Symposium Organizers
Thomas Proffen Los Alamos National Laboratory
Igor Levin National Institute of Standards and Technology
Frank (Bud) Bridges University of California-Santa Cruz
David Keen ISIS Facility
Rutherford Appleton Laboratory
HH1: Spatially Resolved Techniques I
Session Chairs
Tuesday PM, April 14, 2009
Room 3009 (Moscone West)
9:30 AM - **HH1.1
STM Measurements of Metallic and Molecular Nanostructures on Metallic Surfaces.
Karina Morgenstern 1
1 Institute for Solid State Physics, Leibniz University of Hannover, Hannover Germany
Show AbstractScanning tunnelling microscopy (STM) measures the local density of states of a conducting sample with sub-atomic precision in real space. The interpretation of STM images is not always straightforward because of the superposition of electronic with topographic information. On the other hand this superposition allows determining both, the topology of a surface structure directly and its electronic structure by employing elastic and inelastic scanning tunnelling spectroscopy. In this talk I will present results on metallic Cu islands on Ag(100) and small organic molecules on the (111) faces of Cu and Au, where both the topology of the nanostructures and their electronic signature will be discussed. For the metallic Cu islands we resolve a critical size that determines the diffusion and decay behaviour of these nanostructures. For nitrobenzene on Cu(111) and diclorobenzene on Au(111) we find a local variation of the spectroscopic signature with submolecular resolution.
10:00 AM - HH1.2
Quantitative Atomic Resolution Imagining with Scanning Transmission Electron Microscopy
James LeBeau 1 , Scott Findlay 2 , Leslie Allen 3 , Susanne Stemmer 1
1 Materials Department, University of California, Santa Barbara, California, United States, 2 Institute of Engineering Innovation, The University of Tokyo, Tokyo, 113-8656, Japan, 3 School of Physics, University of Melbourne, Melbourne, Victoria, Australia
Show AbstractQuantitative imaging at the atomic scale remains an active area of research within the electron microscopy community. For instance, high angle annular dark-field (HAADF) in scanning transmission electron microscopy (STEM) provides atomic resolution and atomic number sensitive imaging of nanostructures. However if quantitative information is to be extracted from HAADF STEM images, then complete understanding of the electron scattering theory is required. Previous studies have reported a mismatch between experimental and simulated image contrast for HAADF STEM. However, these previous studies have been hampered by the lack of an absolute intensity scale. Without an absolute measure of image intensities, two possible explanations for the mismatch become indistinguishable: an overestimated signal at the atom columns or an underestimated background (the intensity between the atom columns). Since simulations provide the image intensities on a scale that is normalized to the incident beam intensity, experimental images must be normalized in the same way.For this study, an FEI Titan 80-300 STEM/TEM was operated at 300 kV and equipped with a scintillator-based ADF detector. We will show that the normalization of HAADF images relative to the incident beam intensity is possible using the annular dark field detector that has an output voltage that is proportional to the incident flux averaged over time (intensity). In addition, we will present a method to ensure that the detector does not saturate when measuring the incident beam intensity and show that the typical ADF detector exhibits highly non-uniform detection efficiency as a function of scattering angle. After ensuring that the detector does not saturate and correcting for non-uniformities of the detector efficiency, we construct normalized intensity images of an SrTiO3 single crystal for regions of different thickness.Electron energy loss spectroscopy (EELS) was used to measure the thickness of each image region, but due to surface contributions was found to be in error. We will discussion how the combination of EELS the absolute HAADF background signal can provide improved estimates of the thickness. The normalized intensity images are then compared directly with Bloch wave and frozen phonon image simulations that incorporate thermal diffuse scattering. Once spatial incoherence of the probe is taken into account for the simulations, almost perfect agreement is found between simulation and experiment.
10:15 AM - HH1.3
X-ray Photoelectron Microscopy (X-PEEM) Measurements of Local Conduction Band Changes in Si Nanomembranes Induced by SiGe Quantum Dot Nanostressors.
Clark Ritz 1 , Chanan Euaruksakul 4 , Feng Chen 2 , Rebecca Metzler 1 , Mike Abrecht 3 , Narayana Appathurai 3 , Pupa Gilbert 1 , Max Lagally 2 1
1 Physics Department, University of Wisconsin, Madison, Madison, Wisconsin, United States, 4 Electrical and Computer Engineering, University of Wisconsin, Madison, Madison, Wisconsin, United States, 2 Materials Science and Engineering, University of Wisconsin, Madison, Madison, Wisconsin, United States, 3 Synchrotron Radiation Center, University of Wisconsin, Madison, Madison, Wisconsin, United States
Show AbstractIt is known that strain affects the carrier mobility in semiconductors by splitting and shift-ing bands, but until recently quantitative measurements have not been possible. The availability of elastically strained Si nanomembranes (SiNMs) [1] and high-resolution x-ray absorption spectroscopy (XAS) recently made such measurements possible [2]. The nanomembranes provide large areas of uniformly strained Si, through elastic strain shar-ing in multilayer Si/SiGe/Si sandwich structures. XAS measurements of the Si 2p to conduction band edge transition in strained SiNMs can be used to determine the strain-induced shifting and splitting of minima in the Si conduction band. The growth of epitaxial SiGe quantum dots (QDs) on free-standing SiNMs creates a need to make such measurements of the band edge shifts on a spatially local scale. It is known that these QDs act as nanostressors, with a high local stress, which should cause local variations in the band structure. Because of elastic interactions between strained QDs and the thin SiNM substrate, highly ordered arrays of QDs are formed. We use the “Spectromicroscope for Photoelectron Imaging of Nanostructures with X rays” (SPHINX) at the University of Wisconsin Synchrotron Radiation Center to measure, with better than 100nm spatial resolution, shifts in transition energies in x-ray absorption spectra of SiNMs that have been locally strained with QD nanostressors. We observe local shifts in the L-edge absorption spectra on the order of 100 meV, of the same magnitude as macro-scopic measurements at the same strain. The results support theory predicting local band shifts in the QD-strained SiNMs. [3] This work was supported by DOE, AFOSR, and NSF. [1] M. M. Roberts et al., Nat. Mater. 5 388-393 (2006).[2] C. Euaruksakul et al., PRL 101 147403 (2008).[3] M.-H. Huang et al., Nat. Mater., submitted
10:30 AM - HH1.4
Near Nanometer-Resolution Quantitative STEM-EDS Chemical Mapping of Ultrathin Film Multilayer PLZT Capacitors.
Bruce Tuttle 1 , Chad Parish 1 , Geoff Brennecka 1 , Luke Brewer 1 , Jill Wheeler 1 , Jacob Jones 2 , John Ekerdt 3
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , University of Florida, Gainesville, Florida, United States, 3 , University of Texas at Austin, Austin, Texas, United States
Show AbstractQuantitative analysis of nanometer-scale chemical inhomogeneities has led to the development of lead zirconate titanate (PLZT) ultrathin film multilayer capacitors that have the highest known extended temperature range (-55oC to 125oC) areal capacitance densities reported to date. These advanced multilayer ultrathin film nanostructures were developed to meet areal capacitance requirements for next generation medical electronics, miniaturized sensor devices and energy storage components. In order to achieve this technical break through, it was necessary to quantitatively understand the nanometer-scale structure and chemistry of these materials. Traditional chemical nanoanalysis techniques, such as point or line analyses in electron microscopy or surface-analysis depth profiling, are poorly suited to resolve these fine-scale chemical inhomogeneities. Assisted by computational multivariate statistical analysis, we have developed an X-ray spectroscopy technique in scanning transmission electron microscopy to map cation distributions at the sub-10-nm level in PLZT. We will summarize the developed technique and discuss artifacts and technical challenges as well the many benefits. Results obtained with this technique indicate that significant Zr/Ti segregation occurs in the growth direction for some ultrathin-film PLZT compositions and is nearly absent in others. It has been determined that this nanoscale inhomogeneity can have a significant impact on both piezoelectric and dielectric properties. We have also quantified La segregation at perovskite – fluorite interfaces during perovskite growth stages. La segregation was less significant than Zr/Ti segregation for our ultrathin film multilayer capacitors. Optimization of single layer ultrathin films and multilayer capacitor fabrication was significantly aided by the analyses of the electrode/dielectric interface(s) at the nanoscale to evaluate low temperature interactions of ultrathin film PLZT with underlying Pt and ZrB2 electrode technologies. Techniques were developed to fabricate ultrathin film lead lanthanum zirconate titanate (PLZT) dielectric layers less than 50 nm thick using chemical solution deposition (CSD) techniques. PLZT ultrathin films 40 nm thick exhibited dielectric constants greater than 1000 and large maximum polarization values exceeding 40 μC/cm2. Since areal capacitance density - a primary metric for our applications - increases as dielectric layer thickness decreases, the thinnest dielectric thickness values possible with our technology were determined. Functional single layer PLZT ultrathin films of 9 nm thickness have been fabricated using our CSD procedure. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
10:45 AM - HH1.5
Advanced TEM Characterization for Catalyst Nanoparticles Using Local Adaptive Threshold (LAT) Image Processing.
Petra Bele 1 , Ulrich Stimming 1 2
1 Department of Physics E19, Technical University Munich TUM, Garching Germany, 2 Division 1 , The Bavarian Center for Applied Energy Research ZAE, Garching Germany
Show AbstractMetallic and non-metallic nanoparticles, usually supported on non-metallic substrates have attracted much interest concerning their application in the field of electrocatalysis. To determine a catalyst system by means of detailed information about size, morphology, structure and composition (alloys or core-shell) of nanoparticles and their associated electrocatalytic activity, transmission electron microscopy (TEM) is the state of the art method.For a thorough structural characterization of a catalyst system, represented by small nanoparticles on a matrix, we have to deal with the obstacles due to image detection and image processing; in case of the image detection with: i. a variation of image contrast due to local thickness changes of the support material, ii. intensity variation of similar nanoparticles based on diffraction contrast, iii. a weak signal-to noise-ratio due to the difficulty to distinguish particles in the sub-nanometer scale from the matrix, and iv. an overlapping of different particles when imaged in projection.In order to overcome these problems, computer image processing methods offer a major advantage in the data evaluation process. However, computer-assisted analyses of TEM images dealing with nanoscaled or even sub-nm particles have their own difficulties arising from the applied image processing routines itself. Therefore, a function is needed to obtain the image segmentation, which involves the classification of each image pixel to one of the image parts, either object or background. To strive for the most objective results we introduce an advanced computerized image processing routine to evaluate particle size and size distribution. The key for the final determination of the particle diameter is to use the so-called local adaptive thresholding (LAT) instead of the standard global threshold routine before particle picking. By using just a global threshold, one typically has to deal with loosing too much of the desired region or getting too many extraneous background pixels resulting in an under- or overestimation of the desired region. In addition, illumination changes across the image occur causing brighter and darker parts not correlated to the real objects in the image.LAT typically takes a grey-scale image as input and outputs a binary image representing the segmentation assuming that smaller sub-image regions are more likely to have approximately uniform illumination compared to the complete image. Applying the LAT is the key for an exact determination, even for particles in the sub-nanometer scale, leading to a higher degree of accuracy concerning the complete data analysis process. This is demonstrated by a study using different catalysts on different support materials combining TEM data with results received from other electrochemical experiments.
