222 results on '"James M. LeBeau"'
Search Results
152. Origin of Ferroelectricity in Thin Film HfO2 Probed by Revolving STEM and PACBED
- Author
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Everett D. Grimley, James M. LeBeau, Uwe Schroeder, Xiahan Sang, and Tony Schenk
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Materials science ,Nanotechnology ,Thin film ,Instrumentation ,Ferroelectricity - Published
- 2015
153. Inconsistent Normalized Intensities for Quantitative STEM: Detector Scans and Single Electron Counting
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Xiahan Sang and James M. LeBeau
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Single electron ,Optics ,Materials science ,business.industry ,Detector ,business ,Instrumentation - Published
- 2015
154. Airbrushed nickel nanoparticles for large-area growth of vertically aligned carbon nanofibers on metal (Al, Cu, Ti) surfaces
- Author
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Mehmet Fahri Saraç, Justin G. Railsback, James M. LeBeau, A. A. Oni, Bryan D. Anderson, Ryan M. White, Dale K. Hensley, Joseph B. Tracy, Anatoli V. Melechko, and Ryan C. Pearce
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Materials science ,Carbon nanofiber ,chemistry.chemical_element ,Nanoparticle ,Nanotechnology ,Carbon nanotube ,Chemical vapor deposition ,Copper ,Catalysis ,law.invention ,Nickel ,chemistry ,law ,Plasma-enhanced chemical vapor deposition ,General Materials Science - Abstract
Vertically aligned carbon nanofibers (VACNFs) were grown by plasma-enhanced chemical vapor deposition (PECVD) using Ni nanoparticle (NP) catalysts that were deposited by airbrushing onto Si, Al, Cu, and Ti substrates. Airbrushing is a simple method for depositing catalyst NPs over large areas that is compatible with roll-to-roll processing. The distribution and morphology of VACNFs are affected by the airbrushing parameters and the composition of the metal foil. Highly concentrated Ni NPs in heptane give more uniform distributions than pentane and hexanes, resulting in more uniform coverage of VACNFs. For VACNF growth on metal foils, Si micropowder was added as a precursor for Si-enriched coatings formed in situ on the VACNFs that impart mechanical rigidity. Interactions between the catalyst NPs and the metal substrates impart control over the VACNF morphology. Growth of carbon nanostructures on Cu is particularly noteworthy because the miscibility of Ni with Cu poses challenges for VACNF growth, and carbon nanostructures anchored to Cu substrates are desired as anode materials for Li-ion batteries and for thermal interface materials.
- Published
- 2013
155. Structural Changes Underlying Field‐Cycling Phenomena in Ferroelectric HfO 2 Thin Films
- Author
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Uwe Schroeder, Xiahan Sang, James M. LeBeau, Everett D. Grimley, Milan Pešić, Thomas Mikolajick, and Tony Schenk
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010302 applied physics ,Materials science ,Condensed matter physics ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,Polarization (waves) ,01 natural sciences ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Dielectric spectroscopy ,Hysteresis ,Crystallography ,Tetragonal crystal system ,0103 physical sciences ,Scanning transmission electron microscopy ,Thin film ,0210 nano-technology - Abstract
Since 2011, ferroelectric HfO2 has attracted growing interest in both fundamental and application oriented groups. In this material, noteworthy wake-up and fatigue effects alter the shape of the polarization hysteresis loop during field cycling. Such changes are problematic for application of HfO2 to ferroelectric memories, which require stable polarization hystereses. Herein, electrical and structural techniques are implemented to unveil how cyclic switching changes nanoscale film structure, which modifies the polarization hysteresis. Impedance spectroscopy and scanning transmission electron microscopy identify regions with different dielectric and conductive properties in films at different cycling stages, enabling development of a structural model to explain the wake-up and fatigue phenomena. The wake-up regime arises due to changes in bulk and interfacial structuring: the bulk undergoes a phase transformation from monoclinic to orthorhombic grains, and the interfaces show changes in and diminishment of a nonuniform, defect rich, tetragonal HfO2 layer near the electrodes. The evolution of these aspects of structuring contributes to the increase in Pr and the opening of the constricted P–V hysteresis that are known to occur with wake-up. The onset of the fatigue regime is correlated to an increasing concentration of bulk defects, which are proposed to pin domain walls.
