Symposium Organizers
Gertjan Koster University of Twente
Gyula Eres Oak Ridge National Laboratory
Fabio Miletto Granozio Complesso Universitario di Monte St. Angelo
Chang-Beom Eom University of Wisconsin-Madison
Nicholas Ingle University of British Columbia
UU1: Diffraction Techniques I
Session Chairs
Monday PM, November 29, 2010
Hampton (Sheraton)
9:30 AM - **UU1.1
Time-Resolved X-ray Studies of the Layer-by-Layer Growth Mode of Complex-Oxide Thin-Films During Pulsed Laser Deposition.
Joel Brock 1
1 Applied & Engineering Physics, Cornell University, Ithaca, New York, United States
Show AbstractPerforming simultaneous X-Ray Reflectivity and Diffuse X-ray Scattering measurements during the deposition process, we measure the time-dependent thickness, coverage, and in-plane structure of films in the layer-by-layer growth mode. These rich data sets enable us to extract both the intra-layer and the inter-layer kinetics. Our results on the SrTiO3/SrTiO3 〈001〉 system explicitly limit the possible role of island breakup, demonstrate the key roles played by nucleation and coarsening in Pulsed Laser Deposition, and place an upper bound on the Ehrlich-Schwoebel barrier. Using LaAlO3/SrTiO3 〈001〉 as a model system, we demonstrate that the activation energy for diffusion varies with film thickness during the first few layers of heteroepitaxy.
10:00 AM - **UU1.2
Molecular Beam Epitaxy Studied by In Situ Synchrotron X-ray and Electron Diffraction.
Wolfgang Braun 1
1 , Paul-Drude institute for Solid State Electronics, Berlin Germany
Show AbstractCrystal growth by molecular beam epitaxy (MBE) is characterized by a simple principle: in vacuum, atoms or molecules of only the species required to form the layer are supplied to the surface. The surface temperature is chosen such that the adatoms can move along the surface to find low-energy sites where they incorporate into the crystal. MBE is therefore ideally suited to study fundamental crystal growth processes.New device functionalities arise from the synthesis of structurally complex materials or the epitaxial combination of increasingly dissimilar materials at nanoscale dimensions. In such cases of extreme heteroepitaxy, the nature of the chemical bond plays a strong role in interface formation in addition to the lattice mismatch.In our dedicated experiment at the synchrotron source BESSY II in Berlin, we study molecular beam epitaxy of metals, semiconductors and insulators on various technologically relevant substrates. X-ray diffraction in surface as well as bulk modes in a variety of geometries can be combined with electron diffraction and other in situ characterization methods.I will give an overview of both the methods and materials we have recently studied, with an emphasis on surface kinetics and heterointerface formation.The stability of the x-ray beam and the growth conditions allows the analysis of growth oscillations and recovery exponents with good quantitative accuracy, allowing conclusions on rate limiting processes on the surface such as diffusion, incorporation or domain wall movements. Combining electron diffraction and x-ray createion, RHEED-induced fluorescence produces qualitative information on the surface chemistry. The time resolution is also a few s, allowing us to monitor surface chemical composition changes across heterointerfaces with close to monolayer resolution. RHEED has high enough sensitivity to measure large reciprocal space areas in short times. Using substrate rotation, we can monitor the evolution of diffuse intensity on planes in reciprocal space with sub-monolayer resolution during growth. We have applied this method to two metals, MnAs and Fe3Si, grown on GaAs. In both cases, we obtain evidence that the simple thermodynamic picture distinguishing wetting and non-wetting growth is much more complex and shows a fascinating variety of atomic scale processes during interface formation. Finally, I would like to present some of our recent work on the growth of epitaxial rare earth oxides on Si(111) as well as epitaxial phase change materials on GaSb(111) and related substrates. In both systems, the interface plays a distinctly different role for epitaxy as in the previous systems where the lattice mismatch dominates interface formation.Recently, we have added real-time mass spectrometry to our range of in situ characterization tools. By placing the instrument in a liquid nitrogen cooled shroud with an aperture system and by shuttering the beams, we can characterize chemical reactions at the surface.
10:30 AM - UU1.3
Growth and Modeling of SrTiO3 (111) on Si (100) by Molecular Beam Epitaxy using a Template Layer.
Agham Posadas 1 , Rytis Dargis 1 , Miri Choi 1 , David Smith 2 , Alexander Demkov 1
1 Department of Physics, University of Texas at Austin, Austin, Texas, United States, 2 Department of Physics, Arizona State University, Tempe, Arizona, United States
Show AbstractEpitaxial SrTiO3 on silicon is of interest as method of integrating the functional properties of perovksite oxides, including high-k dielectric LaAlO3, ferroelectric (Pb,Zr)TiO3 and colossal magnetoresistive (La,Sr)MnO3, onto the widely-used silicon materials platform for various electronics and sensor applications. The growth of SrTiO3 is traditionally done on Si (100) using a lattice-matched silicide template layer, with SrTiO3 growing in the 001 orientation. In this work, we present a method of growing an unconventional 111-oriented SrTiO3 film on Si (100) using molecular beam epitaxy (MBE). The process involves formation of a passivating strontium silicide layer followed by a titanium metal layer, which when oxidized, can easily transition into the 111-oriented perovksite layer. Commercially available 2” Si(100) wafers are exposed to UV/ozone to remove organic contaminants and densify the native oxide. The wafer is then loaded into the MBE chamber and lightly outgassed in vacuum. The native oxide is removed using Sr-assisted deoxygenation allowing native oxide removal at modest temperatures (<800°C). The resulting surface shows a clear 2x1 reconstruction using reflection high energy electron diffraction (RHEED). The wafer is then cooled to about 550°C and Sr metal is deposited until 1/2 monolayer Sr has been deposited. The RHEED shows transitions from to 3x2 and back to 2x1. An additional layer of bulk strontium silicide is formed to protect the underlying silicon from reaction with Ti, and which also serves as a low energy surface for the next layer. One monolayer of Ti metal is then deposited on the low energy silicide surface, resulting in an ordered metal layer. This layer is then oxidized to form a TiO3 seed layer corresponding to the 100 orientation of rutile. Sr and Ti with the appropriate flux ratio are then co-deposited on this seed layer at 550°C in the presence of 5x10-7 torr of molecular oxygen. The evolution of the RHEED pattern as each layer is deposited will be discussed and compared to theoretical modeling of the surface of each deposited layer. The resulting SrTiO3 film was also characterized using plan view and cross-section transmission electron microscopy, showing the surface and interface structure of the film. The 111 orientation of the SrTiO3 film is also confirmed by x-ray diffraction measurements.
10:45 AM - UU1.4
In-situ X-ray Diffraction Studies During Magnetron Co-sputtering of Ni-Ti Shape Memory Alloy Films.
Rui M. Martins 1 2 3 , Norbert Schell 4 , Karimbi Mahesh 5 , Rui Silva 5 , Francisco Braz Fernandes 5
1 Unit of Physics and Accelerators, Instituto Tecnológico e Nuclear (ITN), Sacavém Portugal, 2 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden- Rossendorf , Dresden Germany, 3 , Centro de Física Nuclear da Universidade de Lisboa (CFNUL), Lisboa Portugal, 4 , GKSS Research Center Geesthacht, Geesthacht Germany, 5 CENIMAT/I3N, New University of Lisbon, Monte de Caparica Portugal
Show AbstractThe study of Ni-Ti shape memory alloy films is of great technological interest for applications in the field of microengineering. They can work as sensors and actuators at the same time. However, there are still important issues unresolved like formation of film texture and its control. Films exhibiting the two-way shape memory effect are also required.A better understanding of the underlying growth mechanisms and their microstructural development requires sophisticated in-situ techniques. A two-magnetron sputter deposition chamber mounted into the six-circle diffractometer of the Rossendorf Beamline at the European Synchrotron Radiation Facility has been used for the processing of the Ni-Ti films. The in-situ x-ray diffraction studies enabled us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters (Ti target power) during film growth.It has been found that the type of substrate plays an important role for the preferential orientation of sputtered Ni-Ti films. In some cases they exhibit a pronounced depth dependence of their preferential orientations. Amorphous SiO2 and TiN buffer layers have been used to successfully control their crystallographic orientations. This is an important achievement since the texture has a strong influence on the extent of the strain recovery of the Ni-Ti films. The deposition conditions leading to films mainly containing grains with (100) or (110) planes of the B2 phase parallel to the film surface are presented.The deposition of graded Ni-Ti films by changing deliberately the Ti:Ni ratio, thereby altering microstructure and transformation temperatures across the film thickness, has also been performed. The aim has been the optimization of the deposition parameters in order to fabricate films with a “two-way” actuation (films with a combination of superelasticity and shape memory characteristics). It will lead to the development of smaller devices due to an optimal design of microdevices regarding size and weight (i.e., no consideration has to be paid to a resetting spring).
11:00 AM - UU1:Diffraction1
BREAK
11:30 AM - **UU1.5
LEEM Studies of Graphene Thin Film Gorwth.
Rudolf Tromp 1 , James Hannon 1
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractGraphene has become one of the most actively studied materials for numerous novel electronic applications, as well as being of interest to fundamental science. Successful practical applications of graphene require a method of synthesis that results in high electronic quality material, scales well to large areas, is low in cost, and preferably requires relatively simple processing equipment. Low Energy Electron Microscopy (LEEM) has become one of the premiere techniques for in-situ studies of the synthesis and growth of graphene on a variety of substrates. It allows graphene growth to be observed in real time, with spatial resolution down to a few nanometers. In addition to morphological and structural characterization, LEEM and its cousin PEEM (Photo Electron Emission Microscopy) can also provide electron structure information on similar length scales. These capabilities enable a direct correlation of growth method, structure, and properties, all in a single experimental environment. In this talk, I will present recent results and progress.
12:00 PM - UU1.6
In situ Observation of Grain Boundary Properties using High Energy X-ray Diffraction Microscopy.
Shiu Fai Li 1 , Christopher Hefferan 1 , Jonathan Lind 1 , Ulrich Lienert 3 , Athony Rollett 2 , Robert Suter 1
1 Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 3 Advanced Photon Source, Argonne National Lab, Lemont, Illinois, United States, 2 Material Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractWe demonstrate the capability of non-destructively mapping crystallographic orientation fields and grain boundaries in three dimensions inside of bulk polycrystals using high energy x-ray diffraction microscopy. An ensemble of highly defected grains in a high purity aluminum sample is followed through three annealing states. Crystalline grains are imaged and the boundaries between them are mapped in 3D, but each grain contains significant geometrically necessary dislocations as indicated by the non-uniform orientation gradients resolved at ~0.1 degrees. Small differential annealing was observed in the form of movement in a subset of the reconstructed grain boundaries. Measurements are carried out at the Advanced Photon Source at Argonne National Laboratory at beamline 1-ID using a near-field high resolution imaging detector that senses the diffraction signal arising from an entire layer or cross-section of material as the sample is rotated in a planar, micro-focused 50keV x-ray beam. The reconstructions are done by forward modeling computational code that simulates the measurement and matches the simulated orientation field to the observed diffraction patterns.
12:15 PM - UU1.7
Analysis of Grain Boundary Motion Observed by 3D High Energy X-ray Microscopy.
Anthony Rollett 1 , Chris Hefferan 2 , Frankie Li 2 , Jonathan Lind 2 , Ulrich Lienert 3 , Robert Suter 2
1 Materials Sci & Eng, Carnegie Mellon Univ., Pittsburgh, Pennsylvania, United States, 2 Physics, Carnegie Mellon Univ., Pittsburgh, Pennsylvania, United States, 3 Advanced Photon Source, Argonne National Laboratory, Chicago, Illinois, United States
Show AbstractAdvances in three-dimensional materials science are reviewed and an example is given of progress in characterization and evolution during grain growth. Analysis of grain boundary motion was characterized by a non-destructive high-energy x-ray diffraction method. Measurements were carried out at the Advanced Photon Source at Argonne National Laboratory at beamline 1-ID using a near-field high resolution imaging detector that senses the diffraction signal arising from an entire layer or cross-section of material as the sample is rotated in a planar, micro-focused 50keV x-ray beam. The reconstructions of the 3D images used a forward modeling technique that indexes the orientation of each point in the sample independently of all others. A grain growth experiment was performed by first characterizing a polycrystalline aluminum wire sample using HEDM. Eleven layers were measured and analyzed; the resolution is given below. The grain size was of the order of 150 microns, in a cross section of order 600 microns diameter. Each layer spans the entire cross-section of the wire. The sample was then exposed to elevated temperature in order to induce grain growth by annealing in increments of about 8°C for ten minutes, then allowing the microstructure stabilize to room temperature. The final anneal put the sample at ~70°C for about 15-20 minutes. A minority of grain boundaries exhibited motion whereas the majority remained stationary. The 5-parameter grain boundary character distribution was compared for the mobile versus stationary boundaries.
12:30 PM - UU1.8
Real-time Structural and Electrical Investigation of PDI8-CN2 based OFET.
Silvia Milita 1 , Fabiola Liscio 1 , Santiago David Quiroga 2 , Arian Shehu 2 , Fabio Biscarini 2 , C. Frank 3 , F. Schreiber 3 , S. Kowarik 4
1 IMM, CNR, Bologna Italy, 2 ISMN, CNR, Bologna Italy, 3 Institut fuer Angewandte Physik, Universitaet Tuebingen, Tuebingen Germany, 4 , Humboldt-Universitaet, Berlin Germany
Show AbstractSemiconductor thin-film devices based on organic molecules are of great interest for the development of high performance organic field effect transistors (OFETs) and organic light emitting diodes (OLEDs), as well as to underscore fundamental charge transport effects in molecular solids.Among the n-type organic molecules, perylene derivatives are very promising. In particular PDI-8CN2, N,N’-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis (dicarb-oximide), has been reported to allow the fabrication of OFETs with excellent electrical performance (high-mobility: 0.16-0.6 cm2 V-1s-1) and remarkably high stability in air.In these systems, the charge mobility depends on the overlap between π-π orbitals of vicinal molecules, which is mainly influenced by the structure and morphology of the first layers of organic film at the interface with the dielectric. Since the structure of these first layers may significantly differ from that of the bulk, the determination of the molecular orientation and packing of organic molecules at the substrate interface is a crucial input for modelling the electronic band structure and the associated charge-transport properties.For this reason we have performed Grazing Incidence X-ray Diffraction (GIXD) and X-Ray Reflectivity (XRR) measurements, in situ and real time during the UHV deposition of PDI-8CN2. Moreover, in situ and real time electrical measurements were performed on FET structures during the semiconductor deposition. Thanks to these time resolved measurements we could describe i) the thin-film growth dynamics, ii) the molecular packing and microstructure of the organic thin film, iii) the influence of the substrate temperature and the deposition flux, and iv) the relation between the charge transport properties and the growth mechanism of the thin film.
12:45 PM - UU1.9
Pressure-dependent Transition from Atoms to Nanoparticles in Magnetron Sputtering Flux: Effect on WSi2 Film Roughness and Stress.
Lan Zhou 1 , Minghao Li 1 , Hua Zhou 2 , Randall Headrick 1 , Kimberly MacArthur 3 , Bing Shi 3 , Ray Conley 4 , Albert Macrander 3
1 Department of Physics and Materials Science Program, University of Vermont, Burlington, Vermont, United States, 2 Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 4 National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractWe report on the transition between two regimes from several-atom clusters to much larger nanoparticles in Ar magnetron sputter deposition of WSi2, and the effect of nanoparticles on the properties of amorphous thin films and multilayers. Sputter deposition of thin films is monitoredby in-situ x-ray scattering, including x-ray reflectivity and grazing incidence small angle x-ray scattering (GISAXS). The results show an abrupt transition at a critical Ar background pressure Pc. Below Pc smooth films are produced, while above Pc, roughness increases abruptly due to the granularity of particles that have aggregated in the deposition flux before reaching the growth surface. The results from WSi2 films are correlated with in-situ measurement of stress in WSi2/Si multilayers, which exhibits a corresponding transition from compressive to tensile stress at Pc. The tensile stress is attributed to coalescence of nanoparticles and the elimination of nano-voids. The observed pressure-dependent transition is a general effect that is expected to occur in many different materials systems, and will play a role in determining the physical and mechanical properties of films deposited from high-density plasmas.
UU2: Diffraction Techniques II
Session Chairs
Tadashi Abukawa
Elias Vlieg
Monday PM, November 29, 2010
Hampton (Sheraton)
2:30 PM - **UU2.1
In situ X-ray Scattering for Everything?
Elias Vlieg 1
1 Institute for Molecules and Materials, Radboud University Nijmegen, Nijmegen Netherlands
Show AbstractThe technique of surface X-ray diffraction is approaching its thirtieth birthday. It started as a crystallography tool for surfaces in ultrahigh vacuum, but its range of applications has dramatically broadened over the years. In this contribution, I will review the main developments and describe the current state-of-the-art in terms of both sample environments and instrumentation. This will be done based on specific examples, including the growth of oxide films using pulsed laser deposition, wet chemical etching of Si, formation of graphene layers on SiC and the formation of liquid films on crystal surfaces.
3:00 PM - UU2.2
Sub-millisecond X-ray Microdiffraction Studies of Irreversible Phase Transformations During Rapid Heating.