11:30 AM - HH1.6
Quantitative Scanning Transmission Electron Microscopy for the Measurement of Thicknesses and Volumes of Individual Nanoparticles.
Helge Heinrich 1 2 , Biao Yuan 1
1 AMPAC, University of Central Florida, Orlando, Florida, United States, 2 Physics Department, University of Central Florida, Orlando, Florida, United States
Show AbstractIn Scanning Transmission Electron Microscopy (STEM) the High-Angle Annular Dark-Field (HAADF) signal increases with atomic number and sample thickness, while dynamical scattering effects and sample orientation have little influence on the contrast. The sensitivity of the HAADF detector for a FEI F30 transmission electron microscope has been calibrated. Additionally, a nearly linear relationship of the HAADF-signal with the incident electron current is confirmed. Cross sections of multilayered samples for contrast calibration were obtained by focused ion-beam (FIB) preparation. These cross sections contained several layers with known composition. A database with nine pure elements and seven compounds has been compiled so far, containing experimental data on the fraction of electrons scattered onto the HAADF detector for each nanometer of sample thickness. Furthermore, the HAADF-scattering cross sections for several elements have been determined using the FIB samples for calibration.Contrast simulations are based on the multislice formalism and confirm the differences in HAADF-scattering contrast for the elements and compounds.TEM offers high lateral resolution, but contains little or no information on the thickness of samples. Thickness maps in energy-filtered transmission electron microscopy, convergent-beam electron diffraction and tilt series are so far the only methods to determine thicknesses of particles in a transmission electron microscope.We show that the calibrated HAADF contrast can be used to determine the thicknesses of individual nanoparticles deposited on carbon films. With this information the volumes of these nanoparticles were determined. The HAADF-STEM contrast was used to obtain thickness and volume information for FeAu, Pt, Au, and Ag nanoparticles.
11:45 AM - HH1.7
WITHDRAWN 03/24/09 Characterization of Synthesized Free Standing Graphene using TEM
Zonghoon Lee 1 , Albert Dato 2 , Ki-Joon Jeon 3 , Rolf Erni 1 , Thomas Richardson 3 , Michael Frenklach 4 , Velimir Radmilovic 1
1 National Center for Electron Microscopy, Lawrence Berkeley National Lab, Berkeley, California, United States, 2 Applied Science & Technology Graduate Group, University of California, Berkeley , Berkeley, California, United States, 3 Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Department of Mechanical Engineering, University of California, Berkeley , Berkeley, California, United States
Show AbstractA synthesized free-standing graphene layer, i.e. a two-dimensional (2D) single atomic sheet of carbon, is imaged successfully on the lately developed TEAM 0.5 instrument under the TEAM (Transmission Electron Aberration-Corrected Microscope) project. The TEAM 0.5 is equipped with two aberration correctors for illumination and projection systems and with an electron monochromator, which have been optimized in 80-300 kV. High resolution imaging of the graphene layers are very hard in any conventional microscopes because a higher kV beam damages the thinnest carbon layers and a lower kV operation deteriorates resolution for the light atoms. However, the TEAM instrument brings us a high resolving power capability even at 80kV for imaging and spectroscopy of the preserved graphene layers. TEM imaging from a typical region of synthesized free-standing graphene layer displays densely packed hexagonal single-layer of carbon and unambiguous Moiré patterns formed from superimposed two individual graphene layers, which represent a coincidence site. Exit wave reconstructions were performed from a through-focus image series and the corresponding high resolution images were simulated using MacTempasX software for comparison. Monochromated electron energy loss spectra (EELS) of free-standing graphene sheets were also obtained. The carbon K-edge in EELS can be used to identify the structure of graphene sheets. The EELS of single layer sheet exhibits unique graphitic characteristics, which has the 1s-π* and 1s-σ* transition at 285 eV and 291 eV. It is also challenging to distinguish fine-scale single-layer graphene from other carbon nano-structures. We are able to perform STEM parallel beam diffraction on nano region of graphene single-layer and bilayer using a Zeiss Libra 200 FE-TEM operated at 200kV with Koehler illumination. The several sets of diffraction patterns from single graphene layers and two layers of graphite appear differently because the synthesized graphene sheets exist typically in overlapped and folded sheets on TEM sample grids. A set of hexagonal diffraction spots from a single graphene layer can be identified by simulated diffraction patterns.
12:00 PM - HH1.8
TEM Lattice Imaging with FFT Analysis of InGaN QWs in GaN Nanowires.
Roy Geiss 1 , Kris Bertness 1 , Alexana Roshko 1 , David Read 1
1 , NIST, Boulder, Colorado, United States
Show AbstractAnalysis of fast Fourier transforms (FFTs) of lattice images obtained using transmission electron microscope (TEM) imaging of GaN nanowires containing InGaN quantum wells (QWs) showed a 4 to 10% increase of the c-axis lattice parameter values and essentially no change in the a-axis values. Sub-pixel analysis of the FFTs provided picometer (pm) precision in the measurements. Further, multi-colored lattice images made by constructing multiple inverse FFTs (IFFTs) from selected values in the FFT covering the range of measured c-axis parameters provided a clear representation of the variations in the c-axis lattice. The nanowires containing the QWs were grown by molecular beam epitaxy (MBE) using elemental Ga and In and an RF-plasma N2 source on heated Si(111) substrates. Individual nanowires were collected onto holey carbon grids by dragging the grids across the substrate. These nanowires, which are dislocation-free single crystals with a wurtzite structure, grew in the <0001>. They were approximately 1000 nm long and 60 to 130 nm wide and had hexagonal cross-sections. The In concentration in the QWs ranged from 12 to 15% as determined by a standardless analysis using energy dispersive spectroscopy (EDS). The magnitude of the changes in the c-axis values exceeds values that might be expected considering this In concentration using a linear Vegards law for GaN – InN. Therefore at least some of the observed expansion of the c-axis in the QWs is thought to be associated with strain in the <0001>. The FFT analysis showed that the c-axis lattice expansion tracked with the specimen width, being larger by a factor of ~3% for nanowires having two times the width. Convergent beam electron diffraction (CBED) in the TEM was also used, and showed similar changes in <0001> direction in the QW. The same specimens used for the TEM study were analyzed using a newly developed transmission electron diffraction technique in the scanning microscope (SEM). Strain analysis, incorporating electron backscattered diffraction (EBSD) patterns in this completely new and different venue, confirmed the TEM FFT observations. Finally, finite element modeling (FEM), considering elastic behavior, was used to examine the consistency of the observed behavior with expectations from linear elasticity.
12:15 PM - HH1.9
Chemical Nano-tomography of Self-assembled Ge-Si:Si(001) Islands from Quantitative High Resolution Transmission Electron Microscopy.
Luciano Montoro 1 , Marina Leite 1 , Daniel Biggemann 1 , Fellipe Peternella 1 , Joost Batenburg 3 , Gilberto Medeiros-Ribeiro 1 2 , Antonio Ramirez 1
1 Laboratório de Microscopia Eletrônica, Laboratório Nacional de Luz Síncrotron, Campinas Brazil, 3 , University of Antwerp, Wilrijk Belgium, 2 , Hewlett-Packard Laboratories, Palo Alto, California, United States
Show AbstractThe knowledge of composition and strain distribution with atomic resolution are fundamental steps for the understanding of the chemical and electronic properties of nanostructures. Applications of nanostructured semiconductors in electronic and optoelectronic require a precise knowledge of these features. However, an evaluation of the quantitative 3D chemical distribution on such nanostructures is a major challenge. In this work is presented an advanced methodology for a 3D quantitative chemical mapping based on a quantitative TEM technique. This methodology is applied to GexSi1-x islands grown on Si (001). This material has emerged as the model system for the study of self-assembled nanocrystals, due to explore the conventional Si technology and involve only two miscible elements. In these self-assembled semiconductor islands the chemical composition is a key factor, which determines their size, stability and physical properties. Over the past, many studies considered the islands to have a constant and uniform composition over time. However, recently have been shown that its composition is not only different from the nominally deposited material, but is also non-uniform as a result of the interdiffusion process explained from interplay between thermodynamic, and kinetic effects. The procedure involves the use of geometric phase analysis (GPA) to measure displacement fields in high resolution transmission electron microscopy (HRTEM) images. The GPA method is a powerful tool to quantify small periodicity changes in the HRTEM images, allowing the determination of lattice distortions. From the distortion maps and applying a mathematical algorithm which takes into account Vegard’s Law and classical elastic theory (Poisson ratio) it is possible to obtain 2D chemical maps with atomic column resolution. To improve the accuracy of these quantitative chemical maps, the HRTEM images were obtained from an exit-plane wave-function reconstruction method, obtaining aberrations-free images. The samples were grown by CVD method and the specimens for HRTEM analyses were prepared by cross-section method in the [100] and [110] zone axis. A JEM-3010 URP with LaB6 electron gun was used at 300 kV. Thus, 2D projected chemical maps with atomic-column resolution were obtained from representative islands viewed from two crystallographic directions [110] and [100]. Systematic differences in these projected chemical maps reveals non-cylindrically symmetric 3D chemical features. By using the two projected maps, and due to the structural symmetry of the islands, one can infer the 3D chemical distribution in a self-consistent fashion. A mathematical algorithm was used to iteratively reconstruct the 3D chemical distribution, revealing a four-fold symmetry chemical arrangement within these nanostructures. Therefore, the proposed methodology emerges as a chemical nano-tomography technique that can be especially applied to epitaxially grown nano-structured materials.
12:30 PM - HH1.10
Characterization of the NaCl Suzuki Nanoprecipitate Structure by Scanning Force Microscopy.
