Symposium Organizers
Frank (Bud) Bridges University of California Santa Cruz
Igor Levin National Institute of Standards and Technology
Valeri Petkov Central Michigan University
Thomas Proffen Oak Ridge National Laboratory
Matt Tucker ISIS Facility
Symposium Support
National Science Foundation
U.S. Department of Energy
DD3: Poster Session I
Session Chairs
Igor Levin
Thomas Proffen
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
1:00 AM - DD3: Poster I
DD3.3 Transferred to DD6.19
Show AbstractDD1: Total Scattering PDF and Electron Microscopy of Nanocrystals
Session Chairs
Tuesday PM, April 26, 2011
Room 3024 (Moscone West)
9:30 AM - **DD1.1
Refinement of Nanoparticle Structures via Pair Distribution Function Data.
Reinhard Neder 1
1 Crystallography and Structural Physics, University Erlangen, Erlangen Germany
Show AbstractDiffraction pattern of small nanoparticles with diameters less than 4 nm are characterized by broad maxima that start to overlap at comparatively small values of sin(Θ)/λ. This is due to the very small size and in addition caused by an extensive diffuse background due to internal defects and the presence of organic ligand molecules used to stabilize the nanoparticle. Standard characterization techniques use the Scherrer equation to estimate particle diameters, yet this extracts too little information from the diffraction pattern. Rietveld refinement techniques to not work well any longer. Both method inherently rely on the assumption of a perfectly periodically ordered crystal. These assumptions do not hold, however, for small nanoparticles. The finite particle size and its shape need to be taken into account. Additionally, relaxations due to the large fraction of atoms on the particle surface are important. Finally, nanoparticles often contain large amounts of defects like stacking faults, and twin boundaries. The combination of these substantial deviations from the long range order requires an adequate analysis of the diffraction data. The analysis of the local structure via the PDF on the other hand allows not only a structure determination but also a detailed refinement of the nanoparticle structure, shape and size and the distribution of these parameters.Due to the very small size, however, an individual simulated nanoparticle is just one of many possible defect conformations. Accordingly the PDF has to be calculated via an ensemble modeling that is based on the incoherent average of the PDF's of several nanoparticles. This ensemble modeling allows to refine defect probabilities as well as properties that underly a distribution such as shape and size.Results will be presented for nanoparticles of semiconductor materials like ZnSe and CdSe/ZnS core shell particles. Further results concern iron oxide materials, where the main focus of the application is a distinction between the magnetite and maghemite structures. These examples will be used to illustrate the superior possibilities offered by the PDF compared to reciprocal space methods.
10:00 AM - DD1.2
Lessons Learned from Simulation Studies Involving the Pair Distribution Function of Simple Elemental Nanoparticles.
Katharine Mullen 1 , Igor Levin 1
1 Ceramics Division , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractInformation on the size and structure of nanoparticles may be obtained via analysis of the atomic pair distribution function (PDF), which is calculated as the Fourier transform of scattering measurements. The fit of a PDF model based on a real-space structural representation of the nanoparticles is often used to obtain estimates for lattice constants, the degree of thermal motion, particles sizes, etc. This talk examines several sources of errors in fitting such models for PDF data. Methods used to model isotropic thermal motion are examined, and errors associated with use of commonly employed Gaussian broadening models are quantified. Errors introduced via improperly modeling the contribution of small-angle scattering (SAS) to the PDF are described, and the incorporation of the Fourier transform of SAS data into the PDF model is developed. Finally, the use of smoothing to mitigate errors arising from counting statistics in the scattering data used to obtain the PDF is discussed. These subjects are explored via simulation studies involving the pair distribution function of simple elemental nanoparticles.
10:15 AM - DD1.3
Advanced Characterization of Core-shell `Reverse' Magnetic Nanoparticles.
Sophie Carenco 1 2 , Xavier Le Goff 2 , Lucian Roiban 3 , Ovidiu Ersen 3 , Cedric Boissiere 1 , Nicolas Mezailles 2 , Clement Sanchez 1
1 Laboratoire de Chimie de la Matiere Condensee de Paris, College de France, CNRS, UPMC, Paris France, 2 Laboratoire Heteroelements et Coordination, Ecole Polytechnique, CNRS, Palaiseau France, 3 Institut de Physique et Chimie des Materiaux de Strasbourg, UMR 7504 CNRS – Universite de Strasbourg, Strasbourg France
Show AbstractOptics and plasmonics benefit from a wide range of core-shell nanocomposites for the development of emitters, sensors, etc. On the contrary, nanomagnetism is still at dawn, because of a lack of core-shell magnetic nanostructures, required both for fundamental studies and the design of new applications. Such nanocomposites are rare and exhibit most of the time a magnetic core surrounded by a protective, blocking shell. This non magnetic shell prevents interactions between nanoparticles and with their environment, which is compulsory for the development of innovative data-storage devices and magnetic biomedical vectors.Using a one-pot colloidal route, we have synthesized monodispersed core-shell nanoparticles exhibiting a magnetic shell, which we call 'reverse magnetic nanoparticles'. The Ni2P diamagnetic core (ca 20 nm diameter) is surrounded by a Ni ferromagnetic, size tunable shell (between 1 and 4 nm). This unprecedented nanostructure was obtained using various substoichiometric amounts of white phosphorus (P4) acting as a quantitative ‘P’ atom donor at moderate temperatures (r.t. to 220°C).The nanoparticles external surface is stabilized by a phosphorus-containing ligand (trioctylphosphine) to ensure size-control. The precise knowledge of the composition and thickness of the active Ni layer is critical for the magnetic properties/applications. A comprehensive study using advanced HRTEM, HAADF-STEM, EFTEM cartography, XPS, XRD and SQUID measurements was therefore carried out which allowed us to fully characterize this nanocomposite. The careful monitoring of the evolution of magnetization with time and heat leads us to propose a mechanism involving a two-step crystallization process leading to well-defined core-shell Ni2P-Ni nanoparticles. Combined nanoscale analyses resulted in a space-resolved structure determination and a kinetic study of these functional 'reverse' Ni2P-Ni nanomagnets. Surface effects were quantified from a detailed analysis of the shell-thickness/magnetization relation. Finally, an unprecedented nanoscaled-induced phase segregation process was fully described for the first time and discussed from the kinetic and thermodynamic points of view. [1] Carenco S, Resa I, Le Goff X, Le Floch P, Mézailles N, Chem. Commun. 2008, 2568 [2] Carenco S, Boissière C, Nicole L, Sanchez C, Le Floch P, Mézailles N, Chem. Mater. 2010, 22, 1340[3] Carenco S, Le Goff X, Shi J, Roiban L, Ersen O, Boissière C, Sanchez C, Mézailles N, 2010, submitted paper
10:30 AM - DD1.4
Dopant Induced Shape Evolution of Colloidal Nanocrystals: The Case of Zinc Oxide.
Yefeng Yang 1 , Yizheng Jin 1 , Zhizhen Ye 1 , Haiping He 1
1 Department of Materials Science and Engineering, State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, Zhejiang Province, China
Show AbstractThe electrical, optical and other important properties of colloidal nanocrystals are determined mainly by the crystals’ chemical composition, size and shape. The introduction of specific dopants is a general approach of modifying the properties of such nanocrystals in well-controlled ways. Here we show that in addition to altering the atomic composition of the nanocrystals the introduction of specific dopants can also lead to dramatic changes in morphology. The creation of Mg doped ZnO nanocrystals provides an excellent example of this procedure: depending on the molar ratio of dopant precursor in the reagents, doped nanocrystals with well defined shapes, from tetrapods to ultrathin nanowires, which exhibit tunable optoelectronic properties, are obtained for the first time. The details of the structural features and chemical compositions of the nanocrystals are revealed by a number of techniques, such as HRTEM, STEM, XRD, EDX, XPS and ICP-AAS. It is of interest to reveal the distribution of dopants in the Mg-doped ZnO nanocrystals. STEM and line-scan EDX analyses on a number of tetrapods and ultrathin nanowires indicate no segregation of Mg-rich domains within the nanocrystals. We further adopted a quantitative etching procedure, which was developed for determining the radial distribution of the elements in core/shell nanocrystals, and concluded that a reasonable homogeneous distribution of Mg dopants was present in the nanocrystals.The mechanism related to the shape evolution of the Mg-doped ZnO nanocrystals was explored. We find that the Mg dopants play an important role in the primary growth stage, resulting in initial growth seeds having diverse crystallographic structures, which are critical for the generation of doped nanocrystals with different shapes. We demonstrate that this “greener” synthetic scheme can be extended to other dopant systems and provides an attractive and effective strategy for fabricating doped ZnO nanocrystals with interesting compositional and spatial complexity.
10:45 AM - DD1.5
Ultrathin Bismuth Sulfide Nanowires: Surface and Core Structure at the Cluster-nanocrystal Transition.
Jordan Thomson 1 , Ludovico Cademartiri 3 , Mark Macdonald 2 , Srebri Petrov 1 , Gianluca Calestani 4 , Peng Zhang 2 , Geoffrey Ozin 1
1 Chemistry, University of Toronto, Toronto, Ontario, Canada, 3 Chemistry and Chemical Biology, Harvard University, Boston, Massachusetts, United States, 2 Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada, 4 Chemistry, Universita di Parma, Parma Italy
Show AbstractRecently, our lab synthesized bismuth sulfide nanowires with a diameter of less than 2 nm and lengths as long as microns. At this length scale the transition between a cluster, typically with point symmetry, and a nanocrystal, a subset of the bulk lattice, often occurs depending on the particular material. This can allow for properties rarely seen for larger nanocrystals to be observed. For instance, our nanowires show the unusual property of flexibility based on static and dynamic light scattering experiments, a property typically reserved for organic polymers. The characterization of structures lying at the cluster-to-nanocrystal transition, where the size of the structure is comparable to the size of the bulk lattice unit cell, is remarkably complex. Attempts to characterize the nanowires at the atomic scale with traditional techniques such as Powder X-ray Diffraction (XRD) and High-Resolution Transmission Electron Microscopy (HRTEM) provided little information due to the very small crystal size and susceptibility to beam damage, even at cryogenic (77 K) temperatures. Moreover, these methods are performed on dry samples and provide no information on the effect of solvent or capping ligands on structure. In order to generate a quantitative and atomically precise model, we applied three complementary methods: X-Ray Absorption Spectroscopy, including both fine structure (EXAFS) and near-edge structure (XANES), solution phase Nuclear Magnetic Resonance (NMR), and X-Ray Photoelectron Spectroscopy (XPS). The combination of these techniques led to an internally consistent model. The nanowire core is composed of the bulk bismuthinite phase of Bi2S3, but with one important difference. The average coordination number of Bi atoms is significantly larger than in the bulk. The increased coordination number can only be explained by the large percentage of Bi atoms located on the surface that engage in at least one, and up to two, neutral metal-ligand bonds with capping oleylamine molecules.
11:30 AM - **DD1.6
Surface Stucture and Chemistry in Metal and Metal Oxide Nanoparticles.
Angus Kirkland 1 , Neil Young 1
1 Department of Materials, Oxford University, Oxford United Kingdom
Show AbstractMorphology and surface structure in nanocrystalline metals and metal oxides is a key feature in determining their fundamental properties and in particular their catalytic activity and selectivity. This paper will discuss the characterisation metal and metal oxide nanoparticles using aberration corrected electron microscopy and exit wavefunction reconstruction. The correlation of this data with thermodynamic models of morphology and surface structure to produce quantitative phase diagrams that predict stable forms as a function of particle size and temperature for nanoscale systems will also be described.With reference to the above a number of representative example systems will be highlighted.Nanocrystalline gold has also been demonstrated to show specific catalytic activity at small particle size. In situ imaging experiments at elevated and depressed temperatures provide direct evidence for morphological changes that can be correlated with theoretical models to construct the first quantitative nanoscale phase diagram relating local structure and morphology to temperature and particle size in this system. Cerium dioxide nanocrystals, have attracted considerable interest due to their properties that lead to applications as efficient oxygen buffers in three-way automotive catalysts. These buffers are essential in stabilizing the air-to-fuel ratio necessary to achieve simultaneous conversion of NO, CO, and hydrocarbons during both the fuel-lean and fuel-rich stages of the combustion cycles. Aggregation behaviour in this system is driven by the compatibility of the shape of individual nanoparticles (characterized by the relative fractions of different crystallographic facets and their surface terminations) and can be substantially reduced by control of the shape of individual nanoparticles during synthesis. Experimental and theoretical data has been used to characterise the surface structure and chemistry within this system, which has lead to a detailed understanding of the factors controlling morphology and the frequently observed oxygenated surface termination which is driven by migration of oxygen defects from the bulk of the particle.Finally, the issue of atomic scale structure determination of complex nanoparticles particles will be discussed. In particular the use of quantitative High Angle Annular Dark Field Imaging and atom probe studies has provided quantitative characterisation of core shell structures in bi-metallic systems and has enabled the form of these to be correlated with catalytic activity.
12:00 PM - **DD1.7
Pair Distribution Function Studies of Core and Surface Effects in Gold Nanoparticles.
Joshua Kurzman 1
1 Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractObtaining detailed structural information about nanoparticle ensembles is an ongoing challenge of great importance to the field of catalysis. The greatest difficulty in modeling such systems stems from the atomic relaxations that occur near nanoparticle surfaces and edges, which cannot be accounted for using a traditional unit cell description. Atomistic modeling has previously been applied to Bragg scattering data with some success, but the exclusion of diffuse scattering inherently results in a loss of information about local atomic environments; this information can be recovered by extracting the pair distribution function (PDF) from total scattering data. The challenges of model construction and refinement are discussed with respect to X-ray and neutron PDF studies of small (< 5 nm) gold nanoparticles, where contributions to the PDF from surface atoms is readily apparent, particularly for particles smaller than ~2 nm. Advances in modeling these systems are presented, highlighting strategies for model development and the application of coordination number dependent restraints.
12:30 PM - DD1.8
Atomic-scale Mapping of Ferroelectricity in Individual Colloidal Nanocrystals.