Stephen Kelly 1 , Sara Barron 1 , Timothy Weihs 1 , Eric Dufresne 2 , Todd Hufnagel 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe presence of a large number of interfaces can significantly alter the behavior of a material. This is dramatically showcased in metal nanolaminate foils, which can exhibit high temperature exothermic synthesis reactions where the reaction propagates as a thin (~100 µm) concerted front moving along the length of the foil at ~10 m/s, reaching temperatures in excess of 1500 °C in under 100 µs. While pump-probe scattering techniques are well established for investigating reversible transitions in materials with better than nanosecond resolution, these irreversible transformations require single-shot techniques. In addition, the rapid and highly localized nature of these reactions requires a technique with both high spatial and temporal resolution.We have developed a time-resolved x-ray microdiffraction technique capable of revealing the sequence of phase formation under these extreme conditions. We use Kirkpatrick-Baez mirrors to focus a pink (~12 keV wtih ~2% bandwidth) x-ray beam with a flux of ~1014 ph/s into a small (~10 µm) spot. We produce short (~75 µs) pulses from the focused beam, recording the x-ray diffraction pattern in transmission through the multilayer foil on a fiber-optic coupled x-ray CCD camera. Using a photodiode to sense the light emitted by the passing reaction front, we can trigger the shutter to produce an x-ray pulse at a predetermined time in the reaction sequence. Simultaneous to this we record optical pyrometry data, allowing us to precisely locate each diffraction pattern in the reaction sequence. While the readout time of the CCD camera limits us to one exposure per specimen, we can build up a detailed description of the reaction by performing multiple experiments on different foils.As an example, we describe recent experiments on Al-Zr multilayer foils with overall composition Al3Zr and 95 nm bilayer period (the combined thickness of one Al and one Zr layer), showing that the transformation from an Al/Zr multilayer structure to the stable intermetallic Al3Zr occurs in less than 200 µs without formation of transient crystalline phases. This is in contrast to earlier experiments on Al-Ni multilayers, which show a more complex phase formation sequence.
3:15 PM - UU2.3
Real time Investigation of Crystallization and Phase Segregation Dynamics in Polymer:Fullerene Solar Cells during Thermal Annealing.
Tiziano Agostinelli 1 , Samuele Lilliu 2 , John Labram 1 , Jarvist Frost 1 , Anne Guilbert 1 , Mariano Campoy-Quiles 1 , Mark Hampton 2 , Ellis Pires 2 , Donal D Bradley 1 , Thomas Anthopoulos 1 , Natalie Stingelin-Stutzmann 1 , Jenny Nelson 1 , Emyr MacDonald 2
1 Physics, Imperial College of London, London United Kingdom, 2 Physics, University of Cardiff, Cardiff United Kingdom
Show AbstractUnderstanding the length and time scales upon which crystallization and phase segregation occur in polymer:fullerene solar cells is important to better control nanomorphology and therefore device performances. We report studies of the dynamics of crystallization and phase segregation during thermal annealing for a set of materials including poly(3-hexylthiophene)(P3HT), poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b’]dithiophene)-alt 4,7(2,1,3-benzothiadiazole)](PCPDTBT), poly[(4,4’-bis(2-ethylhexyl)dithieno[3,2-b:2’,3’-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl](Si-PCPDTBT), as well as fullerenes and corresponding polymer:fullerene blends.For P3HT based blends, we monitor changes in (i) polymer crystallization, by means of Grazing Incidence X-ray Diffraction (GIXRD) (ii) film density, by means of spectroscopic ellipsometry and (iii) field effect carrier mobilities, all in real time during thermal annealing. We study the effect of blend composition ratio to understand how the polymer and fullerene phases interact. From the combination of these measurements with measurements of device performance after different annealing times, we conclude that the evolution of morphology consists of two phases: (i) a first phase, lasting 5 min at 140°C, during which the polymer crystallizes and a major increase of power conversion efficiency results and (ii) a slower phase, lasting up to 30 min, during which aggregation of PCBM molecules continues and efficiency increases more gradually.For PCPDTBT based blends, crystallization is studied using GIXRD for both pristine PCPDTBT and PCPDTBT:fullerene blend films, with and without the use of octanedithiol (ODT) as a solvent additive. We conclude that ODT promotes the crystallization of the polymer phase alone, thus assisting phase segregation. This is supported by Differential Scanning Calorimetry (DSC) measurements.More recently, the efficiency of PCPDTBT:PC70BM solar cells has been increased by substituting the C bridging atom on the dithiophene unit with a Si atom. GIXRD highlights that the Si bridging atom promotes crystallization without need for processing additive. To understand this observation we investigate the effect of substitution on polymer chain conformation computationally using molecular dynamics simulation of the polymers and polymer films. These studies indicate a significant effect of Si substitution on side chain flexibility. Finally we correlate the structural studies with device measurements.In summary, we have investigated the evolution of crystallization in different pairs of polymer:fullerene blends by means of real time GIXRD during thermal annealing, and we correlate our observations with several techniques including real time ellipsometry, real time FET mobilities, DSC, solar cell performance and modeling. We conclude that crystallization of the polymer phase is a primary driving force for phase separation and performance optimization in organic solar cells.
3:30 PM - UU2.4
In-situ Synchrotron X-ray Scattering Study of the Order-Disorder Transition in NiPt Bimetallic Nano Alloy Crystals.
Okyun Seo 1 , Pilgun Oh 1 , Jae Sung Hwang 1 , Sanghun Um 3 , Hyon Chol Kang 3 , Jinwook Chung 2 , Do Young Noh 1
1 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 3 Advanced Materials Engineering, Chosun University, Gwangju Korea (the Republic of), 2 Physics, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractSince the discovery of electrochemically active nano-crystals such as Pt-bimetallic alloys, there has been vast research on their physical and chemical properties. Understanding the behavior of the ordering and the possible order-disorder transition in nano-scale bimetallic alloy crystals are important in the perspective of both basics physics and their applications as catalyses. In this paper, we present an observation of the ordering and the order-disorder transition in NiPt bimetallic nano crystals using in-situ synchrotron x-ray scattering. The NiPt nano crystals of about 200 nm were formed by depositing Pt (10 nm)- Ni(10nm) thin films and annealing them rapidly to 1100°C in a high vacuum environment. The existence of the superlattice (100) Bragg peak indicated that the Ni and Pt atomic positions are ordered similar to those in bulk NiPt crystals. With increasing the temperature, the superlattice peak became more intense and sharper continuously, which was caused by the annealing of the ordered domains. The peaks started to decreases above 674°C and completely disappeared at 829°C. We also observed that NiPt bimetallic nano-crystal alloys were separated into two crystalline domains from 714°C to just below the transition temperature. In the decreasing temperature direction, however, the super lattice peak reappeared at 716°C, indicating that there is a significant hysteresis involved in the order-disorder transition. The crystal structure of the NiPt nano crystals also changed back from FCC back to L10 structure. We think that the hysteresis is related to the lattice relaxation of NiPt alloy systems.
3:45 PM - UU2.5
Multiscale Simulation of Processing of New Functional Coatings by Laser Sintering of Ultrafine Composite Powders.
Mikhail Krivilyov 1 , Denis Danilov 2 , Peter Galenko 3 1 , Vladimir Lebedev 1
1 Physics and Energy Engineering, Udmurt State University (UdSU), Izhevsk Russian Federation, 2 Theoretical Biophysics, Karlsruhe Institute of Technology (KIT), Karlsruhe Germany, 3 Institute of Materials Physics in Space, German Aerospace Center (DLR), Cologne Germany
Show AbstractLaser sintering of powder materials is a new promising technique suitable for production of a wide range of wear-resistant and corrosion-proof materials. Theoretical analysis of laser sintering of composite powders has been performed to get a robust description of rapid solidification processing leading to durable coatings. Therefore multiscale modeling of this process at the macro, meso and microscopic spatial scales was accomplished to get a closer agreement with experimental regimes. Microscopic modeling of solute segregation and phase transformation was performed using the phase field method formulated for multi component metallic alloys. Macroscopic study included modeling of transient heat transfer in a porous layer by the modified mushy zone method.According to the results of modeling, there is a distinctive difference in the final microstructure depending on the processing conditions. Under continuously operating laser significant powder compaction occurs coupled with enhanced solute redistribution driven by convection in the melted zone. Impulse laser treatment allows to achieve partial melting of the powder leaving the porous structure of the layer. This effect is potentially useful for producing chemically active/inactive coatings. Comparison between 2D and 3D simulations revealed a large deviation in the depth of the sintered zone if impulse laser processing is used. So application of the 2D model for description of the periodic thermal treatment is not appropriate if the relaxation time of the thermal field is comparable to the impulse periodicity.Phase field modeling showed the effect of solute trapping in high-speed scanning laser sintering. This happens due to high solidification velocities up to 1-5 m/s in the skin shells of the particles. Combined with the large temperature gradient up to 10^6 K/m, absolute stability of the solidification front is realized leading to chemically homogeneous composition. This effect is important in development of chemically heterogeneous coatings preserving their composite structure after sintering. Comparison of the modeling results and experimental data is performed for the Fe-Ni system.
4:00 PM - UU2:Diffraction3
BREAK
4:30 PM - **UU2.6
Three-dimensional Reciprocal Mapping and Kinematical Surface Structural Analysis by Electron Diffraction.
Tadashi Abukawa 1
1 IMRAM, Tohoku University, Sendai Japan
Show AbstractElectron diffraction such as low-energy and reflection high-energy electron diffraction (LEED and RHEED) have played an important role in surface crystallography. However, as dynamical effects are inherent in electron diffraction, a time-consuming dynamical analysis was usually required to fit the diffraction pattern. Real-time structure imaging is a dream in far distance. The constant momentum-transfer averaging (CMTA) method is an approach to suppress the dynamical effect by using a large amount of data set [1]. Both incident angle and energy were changed to obtain multiple reciprocal-space maps for CMTA-LEED, and thus it take several days for measurements. RHEED is suitable to survey the reciprocal-space because of a large wave number of the high-energy electron. When the sample rotation is combined, it becomes a powerful method to map the reciprocal space with a short period [3,4]. We call this method as Weissenberg RHEED (W-RHEED)[4], because the principle is the same as that of a Weissenberg camera for X-ray crystallography. A three-dimensional reciprocal space map, up to the temperature limit, can be obtained by a single azimuthal turn. It takes only a few minutes at the present stage. Thus we might be able to investigate changes of 3D maps during a thin film growth with very slow rate. The map is very useful to understand crystal structure on surfaces. In order to enable a quick kinematical analysis, we reduced the dynamical effect by using an energy filter (EF). When one observes only elastically scattered electrons, the inelastic mean free path guarantees the short path length of the observed electrons in the solid. Otherwise the electrons, which travel longer in solid, have a higher chance to suffer the dynamical scattering. With the EF, Kikuchi patterns, one of the dynamical clear effects, were obviously reduced. A retarding field energy filter consists of three spherical grids was used for the measurements. Surface structures can be determined from a simple kinematical analysis based on a Fourier transformation of the obtained reciprocal data. Effects of the energy filter for the kinematical analysis and the phase retrieve method for a direct structure determination will be discussed.[1] M.G. Lagally, T.C. Ngoc, M.B. Webb, Phys. Rev. Lett. 26, 1557 (1971).[2] T. Abukawa, T. Yamazaki, S. Kono, e-J. Surf. Sci. Nanotech. 4, 661-668(2006)[3] O. Romanyuk, K. Kataoka, F. Matsui, K. Hattori, H. Daimon, Czechoslovak. J. Phys. 56, 267(2006).[4] T. Abukawa, T. Yamazaki, K. Yajima, K. Yoshimura,Phy. Rev. Lett. 97, 245502(2006).
5:00 PM - UU2.7
Far-From-Equilibrium Morphological and Compositional Evolution during Metal Film Growth on Binary Alloy Surfaces: Ni, Al,… on NiAl(110).
Jim Evans 1 , Yong Han 1 , Dapeng Jing 1 , Baris Unal 1 , Chad Yuen 1 , Thomas Duguet 1 , Patricia Thiel 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractDeposition of metals on binary alloy surfaces offers new possibilities for guiding the formation of functional metal nanostructures (motivated by applications to catalysis, magnetic thin films, plasmonics, etc.). Our goal is to develop predictive atomistic multi-site lattice-gas models which can describe the evolution during deposition of far-from-equilibrium growth morphologies and also of imperfect alloy ordering for co-deposition. Models are validated by comparison with STM studies. We have explored Ag/NiAl(110) producing novel bliayer fcc(110) “quantum” islands versus Au/NiAl(110) producing complex monolayer island structures [1,2]. This talk focuses on a more complex co-deposition system, Ni+Al/NiAl(110), which offers the opportunity for fundamental studies of self-growth of alloys [2]. Although, the equilibrium film structure corresponds to perfect alloy ordering for stoichiometric codeposition, we find various far-from-equilibrium growth morphologies depending on the deposition protocol. KMC simulation of our atomistic model describes and elucidates the observed behavior. [1] Y. Han et al., PRL 100 (2008) 116105; PRB 81 (2010) 115462[2] T. Duguet et al., PNAS (Special Issue on Surface Chemistry), invited submission (2010).
5:15 PM - UU2.8
Atomically Flat Epitaxial Biferroic Bilayers of Dissimilar CoFe2O4 Spinel and BaTiO3 Perovskite.
Romain Bachelet 1 , Nico Dix 1 , Gervasi Herranz 1 , Florencio Sanchez 1 , Josep Fontcuberta 1
1 , Institut de Ciencia de Materials de Barcelona - CSIC, Bellaterra Spain
Show AbstractInterfaces play an active role when ferromagnetic (FM) and ferroelectric (FE) materials are combined, arising new functional properties from elastic coupling or electronic interactions. To understand the phenomena and eventually to exploit the properties interfaces atomically flat are usually very convenient and often required. However, when materials with dissimilar structure as FE perovskite and FM spinel are combined in bilayers, the control of the growth is still not yet solved. Typically, the growth of these bilayers, either spinel on BTO or BTO on spinel, causes 3D growth with rough morphology.Here we will show that this tendency to 3D growth can be suppressed using proper deposition conditions. In our study, epitaxial bilayers combining FE perovskite BaTiO3 (BTO) and FM spinel CoFe2O4 (CFO) have been grow by pulsed laser deposition with real time control by reflection high energy electron diffraction (RHHED). We show here that both CFO/BTO and BTO/CFO bilayers with atomically flat surfaces can be obtained on La2/3Sr1/3MnO3(001) (LSMO) and SrRuO3 electrodes. We use reduced deposition temperature to limit kinetically the growth of CFO, suppressing the surface energy driven tendency to 3D growth of (001)-oriented spinels on both LSMO and BTO surfaces. BTO can be grown 2D on CFO using the same conditions that on LSMO electrodes, indicating that the structural dissimilarities with CFO do not drive to 3D growth. However, the higher lattice matching causes reduced tetragonality in BTO on CFO respect to BTO on LSMO. Thickness dependence of in-plane lattice parameters of CFO and BTO, and the resulting critical thicknesses, are determined from recorded RHEED patterns.
5:30 PM - UU2.9
Two-dimensional Growth of (001) and (110) SrTiO3/La2/3Sr1/3MnO3 Bilayers by Kinetic Limitations.
Romain Bachelet 1 , David Pesquera 1 , Gervasi Herranz 1 , Florencio Sanchez 1 , Josep Fontcuberta 1
1 , Institut de Ciencia de Materials de Barcelona - CSIC, Bellaterra Spain
Show AbstractInterfaces between dissimilar materials can be not only a passive boundary, but they can play an active role causing new properties to emerge. Clearly, understanding and use of these properties require atomically flat interfaces. This typically requires epitaxial heterostructures in which each layer is grown two-dimensionally. However, in the growth of many complex oxides this is still challenging. In particular, La2/3Sr1/3MnO3 (LSMO) films with (001) orientation can start growing two-dimensionally but usually they become rough due to formation of multilayered islands after coverage of few monolayers. Getting flat films is even more difficult in the case of (110) films, with growth of facetted islands thermodynamically favoured due to surface energy anisotropy. These problems, very recently identified in the fabrication of oxide heterostructures, are critical and thus, new growth engineering strategies are necessary to be developed. To advance in this direction, we have investigated the growth of LSMO films on (001) and (110) oriented SrTiO3 substrates, using pulsed laser deposition assisted with real time reflection high energy electron diffraction (RHEED). We will show by properly controlling the deposition conditions, the growth can be kinetically limited thus affecting surface diffusivity of adatoms and island nucleation, allow persistent two-dimensional growth of (001) and (110) oriented LSMO films. Finally, we will also demonstrate that SrTiO3 top layers can be grown two-dimensionally on the (001) and (110) LSMO bottom layers, thus forming atomically flat surfaces.
5:45 PM - UU2.10
Real Time Reciprocal Space Mapping During Quantum Growth of Nano-Islands.
Hawoong Hong 1 , Aaron Gray 2 , Tai-C. Chiang 2
1 , Argonne National Lab, Argonne, Illinois, United States, 2 , University of Illinois, Urbana-Champaign, Illinois, United States
Show AbstractA real time method has been developed to collect 2 and 3-dimensional maps of the surface x-ray diffraction using a CCD camera. Large ranges of the reflectivity curves, with rocking curves at every point on the reflectivity curves could be continuously measured in a relatively short amount of time. The abundance of information from 2-D k-space maps helped to reveal clear indications in the quantum-controlled growth modes of thin Pb films. With the 3-D extension of this method, it was also possible to observe the ordering of the islands. The islands maintain a nearly uniform inter-island distance without any angular correlation. The inter-island ordering is well correlated with the development of island height distribution dictated by electron confinement. The evolution of these nano-islands on Si (111)-(7x7) and sapphire (001) surfaces has been successfully studied with this new x-ray diffraction method.
Symposium Organizers
Gertjan Koster University of Twente
Gyula Eres Oak Ridge National Laboratory
Fabio Miletto Granozio Complesso Universitario di Monte St. Angelo
Chang-Beom Eom University of Wisconsin-Madison
Nicholas Ingle University of British Columbia
UU3/SS3: Joint Session: Fast Electron Microscopy & Scattering
Session Chairs
Tuesday AM, November 30, 2010
Room 309 (Hynes)
9:30 AM - **UU3.1/SS3.1
The Dynamic Transmission Electron Microscope (DTEM): In-situ Microscopy with Nanometer and Nanosecond Resolution.