Adam Foster 1 , Clemens Barth 2 , Claude Henry 2
1 Laboratory of Physics, Helsinki University of Technology, Helsinki Finland, 2 , CRMCN-CNRS, Marseilles France
Show AbstractDue to their insulating character, the (001) surfaces of bulk alkali halide crystals are emerging as important substrates in many nanosystems. Particular focuses are supported metal nanoclusters for the study of catalytic properties and the adsorption of molecules to the surface for applications in nanoelectronics. For simultaneous characterization of both the substrate and nano-object at the atomic scale, Scanning Force Microscopy (SFM) remains the tool of choice, but on the highly symmetric alkali halide surfaces, unambiguous interpretation of contrast is difficult. Possible solutions, such as using force spectroscopy, are extremely challenging both experimentally and theoretically, and do not offer a routine approach to the problem. It is clear that a much more desirable setup would provide interpretation directly from images alone. Recently, NaCl crystals were doped with divalent impurity cations as part of a combined SFM and Kelvin probe microscopy study [1]. Above a certain divalent impurity content, the doped NaCl system creates precipitates in their well-known Suzuki phase [2] on the surface. The precipitates are embedded in the NaCl(001) matrix, so that two different types of surfaces regions, which are well separated, can be found. The atomic unit cell of the Suzuki phase is twice as large as the one of NaCl(001) and is composed of three different ions including Na vacancies. In this work we combine SFM experiments with ab initio and atomistic simulations to show quantitatively that all ions in the Suzuki structure (NaCl:Mg2+ or NaCl:Cd2+) can be unambiguously identified in images with atomic resolution, independently of the tip's polarity and the chemical nature of the divalent impurity ions. We explore in detail the dependence of contrast on the tip-surface distance dependence and the role of atomic displacements in observed features. Our results demonstrate that doping NaCl crystals with divalent impurity cations nanostructures the (001) surfaces with Suzuki precipitates, offering templates for adsorption and growth. The resulting ease of interpretation of atomically resolved SFM images, means that the contrast formation is also expected to be much more accessible for supported nano-objects. [1] C. Barth and C.R. Henry, Phys. Rev. Lett. 100, 096101 (2008) [2] K. Suzuki, J. Phys. Soc. Jpn. 10, 794 (1955) and 16, 67 (1961)
12:45 PM - HH1.11
Combination of Transmission Electron Microscopy and Fluorescence Spectroscopy of Single Semiconductor Nanocrystals.
Sebastian Jander 1 , Andreas Kornowski 1 , Horst Weller 1
1 Institute of Physical Chemistry, University of Hamburg, Hamburg Germany
Show AbstractDue to the manifold application of semiconductor nanocrystals, like biolabeling and optoelectronic devices, their fluorescence properties are of great interest. Especially on the single particle level quantum dots (QDs) show outstanding optical behavior (e.g. blinking, spectral diffusion), that helps to understand their electronic structure. Since small changes in size, orientation and structure of nanocrystals lead to large changes in their optical properties a comparison of both attributes is essential. We present a method to correlate fluorescence and structural properties of single semiconductor nanocrystals. To investigate the same particle in a confocal laser scanning microscope (CLSM) and a high resolution transmission electron microscope (TEM) different substrates were used. We found that polyvinyl formal covered copper grids and ultrathin silicon nitride membranes can be used to combine both methods. For combined investigations a highly diluted CdSe/CdS/ZnS quantum dot solution was spin coated on the substrate whereas small silicon dioxide spheres were applied to localize the single nanocrystal in TEM and CLSM. Time traces and emission spectra of a single quantum dot were measured. A following TEM correlation brought forward proof that the measured fluorescence originates from a single isolated nanocrystal.
Symposium Organizers
Thomas Proffen Los Alamos National Laboratory
Igor Levin National Institute of Standards and Technology
Frank (Bud) Bridges University of California-Santa Cruz
David Keen ISIS Facility
Rutherford Appleton Laboratory
HH3: Local Structure
Session Chairs
Wednesday AM, April 15, 2009
Room 3009 (Moscone West)
9:30 AM - **HH3.1
Atomic Structure of Nano-Particles.
Takeshi Egami 1 2 , Wojtek Dmowski 1
1 Mater. Sci./Physics, University of Tennessee, Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractOften nano-particles exhibit unique or different properties not just because of the particle size, but the structural modification that small size makes possible. Small angle scattering that determines the particle size thus will not be sufficient in characterizing nano-particles. The PDF technique provides information on both the local structure and the particle size, although the information is averaged over the entire sample. We discuss the structure of nano-particles determined by high-energy x-ray PDF method for hydrated ruthenia (RuO2) used for super-capacitance and fuel cells, and gold nano-particles that are catalytically active. Judged from diffraction patterns and EXAFS results strongly hydrated ruthenia nano-particles were considered to be amorphous. But the PDF clearly shows that they are nano-crystalline, and local crystal structure is relevant to electron conduction, while water in-between and interface allow proton conduction. Bulk or crystalline gold (Au) is inactive as a catalyst, but nano-crystalline gold particles within a certain range of size are catalytically active for CO oxidization. High-energy in-situ X-ray PDF has shown that the atomic structure of gold particles locally change with temperature, departing from the usual f.c.c. structure and resembling the b.c.c. structure. Even at room temperature a portion of the surface appears to show the transformed structure. We conjecture that the change in the electronic structure due to the atomic structure modification, widening of the d-band in particular that will create holes in the d-band, is responsible for the catalytic activity. The PDF technique is a powerful tool to characterize these local changes in the atomic structure that are relevant to the properties of nano-particles.
10:00 AM - **HH3.2
Resolving Complexity of Nanoscale Metal Clusters.
Anatoly Frenkel 1
1 Physics, Yeshiva University, New York, New York, United States
Show AbstractNegative thermal expansion (NTE), a peculiar effect reported in 1996 in zirconium tungstate and other framework solids and not expected in fcc metals, was recently observed in alumina-supported Pt nanoparticles. In the smallest particles studied (0.9nm in diameter) the Pt-Pt distance decreased gradually by 0.04 Å over the 500 K range. Such effect was attributed to the charge transfer between the cluster and support. I will review recent experiments using x-ray and electron microscopy techniques that allow to resolve competing interactions between metal and substrate, metal and adsorbate, and between alloying metals (for bimetallics). Experimental (x-ray spectroscopy and electron microscopy) results combined with the first principles, real-time calculations uncover dynamic structure and mobility of supported metal clusters that. This dynamic behavior is the origin of very peculiar electronic and structural effects in these supported clusters that explains their observed anomalies.
10:30 AM - HH3.3
Using First Principles Based Simulations to Solve the Nanotructure of a Relaxor Ferroelectric.
Benjamin Burton 1 , Eric Cockayne 1 , Panchapakesan Ganesh 2 , Ronald Cohen 2
1 Ceramics Division, NIST, Gaithersburg, Maryland, United States, 2 , CIW, Washington DC, District of Columbia, United States
Show AbstractMolecular dynamics simulations were performed on a first-principles-based effective Hamiltonian for the relaxor ferroelectric system: Pb(Sc1/2Nb1/2)O3 (PSN). Temperature-dependent polar ordering was simulated in a nano-ordered (NO) Sc:Nb-configuration with 20 approximately spherical chemically ordered regions (COR) in a percolating random matrix (PRM). The model was used to generate simulated neutron and X-ray diffuse scattering (DS) patterns. In agreement with experiment: 1) in the temperature/pressure range in which the model yields a relaxor-like state, calculated DS patterns for the [110] peak are lozenges with their long dimensions perpendicular to [110], and for the [010] peak are "butterflies" (crossed lozenges); 2) at temperature/pressures above which the model yields a transition to the paralectric phase, the lozenges and butterflies disappear. The characteristic DS of the model arises from the formation of polar nanoregions (PNR) centered on the COR. It is more challenging to explain the full three-dimensional experimental diffuse scattering pattern, which may require an effective Hamiltonian with more parameters, or a more realistic representation of the chemical ordering. By systematically varying the simulation box configuration, however, we expect the nature of the nanostructure can ultimately be identified. The general idea is an old one, to solve a (nano)-structure: build a model, calculate the scattering (diffraction), vary the model to optimize the fit between experiment and theory. The nanostructural picture that emerges from our simulations is one of PNR that, to first order, are spatially static but orientaionally dynamic. Spatially static because PNR are strongly correlated with COR. Orientationally dynamic because the simulations exhibit PNR/COR in which local-mode displacements are more strongly correlated than in the PRM, whith average orientations that rotate rather freely.
10:45 AM - HH3.4
Atomic and Electronic Structure of Graphene-Oxide.
K. Mkhoyan 1 2 , Alexander Contryman 2 , John Silcox 2 , Derek Stewart 3 , Goki Eda 4 , Cecilia Mattevi 4 , Steve Miller 4 , Manish Chhowalla 4
1 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 Applied Physics, Cornell University, Ithaca, New York, United States, 3 Cornell Nanoscale Facility, Cornell University, Ithaca, New York, United States, 4 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractThe solubility of graphene oxide (GO) sheets, which recently emerged as a new carbon-based nanoscale material, in water allows it to be uniformly deposited in the form of thin films or networks which makes them potentially useful for macroelectronics [1,2]. Graphene oxide is an insulator but controlled oxidation provides tunability of the electronic and mechanical properties including the possibility of accessing zero-band-gap graphene via complete removal of the C-O bonds. The structure of GO is often simplistically assumed to be a graphene sheet bonded to oxygen in the form of carboxyl, hydroxyl or epoxy groups. Here, we elucidate the atomic and electronic structure of GO using composition sensitive annular dark field (ADF) imaging of single and multilayer sheets and electron energy loss spectroscopy (EELS) for measuring the fine structure of the carbon and oxygen K-edges as well as low-loss electronic excitations in a scanning transmission electron microscope (STEM). The results reveal that the GO sheets are rough with an average roughness of 0.6 nm and the structure is predominantly amorphous due to distortions from the high fraction of sp3 C-O bonds. Our results suggest that chemical removal of oxygen, using hydrazine for example, may leave behind a highly distorted reduced graphene oxide sheet which is likely to have substantially lower carrier mobilities than pure graphene, as has been observed in several device studies [2].Electron energy loss spectroscopy combined with STEM-ADF imaging and AFM-depth profiling shows that graphene oxide films have substantially different density-of-states and resonance electron plasma excitation energy than those in graphene and a-C. It also indicates that oxygen atoms during the oxidation process attach to graphene sites randomly and convert sp2 carbon bonds in graphene to sp3 bonds. While the structural modifications of graphene are dependent on the oxidation level, the results show that a ratio of 1 to 5 oxygen to carbon atoms is sufficient to transform the measured 40% of the carbon bonds into sp3 bonds. As a consequence, the atomic structure of oxidized graphene sheets is highly distorted, becoming a semi-amorphous sheet of solid carbon-oxide with undulations resulting in a surface roughness of about 0.6 nm. These results are also supported by our ab initio calculations. Our results provide new insight into the structure of graphene oxide and indicate that in addition to the removal of oxygen, structural ordering of the remaining graphene sheets is necessary if high mobilities from reduced graphene oxide devices are to be achieved [3].[1] S. Stankovich et al., Graphene-based composite materials, Nature 442, 282-286 (2006).[2] G. Eda et al., Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material, Nature Nanotechnology 3, 270-274 (2008).[3] K.A. Mkhoyan et al., Atomic and electronic structure of graphene-oxide, (submitted).