Mark Polking 1 , Myung-Geun Han 2 , Shiva Reddy Adireddy 3 , Peter Ercius 4 , Thomas Duden 4 , Ramamoorthy Ramesh 1 , Paul Alivisatos 1
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States, 3 , University of New Orleans, New Orleans, Louisiana, United States, 4 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractTheoretical predictions of vortex polarization states have fueled renewed interest in the nature of ferroelectric order in low-dimensional nanomaterials. Experimental studies of nanodimensional ferroelectrics, however, have been stymied by a lack of high-quality ferroelectric nanomaterials and the limited resolution of traditional scanned-probe characterization techniques. The combination of aberration-corrected transmission electron microscopy and off-axis electron holography provides a powerful set of tools for the characterization of ferroelectrics on a local scale. The former technique enables the direct imaging of the sub-Ångstrom atomic displacements that accompany ferroelectric polarization, and the latter enables imaging of the resulting electrostatic potential distribution in the sample. Here, these techniques are applied to probe ferroelectric order at atomic dimensions in size-controlled colloidal nanocrystals of the novel ferroelectric semiconductor GeTe and the traditional perovskite ferroelectric BaTiO3. Atomic column positions, including those of oxygen, are extracted with sub-Ångstrom precision in particles oriented along different zone axes using exit-wave reconstruction of HRTEM focal series, enabling atomic-scale mapping of ferroelectric displacements and unit cell distortions. Polar sublattice displacements on the order of 0.2 Å in GeTe and 0.1-0.2 Å in BaTiO3 are observed using this approach. Real-space displacement maps derived from these reconstructions reveal large local deviations from the overall structure, including some unusual vortex-like displacement patterns. Many of these local atomic displacements and unit cell distortions are comparable to or larger than those of bulk material on a local scale, although the overall distortion is of smaller magnitude. These structural studies are complemented with off-axis electron holography experiments that enable direct observation of internal polarization fields and external fringing fields. The polarization in monocrystalline BaTiO3 nanocubes with side lengths of 10-20 nm has been directly imaged with sub-nanometer resolution using electron holography. This approach was also applied to image the in-situ manipulation of ferroelectric polarization in single nanocubes using an integrated STM tip. These experiments provide, to our knowledge, the first atomic-scale picture of ferroelectric ordering in individual nanocrystals.
12:45 PM - DD1.9
True Atomic Level Imaging of Shaped Nanoparticles Composed of Bismuth, Antimony and Tellurium Using Scanning Transmission Electron Microscopy.
Derrick Mott 1 , Nguyen Mai 1 , Teruyoshi Sakata 1 , Mikio Koyano 1 , Koichi Higashimine 1 , Shinya Maenosono 1
1 Materials Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa, Japan
Show AbstractNanotechnology is an area of research that is highly intriguing because of the novel properties often observed for materials whose sizes are reduced to the nanoscale. However, one of the biggest challenges is understanding the underlying principles that dictate the particles resulting properties. The atomic level structure for nanoparticles is suspected to vary from that for the corresponding bulk materials, however, direct observation of this phenomenon has proven difficult. Until recently only indirect information on the atomic level structure of such materials could be obtained with techniques such as XRD, HR-TEM, XPS, etc… However, recent advances in Transmission Electron Microscopy techniques now allow true atomic scale resolution, leading to definitive confirmation of the atomic structure. Namely, Scanning Transmission Electron Microscopy coupled with a High-angle Annular Dark Field detector (STEM-HAADF) has been demonstrated to be capable of achieving a nominal resolution of 0.8 nm (the JEOL JEM-ARM200F instrument). The ability is highly exciting because it will lead to an enhanced understanding of the relationship between atomic structure of nanoparticles and the resulting novel properties. In our own study, we focus on the analysis of the atomic level structure for nanoparticles composed of bismuth, antimony and tellurium for thermoelectric materials. This area has recently received much interest because of the realization that nanotechnology can be employed to greatly enhance the efficiency (dimensionless figure of merit ZT) of this class of materials. One of the most intriguing parameters leading to the enhanced TE activity is the relationship between composition and structure that exists within individual nanoparticles. We report our results on a study of the atomic level structure for both nanowires and nanodiscs composed of bismuth, antimony and tellurium. It was found that the nanoparticles have a complex structure that cannot be elucidated by conventional techniques such as XRD or HR-TEM. In addition, by employing Energy Dispersive Spectroscopy (EDS), a greater understanding of the composition-structure dependence was gained. The results are primarily discussed in terms of the atomic level resolution images obtained with the STEM-HAADF technique.
DD3: Poster Session I
Session Chairs
Igor Levin
Thomas Proffen
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
6:00 PM - DD3.1
Growth of Shape-selected Metal Nanocrystals on Oxide Surface.
Fabien Silly 1
1 DSM, IRAMIS, SPCSI, CEA Saclay, Gif sur Yvette France
Show AbstractMetallic nanocrystals and clusters on oxide supports are in widespread use for heterogeneous catalysis and gas sensing. The size and shape of the nanocrystals is an important factor which determines physical and chemical properties. Extensive studies have been undertaken into the metal-oxide interface and to monitor the growth of small cluster and nanocrystal, but until now it has not been possible to select their shape and their structure.We investigated the growth of Pd and Cu nanocrystals on differently-reconstructed SrTiO3 surfaces. We observed that Pd forms nanocrystals on the surface of SrTiO3(001), and depending on the crystallographic interface of the Pd with the substrate three shapes can be created: truncated pyramids, huts, and hexagonal shaped discs. Scanning tunnelling microscopy (STM) reveals that the nanocrystal shapes are determined by the substrate reconstruction and the substrate temperature during deposition. The experimental data allow us to estimate the surface energy of the substrate minus the nanocrystal interface energy for each shape. A thermodynamic model of this metal-on-oxide system shows that the pyramids and huts are stable structures, and that the hexagons are trapped in a metastable state.In comparison, we observed that Cu deposited on SrTiO3(001) leads to the formation of five-fold symmetry nanocrystals and fcc nanocrystals. We experimentally determine the phase map of supported Cu icosahedral, decahedral, and truncated octahedral nanocrystal shapes as a function of substrate temperature during Cu deposition. We show that a supported nanocrystal of 8500 atoms at a nucleation temperature of 480°C has the same probability of adopting an icosahedral or octahedral shape [3].[1] F. Silly and M. R. Castell, Physical Review Letters 94, 046103 (2005)[2] F. Silly, et al., Physical Review B 72, 165403 (2005)[3] F. Silly et al., ACS Nano 3, 901 (2009).
6:00 PM - DD3.10
Description of the Physical Properties of Nanostructured Hybrid Materials Based on Biopolymer Templates.
Marco Garza-Navarro 1 2 , Alejandro Torres-Castro 1 2 , Martin Reyes-Melo 1 2 , Domingo Garcia-Gutierrez 1 2 , Moises Hinojosa-Rivera 1 2 , Virgilio Gonzalez-Gonzalez 1 2
1 Materials Science and Engineering, UANL-FIME, San Nicolás de los Garza, Nuevo León, Mexico, 2 Advanced Materials, UANL-CIIDIT, Apodaca, Nuevo León, Mexico
Show AbstractThe analysis of the crystalline, morphological and magnetic properties of magnetic nanostructured hybrid materials, between spinel ferrite nanoparticles and biopolymer chitosan (CHN), is reported. Nanostructured hybrid materials were prepared following a soft chemistry approach of in situ co-precipitation, from chelated transition metal cations into aforementioned biopolymer template. Crystalline and morphological characteristics were studied by high resolution transmission electron microscopy (HRTEM), in a FEI Titan3 G2 microscope, operated at 300 kV. The interactions between nanoparticles and biopolymer template were analyzed by infrared spectroscopy (IR), in a Perkin-Elmer Paragon 1000PC equipment. The study of magnetic properties was performed by both static and dynamic measurements, using Quantum Design equipments, such as MPMS SQUID-VSM magnetometer and PPMS-9. From the results obtained by the HRTEM technique, it is possible to state that crystalline structure of nanoparticles in the hybrid materials corresponds to spinel ferrite phase. Furthermore, they present a cuasi-spherical morphology with diameters between 2 and 8 nm. The IR results shows that this narrow particle size distribution could be related to the adhesion of biopolymers chains onto particles surface, due to the coordination of surface-cations with amine and hydroxyl groups of the biopolymer template. These results suggest that particle size stabilization occurs due to (1) limitation of the particle growth at intermolecular sites between CHN chains and (2) steric repulsion between CHN chains which are adsorbed onto the nanoparticle surface. Moreover, due to its sizes, it was found that surface-cations induce a frustrated magnetic response on spinel ferrite nanoparticles, which, in addition to the also observed particle dipole-dipole interactions, leads the relaxation of the spins in the hybrid materials. These contributions, in addition to that related to intrinsic magneto-crystalline anisotropy, were considered to propose a model based on fractional calculus to describe the dynamic magnetic response of the studied magnetic hybrid materials. From this approach it was to possible to describe the manner that spins relaxes over the energetic barrier imposed by each contribution.
6:00 PM - DD3.12
Nanostructured Substrates for Surface Enhanced Raman Spectroscopy and Detection of Engineered Nanoparticles.
Sabrina Darmawi 1 , Limei Chen 1 , Torsten Henning 1 , Peter Klar 1
1 I. Physikalisches Institut, Justus-Liebig-Universitaet, Giessen Germany
Show AbstractWith the rapid growth of nanotechnology and the application of manufactured nanoparticles, such as metal oxides, in our daily products, there are increasing concerns about the safety and impact of those applications. Metal oxides, such as ZnO or TiO2, can be easily identified by Raman spectroscopy. However, for detecting a low concentration of nanoparticles within a complex chemical system or a single nanoparticle, it is urgent to develop a much more sensitive approach of detection.With surface enhanced Raman spectroscopy (SERS) the weak Raman signal can be amplified considerably. To achieve this we employ arrays of rhombes patterned via electron beam lithography on a silicon substrate. As an alternative pathway to the substractive method, the additive technique (lift-off) is used by evaporating silver or gold layers on the developed structure. Interactions between the analyte and a metallic lateral tip nanostructured surface lead to plasmonic excitations which cause a high electromagnetic field enhancement at the tips of the rhombes.For purposes of testing, engineered nanoparticles such as ZnO are deposited on the structured substrate. The resulting system is investigated by SERS and we will report on the dependence of the Raman signal on the tip parameters.
6:00 PM - DD3.13
Three-axis Correction of Distortion in Scanning Probe Microscopy.
Matthew Trawick 1 , Nathan Follin 1 , Christopher Musalo 1
1 Physics Department, University of Richmond, Richmond, Virginia, United States
Show AbstractTwo common sources of distortion in scanning probe microscopy are piezo creep and thermal drift, the latter caused by slow thermal expansions of materials in the sample and microscope due to small changes in temperature over the course of a scan. We present a technique for correcting distortion due to thermal drift along all three axes, along with simultaneous correction of z-axis piezo creep. Our method works by comparing each scanned topographical image to a second, partial scan, taken immediately afterwards, on which the fast and slow scan axes have been reversed. We model the positional distortion as a low-order polynomial function in three dimensions, searching for the set of correctional coefficients that minimizes the differences between the two scans. Using this technique we have successfully reduced z-axis spatial distortion by a factor of 50, and xy-plane spatial distortion by a factor of 20, ultimately obtaining nanometer scale precision from images with initial positional drift of tens of nanometers.
6:00 PM - DD3.14
Solid-state NMR Study of Gold Nanoparticle-polymer Composites.
Agustina Leonardi 1 , Gilles Bourret 1 , Jonathan Milette 1 , Violeta Toader 1 , Linda Reven 1 , Bruce Lennox 1
1 Department of Chemistry, McGill University, Montreal, Quebec, Canada
Show AbstractRational combination of nanoparticles (NPs) and polymers opens new ways to the development of advanced materials with potential applications in optoelectronic, sensing, catalysis, magnetic recording and several other fields.1 The technological applications of these composites depend on the ability to control the aggregation and spatial distribution of the particles in the matrix. A common strategy to create a stable dispersion in a polymeric host consists in the surface functionalization of the NPs through weak electrostatic interactions, ionic interactions or covalent bonding.In this work, the dispersion of 4-5 nm dia. functionalized-gold nanoparticles (AuNPs) into two polymers, polystyrene (PS) and poly-ethylene-oxide (PEO), is reported. Homogeneous dispersions are promoted by matching the AuNP ligands with the matrix in terms of the type of polymer and molecular weight. DMAP (4-dimethylaminopyridine)-coated AuNPs are synthesized and functionalized with ω-mercapto functionalized PS or PEO chains via a thiol-for-DMAP exchange reaction by adding a solution of the polymeric ligand as described in previous work.2 Deuterium labeled samples are also used to selectively characterize the chain mobilities of the AuNPs ligands versus those of the matrix through solid-state 1H, 13C NMR relaxation parameters and 2H NMR line shape measurements. The properties of the matrix, i.e. the glass transition temperature, and the chain dynamics are studied as a function of NP concentration and the molecular weights of the polymer ligands and matrix. 1.Shenhar, R.; Norsten, T. B.; Rotello, V. M. Polymer-Mediated Nanoparticle Assembly: Structural Control and Applications. Adv. Mater. 2005, 17, 657.2.Rucareanu, R.; Maccarini, M.; Shepherd, J.L.; Lennox, R.B. J. Mater. Chem. 2008, 18, 5830-5834.
6:00 PM - DD3.15
Manipulation of Nanoparticles Inside Scanning Electron Microscope.
Rynno Lohmus 1 , Sergei Vlassov 1 , Boris Polyakov 1 2 , Leonid Dorogin 1 , Ants Lohmus 1 , Martin Timusk 1 , Margo Plaado 1
1 , University of Tartu, Institute of Physics, Tartu Estonia, 2 , 2Institute of Solid State Physics, University of Latvia, Latvia, Riga Latvia
Show AbstractManipulation experiments have two general purposes. On one side it contributes to fundamental understanding of the friction by providing information about interactions at nanoscale. From the other side, manipulation experiments have practical aspect - exact 2D positioning and assembly of nanoparticles is essential for nanotechonological applications, e.g. creating nanoelectromechanical systems or digital information storage etc. The aim of the work is to study the interaction (adhesion and frictional forces) between single nanoparticles and different surfaces. This is implemented by measuring the force needed to move individual 100 nm spherical or triangular gold nanoparticle across a Si/SiO2 surface inside Scanning Electron Microscope (SEM). Moreover, deformation threshold for Au nanoparticles is found experimentally.Experimental set-up consists of Quartz Tuning Fork (QTF) with glued Atomic Force Microscope (AFM) tip and mounted onto nanomanipulator. The whole system is installed inside SEM. QTF is working on its resonance frequency in self-excitation mode providing feedback and information about force (when calibrated). QTF can be oscillated perpendicular (normal mode) and parallel (shear mode) to the surface.