Nigel Browning 1 2 3 , Marta Bonds 1 , Geoffrey Campbell 3 , James Evans 2 1 , Katherine Junjohann 1 , Joseph McKeown 3 , Thomas LaGrange 3 , Bryan Reed 3 , Melissa Santala 3
1 Chemical Engineering and Materials Science, University of California at Davis, Davis, California, United States, 2 Molecular and Cellular Biology, University of California at Davis, Davis, California, United States, 3 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractThe dynamic transmission electron microscope (DTEM) has been developed to obtain both high spatial (~1nm or better) and high temporal (~1microsecond or faster) resolution. The high temporal resolution is achieved by using a short pulse laser to create the pulse of electrons through photo-emission. This pulse of electrons is propagated down the microscope column in the same way as in a conventional high-resolution TEM. The only difference is that the spatial resolution is limited by the electron-electron interactions in the pulse (a typical 10ns pulse contains ~109 electrons). To synchronize this pulse of electrons with a particular dynamic event, a second laser is used to “drive” the sample a defined time interval prior to the arrival of the laser pulse. The important aspect of the DTEM is that one pulse of electrons is used to form the whole image, allowing irreversible transitions and cumulative phenomena such as nucleation and growth, to be studied directly in the microscope. The use of the drive laser for fast heating of the specimen presents differences and several advantages over conventional resistive heating in-situ TEM – such as the ability to drive the sample into non-equilibrium states. So far, the drive laser has been used for in-situ processing of nanoscale materials, rapid and high temperature phase transformations, and controlled thermal activation of materials. In this presentation, a summary of the development of the DTEM and in particular, in-situ stages for both the existing DTEM at LLNL and a new DTEM at UC-Davis will be described. Particular attention will be paid to the potential for gas stages to study catalytic processes and liquid stages to study biological specimens in their live hydrated states. The potential improvements in spatial and temporal resolution that can be expected through the implementation of upgrades to the lasers, electron optics and detectors used in the new DTEM will also be discussed.Development of the DTEM at LLNL was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory and supported by the Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under Contract DE-AC52-07NA27344. Development of in-situ stages for the DTEM at UC-Davis was supported by DOE NNSA-SSAA grant number DE-FG52-06NA26213 and NIH grant number RR025032-01.
10:00 AM - UU3.2/SS3.2
Dynamic Transmission Electron Microscope Investigations of Chalcogenide-based Phase Change Materials.
Melissa Santala 1 , Bryan Reed 1 , Stefan Meister 2 , Thomas LaGrange 1 , Geoffrey Campbell 1 , Nigel Browning 1 3 4
1 Condensed Matter & Materials Division, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Materials Science & Engineering, Stanford University, Stanford, California, United States, 3 Department of Chemical Engineering and Materials Science, University of California, Davis, California, United States, 4 Department of Molecular & Cellular Biology, University of California, Daivs, California, United States
Show AbstractGe2Sb2Te5 is a chalcogenide-based phase-change material that is technologically significant because of its wide use in optical recording media and its potential for use in non-volatile electronic memory [1]. For either application, rapid switching between the amorphous and crystalline phases is necessary for recording data, and understanding the changes to the crystal structure and microstructure during phase transitions at very short time scales is of scientific and technological interest. The time for laser-induced crystallization (~100ns) and amorphization (~10ns) [2] are difficult to probe with conventional imaging and scattering instrumentation, but are on the scale ideally probed with the dynamic transmission electron microscope (DTEM).The DTEM is a unique, highly-modified electron microscope capable of nanosecond-scale time-resolved imaging and diffraction. It is a powerful tool for the study of dynamic events, such as phase transformations, as demonstrated in metals and semiconductors [3] and is applied here to the study of Ge2Sb2Te5. Phase transformations in continuous and micro-patterned thin films of Ge2Sb2Te5 were induced with a laser in the DTEM. The amorphous-crystalline and melting-solidification transitions were observed and the kinetics of these processes were revealed by time-resolved TEM imaging and electron diffraction on nanosecond time scales. Using an unconventional specimen geometry, repeated switching between the amorphous and crystalline phases has been achieved in the DTEM enabling in situ study of structural changes after repeated switching, which is relevant to device performance. Since the laser absorption and heat transport are sensitive to the specimen geometry, finite element analysis was used to model the laser absorption and heat diffusion in the specimen geometries used. The experimental observations are compared to the modeling results.This work performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.References[1]M. Wuttig and C. Steimer, Appl. Phys. A – Mater. 87 (2007) 411-7.[2]V. Wiedenhof, I. Friedrich, S.Ziegler, and M. Wuttig, J. Appl. Phys. 89 (2001) 3168-76. [3]T. LaGrange et al., Ultramicroscopy 108 (2008) 1441-9.
10:15 AM - UU3.3/SS3.3
Imaging of Solid Growth into a Superheated Liquid during Rapid Solidification of Metal Thin Films by in situ Transmission Electron Microscopy.
Andreas Kulovits 1 , Jorg Wiezorek 1 , Thomas LaGrange 2 , Bryan Reed 2 , Geoffrey Campbell 2
1 Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, Pittsburgh , Pennsylvania, United States, 2 Condensed Matter and Materials Division, Physical and Life Science Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractNanocrystalline metal thin films were molten inside an electron microscope with an excimer laser that illuminates a disk shaped area. With time delays as short as 12nanoseconds ns, an electron pulse illuminates the molten area. This unprecedent nanosecond time resolution in combination with the nanometer spatial resolution allowed us to investigate details of the solidification process. Complete melting in the illuminated area was established by electron diffraction. In imaging mode the character of the advancing liquid solid interface was investigated. The liquid solid interface is planar throughout the entire solidification process. In this process solidification is initiated from the interface between the nanocrystalline solid metal film and the liquid metal once the temperature of the liquid at the interface drops below the melting point. Parallel to the growth direction elongated grains grow from the original liquid solid interface. We used transmission electron microscopy to ex situ analyze the microstructure and defect content of the solidified films. Special attention was paid to the region at the edge of the melt pool to investigate the process of occlusion. We used automated acquisition and indexing of precession diffraction patterns in the TEM (ASTAR/DigiSTAR from NanoMEGAS) to analyze the growth direction of the morphologically elongated grains. No preferential growth orientation was observed. Our observations of a planar liquid solid interface and the lack of a preferential growth direction indicate that the this rapid solidification process despite being orders of magnitude faster than conventional solidification can be described by conventional solidification theory. The Work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory and supported by the Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under contract No. DE-AC52-07NA27344.
10:30 AM - UU3.4/SS3.4
In-situ TEM Observation of Formation-Retraction-Fracture Experiment of Liquid-Like Silicon Nanocontact.
Tadashi Ishida 1 , Kuniyuki Kakushima 2 , Hiroyuki Fujita 1
1 Center for International Research on Micro Mechatronics, Institute of Industrial Science, University of Tokyo, Tokyo Japan, 2 , Tokyo Institute of Technology, Kanagawa Japan
Show AbstractA liquid-like silicon nanocontact was formed when silicon opposing tips were brought into contact with high bias voltage. In-situ observation by a transmission electron microscope (TEM) during the retraction process showed that the nanocontact easily thinned with nano-scaled step propagation along the surface from the contact to the tip. Repeating this thinning process, the nanocontact was finally fractured at 30 nm in diameter. Silicon is the most common material for micro/nano devices. It is important to measure the electronic and mechanical properties of silicon at the nano scale because the properties are expected to be very different in such a small scale from ordinary scales. Thus, we have studied the electronic and mechanical properties of a silicon nanowire and a nanocontact for the further development of nano devices. The silicon crystalline nanocontact showed twice higher strength than micrometer-sized crystalline silicon structures. However, we found a much softer silicon nanocontact when high bias voltages were applied between tips. In our experimental system, MEMS opposing tips with micro electrostatic actuators with one degree-of-freedom were operated inside an ultra-high-vacuum TEM chamber. MEMS structure with micro electrostatic actuators and silicon opposing tips were fabricated with bulk micromachining and focused ion beam, respectively. A driving voltage for the actuators and a bias voltage for an electrical measurement between tips were applied with feed-throughs. Electron beam for TEM observation was 1.6x103 A/cm2 without an appreciable heating. Using this combination between MEMS and TEM, a deformation of a nanostructure between tips can be in-situ visualized with TEM. Silicon tips were brought into contact with 1 V in bias voltage. The bias voltage increased at 1 V/s and then electric current suddenly jumped up from a few micro amperes to 100 micro amperes around 13 volts. A silicon nanocontact of 98 nm in diameter was formed between tips. Then, we set the bias voltage at 1 V again to decrease the influence of electrical voltage and current between tips; the current was 30 nA. The silicon nanocontact without any lattice fringes was retracted at 2.0 nm/s. The diameter of the necking drastically decreased from 98 nm to 30 nm at the speed of 1.8 nm/s. During this deformation, steps of 4.4 nm in height propagated from the neck to the tip at 7.0 nm/s. The nanocontact was fractured without any retraction when the diameter was 30 nm. The corner of the breakage part was rounded like a liquid droplet to 12 nm in radius of curvature in less than 30 ms. The deformation was completely different from the reported silicon nanocontact. According to the literature, silicon nanocontacts showed both elastic and plastic deformation, and the corner rounding at the breakage point. These results suggest that the properties of nanostructures consisted of the same material can be easily affected by the formation methods.
10:45 AM - UU3.5/SS3.5
Sintering of Silver Nanoparticles using In-situ TEM Heating.
Michael Asoro 1 , Desiderio Kovar 1 , Paulo Ferreira 1
1 Materials Science and Engineering, University of Texas at Austin, Austin, Texas, United States
Show AbstractNanoparticles possess a wide range of properties used in many applications such as patterned conductors in microelectronics and catalysts in chemical reactions. During processing or usage, nanoparticles have a strong tendency to agglomerate and sinter over short time scales, which can be either beneficial or detrimental, depending on the application. In the present work, a JEOL 2010F transmission electron microscope (TEM), equipped with a novel Protochips AduroTM heating stage, is used to perform in-situ heating experiments. We observe in real time, the sintering of silver nanoparticles as a function of particle size and temperature. These experiments provide real-time dynamic information for a direct investigation of the evolution of sintering, which post-mortem TEM observations are not capable of conveying. The particle radius, neck radius, and dihedral angle can be measured from the TEM images, using Gatan Digital Micrograph software. These values are then used to calculate fundamental material variables, such as surface and grain boundary diffusion coefficients relevant to the understanding of sintering in nanoparticles.
11:30 AM - **UU3.6/SS3.6
Direct Observation of Structural Dynamics with Ultrafast Electron Diffraction.
Nuh Gedik 1
1 Physics, MIT, Cambridge, Massachusetts, United States
Show AbstractThe interaction between electronic, spin and structural degrees of freedoms leads to fascinating properties in strongly correlated electron materials. Although direct probing of electronic excitations can be achieved with ultrashort laser pulses, only indirect information can be obtained about structural excitations using optical probes. I will report direct measurements of structural dynamics with atomic scale spatial resolution by using ultrafast electron diffraction (UED). In UED, a femtosecond laser pulse is split into two, the first part is used to induce structural change and the second part is used to generate ultrafast high energy electron packets via photoelectric effect. Recording the diffraction pattern of these electron packets at different times after the photo-excitation of the sample provides a movie of the laser induced structural change with sub-picosecond temporal and sub-Angstrom spatial resolution. I will discuss recent experiments where we used UED to observe lattice dynamics in correlated electron materials in response to photo-excitation of the charge carriers.
12:00 PM - UU3.7/SS3.7
Time-resolved Imaging of Catalyst Nanoparticles in the Dynamic Transmission Electron Microscope.
Joseph McKeown 1 , Daniel Masiel 2 , Shareghe Mehraeen 2 , Thomas LaGrange 1 , Bryan Reed 1 , Geoffrey Campbell 1 , James Evans 3 , Nigel Browning 1 2 3
1 Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Department of Chemical Engineering and Materials Science, University of California, Davis, California, United States, 3 Department of Molecular and Cell Biology, University of California, Davis, California, United States
Show AbstractThe dynamic transmission electron microscope (DTEM) has the potential to allow direct in-situ imaging of nanoparticle catalysis at both high spatial and temporal resolution. An in-situ gas stage that was designed and built for the DTEM at LLNL facilitates studies of nanoscale catalysis in environments that otherwise cannot be obtained in the vacuum of the electron microscope. While the spatial resolution of the DTEM has thus far been limited by low contrast and signal-to-noise ratios, making experiments involving dispersed nanoparticles at optimal resolutions difficult, the use of an annular objective-lens aperture has been shown [1] to improve the loss of resolution associated with the imaging conditions in the DTEM.Dynamic measurements of chemical processes such as oxidation/reduction reactions will be conducted in the DTEM to monitor catalyst morphologies and reaction sites between nanoparticles and substrates. The DTEM drive laser can easily generate temperatures required for the reactions to be studied, while the in-situ stage provides the desired gas atmosphere. For example, the infiltration of nanoparticles such as Ni, Co3O4, and CeO2 into porous YSZ electrode skeletons has been shown to significantly improve performance in reduced-temperature thin-film solid oxide fuel cells (SOFCs) [2-4]. Mechanisms for this enhancement can be investigated at the nanometer length scale with nanosecond time resolution in the DTEM. Complementary analysis using high-resolution imaging and spectroscopy will be conducted prior to and after dynamic measurements. The results of initial catalytic experiments will be presented, and all aspects of the design and implementation of the in-situ stage in the DTEM will be discussed [5].References[1]Masiel, DJ, et al. ChemPhysChem 11 2010 1. [2]Yamahara, K, et al. Solid State Ionics 176 2005 275.[3]Sholklapper, TZ, et al. Nano Lett. 7 2007 2136.[4]Imanishi, N, et al. Fuel Cells 9 2009 215.[5]Development of the DTEM at LLNL was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Development of in-situ stages for the DTEM at UC Davis was supported by DOE NNSA-SSAA grant number DE-FG52-06NA26213 and NIH grant number RR025032-01.
12:15 PM - UU3.8/SS3.8
The Solid-liquid Interface and Transformation Behavior in Sub-micron Al Alloy Particles Analyzed by in situ Transmission Electron Microscopy (TEM).
Prakash Palanisamy 1 , James Howe 1
1 Department of Materials Science and Engg., University of Virginia, Charlottesville, Virginia, United States
Show Abstract Understanding the solid-liquid interface and its transformation behavior is critical for crystal growth technology. This presentation reports on two in situ heating and cooling experiments conducted in the TEM to understand the solid-liquid transformation. The first study tries to understand elemental partitioning at the solid-liquid interface in Al-Si-Cu-Mg alloy powder particles. The particles were heated in a JEOL 2000FX TEM fitted with a high-angle energy-dispersive X-ray (EDX) detector. At 585 deg.C, the alloy particles contain two phases, solid Si in contact with liquid Al, with Cu and Mg in solution in the liquid Al. X-ray spectra were acquired at three different temperatures (585 deg.C and then on cooling to 565 deg.C and 470 deg.C) in the solid Si, liquid Al-rich phase, and at the solid Si-liquid Al interface, using a 25 nm diameter electron probe. It was found that Cu segregates to the solid Si-liquid Al interface when the temperature is decreased from 585 deg.C to 470 deg.C. The segregation of Cu is heterogeneous and appears to participate in nucleating a Cu-rich phase (most likely Al2Cu(Theta) equilibrium phase) at a high-index Si facet. The Cu concentration measured at the solid-liquid interface and in the Al-rich liquid phase at 565 deg.C and 470 deg.C at regular time intervals over 1.5 hr remains practically constant, indicating that the heterogeneous segregation of Cu to the solid Si-liquid Al interface thermodynamically and not kinetically driven. The second set of studies focuses on understanding the solid-liquid transformation and supercooling behavior in sub-micron pure Al particles. The particles were heated above the melting temperature (660 deg.C) in a JEOL 2010F TEM containing an electron energy-loss spectrometer (EELS), which provides information about low-energy plasmon losses through valence EELS (VEELS). It was found that the plasmon energy, which is a measure of free-electron density in the material, decreases non-linearly with increasing temperature. The non-linear change can be explained based on phonon anharmonicity. A sharp discontinuity in the plasmon energy corresponding to the melting temperature is characteristic of the first-order phase transformation. The free-electron density change measured at the melting temperature was 6%, consistent with the theoretical volume change calculated for Al. This study shows that liquid Al particles can be undercooled by 100 deg.C prior to their nucleation, in reasonable agreement with earlier supercooling studies in micron-sized Al particles. The present study also reveals that the plasmon energy change during supercooling of liquid Al is not a direct extrapolation from the liquid state. This research was supported by the National Science Foundation under grant DMR-0554792.
12:30 PM - UU3.9/SS3.9
Atomic–Scale Imaging of Cation Intermixing in Ordered LiFePO4 Nanocrystals at High Temperature.
Sung-Yoon Chung 1 2
1 Materials Sci. & Eng., Inha University, Incheon Korea (the Republic of), 2 , Nalphates LLC, Wilmington, Delaware, United States
Show AbstractOlivine-type lithium metal phosphates have attracted a great deal of attention over the last decade as an alternative cathode material in Li-ion batteries. In particular, to improve the electrochemical performance of LiFePO4, numerous investigations have been made in addition to many studies of the intrinsic ionic and electronic properties and the thermodynamic phase equilibria. The achievement of remarkable high-rate capability and outstanding thermochemical stability in LiFePO4 during the intercalation reaction (S.-Y. Chung et al., Nature Mater., 1, 123 (2002)) have resulted in the recent success of the application as a safe power source adopted for power tools and potentially for hybrid electric vehicles as well (Nature, 444, 16 (2006)).Among a variety of factors that govern the electrochemical cycling behavior in this class of compounds, control of their cation partitioning and the resultant degree of ordering among the equivalent interstitials has been a crucial issue due to Li mobility in the lattice. In particular, if the Li diffusion in LiMPO4-type ordered olivine phosphates is considerably dependent on the crystallographic orientation, precise probing of local cation distribution within individual crystals during synthesis is of great significance for better understanding of the correlation between the cation partitioning and resulting Li intercalation reaction kinetics (S.-Y. Chung et al., Angew. Chem. Int. Ed., 48, 543 (2009)).Using in situ high-resolution high-temperature electron microscopy and crystallographic image processing, as shown in the previous study (S.-Y. Chung et al., Nature Phys., 5, 68 (2009)), we directly demonstrate in real time that significantly different local cation intermixing can be kinetically induced by fast crystal growth during crystallization in olivine-type lithium metal phosphates. The presence of lattice distortion and misfit strain resulting from the different cation configurations is also confirmed quantitatively. The findings in this study show that control of nucleation and subsequent growth during synthesis is of importance to attain a high degree of cation ordering in olivine phosphates.
UU4/SS4: Joint Session: TEM and SPM Studies in New Environments
Session Chairs
Guus Rijnders
Frances Ross
Tuesday PM, November 30, 2010
Room 309 (Hynes)
2:30 PM - **UU4.1/SS4.1
Liquid Cell Transmission Electron Microscopy for in situ Studies of Crystal Growth.