- Published
- 2016
156. Structure and chemistry of passivated SiC/SiO2 interfaces
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Weizong Xu, Brett Hull, Daniel J. Lichtenwalner, James M. LeBeau, John W. Palmour, and J. Houston Dycus
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010302 applied physics ,Physics and Astronomy (miscellaneous) ,Passivation ,Chemistry ,Annealing (metallurgy) ,Wide-bandgap semiconductor ,Dangling bond ,Analytical chemistry ,Field effect ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Nitrogen ,stomatognathic system ,0103 physical sciences ,Scanning transmission electron microscopy ,0210 nano-technology ,Spectroscopy - Abstract
Here, we report on the chemistry and structure of 4H-SiC/SiO2 interfaces passivated either by nitric oxide annealing or Ba deposition. Using aberration corrected scanning transmission electron microscopy and spectroscopy, we find that Ba and N remain localized at SiC/SiO2 interface after processing. Further, we find that the passivating species can introduce significant changes to the near-interface atomic structure of SiC. Specifically, we quantify significant strain for nitric oxide annealed sample where Si dangling bonds are capped by N. In contrast, strain is not observed at the interface of the Ba treated samples. Finally, we place these results in the context of field effect mobility.
- Published
- 2016
157. Nanocomposite Bi(Sb)Te(Se) Materials by Cryogenic Mechanical Alloying and Optimized High Pressure Hot-pressing
- Author
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Judy Stuart, Peter Thomas, James M. LeBeau, Carl C. Koch, Tsung-Ta Chan, and Rama Venkatasubramanian
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Materials science ,Nanocomposite ,Metallurgy ,Thermoelectric effect ,Alloy ,engineering ,engineering.material ,Composite material ,Hot pressing ,Microstructure ,Cryogenic processor ,Grain size ,Nanocrystalline material - Abstract
Nanocomposite Bi2Te3 based alloys are attractive for their potentially high thermoelectric figure-of-merit (ZT) around room temperature. The nano-scale structural features embedded in the matrix provide more scattering of phonons and can thus reduce the lattice thermal conductivity. To further take advantage of such nanocomposite structures, we focus on the development of nanocrystalline Bi(Sb)Te(Se) powders by high energy cryogenic mechanical alloying followed by an optimized hot pressing process. This approach is shown to successfully produce Bi(Sb)Te(Se) alloy powders with grain size averaging about 9 nm for n-type BiTe(Se) and about 16 nm for p-type Bi(Sb)Te respectively. This cryogenic process offers much less milling time and prevents thermally activated contamination or imperfections from being introduced during the milling process. The nanocrystalline powders are then compacted at optimized pressures and temperatures to achieve full density compactions and preserve the grain sizes effectively. The resulting nano-bulk materials have optimal Seebeck coefficients and are expected to have improved ZT. Thermoelectric properties and microstructure studies by X-ray diffraction and transmission electron microscopy will also be presented and discussed.
- Published
- 2012
158. Imaging magnetic and ferroelectric domains and interfacial spins in magnetoelectric La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3heterostructures
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Charles Frye, Ying-Hao Chu, Robbyn Trappen, Alpha T. N'Diaye, Jinling Zhou, James M. LeBeau, Guerau Cabrera, Michael S. Spencer, V. Nguyen, Vu Thanh Tra, Chih-Yeh Huang, Ryan M. White, and Mikel B. Holcomb
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education.field_of_study ,Materials science ,Spins ,Condensed matter physics ,Population ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Magnetic field ,Photoemission electron microscopy ,Exchange bias ,Ferromagnetism ,General Materials Science ,education - Abstract
Strong magnetoelectric coupling can occur at the interface between ferromagnetic and ferroelectric films. Similar to work on interfacial exchange bias, photoemission electron microscopy was utilized to image both magnetic and ferroelectric domains and the resulting interfacial Ti spin in the same locations of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures. Multiple image analysis techniques, which could be applicable for a variety of fields needing quantitative data on image switching, confirm both improved magnetic switching and an increased population of interfacial spins with increased thickness of the ultrathin La0.7Sr0.3MnO3 layer. The perpendicular orientation of the interfacial spins is also discussed. This work suggests a magnetoelectric dead layer, with reduced interfacial magnetoelectricity when thin magnetic films are present.