6:00 PM - DD3.16
Structural and Electrical Characterization of Cu-CNT Nanocomposites.
Martin Mendoza 1 , Guillermo Solorzano 1 , Andrea Portocarreiro 2
1 Materials Engineering, PUC-Rio, Rio de Janeiro, Rio de janeiro, Brazil, 2 DIMAT, Inmetro, Rio de Janeiro, Rio de Janeiro, Brazil
Show AbstractMotivation for the production of Cu-CNT nanocomposites relies on the well-established superior mechanical and transport properties of CNTs and their stability when submitted a thermo-mechanical processing together with metal powder. A resulting metal-matrix bulk nanocomposites with improved mechanical and transport properties is expected. This work reports the structural characterization of a Copper–2% wt CNT nanocomposite by means of analytical and high resolution transmission electron microscopy (TEM). In addition, atomic force microscopy has been used to measure mechanical properties at the nano-scale. A homogeneous mixture of metallic Cu nanoparticles with single wall carbon nanotubes (SWCNT) was synthesized by chemical method. Purified SWCNT, from Nano-C (USA), were used with diameters between 2 - 4 nm. X ray diffraction (XRD) and TEM has been routinely used as main characterization tools, confirming the consisting production of pure metallic copper particles, in the 50-300nm range, with carbon.. Bulk nano-composite pellets were obtained by a pre-compactation under uniaxial pressure of 60 MPa followed by isostatic pressure of 150MPa and finally sintering at 650°C under Argon atmosphere . Low temperature electric resistivity measurements have shown that the nanocomposite material has lower value (2x10-6 Ω.cm) at 83 K than the copper without CNTs (6x10-6 Ω.cm). Hardness and elastic modulus were determined by nanoindentation. The composite displayed higher hardness (1,7GPa) compared with copper (1,2GPaMulti Wall Carbon nanotubes (MWCNTs), from UFMG (Brazil), were also used to synthesize the composite Cu-MWCNT. TEM images show good adherence between Cu and MWCNT. The Cu powder nanoparticles decorating MWCNTs were observed to be in the 5 to 45nm range. HRTEM shows Cu nanoparticles well-attached to MWCNTs as a successful consequence of the fictionalization procedure. It is even possible to determine the equilibrium dihedral angles between the nano particles and the surface of individual CNTs. After consolidation into pellet and sintering, Cu matrix presented grain growth (50nm–300nm range), some grains exhibiting characteristic annealing twins. Current structural investigation is carried out using a FEI Titan instrument under accelerating voltage of 300, 200 and 80 KV, the last aiming at minimizing the radiation damage. The instrument is operating in TEM and STEM mode, taking advantage of HAADF imaging modes and EELS capabilities, thereby revealing atomic columns in Z contrast and allowing the spectroscopy image of carbon in elemental mapping.
6:00 PM - DD3.17
In-situ Quantitative Microscopy of Low Dimensional Materials.
Reza Shahbazian Yassar 1 , Anjana Asthana 1 , Kasra Momeni 1 , Hessam Ghassemi 1 , Yoke Yap 1
1 , Michigan Technological University, Houghton, Michigan, United States
Show AbstractNanotubes and nanowires are promising candidates for future micro and small scale energy devices. However, correct calculation of their electrical and mechanical properties has been a challenging task due to uncertainties of contact resistance and complexity of applied force. In-situ electron microscopy can shed light into the electro-mechanical properties of such nanoscale materials. Here we utilized simple beam formulations and buckling theories to explain the mechanics of boron nitride (BN) nanotubes and zinc oxide (ZnO) nanowires. Size scale effects were observed in ZnO nanowires and were explained by the modification of atomic structure at the nanowire surface. In addition, the effective Schottky barrier heights and contact resistance were considered in modeling the experimentally recorded current-voltage data.
6:00 PM - DD3.18
AFM Investigation of Interfacial Degradation in PEM Fuel Cells.
Nishith Parikh 1 , Reza Yassar 1
1 Mechanical Engineering, Michigan Technological University, Houghton, Michigan, United States
Show AbstractAtomic force microscopy is quite valuable for the investigation of components and materials used in PEM fuel cells. In order to provide insight into the interfacial relationships at fuel cell electrodes, new AFM mode based on peakforce microscopy was investigated. The peakforce mode allows quantitative nanomechanical mapping of material properties, including modulus and adhesion, while simultaneously imaging sample topography at high resolution. Nanoindentation experiments were performed along the interfacial layers to understand how the interface mechanics degrades during aging. We also conducted conductive-AFM to map the proton conductivity and ionic channels of membrane. The channels were characterized in terms of size, distribution, and shape.
6:00 PM - DD3.4
Fabrication and Characterization of TiO2 Nanofibers Embedding TiO2 Nanowires.
So-Eun Kim 1 , Jong-Hun Lee 1 , Changwoon Nah 1 , Kwang-Un Jeong 1
1 Polymer-Nano Science and Technology, Chonbuk National University, Jeonju, Jeonbuk provincy, Korea (the Republic of)
Show AbstractTitanium (TiO2) nanofibers were successfully fabricated by the calcination of electrospun poly(vinylpyrrolidone) nanofiber mats containing hydrothermally synthesized TiO2 nanowires and titanium isopropoxide precursor. Utilizing scanning electron microscopy and transmission electron microscopy (TEM), morphological examination was conducted. From high resolution TEM (HR-TEM) and selected area electron diffraction results, it was realized that, during the calcination process at the optimized conditions, titanium isopropoxide precursors were epitaxially crystallized on the surface of single crystalline TiO2 nanowires. Based on the x-ray diffraction, it was confirmed that the crystalline structure of hydrothermally synthesized TiO2 nanowires and epitaxially crystallized TiO2 nanofibers is anatase and TiO2 nanofibers containing TiO2 nanowires show a higher crystallinity compared to that of the pristine TiO2 nanofibers. Improved optoelectronic properties of TiO2 nanofibers were also identified with UV-Vis spectroscopy experiments.
6:00 PM - DD3.5
Magnetic Nanocomposites: Comparison of Severed Routes to Tune the Anisotropy of the Fillers for Controlled Anisotropic Reinforcement.
Anne-Sophie Robbes 1 2 , Fabrice Cousin 1 , Jacques Jestin 1 , Florian Meneau 2 , Francois Boue 1
1 , Laboratoire Leon Brillouin, Gif-sur-Yvette France, 2 , Synchrotron Soleil, Gif-sur-Yvette France
Show AbstractWe are interested in new nanocomposites formed by inclusion of magnetic nanoparticles (γ-Fe2O3) in a polystyrene (PS) matrix following different ways of tuning the dispersion to finally obtain a material with anisotropic macroscopic mechanical properties. The first processing way, directly mixing γ-Fe2O3 nanoparticles (from 6nm to 11nm diameter) with PS, without external magnetic field [1], gives nanocomposites characterized with a combination of SAXS and TEM experiments, organized as compact aggregates at short range. These aggregates form elongated finite size supra-aggregates at longer range, which connected for highest nanoparticles concentration to form a filler network. For high deformations, the reinforcement factor diverges at the connectivity threshold (Φv≈3%) and increases when the nanoparticles size decreases. Under a magnetic field (between 100G and 600G) magnetic particles align along the field forming various tunable anisotropic structures depending on the size and on the nanoparticles concentration (above or beside the network threshold). The reinforcement factor is four times higher when the material is stretched in a direction parallel to the applied magnetic field than stretched perpendicular to it. A second processing way using PS-grafted magnetic nanoparticles (Mngrafted=30K) mixed with the matrix chains (Mnmatrix=300K or 60K) permits to extend the range of nanoparticles dispersion depending on the grafted to free chains mass ratio. For both way of dispersion, specific SANS and deuterated experiments permit to directly measure the chains conformation inside the nanocomposite and their contribution on the reinforcement mechanisms.[1] Robbes, A-S. ; Jestin, J. ; Meneau, F. ; Dalmas, F. ; Sandre, O. ; Perez, J. ; Boué, F. ; Cousin, F. Macromolecules, 2010, 43 (13), 5785-5796.
6:00 PM - DD3.9
Polaronic Effects in Small Colloidal Silicon Nanocrystals.
Katerina Dohnalova 1 , Tom Gregorkiewicz 1 , Jan Valenta 2 , Irina Yassievich 3
1 University of Amsterdam, Van der Waals-Zeeman Institute, Amsterdam Netherlands, 2 Faculty of Mathematics and Physics, Charles University, Prague Czech Republic, 3 A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, Saint-Petersburg Russian Federation
Show AbstractMore than 40% of atoms in small (diameter <2 nm) silicon nanoclusters (SiNCs) are placed on the surface. Therefore, coupling of exciton with surface vibration modes is strongly enhanced and can lead to polaronic states. As a result, optical properties are strongly altered by the surface: (i) phonon replicas can be observed in photoluminescence (PL), excitation and absorption spectra, with energies determined by surface vibration modes; (ii) mixing of the core and surface states can strongly enhance the radiative recombination rate [1]; (iii) probability of surface-trapping of the carriers can be enhanced [2], supressing the Auger-related recombination processes [3]; (iv) hot carrier cooling can be enhanced via energy transfer to surface vibrations. As a result, by a direct engineering of the nanocrystal surface, optical properties can be tuned.In this contribution we demonstrate observation of polaronic features in optical properties of small (1-2 nm) narrow size distribution alkyl-capped SiNCs, prepared by inverse micelles technique [4,5]. The combination of narrow size distribution with large exciton-surface phonon coupling leads to observation of well-resolved phonon replicas even in ensemble PL spectrum at room temperature, with no need for resonant excitation. Taking advantage of the colloidal form, we also demonstrate PL spectra of individual SiNCs – these show similar phonon replicas and exhibit characteristic blinking as commonly observed for emission from individual nanocrystals and molecules. [1] English et al., Nano Letters 2 (2002) 681[2] Martin et al., Nano Letters 8 (2008) 656[3] Kamenev et al., J. Appl. Phys. 90 (2001) 5735[4] Wilcoxon et al., Phys. Rev. B 60 (1999) 2704[5] Rosso-Vasic et al., Small 4 (2008) 1835
Symposium Organizers
Frank (Bud) Bridges University of California Santa Cruz
Igor Levin National Institute of Standards and Technology
Valeri Petkov Central Michigan University
Thomas Proffen Oak Ridge National Laboratory
Matt Tucker ISIS Facility
Symposium Support
National Science Foundation
U.S. Department of Energy
DD6: Poster Session II
Session Chairs
Valeri Petkov
Matt Tucker
Wednesday PM, April 27, 2011
Salons 7-9 (Marriott)
1:00 AM - DD6: Poster II
DD6.11 Transferred to DD8.4
Show AbstractDD4: Structural and Chemical Imaging
Session Chairs
Angus Kirkland
Ralph Nuzzo
Wednesday PM, April 27, 2011
Room 3024 (Moscone West)
9:30 AM - **DD4.1
Visualizing Catalytic Materials Chemistry at Atomic Resolution.
Ralph Nuzzo 1
1 , University of Illinois, Urbana, Illinois, United States
Show AbstractAnalytical electron microscopy, empowered by advances in electron optics and detectors, is poised to radically transform our understanding of the complex phenomena arising from atomic and electronic structure in materials chemistry. When joined to state of the art spectroscopic and theory methods, it is becoming possible to provide a picture of the structural dynamics of nanoscale catalytic materials that is fully rationalized at length scales spanning from mesoscopic limits to the atomic level. This talk will examine the surprising forms of complexity and new understandings of properties these approaches reveal.
10:00 AM - DD4.2
Ag and Ag/Pd Nanoparticles - A Correlated SERS/TEM/EELS/SPR Investigation and Application in NOx/COx Gas Sensing.
Imran Khan 1 , Ai Leen Koh 2 , David McComb 2 , Sorin Lazar 1 , Gerald Kothleitner 4 , Ewen Smith 5
1 Materials Science Research Department, AWE, Reading United Kingdom, 2 Materials, Imperial College London, London United Kingdom, 4 , FEI Electron Optics, Eindhoven Netherlands, 5 FELMI, Graz University of Technology, Graz Austria
Show AbstractIn this paper we present both the fundamental analysis of Ag and mixed AgPd nanoparticles and their application as gas sensors.Correlated analysis of the same SERS active and inactive single nanoparticles and dimers with surface enhanced Raman scattering (SERS), electron energy-loss spectroscopy (EELS) and transmission electron microscopy (TEM) allowed the structural/plasmonic origins of high SERS enhancement to be investigated. Only 2.3 % of single particles were SERS active yet these nanoparticles possessed no unique structural features and the surface plasmon resonance energies were not in close resonance with the excitation. The SERS intensity from nanoparticle dimers was significantly greater than single particles due to the creation of the first interparticle junction. However, further increase in cluster size resulted in a reduced, linear SERS intensity increase that implies a "per particle" increase with no further "aggregation" effect.The use of densely packed AgPd nanoparticle substrates allowed SERS detection of NOx and COx gases at ambient conditions. Ag substrates were unsuccessful for analysis of these gases proving that AgPd substrates that were capable of both strong SERS generation and effective gas adsorption were necessary. The SERS enhancement factor was measured to be approximately 105 for each of the gases and gas desorption/displacement from the substrate was also demonstrated. These results show the potential of SERS for sensitive and selective monitoring of multiple gases.
10:15 AM - DD4.3
Channel Strain Characterization in Semiconductor Device by Techniques Based on Transmission Electron Microscope.