Frances Ross 1
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractThere is a growing interest in liquid cell transmission electron microscopy that has led to unique results in areas such as self-assembly of colloid particles, biomineralization, and electrochemical nucleation and growth. The spatial and temporal resolution offered by liquid cell microscopy provides quantitative information on the physics of crystal growth. However, interpretation is complicated by the effects of the electron beam, the finite liquid thickness and proximity of the cell windows, and chemical interactions with the materials that make up the cell. In this presentation we will describe electrochemical growth of copper and zinc in the context of these effects, comparing the results of liquid cell microscopy with ex situ results and simulations. During copper growth in the presence of additives, we show how information such as surface diffusion parameters and concentration gradients in the liquid phase can be obtained, but also discuss how the electron beam modifies copper nucleation in chloride solutions and polymerizes organic species. The finite electrolyte thickness constrains dendrite growth and affects diffusion fields, and for zinc deposited from KOH, chemical interactions with the cell materials alter nucleation sites. Quantitative analysis thus requires inclusion of several effects, but can lead in interesting directions such as the electron-beam control of nucleation to produce patterned nanostructures.
3:00 PM - UU4.2/SS4.2
Watching Real-time Assembly of Nanopcrystals Using in-situ Liquid Phase TEM.
Jungwon Park 1 2 , Haimei Zheng 2 , Grauer David 1 , A. Paul Alivisatos 1 2
1 Chemistry, UC Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractAs-synthesized nanoparticles (NPs) serve as functional materials in devices such as transistors, thermoelectrics, photodetectors, LEDs, and solar cells. Fabrication of these devices often include controlled, macroscopic arrays of NPs as the functional component. Physical properties such as size, shape, composition of individual particles as well as the optoelectrical coupling and communication between the NPs in these arrays are all critical factors for overall device performance. If we consider a NP device as an ensemble, packing density, interparticle medium, and orientation must also be considered and controlled. NPs can be assembled together either in an amorphous phase or in ordered crystalline structures. Controlled arrays of NPs can be tuned by manipulating a combination of particle-particle and particle-substrate interactions, particle solubility, and solvent evaporation rate. Many types of assemblies have been reported with single and multi-component building blocks of charged, magnetic, and semiconductor NPs. Most of these assemblies were mediated by controlled drying of volatile solvents. However, our understanding of NP dynamics during superlattice formation is still far behind empirical procedures. Here, we show the real time observation of cubic Pt nanoparticle superlattice formation via liquid phase in-situ TEM experiment. Recently, a TEM cell with the capability of observing a thin liquid sample has been developed. This technique enabled us to study real time NP dynamics occurring in liquid phase inside a conventional TEM. Pt cubic nanoparicles were prepared in colloidal phase and dispersed in the mixture of pentadecane and oleylamine. We also simulated the evaporation mediated liquid-substrate-air interface during assembly by electron beam. Solvent in a tightly sealed liquid cell can be heated and stilmulated by heat and momentum transfer from the electron beam when we focus the electron beam onto local spots within the cell window. From the real time observations of individual particle motion, we could track the formation of NP superlattices from an initial random distribution. Interestingly, superlattices evolved through two distinct phases: first, a contraction of nearest neighbor particles via capillary forces and the subsequent relaxation of packed particles into an ordered superlattice by particle-particle interaction. In addition, individual particles undergo lateral diffusion and rotation to fill in lattice defects during superlattice formation. We also studied in-situ assembly formation of nanoparticles with different compositions and aspect ratios. This study provides fundamental mechanistic insights into the formation of NP superlattices. These results can be combined with existing empirical knowledge to provide a platform for the rational, controlled design of NP superlattices.
3:15 PM - UU4.3/SS4.3
Application of in-situ Electron Microscopy in Nanoscience and Energy Research.
Jianyu Huang 1 , Li Zhong 2 , Chongmin Wang 3 , Liang Qi 4 , J. Sullivan 1 , Ju Li 4 , Wu Xu 3 , Hongyou Fan 1 , N. Hudak 1 , Liqiang Zhang 2 , A. Subramanian 1 , S. Mao 2
1 , Sandia National Lab., Albuquerque, New Mexico, United States, 2 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3 , Pacific Northwest National Laboratory, Richland, Washington, United States, 4 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractBy integrating an atomically sharp scanning tunneling microscopy (STM) probe into a transmission electron microscope (TEM), the atomic structure and physical properties of individual nanostructures can be directly probed in real time at the atomic length-scale. Such studies have revealed a number of unexpected phenomena that only present themselves at the nano-scale. We discovered superplastic elongation of carbon nanotubes, salt nanowires, and nanosized metallic glass. A nanobattery comprised of an individual nanowire electrode was constructed inside a TEM, and the charge and discharge process was revealed in real time, pushing the forefront of knowledge in the highly technologically relevant area of Li-ion batteries.
3:30 PM - UU4.4/SS4.4
In situ Liquid Cell Transmission Electron Microscopy of Dendrite Formation at Battery Interfaces.
Prineha Narang 1 2 , Michael Henry 3 , Arthur Ellis 2 , Xiaoyan Shao 2 , Mark Reuter 2 , Yury Gogotsi 1 , Dan Steingart 3 , Frances Ross 2
1 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States, 3 Dept. of Chemical Engineering, City College of New York, New York, New York, United States
Show AbstractThe relationship between the morphology of electrodeposited materials and the conditions under which they are formed is a key issue for the development of improved batteries for energy storage and delivery. Zinc is a particularly important example, as it is an attractive anode material for low cost, cyclable batteries, yet the large body of literature on the microstructure of electrodeposited zinc is inconclusive. Our objective is to establish a mechanism based understanding of dendrite formation and prevention at battery interfaces that eliminates or reduces the need for barriers. Here we show that liquid cell TEM, with its unique ability to provide simultaneous temporally and spatially resolved information, can yield insights into the physics of electrochemical zinc growth. This has been done by directly imaging the morphological evolution of the anode under electrochemical conditions that mimic charge and discharge cycles. We discuss the technique for real time studies of batteries in the TEM in addition to which we show effects of the electron beam on electrolytes commonly used in batteries, impact of the electrochemical cell geometry on simulating battery conditions in situ and correlation with optical electrochemical cell results. Finally we present preliminary analysis of variation in zinc morphologies grown in situ and current- voltage conditions associated with them.
3:45 PM - UU4.5/SS4.5
An In-situ Ex-environmental TEM Study on the Initiation of Pitting Corrosion of Austenitic Stainless Steels in Salt Water.
Xiuliang Ma 1
1 Shenyang National Laboratory for Materials Sciences, Institute of Metal Research, Shenyang China
Show AbstractStainless steels are widely used in modern life for their superior corrosion resistance. However, stainless steels are actually not “stainless”; in the presence of aggressive anionic species they are susceptible to the localized pitting corrosion that is one of the major causes of materials’ failure and hence leads to a huge loss to our society. The pitting event is generally believed to result from the local dissolution in manganese sulphide (MnS) inclusions which are more or less ubiquitous in stainless steels. Nevertheless, the microstructure information on the local site where MnS dissolution preferentially occurs is lacking, which makes pitting corrosion remain the big headache for numerous engineering materials. We have applied in-situ ex-environment transmission electron microscopy to identify the initial site, at an atomic scale, of MnS dissolution which is critically important but unclear so far for understanding the origin of pitting corrosion in stainless steels. We find that a “single-grained” MnS inclusion in the steel is compositionally and structurally inhomogeneous. Fine octahedral precipitates of spinel MnCr2O4 with dimensions of several tens of nanometers, are dispersedly distributed in the MnS inclusions. In-situ TEM studies indicate that the MnS initially dissolves at the MnCr2O4/MnS interface in the presence of salt water, and the dissolution gradually spreads outwards leaving a pit around the MnCr2O4 octahedron. However, the reactivity of these octahedra is various. First-principles calculations indicate that the dynamics of MnS dissolution is the function of the species of terminal ions enclosing the nano-octahedron catalyst. The MnCr2O4 nano-octahedron with metal terminations is more reactive in catalyzing the MnS dissolution than O-terminated ones. This work not only sets up a new basis for understanding the initiation of pitting corrosion, but also presents a novel example of how an inorganic nano-inclusion undermines its metallic matrix in an electrochemical manner which may occur in a wide range of engineering alloys and biomedical materials serving in wet environments.
4:30 PM - **UU4.6/SS4.6
In-situ Monitoring of Oxide Thin Film Growth.
Guus Rijnders 1
1 Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractComplex oxides have attracted great interest since they exhibit a rich spectrum of physical properties such as ferromagnetism, antiferromagnetism, colossal magnetoresistance, ferroelectricity, dielectricity, and superconductivity. Novel heteroepitaxial devices based on these complex oxides, like spin-polarized ferromagnetic tunnel junctions, superconducting devices and piezoelectric devices, have great potential and are currently under investigation in many groups.The nature of the above-mentioned physical properties in complex oxides is determined by very small characteristic length scales, comparable to the unit cell lattice parameters of complex oxide. Because of these small characteristic length scales, growth control on an atomic level as well as understanding of the different mechanisms affecting the growth mode is essential for the fabrication of epitaxial heterostructures. Two independent processes, i.e., nucleation and growth of islands, play an important role during vapor-phase epitaxial growth on an atomically flat surface. Here, nucleation causes the formation of surface steps and subsequent growth causes the lateral movement of these steps. Both processes are determined by kinetics, since they take place far from thermodynamic equilibrium. These kinetic processes affect the final surface morphology and are, therefore, extensively studied. I will demonstrate the applicability of high-pressure RHEED as well as Scanning Force Microscopy (SFM) to monitor to the growth of complex oxides during Pulsed Laser Deposition (PLD). Because of recent developments, SFM is nowadays also used to study dynamic processes, such as thin film growth and surface reaction mechanisms. We have realized a system, in which SFM can be performed during Pulsed Laser Deposition (PLD). Deposition and force microscopy are performed in one vacuum chamber and via a fast transfer (in the order of seconds) the surface of a sample can be scanned. In our system we take advantage of the pulsed deposition process, because microscopy measurements can be carried out between the pulses. This provides real-time morphology information on the microscopic scale during growth. The transfer mechanism allows switching between microscopy and deposition with a re-position accuracy of ±500 nm which gives new opportunities to study growth processes. Furthermore, it can provide information if RHEED is not possible, for example during amorphous and polycrystalline growth. In this contribution, I will highlight recent advances in oxide thin film growth as well as the latest equipment developments.
5:00 PM - UU4.7/SS4.7
In-situ Observations of Domain Wall Motion by STM-(S)TEM.
Hye Jung Chang 1 , S. Kalinin 1 , S. Yang 3 , S. Bhattacharya 2 , P. Wu 2 , L. Chen 2 , R. Ramesh 3 , S. Pennycook 1 , A. Borisevich 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , Penn State University, University Park, Pennsylvania, United States, 2 , University of California, Berkeley, California, United States
Show AbstractIn situ application of bias in Scanning Probe Microscope (SPM) – (Scanning) Transmission Electron Microscope (STEM) offers unique advantages for observations of ferroelectric domain dynamics. The domain structure can be monitored as the bias is applied. Observations through the thickness of the film can be made, making it possible to distinguish events such as nucleation occurring at the surface, at the film-electrode interface and in the bulk of the film. Here we use this method to study domain dynamics in cross sections of thin BiFeO3 (BFO) films grown on SrTiO3 substrate with SrRuO3 (SRO) bottom electrode. Bias is applied locally using the electrochemically prepared W tip.Local bias as low as 3.3 V applied to the cross section sample produces almost instantaneous and persistent changes in domain structure. The structure undergoes complex changes, including domain wall motion, domain growth and coalescence and nucleation of new domains at the film surface and film-electrode interface. The 71° domain walls present in the film can also undergo 90° rotation if the bias sign is switched to opposite. Defects at the SRO-BFO interface can serve as domain nucleation sites. Domain wall pinning by defects such as dislocations, resulting in curved domain walls, is also observed. This research is sponsored by the Division of Materials Sciences and Engineering, Office of BES of the U.S. DOE, and by appointment (H.J.C.) to the ORNL Postdoctoral Research Program administered jointly by ORNL and ORISE. Instrument access is supported by ORNL’s SHaRE User Facility, which is sponsored by the Scientific User Facilities Division, Office of BES, the U.S. DOE.
5:15 PM - UU4.8/SS4.8
Observation Of Real-time Thin Film Evolution Using Microcantilever Sensors.
Alan Schilowitz 1 , Dalia Yablon 1
1 Corporate Strategic Research, ExxonMobil Research and Engineering Company, Annandale, New Jersey, United States
Show AbstractAdsorption and desorption kinetics of thin film formation on metal surfaces has been directly monitored in real-time by optically measuring the deflection of activated atomic force microscope cantilevers (microcantilevers). Microcantilever deflection is caused by stress generated during the formation of an adsorbate layer on one side of the microcantilever. In this work, rapid adsorption of carboxylic acid in hydrocarbon solution onto a gold surface was directly observed as a compressive stress developed on the microcantilever substrate. Upon exposure to alkyl thiol the desorption of acid followed by its displacement by alkyl thiol was continuously monitored in real-time. Kinetic rate constants and thermodynamic properties of the adsorption and desorption processes are also discussed. In addition, ex-situ spectroscopic analysis conducted at discrete times during the adsorption process has been used to determine the state of the adsorbed layer as the microcantilever deflects. This analysis suggests that while some film organization and intermolecular interactions are required before measurable surface stress can be detected, significant surface stress is generated before complete organization of the film occurs.
5:30 PM - UU4.9/SS4.9
In Situ SEM Compression Studies of Vertically and Radially Aligned CNT Arrays.
Qiuhong Zhang 1 2 , Robert Wheeler 3 , Matthew Maschmann 1 4 , Liangti Qu 2 , Liming Dai 5 , Jeff Baur 1
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, United States, 2 , University of Dayton Research Institute, Dayton, Ohio, United States, 3 , UES Inc., Dayton, Ohio, United States, 4 , Universal Technology Corporation, Beavercreek, Ohio, United States, 5 Chemcial Engineering, Case Western University, Cleveland, Ohio, United States
Show AbstractGrowth of carbon nanotubes (CNTs) on a rigid substrate offers a promising approach to tailor mechanical, electrical and thermal interfacial properties. However, there is still a need to understand the influence of structural order and response of CNT arrays in order to fully tailor interfacial properties. The small dimensions of CNTs and diversity of potential morphologies of individual elements present significant challenges for experimental study and understanding of their ensemble properties. Early studies of the mechanical properties of individual CNTs focused on theoretical analyses and numerical simulations. More recent studies have focused on vertically aligned CNT (VACNT) arrays on planar surfaces. Experimental evaluation of the mechanical properties of radially aligned carbon nanotube (RACNT) arrays grown on small diameter fiber substrates have been investigated to a lesser extent. A major focal point of recent VACNT array mechanical analysis has been the measurement of mechanical modulus and yield point. The mechanical behavior of CNT arrays beyond yielding have been sparsely reported. Specifically lacking is in situ observations of VACNT array mechanical behavior and exploration of the initiation and evolution of buckling throughout the length of the VACNT arrays while under load.In this study, in situ SEM analysis is utilized to investigate the mechanical response of VACNT and RACNT arrays under uniaxial compressive loading. Simultaneous SEM imaging and force-displacement data collection facilitates detailed evaluation of the elastic and plastic response during compression. The following observations were made: 1) RACNT/CF and VACNT/Si exhibit similar compressive mechanical behavior but different strain recovery capability; 2) the deformation may follow either beam buckling or collective bending behavior depending on array morphology; 3) CNT fracture was not observed even at very high compressive strains; 4) hysteresis is consistently observed in the loading and unloading force-displacement curves.
5:45 PM - UU4.10/SS4.10
Meta-stable Catalyst Phases and Interfacial Dynamics During Ge Nanowire Growth.
Stephan Hofmann 1 , Andrew Gamalski 1 , Caterina Ducati 2 , Renu Sharma 3 , Jerry Tersoff 4
1 Engineering, University of Cambridge, Cambridge United Kingdom, 2 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 4 , T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractThe physical and chemical state of the catalyst is of key importance to nanowire growth kinetics, orientation and interface sharpness in hetero-structures, since it determines how quickly the chemical potential of the growth species can be raised to overcome nucleation barriers for nanowire and interfacial ledge formation [1]. We present lattice-resolved, video-rate environmental transmission electron microscopy that shows the formation of a liquid Au-Ge layer on sub-30 nm Au catalyst crystals, and the transition of this two-phase Au-Ge/Au coexistence to a completely liquid Au-Ge droplet during isothermal digermane exposure at temperatures far below the bulk Au-Ge eutectic temperature [2]. Upon Ge crystal nucleation and subsequent Ge nanowire growth, the catalyst either re-crystallizes or remains liquid, apparently stabilised by the Ge supersaturation. Kinetic and thermodynamic modeling gives insight into the importance of surface energies and catalyst-interface dynamics to nanowire growth and geometry.[1] Hofmann et al, Nature Materials 7, 372 (2008) [2] Gamalski et al, Nano Letters, submitted (2010)
UU5: Poster Session
Session Chairs
Wednesday AM, December 01, 2010
Exhibition Hall D (Hynes)
9:00 PM - UU5.1
Observation and Characterization of Water-related Charge Trap at the Al/Pentacene Interface.
Chaeho Kim 1 , Dongryul Jeon 1
1 Department of Physics Education, Seoul National University, Seoul Korea (the Republic of)
Show AbstractCharge traps are one of the key issues for completing successful organic electronic devices. Water is abundant in air and known as a significant source of charge traps. To study water-related charge traps, we fabricated Al/pentacene/Au sandwich samples and measured I-V characteristics in vacuum chamber. From the thermally stimulated current (TSC) measurement performed before and after introducing water into the chamber, we found that the water-related trap resides at 0.65 eV above the pentacene HOMO level. It was interesting that when water was present the current slowly increased at the fixed forward bias voltage. In order to understand the reason, we performed electrostatic force microscopy (EFM) and measured I-V curves at different temperatrues. The time variation of the charge density at the Al/pentacene interface was confirmed from the EFM measurement of the cross-section of Al/pentacene/Au. Our results suggest that hole charges accumulate at the Al/Pentacene interface and thus the current increased due to the lowered potential barrier caused by the trapped charges. From the temperature-dependent I-V data, we could estimate the amount of barrier lowering.