11:30 AM - **HH3.5
Periodicity and Atomic Ordering in Nanophase Crystals.
Valeri Perkov 1
1 Physics, CMU, Mt. Pleasant, Michigan, United States
Show AbstractEvidence is mounting that nanophase crystals do not necessarily adopt the periodic structure of their bulk counterparts or any other structure that may be considered as a stack of well defined unit cells/atomic planes, and that this may affect their properties substantially. We will show how a combination of experimental and computational techniques including total x-ray diffraction, EXAFS, Density Functional Theory, “real-space” Rietveld and reverse Monte Carlo simulations may be employed to determine the atomic ordering in nanophase “crystals” with any degree of structural periodicity with success [1,2,3,4].References: 1. M. Gateshki et al. “Atomic scale structure of nanocrystalline ZrO2", Phys. Rev. B 71 (2005) 22410. 2. S. Pradhan et al. “Atomic-scale structure of nanosize titania and titanate: particles, wires and tubes”, Chem. Mat. 19 (2007) 61803. V. Petkov et al. “Periodicity and atomic ordering in nanosized particles of crystals" J. Phys. Chem. C 112 (2008) 8907.4. V. Petkov et al. “Structural Coherence and Ferroelectricity Decay in Submicron- and Nanosized Perovskites”, Phys. Rev. B 78 (2008) 054107.
12:00 PM - HH3.6
Crystallographic Characterization of Nanostructured and Amorphous Materials using High-energy X-rays by means of X-ray Diffraction on a Homelab System.
Hans te Nijenhuis 1 , Milen Gateshki 1 , Detlef Beckers 1 , Martijn Fransen 1
1 Product Management XRD, PANalytical B.V., Almelo Netherlands
Show AbstractRecent interest in the understanding of physical and chemical properties of nanomaterials has increased the need to analyze structures on a local (nano) scale. However, the atomic structures of nanostructured and amorphous materials are not accessible by conventional methods used to study crystalline materials, because of the short ordering range in these materials. One of the most promising techniques to study nanostructures using X-ray diffraction is total scattering pair distribution function (PDF) analysis. The pair distribution function provides information about the probability of finding atoms separated at a certain distance. We have developed the application of PDF analysis on a standard laboratory system. As X-ray source an X-ray tube with a silver anode was used, delivering characteristic Ag Kα radiation with an energy of 22 keV. The corresponding X-ray wavelength is 0.05564 nm. Samples of different nature –crystalline, nanocrystalline, amorphous solid and even liquid -have been used to test the applicability of the PDF calculations on the lab measurements. Meaningful results have been achieved, even though the attainable X-ray photon energies are not as high as with synchrotron radiation. The PDF analysis revealed the short range order by determining the existing interatomic distances. The results allowed for comparison with data reported in literature, obtained using high-energy synchrotron radiation.
12:15 PM - HH3.7
Defect Study of Graphene and Observation of Mis-orientation using Raman Spectroscopy.
Gayathri Rao 1 , Sarah Mctaggart 1 , Robert Geer 1 , Ji Ung Lee 1
1 College of Nanoscale sciences and engineering, University at Albany, Albany, New York, United States
Show AbstractNanoscale metrology (thickness, defectivity) of graphene-based devices is a substantial challenge. The investigation of defects and stacking order is essential for graphene-based device development. Raman spectroscopy has proved to be an appropriate approach in this regard. The defect-induced Raman D and D’ peaks give great insight into study of defects and their potential impact on device structures . Toward this end we have carried out a defect study on customized bi-layer and mono layer graphene samples by analyzing the Raman D, D’ and 2D bands. Defects were introduced via electron irradiation of customized exfoliates at controlled dose in a Leo 1550 scanning electron microscopy. The evolution of the aforementioned Raman spectra as a function of dose was characterized via microRaman spectroscopy and compared with spectra from the same samples prior to irradiation. The impact of the defects created was visible from the intensity ratios of the D to G Raman bands (ID/IG) before and after defect creation. For bilayer graphene, modification to the 2D band peak-shape and 2D FWHM was also observed as a result of electron irradiation. The peak positions and widths of the 4 fitted 2D Raman band component peaks, explained by the process of double-resonance Raman scattering, was used to infer variations in bilayer-graphene band structure due to the electron irradiation. Preliminary analysis of the 2D1B,2D1A,2D2A and 2D2B Raman peaks from electron-irradiated bilayer graphene exfoliates from ZYH, ZYA, and, presumably, Kish graphite imply that induced defectivity impacts mis-orientation (e.g. from Bernal-type bilayer) and impacts the 2D Raman bands accordingly. These results are discussed and compared to recent Raman analysis of CVD bilayer graphene films.
12:30 PM - HH3.8
Synchrotron-Based Analysis of Structural Ordering and its Impact on the Luminescent Properties of Nitride- and Oxynitride-Passivated Silicon Nanoclusters.
P. Wilson 1 2 , T. Roschuk 1 2 , J. Wojcik 1 2 , K. Dunn 1 2 , M. Betti 1 2 , P. Mascher 1 2
1 Engineering Physics, McMaster University, Hamilton, Ontario, Canada, 2 Centre for Emerging Device Technologies, McMaster University, Hamilton, Ontario, Canada
Show AbstractEfficient luminescent from silicon can be obtained through quantum confinement effects in the form of silicon nanoclusters (Si-ncs). The Si-ncs are typically formed within Si-based dielectric films and their luminescent properties exhibit complex behaviour largely dependent on the coordination at the Si-nc/dielectric interface and the physical properties of the dielectric matrix. Due to the potential for developing Si-based light sources using such materials systems, research into understanding this behaviour has garnered much interest.X-ray absorption spectroscopy (XAS) experiments have been conducted on a wide range of samples exhibiting different emission properties in an effort to link observed optical phenomena with the structural ordering of the Si-ncs and dielectric host matrix. Samples were prepared through the deposition of silicon-rich nitride (SRSN) and oxynitride (SRSON) thin films using plasma-enhanced chemical vapour deposition (PECVD). Post-deposition processing involved thermal annealing of the samples in quartz tube and rapid thermal annealing furnaces under flowing ambient gas. Samples with different properties were obtained by varying the deposition gas flow rates as well as the annealing time, temperature, and ambient gas used.The luminescent properties of the films were determined with photoluminescence measurements using a 325 nm HeCd laser source. The XAS experiments were performed at the high resolution spherical grating monochromator and variable line spacing plane grating monochromator beamlines at the Canadian Light Source synchrotron facility using photon energies corresponding to the Si, N, and O K-edges and Si L-edges. These experiments provide access to the electronic structure of the films, which can be used to gain quantitative information on the chemical environment and local bonding coordination of the Si-ncs through a spectral deconvolution analysis. For SRSN films, emission appears to originate from both quantum confinement effects and inter-bandgap defect levels. The results from the XAS experiments show structural reordering of both the Si-ncs and host matrix, with evidence of increased phase separation of the clusters occurring at lower temperatures for samples with higher excess silicon concentration. However, the SRSON films only exhibit defect-related emission and the XAS results do not indicate structural changes in the Si-ncs at any annealing temperature while the host oxide and nitride matrices undergo significant reordering.This work has been supported by the Ontario Research and Development Challenge Fund under the auspices of the Ontario Photonics Consortium, by the Centres for Photonics and Materials and Manufacturing, divisions of Ontario Centres of Excellence Inc, and by the Natural Sciences and Engineering Research Council of Canada (NSERC). Part of this work was performed at the Canadian Light Source facility, which is supported by NSERC, CIHR, NRC, and other government agencies.
HH5: Poster Session
Session Chairs
Thursday AM, April 16, 2009
Salon Level (Marriott)
9:00 PM - HH5.11
Spectroscopic Raman Nanometrology of Suspended and Supported Graphene Ribbons
Irene Calizo 1 , Muhammad Rahman 1 , Alexander Balandin 1
1 Electrical Engineering and Materials Science and Engineering Program, University of California - Riverside, Riverside, California, United States
Show AbstractMicro-Raman spectroscopy is an effective tool for graphene characterization. However, most of the Raman spectroscopy studies of graphene were limited to graphene layers on silicon/silicon-oxide substrates with a carefully selected thickness of the oxide layer. For quantitative characterization of graphene nanostructures and for graphene device applications it is important to investigate how the Raman signatures from graphene are affected by different substrates. Another important issue is the influence of the width of a graphene ribbon and the edge states on the Raman spectrum. Here we review our recent results of the investigation of a large number of graphene flakes and ribbons on various substrates or suspended across trenches in silicon wafers. The number of atomic layers in the examined samples was confirmed by the atomic force microscopy and analysis of the 2D-band in Raman spectrum [1]. We investigated Raman spectra from graphene layers on GaAs, sapphire and amorphous glass substrates and compared them with those from graphene on the standard silicon substrate and graphene flakes suspended over trenches in the wafers. The weak influence of the substrates on the Raman spectra was explained by the polarization and dispersion features of the main phonon branches in graphene. We also studied the effect of temperature on the most characteristic peaks in the Raman scattering spectra of graphene. The measurements were carried out with the external control of the sample temperature. We observed the red shift of G peak of graphene with increasing temperature despite anomalous temperature expansion of the graphene crystal lattice. The value of the temperature coefficients for the G-band peak of the single-layer graphene is -1.6×10-2cm-1/K [2]. The obtained temperature coefficients of graphene Raman peaks allowed us to carry out the first measurements of the thermal conductivity of graphene [3]. A comparison of Raman spectra for the suspended graphene ribbons with those of the supported ribbons and flakes allowed us to further expand the use of Raman spectroscopy as quantitative characterization, i.e. nanometrology, tool for graphene nanostructures.The work in Balandin group was supported, in part, by DARPA – SRC Focus Center Research Program (FCRP) through its Functional Engineered Nano Architectonics (FENA) center and Interconnect Focus Center (IFC). The initial experimental work was done in cooperation with Prof. C.N. Lau (UCR). [1] I. Calizo, W. Bao, F. Miao, C.N. Lau and A.A. Balandin "The effect of substrates on the Raman spectrum of graphene: Graphene-on-sapphire and graphene-on-glass," Appl. Phys. Lett., 91, 201904 (2007).[2] I. Calizo, A.A. Balandin, W. Bao, F. Miao and C.N. Lau, "Temperature dependence of the Raman spectra of graphene and graphene multi-layers," Nano Letters, 7, 2645 (2007).[3] A.A. Balandin, et al., "Superior thermal conductivity of single-layer graphene," Nano Letters, 8, 902 (2008).