Jinghong Li 1 , Dureseti Chidambarrao 1 , Jeff Johnson 2 , Yunyu Wang 1 , Anthony Domenicucci 1
1 , IBM Microelectronics, Hopewell Junction, New York, United States, 2 Microelectronics, IBM, ESSEX JUNCTION, Vermont, United States
Show AbstractThree techniques with a spatial resolution at nano-scale based on transmission electron microscopy (TEM) such as convergent beam electron diffraction (CBED), nano beam diffraction (NBD) and dark-field holography (DFH) have been successfully applied to measure strain/stress in the channel area of PMOS semiconductor devices with embedded SiGe in the source/drain areas. Reliable results of strain/stress measurements within the channel area have been achieved with very good agreement with the technology computer-aided design (TCAD) calculations. Channel strain measurements from the same TEM sample of an eSiGe PMOS with 17% Ge are consistent among these three TEM-based techniques.
10:30 AM - DD4.4
Limits in Detecting an Individual Dopant Atom Embedded in a Crystal.
Anudha Mittal 1 , K. Andre Mkhoyan 1
1 Chemical Eng. and Material Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractAnnular dark field scanning transmission electron microscope (ADF-STEM) images allow detection of individual dopant atoms located on the surface of or inside a crystal. The degree of contrast between intensities of an atomic column containing a dopant atom and a pure atomic column in ADF-STEM image is used to detect a dopant atom. We analyzed ADF-STEM images, simulated using the multislice method, of crystals doped with one dopant atom to determine the visibility of the dopant atom. Elements in group 14 were used as host and for doping. The results of dopant atom visibility were reasoned by studying the incident electron beam’s intensity profile as it propagates along atomic columns of Si, Ge, and Sn, and as it propagates along atomic columns in three different crystallographic orientations: [100], [110], and [111]. Channeling of both aberration-corrected and non-corrected probes is analyzed at different accelerating voltages. The beam intensity profiles are compared with visibility of dopant atoms located at positions expected to receive high and low doses of the incident electron beam. The dopant atom atomic number, host material atomic number, thickness of microscopy specimen, and orientation of specimen with respect to the incident beam, are varied to calculate the degree of contrast in each case. Many of the microscope and specimen parameters that can vary in an experiment designed to determine the atomic structure of a sparsely doped material are studied, revealing interesting trends and non-intuitive behaviors in visibility of a dopant atom. The results provide practical guidelines to determine the optimal microscope and specimen conditions to detect a dopant atom in experiment, obtain information about the 3-d location of a dopant atom, and recognize cases where detecting a single dopant atom is not possible.
10:45 AM - DD4.5
Characterization of Interfaces in Anisotropic Type II Nanocrystal Heterostructures with Atomic Resolution.
Hunter McDaniel 1 , Moonsub Shim 1
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Champaign, Illinois, United States
Show AbstractType II nanocrystal heterostructures (NCHs) exhibit photo-induced charge separation, long fluorescence decay times and broad red-shifted absorption compared with their single phase counterparts. Due to properties that are strongly dependent on size and shape, and furthermore, due to the necessity for physically and chemically accessing both components of the heterostructure (which may be achieved via enhancing anisotropy), the key step towards functional multi-component systems is the ability to control not only the size and shape but also spatial orientation of each component with respect to each other. In order to better understand growth mechanism leading to enhanced anisotropy and charge separation in NCHs synthesized from monodisperse nanorod seeds, we have examined various factors that contribute to and the effects of structural diversification in type II NCH systems such as CdSe/CdTe. Highly Stokes-shifted emission arises from heterointerfacial recombination and can be enhanced or suppressed via controlled positioning of CdTe on CdSe seeds. A careful examination of these NCHs using high resolution TEM allow for size and shape characterization which is then correlated with electronic and optical features. In addition, we have taken advantage of atomic resolution z-contrast in aberration corrected STEM images to identify and characterize the heterointerface in NCHs with unprecedented spatial resolution. We show that interface can be made chemically abrupt or alloyed leading to tunable optical properties. A comparison of highly strained CdSe/CdTe (7.1% bulk mismatch) to better lattice matched CdSe/CdSeTe and CdSe/CdZnTe NCHs (also type II) yields information about how the interfacial strain is relieved in such systems and how it might be engineered to promote charge separation for photovoltaic applications.
11:30 AM - **DD4.6
Electron Holography for Structures and Fields.
Hannes Lichte 1 , Dorin Geiger 1 , Andreas Lenk 1 , Martin Linck 1 3 , Axel Lubk 1 2 , Falk Roeder 1 , Karin Vogel 1 , Daniel Wolf 1
1 Triebenberg Lab, Technische Universitaet Dresden, Dresden, Saxony, Germany, 3 NCEM, LBNL, Berkely, California, United States, 2 , CEMES-CNRS, Toulouse France
Show AbstractTransmission Electron Microscopy (TEM) is the method of choice for analysis of materials structures down to an atomic scale. Point resolution is reaching well beyond 0.1nm allowing interpretation of positions of atoms e.g. at interfaces. However, electron images represent the intensity of the electron wave; the phases are lost, and hence the electric and magnetic fields in the object.The phase-loss is overcome by electron holography [1]: a reference wave is superimposed to the image wave [2]. From the arising interference pattern (“hologram”) the distributions of amplitude and phase are recovered quantitatively. Details and references can be found in [3]. Holography is unique in that, in addition to the amplitude (intensity), it provides the phase distribution from the object. At medium resolution with details larger than 2 nm, the reconstructed phase distribution can directly be interpreted in terms of the object. This is the basis for studying in 2D or 3D [4]Mean Inner Potentials in solids; Soft Matter: Phase contrast in focus without staining; Functional potentials such as pn-junctions in semiconductors; Electric fields controlling growth in biominerals; Depolarizing fields in ferroelectrics; Magnetic fields in and around magnetic structures down to a nanoscale; Coherence of inelastically scattered waves.At atomic resolution, because of the residual aberrations, amplitude and phase of the reconstructed wave may differ considerably from the object wave and hence cannot be interpreted without a-posteriori aberration correction. The resulting phase images allow analyzing details of the atomic structure, such as [3,4] difference of atomic numbers of different constituents; number of atoms in an atomic column; potentials across interfaces. Performance limits are given by both lateral resolution and signal resolution [5]. A lateral resolution of about 0.1nm is reached with holography. The most severe limitation is that of signal resolution in the phase images, which presently is about 2π/70. This is just at the edge for detecting interatomic electric fields. Therefore, we presently focus on improving the phase signal resolution. [1] D. Gabor, Nature 161 (1948), 563 - 564[2] G. Möllenstedt, H. Düker, Z. Physik, 145 (1956), 377 - 397[3] H. Lichte, M. Lehmann, Rep. Prog. Phys. 71 (2008), 016102.[4] H. Lichte, P. Formánek, A. Lenk, M. Linck, Ch. Matzeck, M. Lehmann, P. Simon, Ann. Rev. Mat. Res. Vol. 37 (2007), 539-588[5] H. Lichte, Ultramicroscopy 108 (2008), 256Our work is funded by the German Science Foundation (DFG), the German-Israel Funds (GIF), and the European Union (Framework 6 Integrated Infrastructure, Reference 026019 ESTEEM).
12:00 PM - DD4.7
Quantitative Atomic 3-D Imaging of Single/Double Sheet Graphene Structure by Exit-wave Reconstruction.
Joerg Jinschek 1 , Emrah Yucelen 2 3 , Hector Calderon 4 , Bert Freitag 1
1 Research Market Division, FEI Company, Eindhoven Netherlands, 2 Europe Nanoport, FEI Company, Eindhoven Netherlands, 3 National Centre for HREM, Delft University of Technology, Delft Netherlands, 4 ESFM, IPN, Mexico-City Mexico
Show AbstractGraphene sheets can be regarded as base structure of many carbon nanostructures. The extraordinary behavior of electrons is directly related to the crystal structure and the arrangement of every individual Carbon atom in this single sheet in 2-D, as well as, in case of few-layer graphene (FLG) in 3-D. Exit-wave reconstruction (EWR) has been performed using focal series of high-resolution transmission electron microscopy (HRTEM) images of a graphene layer structure using a low TEM accelerating voltage. A drop in voltage to 80kV improves the ‘signal’ of Carbon atoms, allows for better S/N ratios, and therefore better sensitivity to detect small phase shifts carrying the 3-D structural information. The utilization of a spherical aberration (Cs) corrector is essential to reduce imaging artifacts caused by aberrations in the objective lens, and, in this way, is essential to increase the achievable interpretable resolution and sensitivity to the point that atomic-scale structures and single atom columns can be resolved. With those settings the focal spread (more specific: the energy spread) is now limiting the achievable information limit in a non-chromatic-aberration (non-Cc) corrected microscope at a spatial resolution above the necessary resolution to resolve the C-C bond length in graphene of 1.42 Å. A “rainbow illumination” setting leads to a lower energy spread of about 0.2 eV, and therefore the tuned temporal coherence damping envelope of the phase contrast transfer function (CTF) allows an achievable spatial resolution down to 1Å. Here, we compare experimental EWR data with simulations, and thereby demonstrate “seeing” single Carbon atoms in 3-D on single/double layer graphene model structure. The initial experimental EW images still contain minimal residual aberrations in the nm range - even present when using an “aberration corrector”. However since the complex EW is accessible, residual aberrations can be corrected by application of a numerical phase plate. The data presented can unambiguously distinguish between single and two atom columns in a double layer of graphene. The sensitivity is even sufficient that a phase change caused by single Carbon atom positions can be obtained well above the noise level, which clearly quantitatively matches a position height change of 0.35nm in double layers [1]. The presented single atom sensitivity provides an unprecedented view of the atom arrangement in graphene(-based) nanostructures. This quantitative understanding based on experimentally quantified 3-D atomic positions will finally lead to the long by theoreticians’ desired information to predict the properties of the specific carbon-based nanostructures. [1] J.R. Jinschek et al. Carbon (2011) doi:10.1016/j.carbon.2010.09.058
12:15 PM - DD4.8
Towards Quantitative Nanoscale Analysis in 3D using Electron Tomography.
Christian Kuebel 1 2 , Katja Schladitz 3 , Michael Godehardt 3 , Robert Cieslinski 4 , Steve Rozeveld 4
1 Institute of Nanotechnology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen Germany, 2 , Karlsruhe Nano Micro Facility, Eggenstein-Leopoldshafen Germany, 3 , Fraunhofer ITWM, Kaiserslautern Germany, 4 Analytical Sciences Laboratory, Dow Chemical Company, Midland, Michigan, United States
Show AbstractState-of-the-art electron tomography has been established as a powerful tool to image complex structures with nanometer resolution in 3D. STEM tomography and to some extend also TEM tomography is used extensively in materials science to image samples in such diverse areas as catalysis [1,2], semiconductor materials [1,3], quantum structures [4], block copolymers [5] and composites [6] mainly providing qualitative information on the morphology, shape and distribution of the materials. However, for an increasing number of studies, the qualitative results routinely obtained are insufficient for an appropriate characterization and quantitative information, e.g. surface area, fractal dimensions, particle distribution or porosity, is needed. A quantitative analysis is typically performed based on a segmented representation of the tomographic data. However, the segmentation is one of the main sources of error for the quantification. In addition to noise, systematic errors due to the missing wedge and due to artifacts from the reconstruction algorithm itself are responsible for these segmentation errors. To overcome these systematic errors in a (mostly) automated approach improved reconstruction and segmentation algorithms are needed.This presentation will focus on an overview of both the possibilities and limitations of quantitative nanoscale analysis in materials sciences by electron tomography. Using catalysts, nano composites and quantum dot super-lattices as applications examples, the intensities and intensity variations observed for the 3D volume reconstructed by WBP and SIRT will be compared to alternative reconstruction algorithms as one measure of the reconstruction quality; the implications for quantification of electron and x-ray tomographic data will be discussed. Simulated tilt-series as well as semi-automated and manual segmentations will be used as references and to illustrate the quantification of particle size distributions, particle correlations, surface area, and fractal dimensions of nanoscale materials in 3D. References[1] C. Kübel, A. Voigt, R. Schoenmakers, M. Otten, D. Su, T.-C. Lee, A. Carlsson, J. Bradley, Microsc. Microanal. 11(5) (2005) 378-400.[2] C. Kübel, D. Niemeyer, R. Cieslinski, S. Rozeveld, J. Mat. Sci. Forum 638-642 (2010) 2517-2522.[3] C. Kübel et al in ‘8th International Workshop of Stress-Induced Phenomena in Metallization’, edited by E. Zschech, K. Maex, P.S. Ho, H. Kawasaki, T. Nakamura, AIP Conference Proceedings 817 (2006) page 223-228, American Institute of Physics, Melville, New York.[4] K.J. Batenburg, S. Bals, J. Sijbers, C. Kübel, P.A. Midgley, J.C. Hernandez, U. Kaiser, E.R. Encina, E.A. Coronado, G. Van Tendeloo, Ultramicroscopy 109(6) (2009) 730-740.[5] V.H. Mareau et al., Macromolecules, 40(25) (2007), 9032-9039.[6] K. Gries, R. Kröger, C. Kübel, M. Schowalter, M. Fritz, A. Rosenauer, Acta Biomat. 5(8) (2009) 3038-3044.
12:30 PM - DD4.9
Structural and Electrical Characterization of Carbon Nanotube Interconnects by Combined Transmission Electron Microscopy and Scanning Spreading Resistance Microscopy.