9:00 PM - UU5.2
Growth Model and Nanostructure of a-SiC:H Thin Film Analyzed by In Situ Real-time Infrared Reflection Spectroscopy.
Mitsuya Motohashi 1 , Fumitaka Shimizu 1 , Hideki Nakada 1 , Morishige Yoneda 2 , Masaaki Niwa 1 , Kazuaki Homma 1
1 Engineering, Tokyo Denki University, Tokyo Japan, 2 , Denshi Gakuin Japan Electronics College, Tokyo Japan
Show AbstractHydrogenated amorphous silicon carbide (a-SiC:H) thin films are considered to be useful for the fabrication of quantum-effect and optoelectronic devices. However, so far, the optical properties of nano-ordered a-SiC:H thin films have not been discussed in sufficient detail. Therefore, it has not been possible to control and tailor the physical and chemical properties of the thin films and their surface. In this study, we aimed to clarify the nanostructure of an a-SiC:H thin film in a multilayer film and the growth mechanism of the thin film. The atomic bonding configuration of a film being grown is discussed on the basis of observations obtained by in situ real-time infrared reflection spectroscopy (IR-RAS). The absorption spectra of the C-Si-H stretching mode in the wave number range 2000~2200 cm–1 were measured. Further, the surface morphology of the film was characterized by atomic force microscopy. RF glow discharge plasma was used to prepare a-SiC:H multilayer films. SiH4 and CH4 gases were used as starting materials. The layers in the a-SiC:H multilayer were deposited at various substrate temperatures and gas flow rate ratios; the gas flow rate ratio is given as γ = {CH4/(SiH4 + CH4)}. The substrate temperature was 150~250°C, and the substrate was an aluminum plate. The thickness of each layer in the multilayer was 10~50 nm. The multilayer had two or more layers. In general, the integrated absorption intensity of an a-SiC:H bulk film increased with γ. On the other hand, one of the upper layers (thin film) decreased with an increase in the γ value of a lower layer. When the substrate temperature of the upper layer decreased, the integrated absorption intensity increased. The peak wave number of IR-RAS spectra of the upper layer decreased with an increase in the γ value of the lower layer and with an increase in the substrate temperature of the upper layer. The surface roughness of the upper layer increased the γ value of the lower layer. The above results might be a consequence of the absorption phenomena of the radical in the plasma being strongly dependent on the surface atomic bonding configuration. These results indicate that we should select appropriate film-growth conditions in consideration for this surface configuration. Finally, on the basis of the above results, a growth model for an a-SiC:H thin-film is discussed. This work was partly supported by the Research Institute for Science and Technology, Tokyo Denki University, under grant Q09-06.
9:00 PM - UU5.3
In situ Growth Stresses During the A1 to L10 Chemical Ordering Reaction in Fe(Cu)Pt Thin Films.
Ross Hinson 1 , Gregory Thompson 1
1 Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractL10 FePt is a candidate material for ultrahigh magnetic recording. Considerable interest has developed in the use of ternary additions in FePt that could alter the disorder-order temperature and control the microstructure. To date, little work has been done to quantify the intrinsic stress evolution that accompanies either the ordering phase transformation or microstructure evolution. The effect of Cu on the in situ growth stresses and chemical ordering reaction in Fe45Cu5Pt50 and Fe38Cu12Pt50 thin films has been studied. The films were deposited at ambient temperature and at temperatures between 200 to 500 deg. C. in increments of 75 deg. C. During deposition the stress was quantified using an in situ wafer curvature technique. The films’ phase and microstructure were characterized by TEM and XRD. As the Cu content increased, a suppression of chemical order during growth was observed, which, in general, is opposite to previous ex situ annealing studies. During the initial stages of thin film growth, where films undergo compressive-tensile-compressive behavior, the magnitude of the tensile stress stage increased with increasing temperature. The post-tensile compressive growth regime exhibited a reduction in the compressive stress magnitude with increasing temperature. This suggests limited adatom mobility. The stress evolution is discussed in terms of the degree of order and grain size and their relationship to adatom mobility during the chemical ordering reaction.
9:00 PM - UU5.4
In situ PFM Characterization of Ferroelectric Thin Films.
Brian Smith 1 2 3 , Dave Blank 1 , Guus Rijnders 1 , Andre ten Elshof 1 , Gertjan Koster 1
1 Inorganic Materials Science, University of Twente, Enschede, Overijssel, Netherlands, 2 , Materials Innovation Institute, Eindhoven, Noord-Brabant, Netherlands, 3 , Foundation for Fundamental Research on Matter, Utrecht, Utrecht, Netherlands
Show AbstractPiezoresponce force microscopy (PFM) is a popular technique for the characterization of ferroelectric thin films due the ability of this technique to study ferroelectric properties on the nanoscale [1]. In most cases, PFM characterization of ferroelectric thin films occurs on ex situ PFM systems. Here we report on the in situ characterization of ferroelectric thin films. An Omicron UHV STM/AFM has been equipped for PFM measurements by running the appropriate signals from the cantilever through two external lock-in amplifiers enabling out of plane and in-plane PFM at pressures of 1x10-11mbarr. The PFM is connected to a TSST pulsed laser deposition (PLD) chamber allowing PLD grown ferroelectric thin films to be transferred to the PFM without breaking UHV and exposing the films to atmosphere. In addition, in-situ XPS and XPD characterization of the ferroelectric thin films is also possible, providing complimentary information on the films’ chemical make-up and crystal structure. The combination of in situ PLD, PFM and XPS/XPD provides a powerful tool to study ferroelectric materials of nanosize dimensions.Characterization of ferroelectric thin films before and after exposure to atmosphere provides information on the effect atmosphere has on the films. Also, controlled exposure of the samples to different gases followed by PFM can help determine the origin of any changes that occur in the film when exposed to the atmosphere. Knowing the differences between in situ and ex situ PFM characterization is used to determine the intrinsic effects of ferroelectric films with different thickness grown on varying electrodes and substrates.This research was carried out under the project number M62.2.08SDMP24in the framework of the Research Program of the Materials Innovation Institute, M2i (www.m2i.nl), and the Foundation for Fundamental Research on Matter, FOM (www.fom.nl)[1] S. V. Kalinin and D. A. Bonnell, Phys. Rev. B 65, 125408 (2002)
9:00 PM - UU5.5
Initial Stages of Pt Growth on TiO2-terminated SrTiO3(100) Surface.
Hosung Seo 1 , Agham Posadas 1 , Miri Choi 1 , Rytis Dargis 1 , Jisun Kim 1 , Chih-Kang Shih 1 , Alexander Demkov 1
1 Department of Physics, The University of Texas at Austin, Austin, Texas, United States
Show AbstractIntegration of functional perovskite oxides into electronic devices requires a stable electrode. Pt is a widely studied electrode material due to its chemical inertness and stability in an oxidizing environment [1]. However, the epitaxy of (100)-oriented Pt films even on a nearly lattice matched oxide surface, such as SrTiO3(100) is challenging [2]. Pt tends to grow on oxides as 3D islands (Volmer-Weber growth mode) due to strong Pt-Pt interaction and high surface energy of Pt(100) [3]. Moreover, atomic-level understanding of Pt growth on SrTiO3(100) is lacking. In this work, we study theoretically and experimentally the initial stages of Pt growth on TiO2-terminated SrTiO3(100). We use density functional theory to calculate the potential energy surface for the motion of adsorbed Pt. We find at the 1/8-monolayer (ML) coverage that the unreconstructed (1x1) surface transforms into a (2x2) structure, in which the Pt atom is captured at the hollow site surrounded by 4 oxygen atoms. We show that the formation of the (2x2) structure is driven by strong bonding interaction between Pt d-states and surface oxygen p-states. The energy barrier to the nearest local minimum oxygen site is calculated to be 2.1 eV. Bringing additional Pt atoms to the surface, we show that this (2x2) structure is stable at the 1/4-ML Pt coverage. However, the (2x2) structure becomes unstable and vanishes at the 1ML coverage. Experimentally, we use commercially available TiO2-terminated single crystal SrTiO3(100) substrates. They are prepared to obtain a clean, unreconstructed surface. Pt metal is evaporated using an electron beam evaporator and deposited at room temperature. The Pt flux is adjusted to a very low value of 0.08 ML per minute (~1x1012 Pt atoms cm-2 s-1). The deposition is characterized by in situ reflection high energy electron diffraction (RHEED) with a total deposition time equivalent to 1 ML (2 Å). RHEED shows a 2x reconstruction spot along the [010] azimuth appearing for coverages between 1/4 and 3/8 monolayer, confirming the double periodicity predicted by the calculation. Pt deposition at high fluxes and high temperatures do not show the 2x reconstruction spot. Scanning tunneling microscopy measurements of the Pt sub-monolayer structure will also be discussed.[1] Q. Fu and T. Wagner, Surf. Sci. Rep. 62, 431 (2007)[2] A. J. Francis, Y. Cao and P. A. Salvador, Thin Solid Films 496, 317 (2006)[3] L. Vitos, A. V. Ruban, H. L. Skriver, J. Kollár, Surf. Sci. 41, 186 (1998)
9:00 PM - UU5.6
Time-Resolved Cathodoluminescence Complements Electron Microscopy for Analysis of Photovoltaic and Semiconductor Devices.
Linda Casson 1 , Jean-Luc Domanchin 2 , Didier Hocrelle 2 , Daniel Meyer 1 , Eric Teboul 1
1 , HORIBA Scientific, Edison, New Jersey, United States, 2 , HORIBA Jobin Yvon S.A.S., Chilly-Mazarin France
Show AbstractElectron microscopy, along with many other surface science and analytical techniques, offers an array of complementary sub-techniques that provide additional information to enhance the primary analysis or imaging mode. Most electron microscopes are built with several additional ports for the installation of complementary analysis modules. One type of analysis which is particular useful in characterizing photovoltaic materials, semiconductors and geological samples is cathodoluminescence (CL), both time-resolved and steady-state.As a consequence, HORIBA Scientific has developed a new modular accessory called the Cathodoluminescence Universal Extension (CLUE) module to allow multiple complementary optical measurements compatible with most standard commercial scanning electron microscopes. Among the optical measurements accessible using the CLUE, are CL, Raman and PL spectroscopy and imaging. In this paper, we will focus on comparing results obtained with steady-state and time-resolved cathodoluminescence to characterize photovoltaic and semiconductor devices. Emphasize will be made on the complementary level of information extracted from these two techniques.
9:00 PM - UU5.7
Grazing Incidence X-ray Scattering Measurements of Real-time Structural Evolution of Polyhexylthiophene Nano-gratings.
Xinhui Lu 1 , Htay Hlaing 1 2 , Benjamin Ocko 1
1 Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York, United States, 2 Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York, United States
Show AbstractThe performance of organic electronic devices typically depends on the structure and morphology of conductive polymeric materials and these in turn are sensitive to the processing parameters such as solvent and thermal treatments and confinement effects. In order to understand the real-time evolution of the structural and morphological changes with these parameters, Grazing-Incidence Small-Angle and Wide-Angle X-ray Scattering (GISAXS and GIWAXS) have been employed to probe the surface and interfacial structures as well as molecular-level structures. These techniques are sensitive to both the surface and sub-surface structure of the film. Here report investigations of the change of Polyhexylthiophene (P3HT) nano-gratings, prepared using a stamp with a 100 nm pitch, as a function of annealing temperature by synchrotron GISAXS and GIWAXS. The scattering results show that the initially stamped polymer reproduces most of the features of the stamp. With increasing temperature, the polymer grating pattern smoothes out and there is a corresponding rearrangement of P3HT lamellar structure. Results for stamped P3HT/PCBM films will also be presented.
9:00 PM - UU5.8
Surface Reactions of Molydisulphide in Aqueous Environments.
Christine Orme 1
1 , LLNL, Livermore, California, United States
Show AbstractMolybdenum disulphide (MoS2) is of current interest as a catalyst in petroleum refining due to its high reactivity and resistance to sulfur poisoning. For this reason, there is a desire to more fully understand impurity interactions at surface atomic steps to improve its efficiency, particularly in the presence of Ni and Co atoms, which act as promoters to enhance catalytic activity. In addition there is a need to understand surface modifications in fluids that can mimic catalytic environments. The goal of this work is to quantify surface interactions due to additives and to develop ligands or additives that alter the crystal shape to create a higher percentage of catalytic sites. In this work we describe the use of in situ atomic force microscopy to investigate the evolution of MoS2 surface structure morphology in a range of acidic and alkaline fluid environments. Interestingly, MoS2 is photocatalytic. For this reason, although MoS2 is normally insoluble in mild solutions (Ksp=10-65), the presence of light initiates surface reactions causing it to dissolve even in water. In this work we examine dissolution and subsequent oxide precipitation caused by both chemical and photocatalytic effects. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
9:00 PM - UU5.9
Virtual Substrate: A New Template for Dislocation-free Epitaxial Growth.
Marina Leite 1 , Emily Warmann 1 , Dennis Callahan 1 , Harry Atwater 1
1 , CALTECH, Pasadena, California, United States
Show AbstractThe restricted number of substrates available in bulk form significantly limits the versatility of epitaxial growth. We demonstrate the realization of a “virtual substrate” consisting of 2 inch diameter dislocation-free fully relaxed single crystalline layer, which can be used as a template for material growth. By transferring strained ultrathin III-V semiconductor films from their original substrates to a handling support, full strain relaxation occurs and the material unit cell assumes its bulk value ax. This concept can be expanded to several semiconductors families and ceramics. For the successful fabrication of this new template, 40 - 80 nm thick dislocation-free coherently-strained III-V semiconductor films are grown on a substrate, e. g. InxGa1-xAs on InP or InxGa1-xP on GaAs using AlAs as a sacrificial layer for substrate reuse. A thermoplastic wax support is used to coat the epitaxial film [1]. Once the film is relieved from the substrate by a selective chemical etch it relaxes. The crystalline film, independent of the alloy composition, is always compressed with respect to the wax because of the difference between the thermal expansion coefficient of these two materials (~ 10-6 vs. 6.2 × 10-4 oC-1, respectively). Thus, it is stable against crack formation. The film is then bonded to a handle cheap substrate, e. g. SiO2/Si. X-ray diffraction measurements were used to quantify the virtual substrate relaxation and reconstruct its unit cell. For an In0.43Ga0.57As alloy initially strained by + 0.70 % (aInP = a// = 5.8686 Å, a⊥ = 5.78786 Å), full relaxation was accomplished after film transfer to a SiO2/Si handle substrate. Reciprocal space maps along the asymmetric (2 2 4) reflection showed that a⊥ = 5.82791 Å and a// = 5.82602 Å, matching ax = 5.8275 Å, as predicted by Vegard’s Law and in agreement with simulation. The final in-plane strain was ε// = - 0.03 ± 0.05 % and relaxation equal to 103 ± 5 %. Full relaxation was also achieved for InxGa1-xAs films with compressive and different tensile strain values and their unit cells are in agreement with Vegard’s Law prediction [2]. The creation of a dislocation-free virtual substrate has the potential for new crystalline material designs for technologies such as solar cells. The characteristics of epitaxial films grown on virtual substrates, as well as its mechanical properties will be reported in detail. [1] E. Yablonovitch et al., Appl. Phys. Lett. 51, 2222 (1987).[2] M. S. Leite et al., Submitted.
Symposium Organizers
Gertjan Koster University of Twente
Gyula Eres Oak Ridge National Laboratory
Fabio Miletto Granozio Complesso Universitario di Monte St. Angelo
Chang-Beom Eom University of Wisconsin-Madison
Nicholas Ingle University of British Columbia
UU6: Diffraction Techniques III
Session Chairs
Wednesday AM, December 01, 2010
Hampton (Sheraton)
9:30 AM - **UU6.1
Real-time X-Ray Studies of (In,Ga)N Growth by MOCVD.
Brian Stephenson 1 , M. Richard 2 1 , F. Jiang 1 , M. Highland 1 , T. Fister 1 , Carol Thompson 3 , S. Streiffer 1 , P. Fuoss 1 , K. Elder 4 , J. Mei 5 , A. Munkholm 5
1 , Argonne National Laboratory, Argonne, Illinois, United States, 2 , Université Paul Cézanne Aix-Marseille, Marseille France, 3 , Northern Illinois University, DeKalb, Illinois, United States, 4 , Oakland University, Rochester, Michigan, United States, 5 , Philips Lumileds Lighting Co., San Jose, California, United States
Show AbstractIn-situ, time-resolved x-ray techniques can provide unique insight into the atomic-scale mechanisms occurring during materials synthesis and processing. In this talk we discuss studies of metal-organic chemical vapor deposition (MOCVD) of (In,Ga)N thin films. While high In content is desirable for several applications, InN has a 10% lattice mismatch with the GaN substrate, and is metastable at ambient pressure, requiring a chemically active nitrogen species for growth. Using x-ray scattering and fluorescence, we have studied the coupled strain and composition changes that occur during (In,Ga)N film growth and relaxation. During InN growth, we observe that self-sustaining oscillations in phase stability can occur: islands of relaxed InN nucleate and grow; the InN islands collectively transform into elemental In droplets; the liquid In evaporates; and then another cycle of InN growth begins. These observations indicate key synthesis mechanisms for these metastable materials. Work supported by DOE under contract DE-AC02-06CH11357.
10:00 AM - UU6.2
X-Ray Study of Strained and Strain Balanced Superlattice Materials.