9:00 PM - HH5.12
A Comprehensive Approach for Quantitative Characterization of Nanosturctures by Scanning Probe Microscopy
Amjed Al-mousa 1 2 , Darrell Niemann 1 , Norman Gunther 1 , Mahmud Rahman 1
1 Electron Devices Laboratory, Electrical Engineering, Santa Clara University, Santa Clara, California, United States, 2 , PDF Solutions, San Jose, California, United States
Show AbstractNanoporous and nanocrystalline materials are becoming increasingly important in emerging devices and systems. In order to fully understand the functional properties of the nanostructures in such systems, it is necessary to quantify structural information associated with external surfaces at multiple length scale employing a combined approach. In this paper, an analysis methodology based on our recently developed feature recognition algorithm is presented. This algorithm isolates surface nanostructures and extracts quantitative information such as their shape and size. The algorithm is independent of feature size, and does not require any data-dependent threshold. Here, we successfully employed the algorithm to analyze Atomic Force Microscopy (AFM) data and extracted information about features on the order of tens of nanometers. The algorithm, however, can easily be adapted to process other types of Scanning Probe Microscopy (SPM) measurements.In order to identify the salient features of the surface, a moving average filter is deployed once vertically and then horizontally. The height and slope data along the scan lines and perpendicular to it are then processed separately to identify features such as hills, valleys, and flat areas in each direction. This process identifies regions that correspond to surface structures of interest, which we call Potential Structure Points (PSP). Next, the horizontal and vertical data are overlaid and points which are recognized both horizontally and vertically as PSPs are classified as Structure Points (SP). A clustering algorithm then sweeps the data to organize neighboring SPs into structures.Any discontinuities that may appear in the AFM data due to hysteresis are corrected by the algorithm by calculating the shift in the average of each scan line, and then statistically identifying the lines that show anomalous shifts. Once identified, these scan lines are biased to eliminate the discontinuities. Further, since the measured AFM data are strongly influenced by the size and shape of the AFM tip, our algorithm considers the convoluting effect of the tip shape on sharp edges. In summary, we have developed and tested an algorithm for analyzing surface nanostructures which is independent of the shape and size of the surface features. It is robust to entire classes of data anomalies, such as the raster discontinuities which frequently occur due to substrate hysteresis or to instrument vibration. Probe tip size and shape effects have important impact on the minimum curvature radii which can legitimately be expected in processed data. These expectations have been borne out quantitatively in our tests with AFM data. We apply our methodology to analyze AFM data for crystalline films of organic semiconductors.
9:00 PM - HH5.13
X-ray Scattering Study of Interface Evolution and Grain Growth in Encapsulated Cu films.
Andrew Warren 1 , Yao Bo 1 , Tik Sun 1 , Katayun Barmak 2 , Michael Toney 3 , Kevin Coffey 1
1 Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, Florida, United States, 2 Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 3 , Stanford Synchrotron Radiation Laboratory, Menlo Park, California, United States
Show AbstractThe scattering of electrons by surface roughness and grain boundaries have been considered as key contributors to high resistivity in Cu interconnects as the conductor dimensions approach the mean free path of the conduction electrons. To study the influence of annealing on interface roughness, a series of Cu thin films with thicknesses of 28 to 158 nm, encapsulated in SiO2 and Ta/SiO2, were sputter deposited onto thermally oxidized Si wafers. The samples were annealed at 150°C and at 600°C following deposition. Specular x-ray reflectivity was used to separately determine the root mean square roughness for both the upper and lower Cu interfaces. The lateral correlation length of the roughness was studied by diffuse x-ray reflectivity and grazing incidence small angle x-ray scattering. The roughness of the lower SiO2/Cu interface was constant at an average 1.0±0.1 nm, independent of annealing temperature. By contrast, the roughness of the upper Cu/SiO2 interface decreased from 1.0±0.1 nm to 0.35±0.05 nm upon annealing at 600°C. Such a reduction in roughness with annealing was not observed in the SiO2/Ta/Cu/Ta/SiO2 samples. The lateral correlation length scaled with thickness for all samples, and annealing at 600°C resulted in a longer lateral correlation length. Grazing incidence X-ray diffraction was used to determine the in-plane grain size of the Cu films. This is quantitatively compared to separate grain size measurements performed on the same set of samples using transmission electron microscopy (TEM), wherein hollow cone dark field imaging was utilized to provide enhanced diffraction contrast. Agreement between the TEM and X-ray measures of average grain size is observed for samples with grain size below 80nm.
9:00 PM - HH5.14
Polymeric Hydrophobic Gold Nanoparticles for Optical and X-ray Computed Tomography Imaging Contrast Agent.
Yoonah Kang 1 , Eun-Kyung Lim 1 , Jin-Suck Suh 2 , Yong-Min Huh 2 , Seungjoo Haam 1
1 Department of Chemical Engineering, Yonsei University , Seoul Korea (the Republic of), 2 Department of Radiology, Yonsei University, Seoul Korea (the Republic of)
Show AbstractGold nanoparticles (GNPs) can absorb and scatter the electromagnetic radiation induced from x-ray and enhance their intensities because of strong electric fields at surface. A new computed tomography imaging agent, GNPs not only overcome these limitation but has a higher atomic number and a higher absorption coefficient than iodine (common CT contrast agent). Furthermore, polymer coated GNPs permit longer imaging times since they have longer circulation time.In this study, we synthesized polymeric hydrophobic gold nanoparticles (PHGNs) to serve as nano-probes for optical and x-ray computed tomography imaging contrast agent for breast cancer detection. First, hydrophobic GNPs were synthesized by reduction of tetrachlroloaurate(III) trihydrate, in the presence of sodium borohydride, tetraoctylammonium bromide, and dodecanethiol (DdSH). The refined product was dissolved in chloroform using coated with DdSH because the terminal thiol group of dodecanethiol has a strong attachment to GNPs. Water dispersion polymeric hydrophobic gold nanoparticles were then finally obtained by the encapsulation of hydrophobic GNPs with sodium dodecyl sulfate (SDS) as an amphiphilic surfactant by nanoemulsion method. The morphology of PHGNs was evaluated by transmission electron microscopes and scanning electron microscopic and revealed that DdSH-GNPs were successfully encapsulated by SDS. The DdSH-GNPs was soluble only in chloroform and the PHGNs were dispersed only in distilled water due to the hydrophilic portion of SDS or phase transfer phenomena. PHGNs were demonstrated excellent colloidal stability in water phase because of repulsion force of SDS coated DdSH-GNPs (PHGNs). The chemical structure of the synthesized PHGNs was confirmed by FT-IR. These results suggested that the DdSH-GNPs existed successfully in PHGNs. The quantity of GNPs in PHGNs was measured using a thermogravimetric analyzer. The quantity of GNPs encapsulated in PHGNs was 49.2wt% (25% dodecanethiol, 25.8% SDS). The crystallinity of GNPs in the PHGNs could be evaluated using X-ray diffraction patterns. The surface charge and size distribution of prepared PHGNs were analyzed using dynamic light scattering. The size distribution and zeta potential value of PHGNs were 133 ± 1.1 nm and -13.5 ± 1.4 mV, respectively. We performed a MTT assay to examine the cellular cytotoxicity of PHGNs. A MTT assay was performed using NIH3T3 and NIH3T6.7 cells treated with PHGNs. Furthermore, the scattering image for well-distributed GNPs in the PHGNs can be obtained by dark-field microscopy. We calibrated the x-ray absorption of the PHGNs to investigate CT contrast efficacy of PHGNs. The maximum HU value of PHGNs was reached at 954.9 HU. This result clearly indicates that the PHGNs have a high potential for use in vivo CT imaging. Consequently, these results demonstrate that synthesized PHGNs have highly versatile biomedical characteristic such as optical and x-ray computed tomography imaging contrast agent.
9:00 PM - HH5.15
Characterization of Boron Nitride Films Growth by Chemical Vapor Deposition.
Jose Nocua 1 2 , Gerardo Morell 1 2
1 Physics, University of Puerto Rico, Rio Piedras, Puerto Rico, United States, 2 , Institute for Functional Nanomaterials, San Juan, , Puerto Rico, United States
Show AbstractBoron nitride nanotubes (BNNT’s) shown an insulating character, independent of their diameter and helicity. Are structural analogues of carbon nanostructures, chemically inert, and potentially important in mechanical applications that include the strengthening of light structural materials for the aerospace industry. Using borazine (B3N3H6) as a precursor and technique of chemical vapor deposition and maintaining the temperature of the heater at 800oC for 30 minutes were deposited on silicon substrates boron nitride films. Their morphology was examined by scanning electron microscope (SEM) and transmission electron microscopy (TEM), while its chemical composition was studied by techniques scanning electron microscopy energy dispersive (EDS), Fourier transform infrared spectrometry (FTIR), electron energy loss spectroscopy (EELS) and, X-ray photoelectron spectroscopy (XPS). These results indicate that the material that is obtained is BN with hexagonal structure.