Thomas Hantschel 1 , Xiaoxing Ke 2 , Nicolo Chiodarelli 1 , Andreas Schulze 1 3 , Hugo Bender 1 , Pierre Eyben 1 , Sara Bals 2 , Wilfried Vandervorst 1 3
1 , imec, Leuven Belgium, 2 EMAT, University of Antwerp, Antwerp Belgium, 3 Instituut voor Kern-en Stralingsfysica, K. U. Leuven, Leuven Belgium
Show AbstractCarbon nanotubes (CNT) have been demonstrated as alternatives for Cu interconnects by various groups. For this, a high number of CNTs is grown inside one contact hole and form together one CNT contact. The space in between CNTs is filled with a dielectric material (e.g. Si or Al oxide). Electrical measurements of these CNT-contacts proved that the resistance values entirely depend on the physical structure of the individual CNT and their interfacial contacts. Nevertheless, a direct analysis of the individual tubes inside the contact hole is extremely challenging due to the confined dimensions (sub-10 nm tubes with 0.34 nm distance in between CNT shells). What is required is a methodology which allows to assess both the physical structure with sub-nanometer spatial resolution and to link that structural information also to the electrical properties of the individual tubes. It is clear that this cannot be achieved by one method alone but requires a combined approach. Therefore, we have developed a methodology whereby the structural information is obtained by in-plane high-resolution transmission electron microscopy (HRTEM) and where the local electrical analysis is performed by scanning spreading resistance microscopy (SSRM). SSRM is a method based on atomic force microscopy (AFM) whereby a conductive tip is scanned over a sample surface while measuring the local resistance underneath the tip. We have established a procedure for preparing about 50 nm thick in-plane slices of 300 nm diameter contact holes. This is done by dedicated focused ion beam (FIB) sample preparation. HRTEM imaging shows that the CNT structure remains intact and that the 0.34 nm separated shells are clearly resolved. The CNT density inside the hole is 2*E11/cm2, the CNT diameter is ranging from 5-10 nm and the number of CNT shells is 10-30. The TEM analysis shows also that the dielectric material deposition for filling the space in between CNTs does not cause a visible damage of the individual tubes and actually protects the nanostructure during sample preparation. For SSRM, we have developed a preparation procedure based on chemical-mechanical polishing (CMP) of the wafer top surface. SSRM measurements with inhouse fabricated conductive diamond tips were done on the circular section of the contact hole whereby the electrical current is flowing from the tip through the CNT to the bottom metal contact. In this way, 2D maps of electrically conducting CNTs inside a contact hole were obtained. The maps confirmed that individual tubes are electrically connected to the metal contact at the bottom of the contact hole. In this work, we present the details and results of our methodology enabling the structural and electrical 2D analysis of planar sections of CNTs integrated into 300 nm contact holes.
DD5: X-ray Scattering and X-ray Absorption Spectroscopy
Session Chairs
Frank ``Budquot; Bridges
Valeri Petkov
Wednesday PM, April 27, 2011
Room 3024 (Moscone West)
2:30 PM - **DD5.1
Coherent X-ray Diffraction Mapping of Strains in Nanocrystalline Materials.
Ian Robinson 1 2
1 , UCL, London United Kingdom, 2 , Diamond Light Source, Harwell United Kingdom
Show AbstractCoherent X-ray Diffraction is an analytical method that exploits the high coherence of X-ray beams from the latest synchrotron sources, such as the Diamond Light Source in the UK. When the entire sample is smaller than the beam coherence, its diffraction pattern contains interference from all parts of the sample in the form of a complex speckle pattern [1]. These data can be oversampled, hence phased, hence inverted to a quantitative 3D real-space image of the crystal. If the diffraction pattern is collected around a Bragg peak, the image contains projections of the internal strains of the crystal. In this talk, I will show examples of CXD applied to semiconductor nanowires, ZnO and metals. I will outline our plans to extend this to understand the effects of lithographic processing and microfabrication, seen through the strain imaging.[1] Ian Robinson and Ross Harder, Nature Materials 8 291-298 (2009)
3:00 PM - DD5.2
New Opportunities in Hard X-ray Microscopy at the Nanoscale.
Hanfei Yan 1 , Jorg Maser 2 3 , Hyon Chol Kang 4 , Ray Conley 1 , Deming Shu 3 , Albert Macrander 3 , Brian Stephenson 3 5 , Yong Chu 1
1 National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 4 Advanced Materials Engineering and BK21 Education Center of Mould Technology for Advanced Materials and Parts, Chosun University, Gwangju Korea (the Republic of), 5 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractDue to its penetration ability and sensitivity to chemical and structural information, hard x-ray microscopy provides powerful nondestructive analysis capabilities complementary to other microscopic techniques. However, because of the extremely small difference (~10-5) from unity of the refractive index of a material for hard x-rays, it is very difficult to make focusing optics with high numerical aperture. This is the major obstacle preventing hard x-ray microscopy from achieving a high spatial resolution. Recent advances in mirror, refractive and diffractive lenses have pushed the frontier of hard x-rays focusing to well below 100 nm, opening up new opportunities in this area. We will give an overview of the multilayer Laue lens (MLL) [1], a novel diffractive optic we developed to achieve nanometer x-ray focusing with high focusing efficiency. It is fabricated by sputter deposition of a multilayer film followed by sectioning, allowing the fabrication of very small outmost zones (~nm) with very high aspect ratios (>10,000), two factors required for hard x-ray nanofocusing. Unlike conventional diffractive optics like Fresnel zone plates (FZP), MLL utilizes dynamical diffraction, which leads to better performance and different optimal structures from a FZP. A prototype MLL microscope has been built, enabling us to do elemental imaging at sub-30 nm scale. We will discuss the current capabilities and limitations of this microscope and present some initial scientific applications. Lastly, we will discuss the capabilities of the hard x-ray nanoprobe beamline being constructed at the National Synchrotron Light Source II at Brookhaven National Laboratory, which will provide nanodiffraction and x-ray fluorescence mapping at 10-nm spatial resolution using this optic for user science when it is in operation in 2015. [1] H. C. Kang, J. Maser, G. B. Stephenson et al., "Nanometer Linear Focusing of Hard X Rays by a Multilayer Laue Lens," Physical Review Letters 96 (12), 127401-127404 (2006).
3:15 PM - DD5.3
Local Structure of Dopants in Nanocrystalline Materials Obtained by Reverse Monte Carlo Analysis of EXAFS Spectra.
Markus Winterer 1
1 Faculty of Engineering, University Duisburg-Essen, Duisburg Germany
Show AbstractNanocrystalline materials are heterogeneously disordered materials which results in a distributed local structure. Dopants are often required to generate functional materials, for example yttrium doped zirconia is an ionic conductor, transition metals in zinc oxide introduce magnetism or group III elements in zinc oxide electrons as charge carriers. In all cases the dopand has to be on specific sites in the host lattice in order to generate the desired property. This local structure can be investigated using EXAFS spectroscopy. EXAFS contains element specific information of the local structure through the photoelectron generated by X-ray absorption at the characteristic absorption edge of the element and the amplitude and phase modulation of the signal by the backscattering atoms. The analysis of EXAFS spectra using Reverse Monte Carlo (RMC) simulations makes it possible to refine spectra of different absorbing atoms with one model (a configuration of atoms). The final structural results are the partial pair distribution functions which can itself be analyzed to obtain information about mean coordination numbers, bond distances, root mean square displacements, and higher moments of the distribution. This procedure eliminates ambiguities of the standard EXAFS analysis since it does not rely on a certain shape of the distribution function. RMC uses the complete structural information available in the EXAFS data based on a physical, structural model, e.g., the replacement of atoms by dopants in a host lattice. Because a central issue in the analysis of doped nanocrystals is the location of the dopant, our ability to utilize this technique to characterize the particles that we synthesize is critical to obtain a detailed understanding of these materials.
3:30 PM - DD5.4
An EXAFS Study of Lattice Distortion in the Type-I Clathrate Ba8Ga16Sn30.
Scott Medling 1 , Michael Kozina 1 , Frank Bridges 1 , Koichiro Suekuni 2 , Toshiro Takabatake 3
1 Physics, UC Santa Cruz, Santa Cruz, California, United States, 2 School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa, Japan, 3 Quantum Matter, Hiroshima University, Hiroshima Japan
Show AbstractSemiconducting type I clathrates, such as Ba8Ga16Ge30 (BaGaGe) and Eu8Ga16Ge30 (EuGaGe), have a cage-like crystal structure with "guest" or "rattler" atoms (Ba, Eu, etc.) located near the center of cages formed of Ga and Ge atoms on three crystallographic sites. Such Ga-Ge compounds have a low, glass-like thermal conductivity which has been attributed mainly to the low-energy, large-amplitude vibrations of the "rattler" atoms inside the cages which strongly scatter phonons within the lattice. However, as pointed out by Sales, we still do not have a good understanding of the thermal conductivity in these materials because several mechanisms can play a role in phonon scattering.Recently, samples with Sn replacing Ge, Ba8Ga16Sn30 (BaGaSn), have been prepared that have an even lower thermal conductivity than BaGaGe. To better understand the cause of the lower thermal conductivity and to determine if it would be useful to pursue such materials for thermoelectric applications, we studied samples of BaGaSn using Extended X-ray Absorption Fine Structure (EXAFS). Our initial measurements at the Ga K-edge showed that most of the neighbors about Ga were Sn and, more importantly, the average Ga-Sn distance is significantly shorter than the average Ga-Sn distance from diffraction.We present EXAFS measurements as a function of temperature for Sn and Ba K-edges, and find that the Sn-Sn distance is significantly longer than the average distance in diffraction while the Ba data in r-space have a low amplitude, indicating significant disorder in the Ba-Ga and Ba-Sn distances. These new results, together with the earlier Ga K-edge results, show that the cage-like structure is severely distorted in contrast to the situation for other Ga-Ge compounds such as BaGaGe and EuGaGe; such a large distortion of the lattice will also strongly scatter phonons, and likely explains why the thermal conductivity is so much smaller for BaGaSn. Unfortunately, such distortions of the lattice cages will also somewhat reduce the electrical conductivity. We compare our results for BaGaSn with earlier results for BaGaGe and discuss them in light of recent transport measurements for BaGaSn.
3:45 PM - DD5.5
Synthesis, Micro and Electronic Structure Investigation of Diamond Nanorod Spherules by High Resolution NEXAFS Coupled PEEM and Their Field Emission Performance.
Swathi Iyer 1 , Paul Maguire 1
1 Materials and Nanotechnology, NDSU, Fargo, North Dakota, United States
Show AbstractCarbon, in the form of graphite has been explored extensively at the micro and nanoscale. The excellent properties of diamond, the other allotrope of carbon in the form of nanocrystalline (NCD) and ultra nanocrystalline diamond (UNCD) have been equally exploited. The potential application of these nanostructured allotropes of carbon has lead to their unification at the nanoscale to a new class of materials, hybrid carbon nanostructures, such as the bucky wires, diamond nanotube and diamond nanowires. High resolution techniques such as, the EELS, NEXAFS and XPEEM using very intense synchrotron radiation are a few promising methods to study such a system. Owing to its high spectral resolution (0.1 eV) and spatial resolution of 20 nm XPEEM coupled NEXAFS has the leading edge.We report the synthesis of Diamond nanorods/flake Spherules (DNRS) using a 2.45 GHz, 1.5 kW microwave plasma enhanced CVD system in a gas mixture of CH4 and N2 , predominantly consists of UNCD enveloped by graphite in the form of flake or a rod with nanodimension, arranged perpendicular to the spherule surface and projecting randomly outward in all directions. The diamond nanoflake with a diameter of ~2 nm has a central diamond (111) core encapsulated by graphitic (0002) lacing. The understanding of the growth mechanism of these structures showed that the enhanced surface energy by defects generated due to mechanical scratching with diamond paste played a vital role in the nucleation density of the DNFS. The structure composition by High Resolution Transmission Electron Microscopy (HRTEM) and X ray Photoemission Electron Microscopy (XPEEM) revealed that the nanoflakes predominant with core sp3 laced with sp2, is embedded in carbon matrix consisting of other nanocarbon, such as the nanotubes, nanoonion and nanowires/sheets. Neither the Raman or the XPS could accurately determine the sp3 to sp2 ratio in this complex structure. Raman showed a series of Trans Poly Acetylene (t-PA) peaks considered as a fingerprint of NCD and UNCD materials High resolution localized XPEEM combined with XAS complimented the Raman and the XPS results coupled X-ray Absorption Spectroscopy (XAS) exhibited a weak π* peak, a prominent exitonic and a second band dip, which are the signature of diamond.. The congregated nanorod spherules arranged in a monolayer exhibits a low-threshold, high current-density of 10 mA/cm2 at 2.9 V/ m which appears to be exceptional when compared to many other electron emitting nanostructures. Bias enhanced DNRS were also characterized by XPEEM and compared. The FE of both samples with and no bias were compared.
4:30 PM - **DD5.6
Characterization of Nanomaterials and Particulates by Soft X-ray Scanning Transmission X-ray Microscopy.
David Shuh 1 , Tolek Tyliszczak 1 , Per-Anders Glans 1 , Jinghua Guo 1
1 , LBNL, Berkeley, California, United States
Show AbstractSpectromicroscopy of several distinct classes of particles and nanomaterials have been conducted utilizing the Advanced Light Source-Molecular Environmental Science Beamline (ALS-MES) 11.0.2 soft x-ray scanning transmission x-ray microscope (STXM). The ALS-MES STXM has been used to record images, elemental/species maps, and near-edge x-ray absorption fine structure (NEXAFS) spectra in the energy range from ~100 eV to 2000 eV with routine spatial resolution of better than 25 nm. This spectral range cover the L-edges of the transition metals and importantly, spans the K-edges of the light elements from boron to silicon. Recent results from the investigations of actinide materials, metal oxides, carbon nanotubes, and biological systems will be highlighted. The prospects for future soft x-ray scanning spectromicroscopy including improved resolution, tomography, fluorescence detection, and sample environment will be discussed.
5:00 PM - DD5.7
Overcoming Self-absorption Effects in Bulk Sensitive XANES Analysis of Rare Earth Doped Silicon Oxide Films.