Natee Johnson 1 , Ruth Choa 3 , Liwei Cheng 2 , Fow-Sen Choa 2
1 Mechanical Engineering, University of Maryland, Baltimore County, Baltimore, Maryland, United States, 3 School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, United States, 2 Computer Science and Electrical Engineering, University of Maryland, Baltimore County, Baltimore, Maryland, United States
Show AbstractNano-scale supperlattice (SL) based devices, such as quantum cascade lasers QCLs, have recently become very important due to their capability to identify toxic and explosive chemicals. In manufacturing these Mid-IR photonic devices, atomic-level scanning tunneling microscopes (STM) and transmission electron microscopes (TEM) have been used to characterize the growth quality of superlattice wafers. However, these methods yield observations that are localized and cannot view the entire structure and even now we have not been able to correlate these measured crystal lattice images with device performance. The x-ray scanning technique has greater likelihood of success given that it can observe not only the localized, but also the entire superlattice structure. By extracting special features and key parameters in x-ray diffraction (XRD) patterns, the epitaxial quality of QCL superlattices can be evaluated and correlated to the performance of fabricated QCL devices. We can then differentiate and classify different grades of wafers before starting device fabrication and testing. Such an example of the usefulness of XRD can be found with strain-balanced superlattices, such as InGaAs/InAlAs, where there is notable decrease in laser performance after relaxation. It can also be found with type-II InAs/GaSb strained layer superlattice, which is currently the best candidate for room temperature mid-IR detectors and focal plane arrays. Since strain-balanced superlattices are composed of alternating compressive and tensile strained layers, the thicker layers are sometimes strained too much and lattice relaxation occurs - chemical bonds between atoms break and lead to serious degradation of periodicity. A very small percentage of relaxation can lead to a dramatic broadening of satellite peaks and a serious decrease in laser performance. Through simulations, relaxations in InGaAs and InAlAs layers were found to show distinct patterns, which helps in determining which exact materials are causing the problems in a superlattice. Experimentally measured x-ray patterns are compared to simulation results and problem sources are identified.
10:15 AM - UU6.3
Dynamics of Intermetallic Phase Evolution in Thin Layer Metal Films for Low-temperature Isothermal Diffusion Soldering.
Harald Etschmaier 1 2 , Jiri Novak 2 , Hannes Eder 1 , Peter Hadley 2
1 Unit Process Development, Infineon Technolgies Austria AG, Villach Austria, 2 Institute of Solid State Physics, University of Technology, Graz Austria
Show AbstractIsothermal diffusion soldering (IDS) is a promising method for forming mechanically and thermally stable, Pb-free bonds in semiconductor device packaging. It combines the good joint filling and tolerance to surface roughness of conventional soldering with better control of joint thickness and reduced thermal expansion mismatch stress than is obtained with diffusion bonding. For diffusion soldering, a thin layer (1µm) of a low melting component (Sn, SnAg, AuSn) is sandwiched between the high melting joint components (Cu). Upon heating to the bonding temperature, at first the low melting temperature component is liquefied. It quickly reacts with the high melting temperature component to form an intermetallic phase with a melting point substantially higher than the bonding temperature. This way, highly stable joints are achieved under relatively mild process conditions. The intermetallic phase formation in IDS has so far only been studied ex situ, mainly by optical microscopy, scanning electron microscopy, energy dispersive X-ray analysis, and transmission electron microcopy of joint cross-sections or X-ray diffraction of fractured joints. The drawback of these methods is that they can only give insight in the composition of the quenched sample, and the intermetallic phase evolution at process temperature cannot be observed directly. This is a limitation because certain intermetallic phases that appear during soldering only exist at elevated temperatures. Furthermore the investigated volume of these methods is very small and hardly representative for the whole sample. Therefore an in situ analysis of a macroscopic volume is necessary to trace the course of the reaction. In this contribution we report on the dynamics of the phase evolution in electrochemically deposited Sn, SnAg and AuSn thin films on copper coated substrates studied by in-situ X-ray diffraction and Focused Ion Beam Microscopy A focused ion beam microscope is used instead of a electron microscope because of its superior phase contrast. The data is used to extract the activation energy of the reaction with relatively high precision. Preliminary results indicate that the formation of intermetallic phases in these thin layers, in which the grain size exceeds the layer thickness, is limited not by diffusion but rather by reaction kinetics.
10:30 AM - UU6.4
Discovering the Mechanisms of BaFe12O19/MgO/Silicon Carbide Epitaxy: A Case Study of Using Reflection High Energy Electron Diffraction – Total Reflection Angle X-ray Spectroscopy (RHEED-TRAXS).
Bing Sun 1 , Zhuhua Cai 2 , Katherine Ziemer 1
1 Chemical Engineering, Northeastern University, Boston, Massachusetts, United States, 2 , MIT, Boston, Massachusetts, United States
Show AbstractThin film heterostructures of functional oxides (e.g. magnetostrictive, ferroelectric) integrated on semiconductor platforms can enable tuned coupling between the oxide layers for the development of next-generation multifunctional electronic devices. Multi-element oxides exhibit measurably different functional properties with structure changes or stoichiometry changes of less than one percent. The goal of fabricating multifunctional heterostructures by Molecular Beam Epitaxy (MBE) is to take advantage of this sensitivity to tune properties by controlling the stoichiometry and structure of each layer and the interfaces. While the use of Reflection High Energy Electron Diffraction (RHEED) is well established for real-time structure monitoring of thin films in MBE, there is a need for real time stoichiometry monitoring and control when growing these mulit-element oxides where the same structure could still mean a different stoichiometry. RHEED - TRAXS can potentially provide real-time monitoring of elemental composition and thus assist the study of growth mechanisms and achieve better control of the MBE process. Incident RHEED electrons in the range of 12-20 keV interact with the sample surface to emitt x-ray photons characteristic of the surface atoms. The x-ray intensity is proportional to the composition and thickness of the film, and exhibits a strong angular dependence at near critical-angle conditions. By using a geometry that measures these x-rays at the total reflection angle, RHEED-TRAXS was reported to probe the top 2 to 3 nm of material, thus probing the surface chemistry of growing layers. Absolute x-ray intensity changes were followed using RHEED-TRAXS during MgO deposition on 6H-SiC and BaFe12O19 deposition on MgO//SiC. It has been observed that with the increasing thickness of the deposited MgO layer, the absolute intensity of Mg Kα x-ray increases in the RHEED-TRAXS spectra. As the MgO film once nucleated will not be subject to stoichiometry changes, the increase in absolute Mg intensity (and accompanying substrate Si signal attenuation) is attributed to increased film thickness. Based on x-ray total external reflection and Beer-Lambert’s law, a model was built to approximate film thickness with Si RHEED-TRAXS signal attenuation before and after the deposited MgO layers. Even with this simplified approach to modeling, a useful match between the prediction and experimental data was observed for thicknesses ranging from 2 to 10 nm. In addition, the rate at which the Mg Kα intensity increases with time, suggests two different growth modes during deposition. Monitoring the Ba and Fe x-ray intensities during MBE of BaFe12O19 support the hypothesis of Fe3O4 formation prior to BaFe12O19. Preliminary studies point out some of the difficulties with quantification of this technique, and suggest the usefulness of RHEED-TRAX for real-time stoichiometry monitoring during MBE.
10:45 AM - UU6.5
Real-time Study of Ion Irradiated Silicon Surfaces using Grazing Incidence Small Angle X-Ray Scattering.
Eitan Anzenberg 1 , Charbel Madi 2 , Mike Aziz 2 , Karl Ludwig 1
1 Physics, Boston University, Boston, Massachusetts, United States, 2 Physics, Harvard University, Boston, Massachusetts, United States
Show AbstractNano-structuring of surfaces with ion bombardment yields a rich phase-space of topography. Our facility at the National Synchrotron Light Source (NSLS) allows for real-time characterization of surfaces during such processes using Grazing Incidence Small Angle X-Ray Scattering (GISAXS). We use this technique to measure in reciprocal space the real-time formation and smoothening kinetics of correlated structures on the surface, effectively measuring the evolution of the height-height correlation function S(q). A linear model is used to characterize the early time kinetic evolution during ion bombardment as a function of incidence angle. We study the topographic transition from surface smoothening at low ion incidence angles to instability at high angle incidence for both perpendicular and parallel geometries for 1 KeV Ar+ irradiated Silicon. We find that mass-redistribution on the surface is the dominant kinetic process determining surface morphology, rather than sputter erosion. A linear model including the effect of mass-redistribution explains both the case for surface smoothening at low and instability at high bombardment angle.
UU7: Growth Modeling
Session Chairs
Wednesday PM, December 01, 2010
Hampton (Sheraton)
2:30 PM - UU7.1
Step-bunching-induced Vertical Lattice Mismatch and Crystallographic Tilt in Vicinal BiFeO3(001) Films.
Tae Heon Kim 1 , Seung Hyub Baek 2 , Seung Yup Jang 1 , Sang Mo Yang 1 , Seo Hyoung Chang 1 , Tae Kwon Song 3 , Jong-Gul Yoon 4 , Chang Beom Eom 2 , Jin-Seok Chung 5 , Tae Won Noh 1
1 ReCFI, Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States, 3 School of Nano and Advanced Materials Engineering, Changwon National University, Changwon Korea (the Republic of), 4 Department oh Physics, University of Suwon, Hwaseong Korea (the Republic of), 5 Department of Physics, Soongsil University, Seoul Korea (the Republic of)
Show AbstractHeteroepitaxy through substrate’s vicinality in thin films is of great importance for application to nano-scale devices with high performance. Recently, there were some reports on the improvement of device functionality in epitaxial thin films through substrate’s vicinality. Jang et al. reported that anisotropic strain in vicinal substrates can be utilized to simplify complicated ferroelectric domain structures in BiFeO3 (BFO)(001) films.[1] And, this technique of domain engineering results in increase of remnant polarization and decrease of leakage current. Also, we visualized that the direction of sideways domain wall motion in vicinal BFO(001) films is controlled by the polarity of external electric bias.[2] And, we found that a strain gradient in vicinal BFO(001) films induces the directional motion of ferroelectric domains. However, detailed mechanism on how the vicinality in the epitaxial films influences on their whole crystallographic structure has not been clarified yet.Step bunching process plays a significant role in the growth of vicinal epitaxial films. On a vicinal surface under stress, elastic relaxation at steps produces a long-range attractive interaction between the steps.[3] Energetically, the attractive interaction enables the steps to be bunched in out-of-plane as well as in-plane directions during progressive film growth. Terosoff et al. reported that as the distance between steps increases, the bunching rate decreases, being proportional to the inverse third power of the average step separation. It is highly likely that the variation of the step bunching rate critically affects the ultimate surface morphology in vicinal epitaxial films. Experimentally, there has been little report on how the bunching rate evolves the surface morphology in vicinal epitaxial films. In this presentation, we will show step-bunching-induced vertical lattice mismatch in vicinal BFO(001) films. By extending simple Nagai model, we will elucidate that the vertical lattice mismatch between m BFO layers and (m + 1) BFO sublayer at bunched step edges is responsible for crystallographic tilt in vicinal BFO(001) films. By analyzing the crystallographic tilt angles in vicinal BFO(001) films with different thickness, we investigated the variation of the corresponding bunching rate. Finally, we will make clear the relationship between the bunching rate and the thickness-dependent crystallographic tilt, by displaying number of bunched BFO layers m in terms of the terrace width at top surface.[1] H. W. Jang et al., Adv. Mater. 21, 817 (2009)[2] T. H. Kim et al., Appl. Phys. Lett. 95, 262902 (2009)[3] J. Tersoff et al., Phys. Rev. Lett. 75, 2730 (1995)
UU8/C8: Joint Session: Optical Probes
Session Chairs
Lorenzo Marucci
Mark Rummeli
Wednesday PM, December 01, 2010
Room 304 (Hynes)
2:30 PM - UU8.1/C8.1
A Fully Automated Remote Controllable Microwave-based Synthesis Setup for Colloidal Nanoparticles with an Integrated Absorption and Photoluminescence Online Analytics.
Michael Krueger 1 2 , Simon Einwaechter 1 2
1 Freiburg Materials Research Centre (FMF), University of Freiburg, Freiburg Germany, 2 Institute for Microsystems Technology, University of Freiburg, Freiburg Germany
Show AbstractWe present a fully automated microwave-based synthesis setup for colloidal nanoparticles. An integrated absorption and photoluminescence online analytics opens the possibility to monitor the growth of various nanoparticles at any stage of the reaction. Spectroscopic investigation within the first seconds of a reaction is accessible opening the possibility to detect potential critical size nuclei as a function of the reaction conditions. Beside the possibility to perform systematic mechanistic studies, this system allows a high degree of synthesis control leading to a very good product reproducibility. In conjunction with an automated autosampler unit systematic multiple reactions can be performed one after each other and compared. The setup is intended to be remote-controllable allowing worldwide online control accessibility over the synthesis setup including data processing, visualisation and storage. The performance of the setup will be demonstrated by using the synthesis of CdSe nanocrystals as a model system and will be extended to the synthesis of various metallic and semiconducting nanoparticles.
UU7: Growth Modeling
Session Chairs
Wednesday PM, December 01, 2010
Hampton (Sheraton)
2:45 PM - UU7.2
Role of Diffusion on the Epitaxial Growth of Cu2O Islands on the Cu (100) Surface.
Sangeun Jee 1 , Minyoung Lee 2 , Alan J.H. McGaughey 2 , Judith Yang 1
1 Department of Chemical and Petroleum Engineering, university of pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractIn the oxidation of a Cu(100) surface, Cu2O islands nucleate on the missing-row reconstructed surface, grow, and eventually coalesce into a continuous thin film. However, little is known about the mechanisms by which the islands nucleate. In this study, we use density functional theory (DFT) calculations and kinetic Monte Carlo (KMC) simulations to study the diffusion of oxygen atoms on and into the missing row reconstructed Cu(100) surface, which we believe to be a key step in the island nucleation process. The missing row reconstruction happens when the oxygen coverage reaches 0.5 monolayers through the release of every fourth row of copper atoms from the top copper layer. Using DFT calculations, we find that the energy barrier for atomic oxygen embedment into the subsurface through the missing-row is smaller than that of on-surface oxygen diffusion, suggesting a mechanism for the formation of sub-surface oxygen structures that is consistent with a recent scanning tunneling microscopy (STM) experiment by Lampimaki et al. of the initial surface changes of Cu(001) when exposed to O2. The energy barrier for sub-surface oxygen diffusion is predicted to be less than that for on-surface diffusion, suggesting that the diffusion of oxygen atoms through the subsurface is energetically favorable. Using the DFT-predicted energy barriers, we then model the diffusion of a collection of oxygen atoms in the reconstructed structure using the KMC method. The diffusion of oxygen atoms on the surface as well as in the sub-surface region are studied to examine their role in the initial Cu2O formation. The effect of the oxygen diffusion on the stability of Cu2O islands is studied at various oxygen pressures and temperatures. Once Cu2O islands are formed, the copper mobility is greater as compared to the clean Cu surface. Role of the diffusion of copper and oxygen atoms on the growth of Cu2O islands is examined at various temperatures using the KMC method. Our long term goal is to develop and use multi-scale simulation to directly correspond with in situ STM and transmission electron microscopy (TEM) experiments of early stages of Cu(001) oxidation.
UU8/C8: Joint Session: Optical Probes
Session Chairs
Lorenzo Marucci
Mark Rummeli
Wednesday PM, December 01, 2010
Room 304 (Hynes)
2:45 PM - UU8.2/C8.2
Direct Measurements of Exciton Mobility in Single-walled Carbon Nanotubes Using Far-field Near-infrared Fluorescence Microscopy.
Dmitri Tsyboulski 1 , R. Bruce Weisman 1 , Anton Naumov 1
1 Chemistry, Rice Universtiy, Houston, Texas, United States
Show Abstract The discovered effect of stepwise quenching of photoluminescence (PL) signal from semiconducting single-walled carbon nanotubes (SWCNTs) by single molecule reactions suggested extensive mobility of excitons in these one-dimensional structures. The mobility of excitons can be assessed by measuring a change of SWCNT PL intensity ΔI after the single-molecule quenching event relative to its total PL intensity value I, normalized per unit of SWCNT length L. Thus, the average exciton mobility Λ will be given simply as Λ=L*ΔI/I. Using this method, the range of exciton mobility as high as 240 nm was reported for selected SWCNT structures. This measurement of Λ parameter is valid under assumption that reaction events quench excitons in the vicinity of a defect with a 100% probability. We note, that this underlying assumption has never been verified. In this report, we demonstrate a new method to directly measure exciton mobility with far-field near-infrared fluorescence microscopy. Within a framework of exciton diffusion model, the exciton quenching profile along the nanotube is given as exp(-|x|/Λ), where x is the distance from the defect location. The later function decays slower that the corresponding point spread function (PSF) of an optical system ~ exp(-x2). Hence, it is possible to partially resolve fluorescence quenching profile along SWCNT length. Indeed, when we compute differential images of SWCNTs before and after quenching reaction events, the asymmetric quenching profiles with aspect ratio ~ 2-3 become apparent. The measured profiles are numerically fitted with convolution of PSF and exp(-|x|/Λ) function to determine Λ values for a particular nanotube structure. The measured variations of exciton mobility for a range of SWCNT structures well be presented and discussed.
UU7: Growth Modeling
Session Chairs
Wednesday PM, December 01, 2010
Hampton (Sheraton)
3:00 PM - UU7.3
Influence of Grain Boundary Chemistries in Mix-mobility Thin Film Growth.
Bianzhu Fu 1 , Wei An 2 , Heath Turner 2 , Gregory Thompson 1
1 Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, Alabama, United States, 2 Department of Chemical & Biological Engineering, The University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractThin films exhibit compressive-tensile-compressive stress states during the nucleation of islands, coalescence of islands and post-coalescence stages of growth. Using an in situ wafer curvature measurement technique, the stress evolution in Fe-Pt alloy thin films has been investigated. The stresses were shown to be compositionally dependent. In general, the tensile or compressive stress for the various binary compositions was associated with whichever element enriched the grain boundaries. Under specific growth conditions, a ‘zero-stress’ state could be achieved. The as-deposited alloy stress states do not show significant stress recovery upon ceasing the deposition. Upon annealing, the magnitude of the compressive stress state is reduced with increase in order parameter and is explained in terms of reduced adatom surface migration. Density functional theory calculations were performed to quantify the possible diffusion pathways and binding energies for Fe and Pt on a {111} L10 surface. Upon ceasing deposition, the post-growth stress relaxation rate increased with order parameter and is explained in terms of an increase in interfacial energy contribution at the grain boundaries formed by chemically ordered grains. XRD, TEM, and atom probe tomography have been employed to quantify the phase, grain size and grain boundary chemistries, respectively, as they relate to the preferential segregation and thin film stress measurements.