9:00 PM - HH5.16
Synthesis Processing And Characterization Of CU-CNT Nano-Composites
Martin Mendoza 1 , Guillermo Solorzano 1 , Eduardo Brocchi 1
1 Metallurgic and Materials , PUC-Rio, Rio de janeiro, Rio de Janeiro, Brazil
Show AbstractThe increasing interest in nanostructured materials in recent years has provided incentive to develop new synthesis procedures aiming at obtaining important amounts of this type of material. Leading this effort a new category of materials: carbon nanotubes (CNT)- containing metal-matrix nanocomposites1,2,3. Such motivation relies on the well-established superior mechanical and transport properties of CNT4, In the former CNT exhibits a Young’s modulus of 1 TPa and a tensile strength of 30Gpa 5 , thereby as an ideal reinforcing additive in composites. In the present work, copper matrix nano composite with carbon nanotubos (2% wt) was produced by chemical synthesis method 6,7. The procedure begins by the copper nitrate dissociation containing SWCNT and anionic tensoactive agent at 250°C, followed by in-situ reduction at 350°C, under hydrogen atmosphere at pressure of 1atm. CuO and Cu formation was confirmed by X ray diffraction at the moment of dissociation and reduction respectively. CNTs presence was detected at both steps by this characterization method. Transmission Electron Microscopy analysis, estimate particles grain size of 30nm for CuO powder while Cu powder particles were observed to be in the 100-300nm range, showing good dispersion of CNT. Bulk nano-composite pellets of the reduced material were obtained by pre-compactation under uniaxial pressure of 17 MPa followed by issostatic pressure of 150MPa. Sinterizing of the compacted material was carry out at 650°C under Argon atmosphere by 15 min. Scanning Electron Microscopy and Transmission Electron Microscopy analysis of the sinterized material showed an heterogeneous grain size distribution in the 100nm to 4 um range. Electric resistivity measures show that the nanocomposite material has lower resistivity at low temperature (2x10-6 ohm.cm) at 83°K than the copper without carbon nanotubes (5.9x10-6 ohm.cm). Vickers micro hardness measures, indicate a considerate increasing of hardness of the composite material with CNTs (70HV) when it is compared with copper without nanotubos(32HV), processed at the same conditions.1 Cornelia Otto. Synthesis and Characterization of CNT Reinforced Copper Thin Films. Dissertation Stuttgart University. Bericht Nr. 194 November 2006.2 J.P. Tu, Y.Z. Yang, L.Y. Wang and X.B. Zhang Tribology letters Vol 10 No4, 2001.3 William A. Curtin and Brian W. Sheldon.. Materialstoday November 2004.4 K. T. Kim et al., Materials Science and Engineering A 449-451 (2007) 46-505 P. Quang, S.C. Yoon, Materials Processing Technology187-188 (2007) 318-320.6 P. Ayala, F.L. Freire, , David J. Smith, I.G. Solorzano. Chemical Physics Letters 431(2006) 104-109.7 P.K. Jena, E.A. Brocchi, M.S. Motta. Materials Science & Engineering A313(2001) 180-186.
9:00 PM - HH5.17
In-situ Synchrotron X-ray Scattering Study on the Initial Structure of Ruthenium Atomic Layer Deposition Films for the Electronic Devices.
Yong Jun Park 1 2 , Han-Bo-Ram Lee 2 , Woo-Hee Kim 2 , Dong-Ryeol Lee 4 , Hyungjun Kim 2 , Shi-Woo Rhee 3 , Sunggi Baik 2
1 Beamline division, Pohang Accelerator Laboratory, Pohang, Gyeongbuk, Korea (the Republic of), 2 MSE, POSTECH, Pohang, Gyeongbuk, Korea (the Republic of), 4 Physics, Soongsil Univ., Seoul Korea (the Republic of), 3 CE, POSTECH, Pohang, Gyeongbuk, Korea (the Republic of)
Show AbstractWe report microstructures of initial growth of ruthenium (Ru) films, which were prepared by Atomic Layer Deposition (ALD) method. Ru is a promising material as an adhesion layer or diffusion barrier of copper interconnect in semiconductor electronic device. As devices scale down, the ALD is expected to play an important role for the next generation MOSFET due to its excellent step coverage and precise thickness control. To characterize the microstructure and physical properties during ALD growth, we used the in-situ ALD growth chamber, installed on the diffractometer at 3C2 XRD beamline in Pohang Light Source. Since the ALD growth is strongly dependent on the initial surface state and reaction, we concentrate on the initial structures. Synchrotron X-ray scattering measurement with high photon flux allowed us to characterize the microstructure of 1~2 nm films at initial growth stage, nondestructively.Significant differences between in-situ and ex-situ X-ray scattering measurement will be displayed. And also, we show the strong point of X-ray scattering measurement compare with the conventional methods. The results obtained by the X-ray scattering measurement are consistent with the SEM results. X-ray scattering analysis can be applied an inline characterization method for industry to measure physical morphologies.
9:00 PM - HH5.18
Theoretical Study of Adsorption and Thermal Desorption of Fullerenes on the Crystal Surface.
Svetlana Zaginaichenko 1 , Zinaida Matysina 1
1 67, Institute for Problems of Materials Science of NAS of Ukraine, Kiev Ukraine
Show AbstractA statistical theory of adsorption and thermal desorption of fullerenes in a multi-layer fullerite film on a crystal surface has been developed. These processes for multi-layer film of fullerenes of different kinds (hollow C60, C70 or endohedral M@C60, M@C70 or hydrogenated C60Hn, C70Hn, n > 36) evaporated on the free plane of crystal have been investigated. The calculation of the free energy of the system has been carried out by the method of average energies in approximation of pair interaction between nearest fullerenes and fullerenes with atoms of crystal substrate and also in assumption of geometrical ideality of structures both of substrate and fullerite film. The equilibrium fullerene concentration has been calculated as a function of temperature, film thickness and energy constants of the system. The temperature of desorption its dependence on film thickness have been evaluated. The limitary concentration of fullerenes for different numbers of monolayers has been found. The considerable increase of concentration of adsorbed fullerenes with a rise of film thickness at low temperatures has been justified. The developing processes of adsorption with increase in temperature and desorption at a high temperatures, which were observed experimentally, have been validated.
9:00 PM - HH5.19
The Structure of Amorphous Calcium Phosphate – a Key Intermediate in Skeletal Calcification.
Kate Wetherall 1 , Richard Haworth 1 , Richard Martin 1 , Robert Moss 1 , Danielle Laurencin 2 , Gavin Mountjoy 1
1 School of Physical Sciences, University of Kent, Canterbury, Kent, United Kingdom, 2 Department of Physics, University of Warwick, Coventry United Kingdom
Show AbstractResearch into the process of bone calcification has studied the transformation of calcium and phosphate ions into hydroxyapatite and has identified an intermediate amorphous phase. The precipitate known as Amorphous Calcium Phosphate (ACP) has the approximate composition Ca3(PO4)2.nH2O but its local structure is unknown. The only structural studies carried out were performed decades ago with lab based equipment. They theorised the material was composed of clusters in the order of 10Å, but this hypothesis has never been proven. Presented here are the initial results of a complete structural study of ACP using diffraction, absorption spectroscopy, small angle scattering, microscopy and many more techniques. Results so far have already revealed structure on several length scales. It is hoped that if the structure of this material can be fully understood then it will improve the understanding of the reaction between biomaterials and the body and hence aide in their development.
9:00 PM - HH5.2
Manipulating the Morphology of Polymer-Fullerene Bulk Heterojunctions through Selective Solvent Annealing.
Eric Verploegen 1 2 , Michael Toney 2 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Menlo Park, California, United States
Show AbstractManipulating the Morphology of Polymer-Fullerene Bulk Heterojunctions through Selective Solvent Annealing. The optimization of bulk heterojunction blend morphologies is critical in order to achieve increased performance in organic photovoltaic devices. The nanophase segregated heterojunction domain size must be about the same as the exciton diffusion length in order for efficient conversion of adsorbed photons into electrical current. In addition, the morphology and molecular packing of both the acceptor and donor within their respective domains should be optimized for maximum electron and hole mobilities. Thermal and solvent annealing have shown utility for improving such morphologies. Typically, extended annealing leads to unfavorable coarsening of the acceptor and donor domains, resulting in phase segregation larger than the exciton diffusion length. It is desirable to optimize the morphology/packing – e.g. increase the crystallinity – of these domains without allowing for the size of the domains to grow. We present a selective solvent annealing strategy that allows for each domain to be essentially annealed individually: each domain “locks in” both the nanoscale domain size and optimal morphology/packing. The system is first thermally annealed in order to obtain the desired domain size. By then exposing the blend to solvent vapor that selectively swells the fullerene domains, sufficient mobility is provided to allow for increased crystallization, while the polymer domains prevent the fullerene crystallization from increasing the domain size. A second annealing step, this time with a solvent vapor that is selective for the donor polymer, facilitates crystallization of the polymer domains, while the crystalline fullerene domains prevent coarsening of the domains. The annealing process is monitored in-situ to observe the morphological and structural evolution with grazing incidence diffraction (GID) and small angle X-ray scattering (SAXS) to allow to for effective optimization of the morphologies.
9:00 PM - HH5.20
Low Energy Electron Microscopy of Ge Deposition on Unpatterned and Patterned Si (001) Surfaces.