- Published
- 2015
159. Growth of SrVO3 thin films by hybrid molecular beam epitaxy
- Author
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Everett D. Grimley, Roman Engel-Herbert, Jarrett A. Moyer, Craig Eaton, Matthew Brahlek, Hamideh M. Alipour, and James M. LeBeau
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010302 applied physics ,Materials science ,Analytical chemistry ,Vanadium ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Surfaces, Coatings and Films ,Lattice constant ,chemistry ,Electron diffraction ,Transmission electron microscopy ,0103 physical sciences ,Scanning transmission electron microscopy ,Thin film ,0210 nano-technology ,Stoichiometry ,Molecular beam epitaxy - Abstract
The authors report the growth of stoichiometric SrVO3 thin films on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) substrates using hybrid molecular beam epitaxy. This growth approach employs a conventional effusion cell to supply elemental A-site Sr and the metalorganic precursor vanadium oxytriisopropoxide (VTIP) to supply vanadium. Oxygen is supplied in its molecular form through a gas inlet. An optimal VTIP:Sr flux ratio has been identified using reflection high-energy electron-diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy, demonstrating stoichiometric SrVO3 films with atomically flat surface morphology. Away from the optimal VTIP:Sr flux, characteristic changes in the crystalline structure and surface morphology of the films were found, enabling identification of the type of nonstoichiometry. For optimal VTIP:Sr flux ratios, high quality SrVO3 thin films were obtained with smallest deviation of the lattice parameter from the ideal value and with atomically smooth surfaces, indicative of the good cation stoichiometry achieved by this growth technique.
- Published
- 2015
160. Thickness dependence of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 magnetoelectric interfaces
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Matthew A. Marcus, James M. LeBeau, Srinivas Polisetty, Evan Wolfe, Robbyn Trappen, Jiunn-Yuan Lin, Catherine Jenkins, Jinling Zhou, Charles Frye, Shuai Dong, Mikel B. Holcomb, Ryan M. White, Ying-Hao Chu, and Vu Thanh Tra
- Subjects
Physics and Astronomy (miscellaneous) - Published
- 2015
161. Insulating state of ultrathin epitaxial LaNiO3thin films detected by hard x-ray photoemission
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C. G. Van de Walle, Charles S. Fadley, Junwoo Son, Alexander Kaiser, Susanne Stemmer, James M. LeBeau, Yoshiyuki Yamashita, Ronny Sutarto, Hiroki Wadati, George A. Sawatzky, Anderson Janotti, Alexander X. Gray, Shigenori Ueda, and Keisuke Kobayashi
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Crystallography ,Materials science ,X-ray photoelectron spectroscopy ,Order (ring theory) ,Substrate (electronics) ,Electronic structure ,Thin film ,Condensed Matter Physics ,Epitaxy ,Electron spectroscopy ,Spectral line ,Electronic, Optical and Magnetic Materials - Abstract
In order to understand the influence of strain and film thickness on the electronic structure of thin films of strongly correlated oxides, we have applied hard x-ray photoemission (HXPS) at 6 keV, soft x-ray photoemission (XPS) at 1.5 keV, and transmission electron microscopy to epitaxial LaNiO${}_{3}$ films deposited on two substrates: LaAlO${}_{3}$ (compressive strain) and (LaAlO${}_{3}$)${}_{0.3}$(Sr${}_{2}$AlTaO${}_{6}$)${}_{0.7}$ (tensile strain). Using inelastic attenuation lengths in LaNiO${}_{3}$ determined from the HXPS data, we have decomposed valence-band spectra into layer-specific contributions. This decomposition is validated by comparing with the results of first-principles calculations using a hybrid functional. The resultant thin-film LaNiO${}_{3}$ densities of states exhibit significant differences in spectral weights for the thinnest LaNiO${}_{3}$ films. A gap opening consistent with a metal-to-insulator transition is observed for the thinnest 2.7 nm LaNiO${}_{3}$ film on an (LaAlO${}_{3}$)${}_{0.3}$(Sr${}_{2}$AlTaO${}_{6}$)${}_{0.7}$ substrate, with a similar gap opening also being observed in complementary soft x-ray photoemission at 1.5 keV for a thinner 1.4 nm film on an LaAlO${}_{3}$ substrate. A metal-to-insulator transition in very thin nm-scale films of LaNiO${}_{3}$ is thus suggested as a general phenomenon.