UU8/C8: Joint Session: Optical Probes
Session Chairs
Lorenzo Marucci
Mark Rummeli
Wednesday PM, December 01, 2010
Room 304 (Hynes)
3:00 PM - **UU8.3/C8.3
Laser Interactions and Real-Time Diagnostics in Nanomaterial Synthesis.
David Geohegan 2 3 , Christopher Rouleau 2 3 , Gyula Eres 3 , Mina Yoon 3 , Murari Regmi 3 , Jeremy Jackson 3 , Junsoo Shin 3 , Amit Goyal 3 , Karren More 1 2 , Norbert Thonnard 3 , Jason Readle 3 2 , Gerd Duscher 4 2
2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 1 SHaRE Facility, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Dept. of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractLaser interactions with materials are explored for the growth of novel nanomaterials, both as sources of energy to provide unique, nonequilibrium synthesis conditions and also as spectroscopic probes for real-time diagnostics of the growth environment. Time-resolved, in situ spectroscopy and imaging techniques are described to investigate processes involved in thin film and nanomaterials synthesis through the remote characterization of species concentrations, the measurement of growth kinetics, and the development of growth models. Progress in the design of pulsed laser and pulsed gas-growth environments to explore the synthesis of novel nanomaterials such as carbon nanohorns, graphene, and vertically-aligned carbon nanotube arrays as well as functional oxide nanoparticles and nanowires will be described. Variations in the synthesized product distribution of nanostructures are shown to result from the competition between kinetic and thermodynamic pathways. Examples of laser-synthesized nanomaterials designed for enhanced functionality in energy applications of hydrogen storage and optoelectronics will be presented. This work supported by the U.S. Dept. of Energy, Office of Science, Basic Energy Sciences. Fundamental studies of synthesis are supported by the Division of Materials Sciences and Engineering, with materials characterization support from the Division of Scientific User Facilities. Hydrogen storage measurements provided through the Hydrogen Sorption Center of Excellence, U.S. DOE-EERE.
UU7: Growth Modeling
Session Chairs
Wednesday PM, December 01, 2010
Hampton (Sheraton)
3:15 PM - UU7.4
Stochastic Models of Epitaxial Growth: Mean-field Theory and Kinetic Monte-Carlo Simulations.
Dionisios Margetis 1 2 3 , Paul Patrone 4 , Theodore Einstein 4
1 Mathematics , University of Maryland, College Park, Maryland, United States, 2 Center for Scientific Computation & Math. Modeling, University of Maryland, College Park, Maryland, United States, 3 Institute for Physical Science & Technology, University of Maryland, College Park, Maryland, United States, 4 Physics, University of Maryland, College Park, Maryland, United States
Show AbstractVicinal crystals have nanoscale terraces separated by steps of atomic size. In this talk, I will discuss recent progress in analyzing step fluctuations for various types of noise by use of mean-field theories and kinetic Monte-Carlo (kMC) simulations in one space dimension. First, I will address the case without material deposition from above, when the surface tends to relax and become flat. By introduction of an appropriate mean field for the terrace widths, the problem complexity is reduced significantly. The analytical results compare favorably with kMC simulations. Second, I will include external material deposition and demonstrate analytically the narrowing of the time-dependent terrace width distribution with the external flux. This latter result refines previous work by Hamouda, Pimpinelli and Einstein [Europhys. Lett. 88, 26005 (2009)].
UU8/C8: Joint Session: Optical Probes
Session Chairs
Lorenzo Marucci
Mark Rummeli
Wednesday PM, December 01, 2010
Room 304 (Hynes)
3:30 PM - UU8.4/C8.4
Temperature Dependence of Silver Nanoparticles Dielectric Function as Observed by in situ and Real Time Spectroscopic Ellipsometry.
Scott Little 1 , Sylvain Marsillac 1 , Robert Collins 1
1 Physics and Astronomy, University of Toledo, Toledo, Ohio, United States
Show AbstractA broadband analysis of silver nanoparticles optical properties was achieved as a function of temperature via in situ real-time spectroscopic ellipsometry (RTSE). The silver nanoparticles were deposited at room temperature by d.c. magnetron sputtering onto thermally oxidized Si (100) wafers using a high purity 2 in diameter silver target in argon. A 4 mTorr argon pressure and 10 W d.c. target power was maintained throughout the deposition process. Various deposition times were employed, varying from 30 seconds to 2 minutes. RTSE data were acquired in situ using a rotating-compensator multichannel ellipsometer spanning the photon energy range from 0.75 to 6.50 eV at an angle of incidence of 65°. The presence of nanoparticles was confirmed via the analysis of the imaginary part of the dielectric function, where no free electron behavior was observed while a particle plasmon polariton (PPP) transition as well as an interband transition were modeled by a Lorentzian oscillator and a generalized critical point oscillator, respectively. Ex situ measurements were also used to confirm the presence of nanoparticles. The temperature dependence of the dielectric function of these films was monitored in situ and in real time from room temperature up to 873 K, and back down to room temperature. A steep reduction in PPP oscillator strength and increase in PPP energy suggests an increase in void fraction which may arise due to melting of small particles and wetting of the surface, or suggests a change in the particle shape. The lifetime term of the PPP oscillator is also changing due to the temperature, in agreement with the Mayadas equation, which relates the lifetime term to the particle size. A more abrupt change in these parameters at specific temperatures, varying with particle size, suggests that the melting point of particles of average size has been reached. This lower melting temperature for the silver nanoparticles, compared to bulk material, is consistent with previous studies that demonstrate the depression of the melting point.
3:45 PM - UU8.5/C8.5
Absorption Backgrounds in Single-walled Carbon Nanotube Spectra.
Anton Naumov 1 , Saunab Ghosh 2 , Dmitri Tsyboulski 2 , R. Bruce Weisman 2
1 Applied Physics Program, Rice University, Houston, Texas, United States, 2 Chemistry, Rice University, Houston, Texas, United States
Show AbstractThe source of broad backgrounds in visible-near-IR absorption spectra of single-walled carbon nanotube (SWCNT) dispersions was explored through a series of controlled experiments. Chemical functionalization of nanotube sidewalls generates a background absorption while broadening and red-shifting resonant transitions. Extensive ultrasonic agitation can induce a similar background component that may reflect unintended chemical changes to the SWCNTs. Only minor spectral differences are seen among length-separated fractions with nanotube lengths down to ~50 nm. If present, amorphous carbon content contributes to background absorption. Samples containing many SWCNT structural species can have overlapping resonant absorption bands that lead to elevated backgrounds from spectral congestion. Nanotube aggregation broadens resonant bands and increases such congestion backgrounds. However, there is essentially no background in well-dispersed samples enriched in a specific pristine semiconducting(n,m) species. By contrast, samples enriched in metallic SWCNTs show broad absorption backgrounds that appear to be intrinsic. Knowledge of spectral background effects should enhance the value of absorption spectroscopy for analyzing the compositions and purity of SWCNT samples.
4:00 PM - UU8/C8:Optical1
BREAK
UU9: Photoelectron Spectroscopy
Session Chairs
Wednesday PM, December 01, 2010
Hampton (Sheraton)
4:30 PM - **UU9.1
In Situ X-ray Photoelectron Spectroscopy during Aluminum Oxide Atomic Layer Deposition.
Paul McIntyre 1
1 , Stanford University, Stanford, California, United States
Show AbstractAtomic layer deposition (ALD) is a film growth method that offers unprecedented control of film thickness, uniformity of deposition and low temperature processing on substrates with complex topography. As such, ALD is increasingly being used in new applications in microelectronics, photonics, MEMS and energy technologies. Because ALD occurs by a series of self-limiting surface reactions of vapor phase precursors, there is great interest in understanding the mechanisms of precursor adsorption and how they affect the structure and properties of ALD-grown films and their interfaces with technologically-relevant substrates. However, many of the in situ characterization methods employed in other film deposition methods are not practical in the ALD environment because of the relatively high pressures (~ 1 Torr) typical of ALD. In this presentation, results obtained with a differentially-pumped x-ray source and photoelectron spectrometer installed in an ALD chamber will be described. This in situ XPS system is capable of collecting data within 10’s of seconds of an ALD precursor pulse, without moving the substrate or changing its temperature. Applications of this system to studies of the early stages of ALD of alumnium oxide on Ge (100) and InGaAs (100) substrates will be reported. The variation of stoichiometry of the aluminum oxide film during the early stages of deposition using trimethyl aluminum precursor and water vapor oxidant, and the effect of precursor pulsing on substrate surface oxidation will be highlighted.
5:00 PM - UU9.2
In-situ XPS of Graphene CVD.
Robert Weatherup 1 , Bernhard Bayer 1 , Raoul Blume 2 , Carsten Baehtz 3 , Robert Schloegl 2 , Stephan Hofmann 1
1 Engineering, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom, 2 Inorganic Chemistry, Fritz-Haber-Institut, Berlin Germany, 3 , Forschungszentrum Dresden-Rossendorf, Dresden Germany
Show AbstractThe widespread exploitation of graphene is currently constrained by the lack of a low-cost method of producing high quality graphene across large areas. Chemical vapour deposition (CVD) with a hydrocarbon precursor may offer a solution to this problem, but at present the growth mechanism(s) are not well understood. We perform high-pressure X-ray photoelectron spectroscopy (XPS)[1] and in-situ X-ray diffraction (XRD) on thick (>300 nm) transition metal catalysts during hydrocarbon exposure at temperatures between ~300-700C, and during subsequent cooling. We focus on graphene nucleation and graphene domain size in relation to the catalyst grain size distribution and the C chemical potential. Time-resolved XPS allows a detailed comparison of transient states prior to graphene formation and C/metal core level signatures for CVD and bulk precipitation experiments, based on which we model the growth process.[1] Hofmann et al., J. Phys. Chem. C 113, 1648 (2009)
5:15 PM - UU9.3
Photoemission Studies of Au-GdxGa1-xN Schottky Barrier Formation.
Stephen McHale 1 , John McClory 1 , James Petrosky 1 , Peter Dowben 3 , Yaroslav Losovyj 3 4 , J. Wu 2 , A. Rivera 2 3 , A. Martinez 2 , R. Palai 2
1 Engineering Physics, Air Force Institute of Technology, Wright Patterson AFB, Ohio, United States, 3 Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States, 4 Physics, Louisiana State University, Baton Rouge, Louisiana, United States, 2 Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractTo build efficient devices, it is vital to fully understand effects of material interfaces. The benefit of direct surface barrier height measurements using photoemission is that the technique is both extremely surface sensitive and can avoid complications associated with other experimental techniques. For example, defects at the metal-semiconductor interface can lead to complications, such as an overestimate, of the surface barrier height calculation when using traditional I-V and C-V measurements. With this is mind, we have engaged in investigations of the band engineering and interface properties of RExGa1-xN semiconductors (RE = rare earth) with Au metal overlayer deposition under UHV conditions.Rare-earth elements play an important role in many functional materials and exhibit interesting magnetic andelectronic properties. GaN (Eg ≈ 3.45 eV at 300 K) is considered one of the most important semiconductor materials after silicon, and is widely used for the production of green, blue, UV, and white LEDs. Recently, it has been found that rare earth (Gd and Eu) doped/ion implanted GaN shows ferromagnetism above RT. However, the origin of RT ferromagnetism has not been well understood. Due to the highly localized 4f electrons, the direct f-finteractions between the neighboring rare-earth atoms are very weak. As a device material, GdxGa1-xN is likely to result in changes to the barrier heights and the band gap of GaN as a result of the RE induced local strain, while the large neutron capture cross-section of Gd of 103 to 105 barns (for incident neutron energies as high as 300 meV) may provide a novel route for the fabrication of solid state neutron detectors.Two spectroscopic techniques, UV photoemission spectroscopy (UPS) and Low Energy Electron Diffraction (LEED) spectroscopy, were used to explore the structure and carrier energy in this study. The experiments were conducted at the Louisiana State University (LSU) Center for Advanced Microstructures and Devices (CAMD), using synchrotron radiation dispersed by the 3 m toroidal grating monochromator (TGM) beamline. The beamline is equipped with a photoemission endstation with a 50 mm hemispherical electron energy analyzer, configured for angle resolved photoemission. The combined resolution of the beamline and photoemission endstation is approximately 70 meV. Au deposition was made by exposing the sample to a stream of Au atoms emerging from an evaporator consisting of an Au bead suspended in a coil of W wire. The coverage in monolayers, where one monolayer is defined to be one Au atom per surface atom, was deposited at a rate of 4.0 ± 1.0 monolayer/hour. The deposition rate was monitored by LEED pattern identification, where prior research at the same facility provided a benchmark for comparison.
5:30 PM - UU9.4
A New Method: Thickness Determination of Thin Films by Energy Dispersive X-ray Spectroscopy.
Sedat Canli 1 2 , Mustafa Kulakci 3 , Urcan Guler 3 , Rasit Turan 2 3
1 Micro and Nanotechnology Department, Middle East Technical University, Ankara, Ankara, Turkey, 2 Central Laboratory, Middle East Technical University, Ankara, Ankara, Turkey, 3 Department of Physics, Middle East Technical University, Ankara, Ankara, Turkey
Show AbstractEDS is a tool for quantitative and qualitative analysis of the materials. In electron microscopy, the energy of the electrons determines the depth of the region where the x-rays come from. By varying the energy of the electrons, the depth of the region where x-rays come from can be changed. Different quantitative ratios of the elements for different electron energies can be obtained using a thin film. The thickness of a specific film on a specific substrate corresponds to a unique energy-ratio diagram. In this study, it is shown that thickness of a thin film can be obtained by an appropriate analysis of the energy-ratio diagram of the EDS data obtained from the film.
5:45 PM - UU9.5
Characterisation of Organic Multilayer Device Structures using Real-time Electron Spectroscopy.
Andrew Evans 1 , Gruffudd Williams 1 , Owain Roberts 1 , David Langstaff 1
1 Institute of Mathematics and Physics, Aberystwyth University, Aberystwyth United Kingdom
Show AbstractIn optimising multilayer structures for semiconductor device operation, it is crucial to know the energetics (energy band alignment) for each of the interfaces (electrode-semiconductor and semiconductor-semiconductor) in the device. Furthermore, it is useful to correlate the evolving energetics with chemical bonding at the interfaces and with the thin film morphology and structure. Photoelectron spectroscopy is a technique that can simultaneously probe energetics, bonding and morphology but is traditionally rather complicated, expensive and slow. Using efficient electron detectors coupled to advanced energy analysers and UV / soft x-ray sources in a dedicated OMBD chamber, the fabrication of simple organic PV and hybrid organic-inorganic device structures from electrode to electrode can be monitored in real-time. This approach provides not only the device energetics but also the layer-thickness dependence of the energy bands and the morphology of each layer. New insights into the adsorption of metal phthalocyanines and fullerenes on metal, oxide and inorganic semiconductor substrates are revealed, in particular in relation to electronic and morphological changes that occur on the timescale of thin film growth.
Symposium Organizers
Gertjan Koster University of Twente
Gyula Eres Oak Ridge National Laboratory
Fabio Miletto Granozio Complesso Universitario di Monte St. Angelo
Chang-Beom Eom University of Wisconsin-Madison
Nicholas Ingle University of British Columbia
UU10 :Optical Techniques
Session Chairs
Thursday AM, December 02, 2010
Hampton (Sheraton)
9:30 AM - **UU10.1
Homodyne Optical Second Harmonic Generation as a Sensitive, Potentially Real-time, Probe of Transition-Metal Oxide Unterfaces.
Lorenzo Marrucci 1 2 , Paparo Domenico 2
1 Dipartimento di Scienze Fisiche, Universita' di Napoli Federico II, Napoli Italy, 2 , CNR-SPIN, Napoli Italy
Show AbstractAtomic-scale engineering of transition-metal oxide interfaces and heterostructures is currently approaching a level that is comparable to what has been achieved in the past with semiconductors [see, e.g., R. Ramesh & D. G. Schlom, MRS Bullet. 33, 1006 (2008)]. The intrinsic potential for functionality of interface-based devices is combined, in this case, with the particularly rich and complex physics that is typical of these oxides, thus disclosing the way to a variety of new and often unexpected phenomena, and to possible future applications. A notable example is the conductivity of the interface between band insulators SrTiO3 (STO) and LaAlO3 (LAO) [see, e.g., J. Mannhart & D. G. Schlom, Science 327, 1607 (2010); M. Huijben et al., Adv. Mater. 21, 1665 (2009); and C. Chen et al., Adv. Mater., DOI: 10.1002/adma.200903800 (2010)].This progress is pushing the need for new diagnostic tools capable of analyzing and assessing the structure, morphology and quality of the interfaces. In this presentation, we will argue that the nonlinear optical technique of second harmonic generation (SHG), an already well developed technique in other fields of surface physics, has a very good yet largely unexploited potential for providing a new diagnostic tool for oxide interfaces. SHG can combine an atomic-scale surface sensitivity comparable to that of some particle-based surface-science tools with the spectral resolution, capability for accessing non-vacuum environments, and convenience that is typical of table-top optical techniques.Generally speaking, the ionic character of most oxides creates the conditions for the presence of strong interfacial polarizations that can be sensitively probed with SHG. We will show for example that SHG can be used to sensitively probe the interfacial electronic reorganizations occurring in the LAO/STO system, detecting transformations that are not visible with other techniques. Furthermore, spectroscopic SHG has the potential for providing a well resolved interface-selective in-situ electronic spectroscopy, without the need for vacuum or recurring to large-scale facilities. Again we will show examples taken from the LAO/STO system.Finally, we will show preliminary results of homodyne optical-phase-sensitive SHG from different heterostructures with STO films grown on NdGaO3 (NGO), capped or not capped with LAO, that show large signal variations in the presence of minute structural changes, possibly related with the specific atomic termination of the STO film, i.e. either TiO2 or SrO. Despite this extreme sensitivity, the SHG signal is highly reproducible and stable in time. Although the exact attribution of SHG signal variations to well defined structural features requires further investigation, there are indications that homodyne SHG can provide an extremely useful novel diagnostic tool for the growth and quality check of oxide heterostructures in real time.
10:00 AM - UU10.2
In situ, Real-Time Investigation of the Growth of Solution-Cast Molecular and Polymer Thin Film.