Jacob Thorp 1 , Jeremy Graham 1 , Jerrold Floro 1 , Robert Hull 2 1
1 Materials Science & Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Materials Science & Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractLow Energy Electron Microscopy (LEEM) using a SPECS P90 system has been used to observe the growth of Ge wetting layers and quantum dots on patterned and unpatterned Si (001). LEEM allows for in situ growth of thin films (in this case, deposition of Ge from an effusion cell) to be observed in real time with image acquisition rates as low as tens of ms and lateral spatial resolutions of ~ 5-10 nm. Diffraction contrast imaging using the orthogonal 2x1 and 1x2 reflections from the reconstructions of the Si (001) surface in the Low Energy Electron Diffraction (LEED) pattern enables high contrast imaging of surface domains and intervening atomic steps.[1] Our LEEM experiments on unpatterned surfaces enable us to study the atomic evolution of the surface structure during Ge wetting layer deposition. In particular we are studying the relative degrees of terrace nucleation vs. step attachment during Ge wetting layer growth, and examining the evolution of surface step roughness following previous STM studies that show reversal of type SA and SB step roughness during wetting layer growth.[2] We are also studying the evolution of the Ge wetting layer and subsequent quantum dot nucleation on surfaces that are patterned with a focused ion beam (FIB). In particular, we pattern the Si surface with a mass selecting FIB that enables generation of a silicon ion beam from an AuSi source to ensure that the surface is not locally doped as it would be for a conventional Ga ion beam. In this manner we also eliminate any role of chemical effects on the templating associated with the localized FIB surface treatment. Following in-situ cleaning of the patterned Si(001) surfaces, LEEM shows highly ordered terraces with large, preferentially directed surface domains around the ion patterned areas. These large area domains are expected to have significant effects on the nucleation of Ge quantum dots on the FIB template sites, as adatoms landing on terraces then typically have to cross very few (if any) steps to reach quantum dot nucleation sites at the FIB pits. This may have significant ramifications for our previous studies of templated Ge quantum dot growth on FIB patterns,[3] and should enable us to develop additional insight into the correlation of quantum dot nucleation kinetics (e.g. the effects of capture zone size) to the detailed local surface structure. 1. R.M. Tromp, IBM J. Res. Dev. 44, 4 (2000)2. Feng Liu, Fang Wu, M.G. Lagally, Chem. Rev., 97, 1045 (1997)3. A Portavoce et al, Nanotechnology 17, 4451 (2006)
9:00 PM - HH5.21
High Resolution TEM Lattice Imaging of Lead Chalcogenide|Cadmium Chalcogenide Colloidal Nanoparticles
Karel Lambert 1 , Bram De Geyter 1 , Iwan Moreels 1 , Zeger Hens 1
1 Physics and Chemistry of Nanostructures, Ghent University, Gent Belgium
Show AbstractCovering colloidal semiconductor quantum dots (QDs) with an inorganic shell of a second material has become a popular approach to tailor the optical properties of these nanomaterials. If the energy levels of the shell encompass those of the core (type 1 band alignment), this results in nanoparticles with an enhanced and stable luminescence quantum yield. A staggered band alignment (type 2) offers much more possibilities since it leads to a spatially separated exciton which feature, for instance, a much lower threshold for light amplification [1]. Core|shell particles are typically made by growing additional material on top of the initial core particle. An apparently straightforward alternative is offered by cationic exchange, where a core|shell particle is grown by partial replacement of the initial cations in the core by others [2]. In this contribution, we use high resolution TEM lattice imaging of PbTe|CdTe and PbSe|CdSe core|shell QDs to evaluate this procedure. First, we show that the slight difference in lattice constant enables the simultaneous imaging of the core and the shell crystal lattice. These images demonstrate that the zincblende CdTe and CdSe shells are fully aligned with the rocksalt PbTe and PbSe cores, suggesting that either the anionic or the cationic sublattice continues coherently throughout the whole heterostructure. Second, we find that core and shell are preferentially separated by {111} interfaces. Since the {100}, {110} and {111} interfaces have similar interfacial energy [3], this points towards an anisotropic growth mechanism. This anisotropy is reflected in a strong increase in sample heterogeneity. We find that cationic exchange leads to a variety of core sizes, core shapes and core positions, from central, quasi-spherical cores to completely eccentric, elongated structures. We conclude that cationic exchange is not as straightforward an approach to make colloidal core|shell QDs particles as it may seem, and that high resolution structural characterization is crucial to its evaluation.[1]Klimov, V. I., Ivanov, S. A., Nanda, J., Achermann, M., Bezel, I., McGuire, J. A., Piryatinski, A., Nature 447, 441-446 (2007).[2]Pietryga, J.M.; Werder, D.J.; Williams, D.J.; Casson, J.L.; Schaller, R.D.; Klimov, V.I.; Hollingsworth, J.A. J. Am. Chem. Soc. 2008 130, 4879-4885[3]Leitsmann, R.; Ramos, L.E.; Bechstedt, F. Phys. Rev. B 2006 74, 085309
9:00 PM - HH5.23
Strained Silicon Nanomembranes using a Polycrystalline Silicon Nitride Stressor.
Anna Clausen 1 , Donald Savage 1 , Chanan Euaruksakul 1 , Chen-Chun Chen 1 , Max Lagally 1
1 Materials Science, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractStrained (001) silicon nanomembranes have recently been produced through epitaxial growth of SiGe stressor layers, with strain up to 1% in the Si layer [1]. These nanomembranes provide flexible, transferable Si with increased electron mobility. Currently, this technique relies on expitaxial growth of the stressor layer by chemical vapor deposition (CVD) or molecular beam epitaxy, techniques that are sensitive to surface conditions and that require great care during growth. We strain thin Si layers in silicon-on-insulator (SOI) using instead a polycrystalline silicon nitride (SiN) stressor layer, grown by plasma-enhanced CVD (PECVD), covering the whole surface. The strained Si can then be released from the buried oxide and transferred to a new substrate. PECVD growth proves to be less sensitive to surface conditions and has several free parameters to control the stress of the nitride layer, from tensile to compressive. Previous efforts to incorporate strain in the template layer of SOI with polycrystalline SiN have been made with low-pressure CVD for terrace [2] and ledge and beam shapes [3]. Our technique is unique because the full release of SiN/Si layers from the oxide creates elastically strain-shared Si nanomembranes that can then be transferred and bonded flat to a new substrate. We analyze the strain in transferred nanomembranes with high-resolution x-ray diffraction (XRD) and Raman spectroscopy. The presence of thickness fringes in XRD indicates the membranes relax elastically without appreciable dislocation formation. Raman spectroscopy confirms the uniformity of strain and its magnitude. Transmission electron microscopy and low-energy electron microscopy are used to examine the Si films for dislocations at densities below what XRD can see. Results are in good agreement with predictions of continuum elasticity theory.This work is supported by the DOE.[1] Roberts, M. et al., Nature Mat. 5, 388-393 (2006). [2] Kosemura, D. et al., J. Electrochem. Soc. 6, 245-250 (2007). [3] Tanaka, M. et al., App. Surf. Sci. 254, 6226-6228 (2008).
9:00 PM - HH5.24
Initial Growth Structure of Ge on GaAs(001).
Jun Nara 1 , Akihiro Ohtake 2 , Takahisa Ohno 1
1 CMSC, National Institute for Materials Science, Tsukuba Japan, 2 QDC, National Institute for Materials Science, Tsukuba Japan
Show AbstractThe heterovalent interface between a group IV elemental semiconductor and a III-V compound semiconductor may cause the charge depletion or the charge oversaturation by 0.25 electron, according to simple bond charge picture. For the polar (001) and (111) orientations of the ideally abrupt interfaces, such electrically charged defects give rise to the formation of a macroscopic electric field, which make the interface unstable. In order to achieve the charge neutrality at the interface, redistributions of the charge and/or atomic rearrangements are required. However, little is known as to how the heterovalent interfaces are formed.It is known that at the initial stage of the Ge growth on GaAs(001), a reconstructed structure with a (1x2) periodicity is formed [1-3]. A structure model built up with Ga-Ge dimer on the As-terminated (001) surface has been proposed for the Ge-induced (1x2) reconstruction [2], and has been found to be stable by first-principles calculations [4]. On the other hand, the previous studies have shown that the As atoms segregate to the growing Ge surface [1,3], suggesting that the formation processes of the interface is more complicated.We have reexamined the atomic structure of the Ge-induced (1x2) reconstruction experimentally and theoretically. We show that the initial growth of Ge on GaAs(001) drives the deposited Ge atoms to subsurface sites and segregates the underlying As atoms at the outermost layer, forming the GaAs(001)-(1x2)-Ge reconstruction consisting of Ga-As dimers. We confirmed that this atomic geometry is energetically favored compared with the previously proposed Ga-Ge dimer model, by using first-principles calculations. Our proposed structure model accounts well for the experimental results from scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and reflection high-energy electron diffraction (RHEED).[1] B. J. Mrstik, Surf. Sci. 124, 253 (1983).[2] X.-S. Wang, K. Self, V. Bressler-Hill, R. Maboudian, and W. H. Weinberg, Phys. Rev. B 49, 4775 (1994).[3] J. R. Power, P. Weightman, and A. A. Cafolla, Surf. Sci. 402-404, 566 (1998).[4] G. P. Srivastava and S. J. Jenkins, Surf. Sci. 352-354, 416 (1996).
9:00 PM - HH5.25
Hollow Nickel Oxide Nanoparticles Synthesized by Polystyrene-Assisited Solution Method.
Mohammad Vaseem 1 , Dong Min Hong 1 , Jin Hwan Kim 1 , Yoon-Bong Hahn 1
1 School of Semiconductor and Chemical Engineering, Chonbuk National University, Jeonju Korea (the Republic of)
Show AbstractHollow nickel oxide nanoparticles have been synthesized via simple solution method by using polystyrene as a sacrificial template. Firstly, nickel material coated over polystyrene spheres, and further calcinations of nickel-coated polystyrene spheres at 450 0 C resulted hollow nickel oxide nanoparticles. The crystallinity and structural properties of as synthesized nickel oxide nanoparticles were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), high-resolution TEM (HRTEM), field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). Optical activity of as synthesized products was characterized by UV-Vis spectrophotometer.
9:00 PM - HH5.26
Gold/Palladium Nanoparticles in Flight Thermal Annealing.
Jose A. Flores 1 3 , S. Mejia-Rosales 1 3 , E. Perez-Tijerina 1 2 3
1 Laboratorio de Nanociencias, Facultad de Ciencias Físico-Matemáticas UANL, San Nicolás de los Garza CP66450, Nuevo León, Mexico, 3 Laboratorio de Nanotecnológia, Cento de Inovación, investigación y Desarollo en Ingenería y Tecnológia (CIIDIT) , Parque de Investigación e Inovación Tecnológia, Nuevo León, Mexico, 2 , Centro de Investigación en Materiales Avanzados (CIMAV), Parque de Investigación e Inovación Tecnológia, Nuevo León, Mexico
Show AbstractGold/Palladium nanoclusters were produced by inert-gas condensation using a DC-sputtering system. The deposition parameters were chosen such that the mean size of the clusters were ~ 5nm. In order to study the structural changes on the AuPd clusters as the temperature is increased along their flight to the substrate, we adapted the IGC technique adding a lineal heater; this in situ modification allows transferring thermal energy to the clusters before deposition. Theoretical studies have demonstrated a correlation between the energy per cluster and their final size and shape; for this reason we produced the particles at several in-flight temperatures in a range that goes from room temperature to 1273 K. HR-TEM micrographs indicate that both morphology and structure of the cluster distribution have marked changes as a function of the on flight temperature.
9:00 PM - HH5.4
Nanostructured Composite of the Binary System W-C on Thin Films Obtained by RF Magnetron Sputtering.
Nelcari Ramirez 1 , Angel Ardila 1 , Victor Garcia 2
1 Grupo de Física Aplicada, Universidad Nacional de Colombia, Bogotá, Cundinamarca, Colombia, 2 Grupo de Física de la Materia Condensada, Universidad de Los Andes, Mérida, Mérida, Venezuela, Bolivarian Republic of
Show AbstractThe Raman scattering spectroscopy of thin films of the system W-C that were deposited on austenitic steel substrates by RF magnetron sputtering, suggests the existence of a nanostructured composite in the obtained films. In the Raman spectra can be observed that the peaks G and D corresponding to disordered and ordered graphite predominate, indicating the presence of graphitic dominions. Studies of Energy dispersive X-Ray Spectroscopy (EDX) and X-Ray Diffraction confirmed the existence of the phases WC (δ) and W2C (β) of tungsten carbide in the different films, as well as the existence of the composite, where both graphitic phases and dominions can be found. Measures of adhesion, hardness and grain size were carried out by the scratch test, microindentación Vickers and atomic force microscopy (AFM) techniques, respectively. The mechanical and tribological properties of the films were related as a function of the deposition temperature, chemical composition and grain size. Calculations of the practical work of adhesion indicate that when increasing the substrate temperature, the film-substrate adhesion increases; which can be explained by the diffusion of constituent atoms of the film in the substrate surface.