Patrick Wilson 1 2 , Tyler Roschuk 1 2 , Sneha Bernard 1 2 , Evgueni Chelomentsev 1 2 , Jacek Wojcik 1 2 , Peter Mascher 1 2
1 Engineering Physics, McMaster University, Hamilton, Ontario, Canada, 2 Centre for Emerging Device Technologies, McMaster University, Hamilton, Ontario, Canada
Show AbstractThe study of luminescence from rare earth doped silicon-based films is of significant importance for applications in integrated photonic devices and solid state lighting. Materials systems such as rare earth doped silicon nanostructures provide a promising platform for developing an efficient monolithic silicon-based light source. However, the mechanisms responsible for emission from such materials are currently not well understood, especially for luminescence in the visible spectrum. To better understand the nature of luminescence in these materials, X-ray absorption spectroscopy experiments have been used to characterize the effects of chemical environment, local bonding coordination, and excitation pathways on emission in different types and compositions of films. Unfortunately, obtaining accurate bulk sensitive X-ray absorption spectra at certain energies can be inhibited by strong self-absorption effects in the total fluorescence yield signal. Here, we have applied the inverse partial fluorescence yield (IPFY) technique to overcome such effects while retaining the bulk sensitivity necessary to properly analyze these materials.Various compositions of silicon oxide films doped with Ce and Tb were deposited on (100) silicon substrates using electron cyclotron resonance plasma-enhanced chemical vapour deposition. Post-deposition annealing was performed at temperatures ranging from 700 – 1200°C in a quartz tube furnace under flowing N2 ambient gas. The film compositions were measured through Rutherford backscattering spectrometry while room temperature ultraviolet-excited photoluminescence measurements were performed using a 17 mW 325 nm HeCd laser to characterize the emission properties of the films. The electronic structure was studied through XANES experiments conducted on the high resolution spherical grating monochromator and variable line spacing plane grating monochromator beamlines at the Canadian Light Source synchrotron facility. X-ray absorption spectra were measured at the Si and O K-edges, the Si L3,2-edge, and the Ce and Tb M5,4-edges while simultaneously collecting XEOL spectra from luminescent films. In samples with high concentrations of rare earth ions, the IPFY technique was employed at the Ce and Tb M5,4-edges to avoid the self-absorption effects observed in these films, allowing for quantitative analysis of the coordination states of dopant ions.Photoluminescence was obtained from both silicon-rich and oxygen-rich silicon oxide films doped with Ce and Tb ions. Analysis of the XANES and XEOL spectra provided insight on the roles of silicon nanocrystals and the silicon oxide host matrix on luminescence as well as interactions between Ce and Tb ions in co-doped films. In addition to energy transfer from the silicon nanocrystals to the rare earth ions, the silicon oxide host matrix was observed to play an active role in the light emission process with strong luminescence excited through oxygen-related electronic states.
5:15 PM - DD5.8
Structural Characterization and Effect of Impurities and Defects in Ga Doped ZnO Nanostructures.
Rodrigo Noriega 1 , Sumohan Misra 2 , Saahil Mehra 1 , Michael Toney 2 , Alberto Salleo 1
1 , Stanford University, Stanford, California, United States, 2 , Stanford Synchrotron Radiation Lightsource, Menlo Park, California, United States
Show AbstractWe study ZnO nanostructures as a potential replacement for ITO in photovoltaic devices. The ultimate goal is to combine the light scattering properties of these nanostructures with a suitable electrical performance, all in a low-cost solution based approach. Solution-grown intrinsic and doped ZnO nanostructures has been shown to possess very competitive optical properties in the visible and near infrared spectral regions, with total transmittances greater than 85% and improved diffuse transmission when compared to sputter-deposited ZnO films used as transparent contacts for amorphous Si solar cells.ZnO nanostructures of varying impurity concentrations, morphologies and sizes were synthesized in the presence of a high boiling point organic solvent and a surfactant. The doping effectiveness depends on the incorporation of these impurities into the electrically active sites in the crystal lattice; in this case, Ga atoms in Zn substitutional sites. We probe the efficiency of solution-based doping using anomalous X-ray diffraction (AXRD), monitoring the intensity of a set of diffraction peaks as a function of photon energy and observing the incorporation of impurities as the incoming radiation energy is scanned across the atomic absorption edge (Ga K-edge, 10370 eV). These type of experiments require the use of a synchrotron lightsource in order to provide the capability to tune the photon energy, achieving an excellent monochromaticity across a wide and continuous range of X-ray energies while maintaining a high brightness, along with the necessary angular resolution.We show that controlling the growth conditions of these nanostructures is critical, as has been observed by an increased doping effectiveness when the reagent to solvent ratio is decreased. The effects of post-processing treatments also affect electrical properties, as thermal annealing has been reported to lower the free charge density in these materials. The mechanism behind this reduction of dopant activation is explored with AXRD as well as sensitive spectroscopic techniques such as photothermal deflection spectroscopy (PDS).
5:30 PM - DD5.9
Structures and Interactions in Neurofilament: Gel Expanded to Gel Condensed Transition.
Roy Beck 1 2 3 , Jonna Deek 4 , Myung Chul Choi 2 3 , Taiji Ikawa 5 , Osamu Watanabe 5 , Erwin Frey 6 , Piliph Pincus 2 , Cyrus Safinya 2 3
1 Physics and Astronomy, Tel-Aviv University, Tel-Aviv Israel, 2 Physics, University of California, Santa Barbara,CA, California, United States, 3 Materials, MCDB, University of California, Santa Barbara,CA, California, United States, 4 Chemistry & Biochemistry, University of California, Santa Barbara,CA, California, United States, 5 , Toyota Central R&D Laboratories, Nagakute, Aichi, Japan, 6 Physics, Ludwig Maximilians Universitaet Muenchen, München Germany
Show AbstractNeurofilaments (NFs) – the major cytoskeletal constituent of myelinated axons in vertebrates – consist of three molecular-weight subunit proteins NF-L (low), NF-M (medium), and NF-H (high), assembled to form mature filaments with protruding unstructured C-terminus sidearms. Liquid crystal gel networks of sidearm-mediated NF assemblies play a key role in the mechanical stability of neuronal processes. Disruptions of the NF-network, due to NF over-accumulation or incorrect sidearm interactions, is a hallmark of motor neuron diseases including amyotrophic lateral sclerosis. Using synchrotron x-ray scattering [1,2], and various microscopy techniques [1,3,4] we report on the role of the subunit sidearms on the structure and interaction of NF. We will show a direct measurement of forces in reconstituted NF-gels under osmotic pressure (P) and elasticity measurements of single filaments. With increasing pressure near physiological salt, NF-LMH, comprised of the three subunits near in-vivo composition, or NF-LH gels, undergo for P>Pc ≈ 10 kPa, an abrupt nonreversible gel expanded to gel condensed transition. The transition indicates sidearm-mediated attractions between NFs consistent with an electrostatic model of interpenetrating chains. In contrast, NF-LM gels, remain in a collapsed state for P
Pc. In addition, single filament AFM measurements show that bending modulus is also regulated via intra-filaments interactions [4]. These findings, which delineate the distinct roles of NF-M and NF-H in regulating neurofilament interactions, shed light on possible mechanisms for disruptions of optimal mechanical network properties. Supported by DOE BES DE-FG-02-06ER46314 (protein purification/assembly), NSF DMR-0803103, and the Human Frontier Science Program organization. [1] J.B. Jones, C.R. Safinya, Biophys. J. 95, 823 (2008); [2] R. Beck et al., Nature Mat. 9, 40 (2010) in press; [3] H. Hess et al. Langmuir 24, 8397 (2008) [4] R. Beck et al. to be published.5:45 PM - DD5.10
Triangular Gold Nanoprism Superlattices: The Role of Attractive Depletion Forces and Repulsive Electrostatic Forces.
Kaylie Young 1 2 , Matthew Jones 2 3 , Jian Zhang 1 2 , Robert Macfarlane 1 2 , Byeongdu Lee 4 , Chad Mirkin 1 2 3
1 Chemistry, Northwestern University, Evanston, Illinois, United States, 2 International Institute for Nanotechnology, Northwestern University, Evanston, Illinois, United States, 3 Materials Science, Northwestern University, Evanston, Illinois, United States, 4 X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe ability to create ensembles of inorganic nanomaterials with a high degree of control is of great interest in the development of new materials for applications in various fields including catalysis, optoelectronics, high-density data storage, and biological sensing. Nanocrystal superlattices often exhibit unique electronic, optical, and magnetic properties that are distinct from both the corresponding individual particles and the bulk solid resulting from interactions between the excitons, surface plasmons, or magnetic moments of individual particles. In order to study the emergent properties of inorganic nanoparticle assemblies and correlate them to the precise structure of the ensemble, a materials-general assembly technique with tunable lattice parameters is preferred. In this presentation, we report the controlled assembly of anisotropic triangular gold nanoprisms into one-dimensional lamellar crystals with lattice parameters that are tunable post-synthesis. Synchrotron small angle X-ray scattering (SAXS) was used to probe the lamellar nanoprism crystals. The interparticle spacing (d-spacing) of the system is determined by a balance between the attractive entropic depletion forces and the repulsive electrostatic forces, both of which can be easily manipulated. In this nanoprism system, both forces arise from the surfactant cetyltrimethylammonium bromide (CTAB). The presence of a CTAB bilayer on the nanoprism surface leads to a slight positive charge, thereby causing the prisms to repel, while the presence of CTAB micelles in solution induces the prisms to assemble. The d-spacing can be reversibly tuned between 17 and 30 nm almost instantaneously by changing the concentration of CTAB, the temperature, and/or the concentration of NaCl. By taking advantage of this synergy of forces, d-spacings as large as 30 nm can be achieved. These are much larger d-spacings than can be realized with either of the forces alone. Additionally, we developed a theoretical model whose predicted d-spacing agrees with that determined experimentally. Finally, we demonstrate that the lamellar ordering can be used to separate nanoprisms from spherical nanoparticles formed concomitantly during synthesis to achieve samples with 99% purity.
DD6: Poster Session II
Session Chairs
Valeri Petkov
Matt Tucker
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
9:00 PM - DD6.1
Charge Transfer Effects in Perovskite Oxide Superlattices.
Meng Gu 1 , Fan Yang 1 , Elke Arehnolz 2 , Michael Biegalski 3 , Hans Christen 3 , Nigel Browning 1 4 , Yayoi Takamura 1
1 Department of Chemical Engineering and Materials Science, UC Davis, Davis, California, United States, 2 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Condensed Matter and Materials Science Division, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractEpitaxial thin film systems composed of perovskite oxide materials have been shown to possess novel properties which differ from those of the bulk constituent materials. For example, the interfaces of SrTiO3 and LaAlO3 have attracted considerable attention due to the observation of unexpected properties associated with interactions that occur at the interfaces.1 In particular, the oxidation states of the B atoms in the ABO3 perovskite structure are crucial in determining the magnetic and electrical properties. In superlattice structures, the B atom valence states depend on the chemical identity of each of the sublayers, the sublayer thickness, and the growth conditions used. The nature of the charge transfer to the ferromagnetic metal La0.7Sr0.3MnO3 sublayer differs when the second sublayer consists of the antiferromagnetic insulator La0.7Sr0.3FeO3 or the non-magnetic metal La0.5Sr0.5TiO3. In this work, atomic resolution Z-contrast imaging in an aberration-corrected scanning transmission electron microscope (STEM) is used to examine the interface structure on the atomic scale. The sensitivity of this technique to small changes in the atomic composition allows the interface quality to the quantified directly from the experimental images. Furthermore, electron energy loss spectroscopy (EELS) can be used to map out the change in valence state as a function of sublayer thickness and across the interface with a spatial resolution approaching that of the image. The valence states of Mn, Fe, and Ti atoms are monitored by L3/L2 ratio, L3,2 edge onset and energy loss near edge fine structure of EELS. The L3/L2 ratio is obtained by fitting Gaussians/ Lorentzians and a 2:1 step on the L3 and L2 peak.2 Additionally, the fine structure of the X-ray absorption and X-ray magnetic dichroism spectra signify an overall valence change in the surface region (top ~10 nm) of the film. Finally, we show that the magnetic and electrical properties of these two sets of superlattices depend strongly on the nature of the charge transfer.1.Okamoto, S.; Millis, A. J., Electronic reconstruction at an interface between a Mott insulator and a band insulator. Nature 2004, 428 (6983), 630-633.2.Wang, Z. L.; Yin, J. S.; Jiang, Y. D., EELS analysis of cation valence states and oxygen vacancies in magnetic oxides. Micron 2000, 31 (5), 571-580.
9:00 PM - DD6.12
TEM Study of Nanometric AlN Interlayers in AlInN/GaN Heterostructures for 2DEG Optimization in High Electron Mobility Transistors.
Arantxa Vilalta-Clemente 1 , Magali Morales 1 , Piero Gamarra 2 , Marie Antoinette Poisson 2 , Ruterana Pierre 1
1 , CIMAP, Caen France, 2 , Alcatel-Thales, III-V Lab, Marcoussis France
Show AbstractAlN layers, when inserted at strained AlGaN/GaN and lattice-matched AlInN/GaN heterostructures, have been observed to improve the mobility of two-dimensional electron gases (2DEGs).The investigated AlInN/AlN/GaN heterostructures were grown by metalorganic vapour phase epitaxy on sapphire templates, and the thickness of the AlN interlayer was varied between 1.0 and 4.0 nm and that of AlInN was around 10 nm. Conventional and high resolution transmission electron microscopy (TEM) are used to characterise the AlN interlayer grown on GaN and investigate the microstructure of InxAl1-xN layer, whereas, the atomic force microscopy for the sample morphologies. The (10-10) reciprocal space maps (RSMs) were performed to evaluate the In composition and the strain in InxAl1-xN layers by high resolution X-ray diffraction.The above characterizations show that in a same growth sequence, the In composition of the layers may oscillate between 17-19%, with a strong dependence on the AlN thickness and AlInN deposition conditions.
9:00 PM - DD6.13
Systematic Electron Crystallographic Characterization of Three-dimensional Binary Nanocrystal Superlattices.