- Published
- 2011
162. Thermal diffuse scattering in transmission electron microscopy
- Author
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James M. LeBeau, Leslie J. Allen, B.D. Forbes, Susanne Stemmer, Scott D. Findlay, Adrian J. D’Alfonso, and D. Van Dyck
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Physics ,Contrast transfer function ,Mathematical model ,business.industry ,Thermal scattering ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Chemistry ,Optics ,Diffuse scattering ,Transmission electron microscopy ,Reciprocity (electromagnetism) ,Scanning transmission electron microscopy ,Thermal ,business ,Instrumentation - Abstract
In conventional transmission electron microscopy, thermal scattering significantly affects the image contrast. It has been suggested that not accounting for this correctly is the main cause of the Stobbs factor, the ubiquitous, large contrast mismatch found between theory and experiment. In the case where a hard aperture is applied, we show that previous conclusions drawn from work using bright field scanning transmission electron microscopy and invoking the principle of reciprocity are reliable in the presence of thermal scattering. In the aperture-free case it has been suggested that even the most sophisticated mathematical models for thermal diffuse scattering lack in their numerical implementation, specifically that there may be issues in sampling, including that of the contrast transfer function of the objective lens. We show that these concerns can be satisfactorily overcome with modest computing resources; thermal scattering can be modelled accurately enough for the purpose of making quantitative comparison between simulation and experiment. Spatial incoherence of the source is also investigated. Neglect or inadequate handling of thermal scattering in simulation can have an appreciable effect on the predicted contrast and can be a significant contribution to the Stobbs factor problem. (C) 2011 Elsevier B.V. All rights reserved.
- Published
- 2011
163. Investigation of Local A-site Chemistry in Barium Strontium Titanate Using Aberration Corrected STEM, EELS and EDS
- Author
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James M. LeBeau, Jing Li, Lauren M. Garten, Jon Paul Maria, Matthew J. Burch, Xiahan Sang, Susan Trolier-McKinstry, and Elizabeth C. Dickey
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Strontium ,Materials science ,Electron energy loss spectroscopy ,Inorganic chemistry ,Analytical chemistry ,chemistry.chemical_element ,Barium ,Dielectric ,Ferroelectricity ,chemistry ,Scanning transmission electron microscopy ,Thin film ,Spectroscopy ,Instrumentation - Abstract
Barium strontium titante (BST) is an important dielectric material because of its high tunability (dielectric constant as a function of applied voltage) and low loss, with specific applications in tunable microwave circuits. However, regardless of processing technique, additives, or synthesis temperatures some remnant ferroelectricity is always observed beyond the paraelectric phase transition [1]. One possible explanation for this remnant ferroelectricity, which has been hotly debated, is that the local stoichiometry of the A-site cations (Ba and Sr) is not globally and locally homogeneous. This hypothesis surmises that local areas, which are barium rich, may result in remnant polarization [1]. However, this hypothesis has never been experimentally shown. In this work, we use an aberration corrected scanning transmission electron microscope (STEM), electron energy loss spectroscopy (EELS), and energy dispersive X-ray spectroscopy (EDS) to investigate the local stoichiometry of arguably the bestengineered barium strontium titanate samples ever fabricated [2] in comparison to BST thin films showing some of the best tunability in thin-film form.