9:00 PM - HH5.5
Characterization of the Interface of SiTiC/TiAl Composites by TEM with or without Interface Modifications.
Takakazu Suzuki 1
1 , AIST, Tsukuba Japan
Show AbstractSiC-fiber-reinforced TiAl composites (SiC/TiAl) have attractive attention due to their potential for replacing titanium and nickel-base alloys in aerospace systems such as advanced turbine engines and hypersonic vehicles where specific strength and stiffness at high temperature are critical. The interface layers of SiC/TiAl are believed to contribute strongly to its mechanical properties. A wide variety of interface modifications, such as C, BN, W, or Mo coating or C/W or BN/W double coatings has been applied to the fiber to produce composites, together with the identification of several new interface modification systems, showing promise for high performance fibers and improved composite properties. A research from a perfect cross-sectional view to get more direct and reliable interfacial information especially about bonding around the fiber circumference, has been limited partly due to the difficulty of preparing suitably thin TEM specimen without damaging the interface layers. We report our preparation method for a perfect cross-sectional TEM specimen of SiC/TiAl and the interface characterization results.Single SiC-based Si60%-Ti2%-C15%-O11% fiber (SiTiC) ~11μm in diameter containing about 2% Ti to improve its thermal stability has been used as a reinforcement. Chemical vapor deposition or sputtering has been used to deposit C or TiAl layer. C layer has been deposited uniformly around the fiber at a thickness of about 100 nm and TiAl coating at about 1400 nm. C layer consisted of large amounts of micro crystals of about 1-30 nm. TiAl layer consisted of crystals of about 60-360nm.The specimen has been annealed at 1173 K for 2 hrs in Ar, and prepared by sandwiching and 3mm disks obtained by ultrasonic drilling and mechanical polishing to ~100 μm. Those disks have been further ground by a dimpler to ~10 μm, and argon-ion-etching for 25-30hrs with GATAN 600 to get an electron-beam-transparent foil. H-9000UHR II TEM accelerrating voltage 300 kV, equipped with EDX (electron prove 1nm) has been used. Interfacial reaction and diffusion mainly occurred in the interface between the C layer and SiTiC fiber and the C and TiAl layers. No direct reaction or diffusion occurred between the SiTiC fiber and TiAl layer. Espesially, small amounts of needle-like compound assigned as Aluminum Titanium Carbide, (Ti3AlC)5C, propagating into the fiber has been found at the interface area without any coating layer. The existance of the compound is indicating there are reaction and diffusion products of SiTiC fiber and TiAl. Such Aluminum Titanium Carbide penetrating into the fiber seems to induce new stress concentration and generate new cracks in the fiber and degrade the fiber and the composite strength. Combined with those tensile testings of SiTiC/TiAl with or without interface modification with Weibull statistic analysys reported previously, we would like to discuss those effectiveness of variuos types of interface modifications with TEM observation.
9:00 PM - HH5.6
Quantitative Characterization of Micro- and Nano-scale Deformation of Solids.
Vitaly Shpeizman 1 , Nina Peschanskaya 1
1 , Ioffe Physical-Technical Institute of the Russian Academy of Sciences, Saint-Petersburg Russian Federation
Show AbstractThe multilevel character of deformation and its localization at different levels is a concept that has been recognized for several decades. However, the process has until now been described only by the average velocity of deformation at the macrolevel. In the traditional techniques of deformation recording, small-scale non-uniformities are averaged out and made invisible. A new method of studying deformations using a laser interferometer makes it possible to observe small deformation jumps and to measure their characteristics. In our experiments, the velocity of the deformation of a sample is found from the interferometric data of a row reflected from the movable edge of the sample and a reference row. The obtained interferogram consists of sequential beats with a period corresponding to a deformation increment of 300 nm. The frequency of the intensity signal is proportional to the current strain rate. Experiments show that interferograms represent the repeated parts with relatively high and low strain rates. The change in the period of strain rate measured in terms of deformation units in many cases correlates with the size of inhomogeneities in the sample structure. To reveal deformation jumps of 150 nm or more, periodic changes in the strain rate were measured at the base of each half of sequential beats in an interferogram, and the dependence of the strain rate on the deformation increment was plotted. Strain rate instability within the beat period was analyzed by comparing the experimentally determined dependence of interferometry intensity on the deformation time with the single frequency dependence (I~cos(wt)), for some part of the period. This technique allows the observation of deformation inhomogeneities of 50-150 nm. We studied nanocrystalline metals (Al, Cu, Ti, Fe), polymers (PMMA, PE and others) and ceramics with nanoparticles. All metals were produced by multiple equal-channel angular pressing (ECAP). Polymers were strengthened by nanoscale particles or irradiation. The region of microplasticity was investigated, the stresses being considerably less than the yield point or fracture point. The role of large deformations was studied on samples which were first deformed up to high strains. It was estimated that the nonuniformity of deformation (its small periodic jumps) is the characteristic feature of deformation at all scales: from nano- to macroscale. First, the nanoscale jumps of deformation were detected. Two characteristics of nanojumps - the jump height and the relation between strain rates at slow and rapid phases of the jump - were measured for different materials. The jump height correlates with the size of structural units which take part in the process of deformation at all structure levels. We believe the result obtained may be useful not only for characterization of bulk nanostructural materials but nanodimensional (films, interfaces and others) subjects as well.
9:00 PM - HH5.7
Quantitative Characterization of Nanomaterial Dispersion.
Shiren Wang 1 , Jingjing Qiu 2
1 Industrial Engineering, Texas Tech Univ, Lubbock, Texas, United States, 2 Chemical Engineering, Texas Tech Univ, Lubbock, Texas, United States
Show Abstract Nanoscale materials, such as fullerene, carbon Nanotubes, graphene, and other metallic nanoparticles, tend to form big clusters due to their large specific surface. It is a big challenge to disperse them uniformly in the matrix and it is also very difficult to characterize the morphology quantitatively. Up to now, there is no attempt found to quantitatively characterize the dispersion results. In this paper, we propose an innovative method to quantitatively characterize the nanoparticle dispersion in the polymer matrix. High-resolution scanning electron microscopy (SEM) or atomic force microscopy (AFM) characterization of nanostructured material samples result in images consisting of distributed nanoscale crystals. In each image, uniformly distributed reference points were generated by the Poisson-process to match the number of nanoparticles observed in the SEM or AFM image in order to guarantee accuracy. The distance between reference points to nanoparticles was calculated and each nearest neighbor distance was normalized to eliminate the effect of density of nanoparticles in the cross-section area. A dispersion index was defined as a deviation of normalized observed nearest neighbor distance. A smaller index means smaller deviation from ideal uniformity and represents more uniform dispersion. Each sample was characterized by SEM and resulted in many images. Average dispersion index from all the images derived from the same sample was used to quantify their dispersion in the specific sample. With the quantified dispersion, the effect of surface-functionalization on carbon nanotubes dispersion was investigated, and it was found the dispersion index is dependent on the surface modification method and functionalization degree. The correlation of functionalization degree with dispersion index was quantified. In addition, a quantitative structure-property relationship in carbon nanotube composites was achieved, providing insight to the nanostructured materials design, fabrication and applications.
9:00 PM - HH5.8
Size Dependence of Nanoparticle Dissolution in a Matrix: Gold Particles in Bismuth.
Parasuraman Swaminathan 1 , Shankar Sivaramakrishnan 1 , Jacob Palmer 1 , John Weaver 1
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractWe discuss the dissolution and phase transformation of Au nanoparticles buried in a Bi matrix as a function of their size. This information allows us to understand the stability of nanoparticles embedded in a matrix. The particles were formed by vapor deposition onto Bi films at room temperature. Subsequently, they burrowed into Bi because of its lower free energy compared to Au and the minimal interfacial energy in this system. At room temperature, burrowing is competitive to particle growth. Since burrowing constantly removes particles from the surface, arriving adatoms diffuse longer and attach to the remaining particles, broadening the size distribution. Post deposition, particles on the surface complete their burrowing. The bulk phase diagram of Au-Bi indicates negligible solid solubility, with an intermetallic, Au2Bi, forming above 120 °C. We have investigated the formation of Au2Bi during annealing by using in-situ transmission electron microscopy and nano beam electron diffraction. Initially, the Au particles dissolve into the Bi matrix to give a solid solution. This is followed by the formation of Au2Bi. We have studied the dissolution kinetics by measuring its rate as a function of particle size at different temperatures and have used these results to calculate the activation energy for this process, which is the energy required for an atom to detach from the particle.
9:00 PM - HH5.9
Raman Topography and Strain Uniformity of Large-Area Epitaxial Graphene.
Joshua Robinson 1 2 , Conor Puls 3 , Neal Staley 3 , Joseph Stitt 2 , Mark Fanton 1 , Konstantin Emtsev 4 , Thomas Seyller 4 , Ying Liu 3 2
1 Materials Division, Penn State Electro-Optics Center, University Park, Pennsylvania, United States, 2 Materials Research Institute, Penn State University, University Park, Pennsylvania, United States, 3 Physics, Penn State University, University Park, Pennsylvania, United States, 4 Lehrstuhl für Technische Physik, Universität Erlangen-Nürnberg, Erlangen Germany
Show AbstractGraphene exhibits extraordinary electronic properties including an unusually high mobility of the charge carriers. Significant progress toward understanding the properties of graphene has resulted from studying graphene flakes mechanically exfoliated from bulk graphite. While these small flakes (< 100 um^2) are suited for studying the fundamental science of graphene, they are not practical for the development of graphene-based technologies. Alternatively, the sublimation of silicon (Si) from silicon carbide (SiC) to form epitaxial graphene is a promising route for the production of wafer size graphene films. Rapid characterization and precise control of properties of epitaxial graphene over a wafer-size area, which are yet to be achieved, are necessary for developing a graphene based technology. Micro-Raman spectroscopy, a rapid, optical characterization technique, was used first on few-layer graphene flakes prepared by mechanical exfoliation, followed by a spatially resolved study. Raman spectroscopy measurements have also been used on epitaxial graphene, yielding important information on the thickness, the charge carrier density, and the strain. However, no studies of Raman topography, the two-dimensional mapping of Raman spectrum over large-area epitaxial graphene, have been carried out to date. We report results of Raman spectroscopy studies of large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large variation in Raman shift resulting from graphene strain inhomogeneity, which is shown to be correlated with physical topography by coupling Raman spectroscopy with atomic force microscopy. We show that graphene strain can vary over a distance shorter than 300nm, and may be uniform only over roughly 1 um. We show that nearly strain-free graphene is possible even in epitaxial graphene.