FIB) deposition of 200 nm diameter amorphous carbon nanopillars as coax inner conductors. The coax annulus was prepared by atomic layer deposition of a 100 nm conformal coating of Al2O3, and sputtered W for outer electrodes. We successfully demonstrate the reception, transmission, and broadcasting of visible light into, along and out of subwavelength nanocoaxes of different lengths, prepared by this in situ FIB method. [1] J. Rybczynski, K. Kempa, A. Herczynski, Y. Wang, M.J. Naughton, Z.F. Ren, Z.P. Huang, D. Cai, and M. Giersig, Appl. Phys. Lett. 90, 021104 (2007)
9:00 PM - M16.9
FIB-deposited C-based superconducting nanowires with Tc ~7K.
Pashupati Dhakal 1 , Gregory McMohan 1 , Jeong-Il Oh 1 , Michael Naughton 1
1 Department of Physics, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractWe have fabricated carbon-containing nanowires by a gallium focused ion beam-induced deposition process from a hydrocarbon precursor. The electrical conductivity of the nanowires is only weakly temperature dependent below 300K, and reveals a superconducting state below Tc ~7 K. We have measured the temperature dependence of the resistive upper critical field Hc2(T), and from these data, estimate the zero temperature critical field and coherence length to be 8.8 T and 6.1 nm, respectively. This Tc is approximately 40% higher than that in any other FIB/direct write nanowire, such as those based on W(Ga).