- Published
- 2014
164. Application of the Projective Standard Deviation to STEM Imaging and Analysis
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Everett D. Grimley, Xiahan Sang, and James M. LeBeau
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Pure mathematics ,Projective test ,Instrumentation ,Standard deviation ,Mathematics - Published
- 2014
165. Putting a New Spin on Scanning Transmission Electron Microscopy
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Douglas L. Irving, Changning Niu, Everett D. Grimley, James M. LeBeau, and Xiahan Sang
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Conventional transmission electron microscope ,Materials science ,Distortion ,Scanning transmission electron microscopy ,Scanning confocal electron microscopy ,Energy filtered transmission electron microscopy ,Instrumentation ,Atomic units ,Image resolution ,Computational physics ,Characterization (materials science) - Abstract
Local atomic scale ordering and structural distortions can significantly modify material properties. Aberration correction dramatically improves spatial resolution into the sub-Angstrom regime, unlocking information about material defects previously beyond reach. While STEM has proven essential to the atomic scale characterization of materials, for example at defects, interfaces, or even in perfect crystals, measurement of atomic displacements and distances has remained challenging due to the presence of sample drift. Distortion proportional to the rate of sample drift during image acquisition hinders the accurate measurement or even representation of atomic structure. Though modern STEM installations are optimized to reduce vibration, air flow/fields, and temperature fluctuations, sample drift generally remains.
- Published
- 2014
166. Correlative Imaging of Stacking Faults using Atom Probe Tomography (APT) and Scanning Transmission Electron Microscopy (STEM)
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Krishna Rajan, James M. LeBeau, Scott Broderick, A. A. Oni, Sonal Padalkar, and Santoshrupa Dumpala
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Nuclear magnetic resonance ,Materials science ,Electron tomography ,law ,Scanning transmission electron microscopy ,Scanning confocal electron microscopy ,Stacking ,Analytical chemistry ,Atom probe ,Correlative imaging ,Instrumentation ,law.invention - Published
- 2014
167. Direct Lattice Parameter Measurements Using HAADF-STEM
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Xiahan Sang, S. V. Raju, Krishna Rajan, A. A. Oni, Susan B. Sinnott, Surendra K. Saxena, James M. LeBeau, Aakash Kumar, and Srikant Srinivasan
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Materials science ,Lattice constant ,Condensed matter physics ,Instrumentation - Published
- 2014
168. Observing the Interplay Between Composition and Phonon Transport in Bi2Te3-xSex Alloys using ADF STEM
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J. H. Dycus, Carl C. Koch, Tsung-Ta Chan, James M. LeBeau, Xiahan Sang, and A. A. Oni
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Materials science ,Condensed matter physics ,Phonon ,Composition (combinatorics) ,Instrumentation - Published
- 2014
169. Application to Semiconductors
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James M. LeBeau, Susanne Stemmer, and Dmitri O. Klenov
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Materials science ,Semiconductor ,Field (physics) ,business.industry ,Scanning transmission electron microscopy ,Gate stack ,Optoelectronics ,business - Abstract
In this chapter, we discuss the application of scanning transmission electron microscopy in the field of semiconductor research, using specific examples from the literature.
- Published
- 2010
170. Standardless atom counting in scanning transmission electron microscopy
- Author
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Susanne Stemmer, Scott D. Findlay, James M. LeBeau, and Leslie J. Allen
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Conventional transmission electron microscope ,Microscopy, Electron, Scanning Transmission ,Materials science ,business.industry ,Chemistry ,Mechanical Engineering ,Scanning confocal electron microscopy ,Atom (order theory) ,Bioengineering ,General Chemistry ,Condensed Matter Physics ,Dark field microscopy ,Molecular physics ,Optics ,Annular dark-field imaging ,Electron tomography ,Nano ,Scanning transmission electron microscopy ,Image Interpretation, Computer-Assisted ,Energy filtered transmission electron microscopy ,General Materials Science ,sense organs ,business ,High-resolution transmission electron microscopy ,Algorithms - Abstract
We demonstrate that high-angle annular dark-field imaging in scanning transmission electron microscopy allows for quantification of the number and location of all atoms in a three-dimensional, crystalline, arbitrarily shaped specimen without the need for a calibration standard. We show that the method also provides for an approach to directly measure the finite effective source size of a scanning transmission electron microscope.