Ruipeng Li 1 , Debora Marques 1 , Mingjie Zhang 1 , Kui Zhao 1 , Lisong Xu 1 , Detlef-M. Smilgies 3 , John Anthony 2 , Aram Amassian 1 , Kang Chou 1
1 Materials Science and Engineering, Division of Physical Science and Engineering, KAUST, Thuwal Saudi Arabia, 3 , Cornell High Energy Synchrotron Source, Ithaca, New York, United States, 2 Chemistry, University of kentucky, Lexington, Kentucky, United States
Show AbstractLow-cost solution processes are deemed to be crucial to the future commercial success of organic electronics and photovoltaics. As such, solution processing of small-molecules, polymers and polymer-molecule blend thin films deserves special attention. The liquid environment, in contrast to vacuum and low-pressure environments, does not lend itself well to in situ probing via traditional surface science tools. We have therefore developed alternative strategies to investigate solution processes (drop- and spin-casting) by simultaneously monitoring the formation of the thin film (i.e., heterogenous nucleation, deposition rate, solvation, crystallization, mosaicity, texture and phase separation) in relation to the state of the solution (i.e., evaporation rate, concentration, aggregation/nucleation) and processing conditions. To do so, we have combined powerful techniques such as fast, in situ optical reflectometry, with quartz crystal microbalance, and/or grazing incidence X-ray scattering, thus gaining unprecedented insight into mechanisms and kinetics of self-assembly, crystallization, and thin film formation. Our results provide new insight into the formation of model solution-cast thin film systems of relevance to organic thin film transistors (e.g., TIPS-pentacene, TES-F-ADT, P3HT) and organic solar cells (e.g., P3HT/PCBM blends) prepared via drop- and spin-casting. Our results point to important differences between the growth behavior of polymers and small-molecules. The benefits of this insight are demonstrated through concrete examples, including carrier transport in OTFTs and efficiency of solar cells.
10:15 AM - UU10.3
Combinatorial SE / QCM-D Approach for Studying Porous Organic Ultra-thin Film Evolution.
Keith Rodenhausen 1 , Tadas Kasputis 2 , Angela Pannier 2 , Tino Hofmann 3 , Mathias Schubert 3 , Mark Solinsky 4 , Matthew Wagner 4
1 Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Biological Systems Engineering, University of Nebraska Lincoln, Lincoln, Nebraska, United States, 3 Electrical Engineering, University of Nebraska Lincoln, Lincoln, Nebraska, United States, 4 , The Procter & Gamble Company, Cincinnati, Ohio, United States
Show AbstractOptical and mechanical in-situ instrumentation is widely used to study the growth and evolution of organic thin films. However, film structure can be independent of the amount of attached film material, forcing other techniques, such as AFM, to be invoked.We report a complementary experimental setup to study porous organic ultra-thin films that consists of in-situ spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D) methods. Using a “virtual separation approach,” we show that SE is only sensitive to the amount of organic adsorbent. On the other hand, the QCM-D measures how much combined adsorbent and coupled solvent is attached. Together, SE and QCM-D can determine the ratio of incorporated solvent to total attached adsorbent and incorporated solvent. This parameter, porosity, can then be used as a measure of film structure.We investigate cetyltrimethylammonium bromide (CTAB) thin films deposited onto a gold-coated quartz crystal as a model system. CTAB grown from a 2.5 mM solution demonstrates several phases in porosity evolution, including a temporary hold in porosity as the film is rinsed off the substrate with water; these effects may be related to the structure of a CTAB bilayer.In addition, we study alkeanethiol self-assembled monolayer (SAM) chemisorption onto gold and show real-time evidence to corroborate a two-phase mechanism. There is a fast initial period of growth followed by a longer phase where the film rearranges itself to pack more uniformly. We relate this behavior to a steadily declining porosity.
10:30 AM - UU10.4
In-situ Observation of the Nucleation and Growth of Sputter Deposited Thin Films.
Sergey Grachev 1 , Marco De Grazia 1 , Remi Lazzari 2 , Elin Sondergard 1 , Etienne Barthel 1
1 Surface du Verre et Interfaces, CNRS/Saint-Gobain UMR 125, Aubervilliers France, 2 Institut des NanoSciences de Paris, Universite Pierre et Marie Curie, Paris France
Show AbstractNucleation and growth are the key processes defining structure and properties of thin films and multilayers. However, industrial conditions, characterized by harsh environment and fast deposition rates, hamper the possibility of in-situ investigations. Therefore most growth studies are carried out at slower kinetics and in ultra-high vacuum conditions. More specifically, the widespread family of deposition techniques based on magnetron sputtering characterized by the high working pressure and the presence of plasma limits our current knowledge. In the following we present an original optical set-up allowing for in-situ UV differential reflectivity characterization of a sample during sputter-deposition. Differential reflectivity methods were already used to investigate the growth and nucleation of metallic thin films and nanoparticles in high vacuum environments using slow effusion cells with evaporations rates of 1 A/min [1]. We optimize this technique for a study of growth of Ag deposited by magnetron sputtering. The challenge of this task was to avoid the background light from the plasma and to collect enough reflected light to follow the fast growth (~10 A/s) in real time during sputter-deposition. We utilized this technique to follow the nucleation and island coalescence of Ag on several substrates (SiOx, ZnO, Al2O3). The growth on SiOx starts by formation of islands which dewet from the substrate surface. The percolation and film formation was observed at ~6 nm equivalent thickness. The percolation can also be detected by following the development of stress in the layer. We realized this by measuring the curvature of a thin substrate by a multi-beam optical method. This data confirm the findings by differential reflectivity. 1. R. Lazzari, G. Renaud, C. Revenant, J. Jupille, Y. Borensztein, Phys. Rev. B 79, 125428 (2009).
10:45 AM - UU10.5
In-situ Adsorption Study of Polyelectrolyte Covered Mesoporous TiO2 Nanocontainers on SAM Modified Metal Surfaces by Means of Quartz Crystal Microbalance.
Agata Pomorska 1 4 , Wim Wijting 1 , Ingo Doench 2 , Diethelm Johannsmann 3 , Dmitry Shchukin 2 , Guido Grundmeier 1 4
1 Technical Chemistry, University of Paderborn, Paderborn Germany, 4 Institute for Polymer Materials and Processes, University of Paderborn, Paderborn Germany, 2 , Max Planck Institute of Colloids and Interfaces, Potsdam-Golm Germany, 3 Institute of Physical Chemistry, Clausthal University of Technology, Clausthal- Zellerfeld Germany
Show AbstractDevelopment of intelligent self-healing coatings loaded with nanocontainers (NCs) is a novel strategy for corrosion inhibition [1]. One of the crucial factors to improve the synthesis and properties of such films is adsorption kinetics of NCs on oxide covered metal substrates. In this work, mesoporous TiO2 NCs were coated with polyelectrolyte multilayers by a layer-by-layer technique and two oppositely charged polyelectrolytes were chosen to obtain nanoparticles with desired surface charge. During the QCM (quartz crystal microbalance) experiments, the NCs were adsorbed onto a metal electrode surface of 5 MHz AT-cut quartz crystals. Prior to deposition, the surface was functionalized with a self-assembled monolayer (SAM) of bi-functional molecules. The charge on the NCs and the substrate was either opposite or the same, providing an excellent system to study the impact of electrostatic attraction on the adsorption processes [2].
Modified metal substrates were examined by means of polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS), to evaluate the self-assembly process. The in-situ adsorption experiments were performed by pumping a dispersion of the NCs in water through the QCM chamber [3]. A base line in pure water was acquired before each experiment. After injection, the bandwidth of the resonance frequency (a parameter strongly related to the energy dissipation from a quartz crystal due to an adsorption process) usually increased for the systems with opposite charge of substrate and NCs. In the case where SAM and NCs charge were the same, much smaller shifts in bandwidth were observed. After the adsorption was completed, a stationary state was reached for all overtones and the cell was purged with pure water. The samples were subsequently examined by PM-IRRAS (polarization modulated infra red reflection adsorption spectroscopy) and SEM (scanning electron microscopy) to reveal the adsorption and the distribution of containers on the surface. Moreover the ζ-potential of the NCs was measured simultaneously during the in-situ QCM adsorption studies. The studies show how the NC adsorption kinetics can be influenced by the surface chemistry of the NCs and the substrate.
[1] D. Shchukin, M. Zheludkevich, K. Yasakau, S. Lamaka, M. G. S. Ferreira and H. Möhwald, Advanced Materials, 18, 1672, (2006)
[2] G. Decher, Science, 277, 1232, (1997)
[3] A. Pomorska, D. Shchukin, R. Hammond, M. Cooper, G. Grundmeier and D. Johannsmann, Analytical Chemistry, 82, 6, 2237, (2010)
UU11: Novel in situ Techniques
Session Chairs
Thursday PM, December 02, 2010
Hampton (Sheraton)
11:30 AM - UU11.1
The Electrical Conduction at Early Stages of Cluster-Assembled Films Growth.
Emanuele Barborini 1 , Gabriele Corbelli 2 3 , Paolo Milani 2 3
1 R&D, Tethis, Milan Italy, 2 Department of Physics, University of Milan, Milan Italy, 3 CIMAINA, University of Milan, Milan Italy
Show AbstractA powerful approach for the synthesis of nanostructured films with tailored properties consists in the deposition of atomic clusters produced in gas phase. The survival of the nanoscale building blocks during the deposition process (memory effect), as well as film growth dynamics, can both deeply influence the transport properties of cluster-assembled systems. In particular their electrical conductivity may differ significantly respect to conductivity of atom-assembled films, due to the presence of finite size effects, nanoscale disorder and peculiar topology evolution at early stages of film growth. To address these issues we studied in-situ the evolution of the electrical conduction of cluster-assembled thin films of Fe, Pd, Nb, W and Mo, during their growth by supersonic cluster beam deposition (SCBD).We observed that electrical conduction evolves according to topological evolution of the films at the nanoscales: from 0D to 1D once the first percolative path among deposited clusters closes; from 1D to 2D when new conduction paths appear as clusters are progressively added and interconnect themselves; from 2D to 3D once 2D conduction becomes saturated for the running out of in-plan conduction paths. Resistivity values of 3-4 orders of magnitude higher than bulk ones were recorded for any metal at any thickness, as well as a non-monotonic behaviour, with a remarkable increasing asymptotic trend with thickness. These features are in substantial disagreement with the bulk-converging behaviour of resistivity in atom-assembled films.Ballistic growth occurring in cluster-assembled films by SCBD may account for minimal cluster-cluster contact area and surface roughness increasing. Nanocrystallinity, minimal contact area, and nanoscale grain boundaries may explain the huge discrepancy between cluster-assembled and atom-assembled thin film resistivity, while surface roughness increasing explains the non-constant resistivity asymptotic trend. All the metals under investigation showed the same behaviour, suggesting that conduction features are largely dominated by topology, no matter the material in itself. This is also supported by the comparison of the resistivities at a given thickness, where the relative values of cluster-assembled metals in some cases are reversed respect to their bulk counterpart.Our results show a bottom-up approach for the synthesis of nanomaterials from nanoscale building blocks, suggesting that memory effect as well as a careful choice of deposition conditions and thicknesses range, can be exploited to control material properties. Beside fundamental insights on conduction process in nanostructured systems, the influence of nanoscale topology on the electrical resistivity may be of relevance, from the technological point of view, for the design of devices with electrical read-out where nanostructured layers are used as active elements, as in the case of chemical sensors.
11:45 AM - UU11.2
Spreading Kinetics at a Molecular Level.
Jean-Luc Buraud 1 , Olivier Noel 1 , Dominique Ausserre 1
1 , University of Maine, LPEC –Molecular Landscapes and biophotonics group, CNRS-UMR 6087, , Le Mans France
Show AbstractThe spreading of a smectic nanodrop (8CB liquid crystal) on a solid surface was investigated by direct and real time imaging using the Surface Enhanced Ellipsometric Contrast (SEEC) microscopy [1-2]. The spreading ends with two molecular terraces (made of one monolayer and a bilayer). Two different behaviors were observed. In the first one the upper layer stays dense while shrinking. At the end of the process, the last molecules to disappear are located at the center of the initial disk. In the second one, nucleation and growth of holes is observed in the upper layer, in addition to shrinking. A model is proposed to describe the time evolution of the late stage structure. This model gives exact solutions of the kinetic equations, it covers strongly layered liquids such as smectic liquid crystals, it introduces the two dimensional Laplace pressure as an essential motor for spreading and it takes into account the liquid/gas transition in the surface layer that was consistently reported in experiments with 8CB. This model is in remarkable agreement with the experimental data and can explain the two observed behaviors [3].[1] Ausserre, D.; Abou-Khachfe, R. Langmuir 2007, 23, 8015-8020[2] Ausserre, D.; Valignat, M. P. Nano-letters 2006, 6, 1384-1388[3] O.Noel, JL.Buraud, L.Berger, D.Ausserre Langmuir, 2010, 26 (8), 6015–6018
12:00 PM - UU11.3
In-situ Surface Characterization of Nanostructured Thin-film Materials Exposed to Controlled Irradiation Fields.
D. Rokusek 1 , O. El-Atwani 1 2 , S. Ortoleva 1 , A. Kacic 1 , C. Taylor 1 , B. Heim 1 , Z. Yang 1 , J. Allain 1 2
1 , Purdue University, West Lafayette, Indiana, United States, 2 , Birck Nanotechnology Center, West Lafayette, Indiana, United States
Show AbstractThe study of surfaces and interfaces and their interaction with radiation and plasma is of great importance to tailor function in low-dimensional systems such as ultrathin multilayers and ion-induced patterned nanostructures. In particular controlling matter at spatial scales the order of the first layer of atoms at the vacuum/film interface is important for applications in materials exposed to extreme environments such as high-density plasma, nuclear fusion edge plasmas, and high current density ion-beams. Also the formation and functionalization of Au nanoparticles on Ni/Co ultra-thin multilayers, for use in biomaterial applications. Directed irradiation synthesis enables the modification of multi-component surfaces self-organizing into regular nanoscale patterns. Recent work has demonstrated the importance of metal seeding and compositional modulation of nanopatterns. In this work design of functional properties for irradiation-driven surfaces is enabled by in-situ characterization during exposure to well-defined and controlled irradiation fields. The resulting nanopatterns can induce changes in the electronic and mechanical properties of these materials. We present in this work the study of two distinct material systems exposed to controlled irradiation environments during surface characterization in-situ. The first, ultra-thin coatings (e.g. Li, Sn) irradiated by low-energy ions near the sputtering threshold. The second, irradiation of III-V compound semiconductor surfaces (GaSb and InP). We study the effect of compositional and chemical states of these multiple-component heterogeneous surfaces on ion-induced nanoscale processes (e.g. erosion dynamics, redeposition, surface diffusion kinetics) and physical properties (i.e. optical, electronic, hydrogen recycling). A recently built experimental facility at Purdue University can perform in-situ atomic scale characterization of elemental, chemical, and electronic properties using complementary surface-sensitive techniques. In-situ real-time techniques used include: low-energy ion scattering spectroscopy (LEISS), angular-resolved photoemission spectroscopy (ARPES), EUV reflectivity, X-ray photoelectron spectroscopy, erosion measurements, and ultraviolet photoelectron spectroscopy (UPS). UPS/ARPES combined with LEISS can give chemical state and elemental information at the first 2-3 monolayers, respectively. The facility is equipped with ion sources capable of delivering hyperthermal and energetic heavy-ions at energies between 10-1000 eV with current densities above 100 uA/cm2. Both ion and electron spectroscopies are conducted using a highly sensitive hemispherical sector energy multi-channel analyzer. Ex-situ atomic force microscopy measures surface morphology. Results elucidate on the synergistic effect between multiple particle-beam exposure on the electronic and optical properties of transition-metal EUV reflective coatings and surface nanopatterning of III-V compound semiconductors.
12:15 PM - UU11.4
Electrochemical and Optical Monitoring of Metal Electrodeposition Interfaces in a Microfluidic Cell.
Joshua Gallaway 1 , Abhinav Gaikwad 1 , Shahab Shojaei-Zadeh 1 , Dan Steingart 1
1 Chemical Engineering, The City College of New York, New York, New York, United States
Show AbstractElectrochemistry performed in microfluidic systems allows several experimental advantages, such as minute control of hydrodynamic conditions at the interface. During electrodeposition of a metal, the reaction is often under mixed control by both reaction kinetics at the interface and transport of metal ions in the electrolyte. In some ways, microfluidic electrochemical cells offer many of the advantages of rotating disk electrodes, while also allowing small reaction volumes, real-time interface visualization, and micron-scale electrodes. The system is useful for studying many industrially and scientifically relevant systems, such as electrodeposition of copper for semiconductor fabrication and electrodeposition of zinc for aqueous, megawatt class zinc metal anode batteries.Zinc is well-known to form protrusions and dendrites during electrodeposition. It is thought that zincate ion transport causes this emergent phenomenon, although the complication of the system is evident: electrolyte flowrate, deposition rate, ppm quantity additive metals, and concomitant hydrogen generation all appear to play a roll in at least some regime of operation. We have used several microfluidic electrochemical cell configurations to study this system, with an eye toward mitigating protrusion formation for use in zinc batteries. In battery application, protrusions are fatal to the cell, causing internal short circuits and loss of capacity.A microfluidic lateral cell was used for real-time microscopy of the growing zinc interface in a flow channel between parallel plate electrodes. We observe that during formation of severe ramifications, the growth velocity of the zinc tips approaches a kinetically controlled rate, independent of electrolyte flowrate. This has implications that flow control of the electrolyte alone cannot stop protrusion formation and propagation. We have also used a microfluidic transparent cell, conprised of thin film electrodes evaporated on glass substrates. In this configuration, light can be passed through the cell, sufficient to use high-speed microscopy to monitor the interface. Bismuth additive in low concentrations was co-deposited with zinc and electrodissolved. High speed microscopy allowed us to observed solid particals leaving the interface, representing a loss of capacity invisible to the naked eye. While bismuth helps suppress dendrite formation, at some concentrations it contributed to capacity loss over time, an effect we are studying in more detail. This system may also be relevant to other co-deposition strategies.