Jun Chen 1 , Xingchen Ye 2 , Christopher Murray 2 1
1 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractMulti-component nanocrystal assemblies have received great attention due to their fundamental role in the study of self-assembly and novel physical properties arising from particle interactions. We have established a framework to systematically study the structure of binary nanocrystal superlattices (BNSLs) using a dual axis tomography TEM holder. The tilt series obtained not only allow us to map the three dimensional structure of icosahdedral AB13 (ico-AB13) and AlB2 type BNSLs, but also uncover the structural differences among the projections of ico-AB13, cuboctahedral AB13 (cub-AB13) and AlB2. Using this structural characterization methodology, we further explore the structural diversity of BNSLs and we are able to identify a new AB6 polymorph with the body-centered cubic (bcc) symmetry. The bcc-AB6 phase, lacking any atomic analogue, is isomorphic to certain alkali-metal intercalation compounds of fullerene C60 (e.g. K6C60). Based on the space-filling principle, we further tailor the relative phase stability of the two AB6 polymorphs—CaB6 and bcc-AB6—from coexistence to phase-pure bcc-AB6, highlighting the entropic effect as the main driving-force of the self-organization of BNSLs. The identification and the ability to tune the relative phase stability of polymorphic structures provide a unique opportunity to engineer the interparticle coupling through controlled clustering and/or interconnectivity of sublattice in BNSLs with identical stoichiometry. The developed structural characterization method is general and is important for further exploration of structural diversity in BNSLs and in the development of rigorous structure-property relationships in BNSLs.Reference1. Chen, J., Ye, X.C., Murray, C.B. Systematic electron crystallographic studies of self-ssembled binary nanocrystal superlattices. ACS Nano, 4, 2374-2381, 2010 (cover article)2. Ye, X.C., Chen, J., Murray, C.B. Polymorphism in self-assembled AB6 binary nanocrystal superlattices. submitted.
9:00 PM - DD6.14
Size Effects in the XPS Analysis of Transition Metal Nanostructures.
Nicola Cioffi 1 , Nicoletta Ditaranto 1 , Rosa Pilolli 1 , Daniela Longano 1 , Luisa Torsi 1 , Luigia Sabbatini 1
1 Dipartimento di Chimica, Università degli Studi di Bari "Aldo Moro", Bari Italy
Show AbstractX-ray photoelectron spectroscopy (XPS) is frequently used as a suitable method to investigate the surface chemistry and core-electronic properties of nanomaterials and nano-sized interfaces. Changes of the electronic properties can occur in metal nanophases, related to extremely reduced size of the photo-emitting material, and they have been shown by different groups to significantly affect XP spectra, thus assessing both quantitative analysis and chemical speciation. This contribution will focus on the latter point. In case of nanomaterials composed (even partially) of transition metals, at least four main effects may influence the peak position and lineshape of core-level photo-electron signals, hence playing a key role in chemical speciation analysis. These effects can be briefly summarized as follows: initial state effects, final state effects, charging or differential charging effects and substrate-nanophase interphase and/or polarization effects. The first two effects account for the different energy spacing between NP core-electron energy levels, as compared to the homologous bulk material [1-2]. The third effect is generated by differential photoemission or grounding properties of the metal nanophase, as compared to the supporting or dispersing substrate [1,3]. The latter effect accounts for the occurrence of a potential barrier at the substrate-NP interface [4-5].All the aforementioned issues can influence both peak Binding Energy and shape; depending on the specific metal behavior and on relative contribution of each effect, core level peak shifts can be either positive [6] or negative [7]; moreover, decreasing the size of the photo-emitting nanophase, the Full Width at Half Maximum (FWHM) value of XP peaks broadens, although the mechanism of the FWHM variation has not been fully elucidated.In this communication, we will report on size-effects highlighted in our laboratory in the XPS characterization of gold, copper and silver nanophases. The nanomaterials have been prepared following electrochemical approaches [8], producing surfactant-capped structures. A critical discussion of the chemical shift generated by the specific nanophases will be presented, based on the analysis of high resolution XP spectra. Alternative spectroscopic signals, such as Auger spectra will be reported as well [9], and the relevant information will be critically compared to that obtained by studying photoelectrons.References1. Di Cenzo, S., et al., Comments Solid State Phys., 1985, 11, 203. 2. Jirka, I., J. Phys. Chem. B 1997, 101, 8133.3. Parmigiani, F., et al., J. of Elec. Spec. and Rel. Phen., 1985, 36, 257.4. Jirka, I., Surface Science, 1990, 232, 307.5. Espinos, J.P., et al., J. Phys. Chem. B, 2002, 106, 6921.6. Wu, Y., et al. J. Vac. Sci. Technol. A, 1996, 14, 1662.7. Radnik, J., et al., Phys.Chem.Chem.Phys., 2003, 5, 172.8. Cioffi, N., et al., Electrochim. Acta, in press.9. Cioffi, N., et al., Anal. Bioanal. Chem., 2009, 394, 1375.
9:00 PM - DD6.15
Role of Size and Shape on the Graphitization of Nanodiamonds.
Ashfaq Adnan 1
1 Mechanical and Aerospace, University of Texas, Arlington, Texas, United States
Show AbstractThe nanoscale (the length scale of approximately 1 - 100 nanometer) version of diamond-based materials is primarily known as nanodiamond. Among various types of naturally/artificially found nanodiamonds, there is a special class of nanodiamond material called 'ultra-nanocrystalline' diamond with the characteristic size in the range of 3-10 nm. This class of nanodiamond material is technologically very important because of their potential applications in thermal conducting and heat sink interface materials, composite electroplating, lubrication oil, biomedical technology and chemistry, structural nanocomposites and so on. Due to the types of applications, nanodiamond nanoparticles often experience high temperature. Recent studies suggest that nanodiamond may undergo graphitization process that converts sp3 carbon atoms on the surface to graphitic sp2. While nanodiamond nanoparticle appears in various shapes and sizes, little is known about the nanodiamond shape and size effect on its graphitization. In this work, we present a combined molecular dynamics simulation and thermodynamics based analytical works on the role of nanodiamond shape and size on graphitization. We have studied five different shapes of nanodiamond including truncated octahedral, cubooctahedral, spherical, cubic and diamond type. The size of the nanodiamond ranges from 2.5 nm to 7.5 nm. Our study reveals that both size and shape of nanodiamond influence the graphitization.
9:00 PM - DD6.16
Measuring the Influence of Metal Ions on the Magnetic Properties in Doped Apatite Nanoparticles.
Robert Usselman 1 , Michael Klem 2 , Collette Chorney 2 , Michael Boss 1 , Rajendra Kasinath 2 , Stephen Russek 1
1 Magnetics Groups, National Institute of Standards and Technology, Boulder, Colorado, United States, 2 Chemistry and Geochemistry, Montana Tech of the University of Montana, Butte, Montana, United States
Show AbstractMulti-modal nanoparticles are of interest in bio-nanotechnology with applications in nanomedicine. There is a need to understand emerging properties in nanoscale magnetic objects that are at the interface between quantum and classical systems. With this regard, hydroxyapatite nanoparticles (nHA, 10 nm) were synthesized with a range of multi-functional properties (magnetic and luminescence) via calcium site substitution with metal ions. Using the apatite lattice as a platform for doping paramagnetic spins, we are able to monitor the evolution of the magnetic properties as doping levels are increased. EPR spectroscopy and SQUID magnetometry were used to monitor nHA magnetic properties as a function of Fe(III) doping levels. The EPR spectra show composite line shapes representative of paramagnet species superimposed onto a broad line width. The residual g = 4.3 peak is due to high spin paramagnetic iron presumably not incorporated into the lattice. Iron incorporated into the lattice quenches the spin orbit coupling and exhibits a broad line width at g = 2. The magnetization data are indicative of a magnetic species present that saturates at high fields for low doping levels accompanied by an increasing anti-ferromagnetic component that does not saturate at higher doping levels. Magnetic nanoparticles that display multi-functionality and enhance T1 and T2 relaxation are desirable for synthesizing "smart" MRI contrast agents. Gadolinium (Gd) doped apatite particles were explored to investigate the relaxivity properties for either T1 or T2 contrast agents. Both relaxation mechanisms can be utilized for MRI enhancement and are mediated to a varying extent by paramagnetic and superparamagnetic particle composition. The ratio r2/r1 determines whether a contrast agent has mainly a T1 or T2 reducing effect. The higher the r2/r1 ratio the better the T2 contrast efficacy. The 5% Gd doped samples has a r2/r1 ratio of 18.9 which is comparable to iron oxide nanoparticles (~23).
9:00 PM - DD6.17
New Methods in Structural Characterization of Biological Nano-fibrils by Production of Oriented Samples for Analysis with Polarized Infrared and Raman Spectroscopy, enhanced by Site-specific Isotope Labelling.
Jose Rodriguez-Perez 1 , Ian Hamley 1 , Adam Squires 1
1 Chemistry, University of Reading, Reading United Kingdom
Show AbstractWe report the use of molecular combing and other alignment methods to obtain macroscopically oriented self-assembled protein fibrils. The aligned fibrils are studied by polarised infrared and Raman spectroscopy. This gives structural information that cannot be obtained from standard spectroscopic experiments on isotropic samples, for example, confirmation of the characteristic cross-beta amyloid core structure, the side chain orientation from specific amino acids, and the arrangement of the strands within the fibrils, as we demonstrate here.We demonstrate that the methodology can be further enhanced by incorporation of site-specific isotope labels including 13C-18O amino-acid backbones and deuterated tyrosine side chains.We employed amyloid fibrils from hen egg white lysozyme (HEWL), and from short model peptides. Our results demonstrate straightforward methods to align nano-fibrils, producing highly anisotropic polarised spectra for detailed structural investigation, enhanced by isotope labelling.
9:00 PM - DD6.18
Preferential Evaporation Effects in GaN Nanowires Studied Using Atom Probe Tomography.
James Riley 1 , Rodrigo Bernal 2 , Qiming Li 3 , Horacio Espinosa 2 , George Wang 3 , Lincoln Lauhon 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractGaN and InGaN alloys are promising materials for light emitting diodes (LEDs) operating in the visible spectrum, but GaN thin-films typically have large numbers of threading dislocations due to a lack of cost-effective lattice matched substrates.[1] Because of the small cross-sectional area of nanowires, however, dislocation-free nanowire heterostructures can be grown on inexpensive substrates, including Si(001).[1] Proof-of-principle nanowire LEDs have been demonstrated with a n-GaN/InGaN/p-GaN core/multishell geometry,[2] but quantitative knowledge about the amount and location of incorporated impurities (both intentional and unintentional) as well as about interface uniformity is necessary to optimize LED performance. This information can be attained using atom probe tomography (APT), an analysis technique that utilizes laser-assisted field evaporation to collect atoms and create an elementally resolved 3-D reconstruction of a nanowire sample with 0.3 nm lateral and atomic-scale depth resolution.[3] We have performed the first APT analysis of Metal Organic Chemical Vapor Deposition (MOCVD) grown GaN nanowires and have found differing evaporation behaviors for elemental Ga and N. While Ga readily evaporates from the nanowires, it is necessary to utilize an increased effective evaporation field to evaporate N. This high-field characteristic is consistent with variations in evaporation for different faces of the [11-20] (a-axis) GaN nanowires. The nanowires have triangular cross sections and (1-10-1), (-110-1), and (0001) (c-axis) side facets. Due to the strength of the N bonds, the polarity of the c-axis facet appears to limit N evaporation. APT concentration profiles indicate a triangular evaporation surface with most N detected along two of the triangular edges. This result supports the hypothesis that N evaporates under high field conditions (electric field will be enhanced at the triangle edges) from the (1-10-1) and (-110-1) nanowire facets. Field ion microscopy (FIM) characterization indicated a flat-topped evaporation surface with a triangular cross section and confirmed the nanowire orientation. This enhanced understanding about the evaporation behavior of elemental Ga and N will inform future APT efforts to quantitatively analyze heterostructure interfaces and impurity incorporation in GaN nanowires. References1. Rigutti, L., et al. Nanotechnology. 2010, 21, (42), 425206. 2. Qian, F., et al. Nano Lett. 2005, 5, (11), 2287–2291.5. Perea, D.E., et al. Nature Nano. 2009, 4, 315–320. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
9:00 PM - DD6.19
Improvement of Atmospheric Pressure Chemical Vapor Deposition Deposited TCO Films: Initial Growth Study with Transmission Electron Spectroscopy.
Gilbere Mannie 1 2 , Joop van Deelen 3 , Hans Niemantsverdriet 2 , Peter Thuene 2
1 , Material innovation institute (M2i), Delft Netherlands, 2 , Eindhoven University of Technology, Eindhoven Netherlands, 3 , TNO Science & Industry, Eindhoven Netherlands
Show AbstractMorphology of transparent conductive oxide films (TCOs) is an important factor for the optical and electrical properties of these films [1]. Until now, investigations of TCO morphology in order to optimize their performance is mostly done by Secondary Electron Spectroscopy (SEM) and Atomic Force Microscopy (AFM) [1]. Although SEM and AFM give topographical information about growing films they give limited information about morphology with respect to crystal orientation and cannot reveal information on the atomic level. A technique which is suitable for detailed morphology down to the atomic detail is Transmission Electron Microscopy (TEM). This technique requires electron-transparent samples. To achieve suitable samples from thin films small slice are (diamond) cut and polished by an focused ion beam. The work of Sundqvist et al. [2] and Mitchell et al. [3, 4] represent elegant examples of this approach in the field of TCOs. Using this method, morphology of the interface of film and substrate can be investigated and overall film morphology determined. However this approach finds its limit when studying the very early stages of film growth (i.e. the first nano crystals formed on the substrate, the nucleation density and the organization of the growing crystals). We therefore developed a method to visualize pristine nano-structures on oxide substrates with TEM in plan-view employing window etched TEM-wafers. This methodology has already successfully been applied for model catalysts with iron oxide nano-particles in morphology studies related to carbon nano-tube growth [5] and Fischer-Tropsch catalysis [6].We can demonstrate this approach on tin oxide films grown by APCVD from tin chloride precursors. The early stages of this film growth were directly analyzed by SEM, TEM, AFM and XPS. While SEM and AFM gave us topographical information about the samples, plan-view revealed very small particles, crystal ordering and crystal defects. We came to the conclusions that thin oxide films grown directly on electron transparent membranes offer a convenient means to visualize the pristine film morphology at atomic detail. We are currently employing this method to systematically investigate the influence of substrate pre-treatment and deposition parameters on film morphology and electrical properties.[1] I. Volintiru, M. Creatore, B. J. Kniknie, C. I. M. A. Spee, and M. C. M. van de Sanden, J. Appl. Phys., 102, 043709 (2007)[2] J. Sundqvist, J. Lu, M. Ottosson, A. Hårsta, Thin Solid Films, 514, 63 (2006)[3] D. R. G. Mitchell, D. J. Attard, and G. Triani, Thin Solid Films, 441, 85 (2003)[4] D. R. G. Mitchell, A. Aidla, and J. Aarik, Appl. Surf. Sci., 253, 606 (2006)[5] P. Moodley, J. Loos, J. W. Niemantsverdriet, and P. C. Thüne, Carbon, 47, 2002 (2009)[6] P. Moodley, F. J. E. Scheijen, J. W. Niemantsverdriet, and P. C. Thüne, Catal. Today, 154, 142 (2010)
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Single Crystalline Zn2SnO4 Rhombohedral Nanoplates Growing as Zigzag Nanowires: Synthesis, Crystallochemical and Electrical Characterization.