- Published
- 2010
171. Quantitative comparisons of contrast in experimental and simulated bright-field scanning transmission electron microscopy images
- Author
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Leslie J. Allen, James M. LeBeau, Scott D. Findlay, Susanne Stemmer, and Adrian J. D’Alfonso
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Contrast transfer function ,Materials science ,business.industry ,Scanning confocal electron microscopy ,Condensed Matter Physics ,Dark field microscopy ,Electronic, Optical and Magnetic Materials ,Optics ,Electron tomography ,Scanning transmission electron microscopy ,Energy filtered transmission electron microscopy ,High-resolution transmission electron microscopy ,business ,Vibrational analysis with scanning probe microscopy - Abstract
Quantitative, atomic resolution bright-field scanning transmission electron microscopy experiments are reported. The image intensities are placed on an absolute scale relative to the incident beam intensity. Features in the experimental images, such as contrast reversals, intensities, and the image contrast, are compared with image simulations that account for elastic scattering and the effect of phonon scattering. Simulations are carried out using both the multislice absorptive and frozen phonon simulation methods. For a ${\text{SrTiO}}_{3}$ sample with thicknesses between 4 and 25 nm, both models agree within the experimental uncertainty. We demonstrate excellent agreement between the simulated and the experimentally observed image contrast. The implications for the contrast mismatch commonly reported for high-resolution transmission electron microscopy using plane-wave illumination are discussed.
- Published
- 2009
172. High-angle scattering of fast electrons from crystals containing heavy elements: Simulation and experiment
- Author
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Susanne Stemmer, Xiqu Wang, James M. LeBeau, Scott D. Findlay, Allan J. Jacobson, and Leslie J. Allen
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Materials science ,business.industry ,Scattering ,Electron ,Condensed Matter Physics ,Molecular physics ,Electronic, Optical and Magnetic Materials ,Optics ,Scanning transmission electron microscopy ,Energy filtered transmission electron microscopy ,Atomic number ,business ,High-resolution transmission electron microscopy ,Single crystal ,Intensity (heat transfer) - Abstract
The paper reports on quantitative comparisons of experimental and simulated image intensities in high-angle annular dark-field imaging in scanning transmission electron microscopy of a ${\text{PbWO}}_{4}$ single crystal. The experimental image intensities are normalized to the incident beam. Provided that the effects of spatial incoherence and multiple thermal diffuse scattering events are taken into account in the simulations, excellent agreement within about 5% is achieved between theory and experiments. The comparisons depend critically on accurate knowledge of the Debye-Waller factors, which were determined by x-ray single-crystal structure refinement, and of the experimental thickness values. The Debye-Waller factors are different for different atomic columns, causing column intensities to not be a simple function of their atomic number. Channeling effects associated with the oxygen columns contribute to intensity variations between the Pb and W columns. The results show that even for single crystals, image simulations are required to correctly interpret the contrast.
- Published
- 2009
173. Position averaged convergent beam electron diffraction: theory and applications
- Author
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Scott D. Findlay, Susanne Stemmer, Leslie J. Allen, and James M. LeBeau
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Diffraction ,Reflection high-energy electron diffraction ,business.industry ,Chemistry ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Optics ,Electron tomography ,Electron diffraction ,Scanning transmission electron microscopy ,Energy filtered transmission electron microscopy ,Electron beam-induced deposition ,business ,Instrumentation ,Electron backscatter diffraction - Abstract
A finely focused angstrom-sized coherent electron probe produces a convergent beam electron diffraction pattern composed of overlapping orders of diffracted disks that sensitively depends on the probe position within the unit cell. By incoherently averaging these convergent beam electron diffraction patterns over many probe positions, a pattern develops that ceases to depend on lens aberrations and effective source size, but remains highly sensitive to specimen thickness, tilt, and polarity. Through a combination of experiment and simulation for a wide variety of materials, we demonstrate that these position averaged convergent beam electron diffraction patterns can be used to determine sample thicknesses (to better than 10%), specimen tilts (to better than 1mrad) and sample polarity for the same electron optical conditions and sample thicknesses as used in atomic resolution scanning transmission electron microscopy imaging. These measurements can be carried out by visual comparison without the need to apply pattern-matching algorithms. The influence of thermal diffuse scattering on patterns is investigated by comparing the frozen phonon and absorptive model calculations. We demonstrate that the absorptive model is appropriate for measuring thickness and other specimen parameters even for relatively thick samples (>50nm).
- Published
- 2009
174. New Approach to Quantitative ADF STEM
- Author
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Scott D. Findlay, Leslie J. Allen, James M. LeBeau, and Susanne Stemmer
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Range (particle radiation) ,Materials science ,Scale (ratio) ,business.industry ,Detector ,Intensity (physics) ,law.invention ,Lens (optics) ,Optics ,law ,Scanning transmission electron microscopy ,Atomic number ,business ,Absolute scale - Abstract
High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM or Z-contrast) has been shown to be remarkably sensitive to atomic number (Z). However, HAADF images are currently formed on an arbitrary intensity scale, thereby limiting the possibility of truly quantitative imaging. Recently, it was reported that a mismatch exists between experimental and simulated image contrast in HAADF STEM [1]. Without an absolute scale, it is impossible to determine the cause of the discrepancy [2]. Additionally, an absolute scale would facilitate composition mapping at atomic resolution. Here we demonstrate that the HAADF detector can measure the incident beam intensity to normalize Z-contrast images onto an absolute intensity scale. We report on a practical approach that ensures that the detector does not saturate and is sufficiently linear over the intensity range of interest. An FEI Titan 80–300 STEM/TEM equipped with a super-twin lens (Cs ∼ 1.2 mm) operating at 300 kV was used for this study.
- Published
- 2009
175. Chemical beam deposition of high-k gate dielectrics on III-V semiconductors: TiO2 on In0.53Ga0.47As
- Author
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James M. LeBeau, Roman Engel-Herbert, Yan Zheng, Yoontae Hwang, and Susanne Stemmer
- Subjects
Materials science ,business.industry ,Dielectric ,chemistry.chemical_compound ,Semiconductor ,X-ray photoelectron spectroscopy ,chemistry ,Transmission electron microscopy ,Optoelectronics ,Thin film ,Titanium isopropoxide ,business ,Leakage (electronics) ,High-κ dielectric - Abstract
We report on the growth of high-permittivity (k) TiO2 thin films on In0.53Ga0.47As channels by chemical beam deposition with titanium isopropoxide as the source. The films grew in a reaction-limited regime with smooth surfaces. High-resolution transmission electron microscopy showed an atomically abrupt interface with the In0.53Ga0.47As channel that indicated that this interface is thermally stable. Measurements of the leakage currents using metal-oxide-semiconductor capacitors with Pt top electrodes revealed asymmetric characteristics with respect to the bias polarity, suggesting an unfavorable band alignment for CMOS applications. X-ray photoelectron spectroscopy was used to determine the TiO2/In0.53Ga0.47As band offsets. A valence band offset of 2.5 ± 0.1 eV was measured.
- Published
- 2009
176. Quantitative Atomic Resolution Scanning Transmission Electron Microscopy
- Author
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James M. LeBeau, Scott D. Findlay, Leslie J. Allen, and Susanne Stemmer
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Physics ,Optics ,business.industry ,Transmission electron microscopy ,Atomic resolution ,Scanning transmission electron microscopy ,Scanning confocal electron microscopy ,General Physics and Astronomy ,Energy filtered transmission electron microscopy ,business ,Absolute scale ,Single crystal ,Intensity (heat transfer) - Abstract
Complete understanding of atomic resolution high-angle annular dark-field ($Z$-contrast) images requires quantitative agreement between simulations and experiments. We show that intensity variations can be placed on an absolute scale by normalizing the measured image intensities to the incident beam. We construct fractional intensity images of a ${\mathrm{SrTiO}}_{3}$ single crystal for regions of different thickness up to 120 nm. Experimental images are compared directly with image simulations. Provided that spatial incoherence is taken into account in the simulations, almost perfect agreement is found between simulation and experiment.