Stevin Pramana 1 , Cheng Sun 1 , Joshua Lim 1 , Nripan Mathews 1 , Lydia Wong 1 , Subodh Mhaisalkar 1
1 Energy Research Institute @ NTU, Nanyang Technological University, Singapore Singapore
Show AbstractZn2SnO4 (Zinc Tin Oxide or ZTO) has attracted technological attention for use in transparent conducting coating in optoelectronics and photovoltaic devices due to its high electrical conductivity, high electron mobility, chemical stability and low visible absorption. In ZTO nanostructures, these properties are strongly influenced by the chemical composition, physical dimensions and morphology (nanowires, nanobelts and microprisms). In this study, the effects of growth parameters on the crystallochemical and physical properties of ZTO nanowires constructed from a zigzag chain of rhombohedral nanoplates were investigated. The synthesis was carried out via a Vapor-Liquid-Solid process of ZnO and SnO2 with Au catalyst, deposited on Si substrate in a tube furnace and characterized by a combination of grazing incidence X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. ZTO nanowires have been successfully grown with the diameter of 25 – 100 nm and length up to tens of micrometers, and crystallized in Fd-3mS with lattice parameter a = 8.6452(5)Å. The selected area electron diffraction along [101] zone axis indicates that the facets of rhombohedral nanoplates are oriented along [12-1] and [10-1], and each nanoplates was joined in a zigzag structure along [11-1]. No twins were observed in all nanowires. Varying SnO2 and ZnO molar ratio and substrate position has a strong influence on the growth mechanism resulting in different morphology of ZTO nanowires which affects the electrical properties and introduction of impurities. The electrical characterization of the ZTO nanostructures was also investigated using a transistor configuration.
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Surface Optical Phonon of Single ZnS Nanobelt.
Hsin-Hua Wang 1 , Cheng-Ying Chen 1 , Linfeng Hu 2 , Xiaosheng Fang 2 , Jr-Hau He 1
1 Institute of Photonics and Optoelectronics, & Department of Electrical Engineering, National Taiwan University, Taipei Taiwan, 2 Department of Materials Science, Fudan University, Shanghai China
Show Abstract ZnS nanostructures with their appealing properties have attracted the intense attention in the past few years [1]. The underlying physics in ZnS nanostructures has thus become important. Surface optical (SO) phonon mode caused by the translational symmetry breaking at the interface between two different materials is usually not observable for bulk material. Recently, SO phonon mode in nanostructures has been studied through Raman spectroscopy [2-6]; however, most of the previous study measure the Raman spectra of an ensemble of the nanostructures, which limits the detail investigation of SO phonon mode. In this study, Raman scattering from a single ZnS nanobelt is investigated for the first time. In addition of the phonon modes of bulk ZnS, strong SO phonon mode of the ZnS nanobelt is observed at ~336 (cm-1), which can be attributed to the high aspect ratio of nanobelt structure. Moreover, the intensity of SO phonon mode is found to be spatial dependent. The dependency on the polarization of excitation source is on the other hand studied in order to understand the selection rule of raman scattering under symmetry breaking condition. The effect of surrounding materials of different dielectric function on frequency of SO phonon modes is also discussed.Reference1.C. Ma, D. Moore, J. Li and Z. Wang, Advanced Materials 15 (3), 228-231 (2003).2.D. Spirkoska, G. Abstreiter and A. F. I Morral, Nanotechnology 19 (43) (2008).3.Q. Xiong, J. Wang, O. Reese, L. C. Lew Yan Voon and P. C. Eklund, Nano Letters 4 (10), 1991-1996 (2004).4.R. Gupta, Q. Xiong, G. D. Mahan and P. C. Eklund, Nano Letters 3 (12), 1745-1750 (2003).5.S. Bhattacharya, A. Datta, S. Dhara and D. Chakravorty, Journal of Raman Spectroscopy, n/a-n/a (2010).6.K. W. Adu, Q. Xiong, H. R. Gutierrez, G. Chen and P. C. Eklund, Applied Physics A: Materials Science & Processing 85 (3), 287-297 (2006).
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Auger-assisted Visible No-phonon Eemission from Si-NCs.
Wieteke de Boer 1 , Tom Gregorkiewicz 1
1 Van der Waals-Zeeman Institute, University of Amsterdam, Amsterdam Netherlands
Show AbstractIt is well-known that quantum confinement (QC) induces relaxation of the momentum conservation restriction in silicon nanocrystals (SiNCs), leading to enhancement of radiative electron-hole recombination. However, the indirect character of the bandgap remains preserved. QC effects on the indirect bandgap in SiNCs are thoroughly investigated and reasonably well understood; upon decrease of NC diameter, QC induces a blueshift of the emission (photoluminescence – PL) maximum from ~1.1 eV (bulk Si) towards the visible. A limitation on the blueshift of the PL occurs for SiNCs in a SiO2-matrix, due to formation of an inter-bandgap O-related energy level, which for NC smaller than ~3 nm stabilizes PL energy at around ~2.5 eV [1]. Next to the indirect bandgap-related PL, we identify a new visible emission band of Si nanocrystals (NCs) embedded in a SiO2-matrix, characterized by picosecond decay. It appears next to the well-known excitonic emission (in the near-infrared, 10 - 100 μs decay) and the oxygen/defect-related band (at ~420 nm, ~10 ns decay). For smaller NCs, its maximum shifts to longer wavelengths, opposite to the well-known blue shift of the excitonic emission. The spectral “red” shift is accompanied by enhancement of PL intensity, indicating increase in quantum efficiency. Based on the detailed experimental study, we identify the newly observed band with radiative no-phonon recombinations of non-equilibrium electron-hole pairs, whose properties are influenced by quantum confinement. We estimate that for NCs of diameter ~2.5 nm, the quantum efficiency of this hot PL band is enhanced by 3 orders of magnitude compared to bulk Si. We discuss the most important consequences of our finding for understanding of quantum confinement effects in Si-NCs, and its application impact [1].1.W.D.A.M. de Boer et al., accepted in Nature Nanotechnology
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Fluorescent Resonance Energy Transfer Between Colloidal Quantum Dots in Polystyrene Thin Films.
Chelsea Haughn 1 , Hao Shen 1 , Chaoying Ni 1 , Michael Mackay 1 , Matt Doty 1
1 Materials Science and Engineering, University of Delaware, Newark , Delaware, United States
Show AbstractUnderstanding the absorption and transport of energy at the nanoscale is critical to the development of next generation photovoltaic (PV) materials. For example, organic PVs incorporate dispersed nanoparticles or colloidal quantum dots that serve as sites for both exciton dissociation and electron transport. Understanding how the nanoscale structure of the incorporated quantum dots controls the energy absorption and transport dynamics will provide critical insights that can drive the design and synthesis of new materials with optimized solar conversion efficiency. We present a study of fluorescent resonance energy transfer (FRET) between colloidal quantum dots. The colloidal quantum dots were either solution cast into thin films or dispersed in polystyrene thin films of varying dot density. Time-resolved photoluminescence measurements were used to analyze the energy transfer between the quantum dots in the films. The results were correlated to TEM images of the thin films to quantify the relationship between the average interparticle distance and the time resolved photoluminescence decay time. The results are an important first step towards a thorough understanding of energy transfer between individual colloidal quantum dots in photovoltaic materials.
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In Vivo Studies of a Nanostructured Titanium Alloy Knee Plate and Pin.
Julia Mirza Rosca 1 , Agustin Santana Lopez 1 , Domingo Herrera Santana 1 , David Gonzalez 2 , Jose-Antonio Garcia 3 , Agurtzane Martinez 3
1 , University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria Spain, 2 , Technological Institute of Canarias, Las Palmas de Gran Canaria Spain, 3 , Advanced Surface Engineering Center AIN, Pamplona Spain
Show AbstractTitanium alloys are among the most used metallic biomaterials, particularly for orthopedic applications. Ever since the pioneer titanium alloy (Ti6Al4V) has been used as biomaterial, lack of biocompatibility has been extensively reported and propelled research on improved materials with appropriate mechanical behavior and adequate biocompatibility. Studies have indicated that vanadium produces oxides harmful to the human body; in order to replace vanadium containing Ti alloys, Ti-6Al-7Nb was developed. Today this alloy is the preferred choice for cementless total joint replacements.It is very important to produce a nanostructured bioactive metal implant with appropriate mechanical properties and we applied a chemical and thermal treatment that converts the surface of titanium alloy into bioactive surface. Therefore, bioactive Ti6Al7Nb might represent an alternative for advanced orthopedic implants under load-bearing conditions. Eleven mini-pigs weighing around 50 kg, with free access to food pellets and water, were the experimental animals for this study. Ten of these pigs (one is the control) were anesthetized and after shaving, disinfection and draping, a straight 3 cm skin incision was made and the implants (plate and pin) were implanted into the epiphyses of the tibiae. Surgical procedures were performed bilaterally. At 6 months after implantation, the mini-pigs were sacrificed.After sacrifice, the segments of the proximal tibia epiphyses containing the implanted plates and pins were cut of, fixed in phosphate-buffered formalin and dehydrated in serial concentrations of ethanol after which they were embedded in polyester resin and then cutted and grounded to a thickness of 75-100 µm. With these samples a lot of observations were made: Scanning Electron Microscopy observations, histological examination at implant surface and histological examination of the bone-implant surface and SEM-EDX examinations were also made.All the results revealed that the plates and pins are in direct contact with the newly formed bone without any intervening soft tissue layer. We regard osteoinductive ability of nanostructured Ti6Al7Nb as one of the advantages of this implant material in consideration for clinical applications.
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Synthesis of N Type Doped Stoichiometric Boron Nitride Nanostructures.
Jose Nocua 1 , Frank Mendoza 1 , Gerardo Morell 1 2
1 Department of physic, University of Puerto Rico, Rio Piedras, Puerto Rico, United States, 2 , Institute for Functional Nanomaterials, San Juan, Puerto Rico, United States
Show AbstractBoron nitride (BN) is a binary chemical compound, consisting of equal proportions of boron and nitrogen and its empirical formula is BN. It’s are structural analogues of carbon nanostructures, chemically inert, and potentially important in mechanical applications that include the strengthening of light structural materials for the aerospace industry. Synthesize sulfur-doped BN nanostructures and films, when BN is doped with sulfur, the sulfur take the place or replace some nitrogen atoms, donating electrons to the lattice. The doped BN has an enhanced ionic character. Using borazine (B3N3H6) as a precursor and technique of chemical vapor deposition were deposited on silicon substrates boron nitride films. Their morphology was examined by scanning electron microscope (SEM) and transmission electron microscopy (TEM), while its chemical composition was studied by techniques scanning electron microscopy energy dispersive (EDS), Fourier transform infrared spectrometry (FTIR), electron energy loss spectroscopy (EELS) and, X-ray photoelectron spectroscopy (XPS). These results indicate that the material that is obtained is stoichiometric BN nanostructure.
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TiO2 Nanotube Growth Mechanism Studied with Scanning Auger Spectroscopy.
John Hammond 1 , Steffen Berger 2 , Felix Schmidt-Stein 2 , Sergiu Albu 2 , Helga Hildegrand 2 , Patrik Schmuki 2 , Dennis Paul 1
1 , Physical Electronics, Chanhanssen, Minnesota, United States, 2 , Physical Electronics, Chanhassen, Minnesota, United States
Show AbstractAnodic TiO2 nanotubes offer unique properties for a wide range of applications including energy conversion, photocatalysis and biomedical devices1, 2, 3. It is widely accepted that the initial growth of the nanotubes is based on the formation of a compact anodic oxide followed by the formation of etching grooves and pores in the oxide4, 5. The mechanism of steady state growth of the nanotubes from the embryonic pores has, however, remained a topic of debate. To evaluate a flow model1, 6 for the formation of the tubular structures, high spatial resolution Scanning Auger Spectroscopy data is used to elucidate the compositional variations across TiO2 nanotube layers grown in a fluoride containing ethylene glycol electrolyte. The layers were fractured parallel to the axes of the nanotubes and quantitative spectra, line scans and elemental maps were acquired along the walls of the nanotubes. The Auger data indicates the presence of a fluoride rich layer located between the tube walls, and in particular, the triple points of the hexagonally ordered nanotube arrays. This data supports fluoride dissolution as the reason for a transition from a porous oxide layer to tubular structures. This data also supports a flow model as a mechanism for the formation of the tubular morphology. . P. Roy, S. Berger, P.Schmuki, Angew. Chem. (accepted 2010)2. A. Ghicov, P. Schmuki, Chem. Commun., (2009) 2791.3. J. M. Macak, H. Tsuchiya, A. Ghicov, K. Yasuda, R. Hahn, S. Bauer, P. Schmuki, Curr. Op. Sol. Stat. Mater. Sci., 11 (2007) 3.4. L. V. Taveira, J. M. Macak, H. Tsuchiya, L. F. P. Dick, P. Schmuki, J. Electrochem. Soc., 152 (10), (2005) B405.5. K. Yasuda, J. M. Macak, S. Berger, A. Ghicov, P. Schmuki, J. Electrochem. Soc., 154 (9), (2007) C472.6. D. J. LeClere, A. Valota, P. Skeldon, G. E. Thompson, S. Berger, J. Kunze, P. Schmuki, H. Habazaki, S. Nagata, J. Electrochem. Soc., 155 (9), (2008) C487.