- Published
- 2008
177. Combination of TEM and STEM to Investigate the Self-Assembly of Epitaxial Nanocomposites
- Author
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Dmitri O. Klenov, Joshua M. O. Zide, Susanne Stemmer, James M. LeBeau, and Arthur C. Gossard
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Nanocomposite ,Materials science ,Nanotechnology ,Epitaxy ,Instrumentation - Published
- 2007
178. Combined Experimental and Computational Methods Reveal the Evolution of Buried Interfaces during Synthesis of Ferroelectric Thin Films
- Author
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Juan C. Nino, Jason Nikkel, Clayton Cozzan, Susan B. Sinnott, Jacob L. Jones, Fang Yin Lin, Sungwook Mhin, Jon F. Ihlefeld, J. Houston Dycus, Geoff L. Brennecka, James M. LeBeau, Aleksandr V. Chernatynskiy, and A. A. Oni
- Subjects
Materials science ,Mechanical Engineering ,Ferroics ,Heterojunction ,Nanotechnology ,Dielectric ,Lead zirconate titanate ,Ferroelectricity ,Characterization (materials science) ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Scanning transmission electron microscopy ,Thin film - Abstract
Understanding interfaces between dissimilar materials is crucial to the development of modern technologies, for example, semiconductor–dielectric and thermoelectric–semiconductor interfaces in emerging electronic devices. However, the structural characterization of buried interfaces is challenging because many measurement techniques are surface sensitive by design. When interested in interface evolution during synthesis, the experimental challenges multiply and often necessitate in situ techniques. For solution-derived lead zirconate titanate (PZT) ferroelectric thin films, the evolution of buried interfaces during synthesis (including dielectric–metal and metal–metal) is thought to dramatically influence the resultant dielectric and ferroelectric properties. In the present work, multiple experimental and computational methods are combined to characterize interface evolution during synthesis of ferroelectric PZT films on platinized Si wafers—including in situ X-ray diffraction during thermal treatment, aberration-corrected scanning transmission electron microscopy of samples quenched from various synthesis states, and calculations using density functional theory. Substantial interactions at buried interfaces in the PZT/Pt/Ti/SiO x /Si heterostructure are observed and discussed relative to their role(s) in the synthesis process. The results prove that perovskite PZT nucleates directly from the platinum (111)-oriented bottom electrode and reveal the roles of Pb and O diffusion and intermetallic Pt3Pb and Pt3Ti phases.
- Published
- 2015
179. Spin-driven ordering of Cr in the equiatomic high entropy alloy NiFeCrCo
- Author
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A.J. Zaddach, Douglas L. Irving, Xiahan Sang, Carl C. Koch, Changning Niu, A. A. Oni, James M. LeBeau, and J. W. Hurt
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Condensed Matter::Materials Science ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Ferromagnetism ,Magnetic structure ,Magnetic moment ,Magnetic domain ,Magnetism ,Intermetallic ,Antiferromagnetism ,Solid solution - Abstract
Spin-driven ordering of Cr in an equiatomic fcc NiFeCrCo high entropy alloy (HEA) was predicted by first-principles calculations. Ordering of Cr is driven by the reduction in energy realized by surrounding anti-ferromagnetic Cr with ferromagnetic Ni, Fe, and Co in an alloyed L12 structure. The fully Cr-ordered alloyed L12 phase was predicted to have a magnetic moment that is 36% of that for the magnetically frustrated random solid solution. Three samples were synthesized by milling or casting/annealing. The cast/annealed sample was found to have a low temperature magnetic moment that is 44% of the moment in the milled sample, which is consistent with theoretical predictions for ordering. Scanning transmission electron microscopy measurements were performed and the presence of ordered nano-domains in cast/annealed samples throughout the equiatomic NiFeCrCo HEA was identified.
- Published
- 2015
180. On the structural origins of ferroelectricity in HfO2 thin films
- Author
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Tony Schenk, Xiahan Sang, Uwe Schroeder, James M. LeBeau, and Everett D. Grimley
- Subjects
Condensed Matter::Materials Science ,Materials science ,Lattice constant ,Physics and Astronomy (miscellaneous) ,Electron diffraction ,Condensed matter physics ,Transmission electron microscopy ,Scanning transmission electron microscopy ,Orthorhombic crystal system ,Crystal structure ,Thin film ,Ferroelectricity - Abstract
Here, we present a structural study on the origin of ferroelectricity in Gd doped HfO2 thin films. We apply aberration corrected high-angle annular dark-field scanning transmission electron microscopy to directly determine the underlying lattice type using projected atom positions and measured lattice parameters. Furthermore, we apply nanoscale electron diffraction methods to visualize the crystal symmetry elements. Combined, the experimental results provide unambiguous evidence for the existence of a non-centrosymmetric orthorhombic phase that can support spontaneous polarization, resolving the origin of ferroelectricity in HfO2 thin films.
- Published
- 2015
181. Direct observation of charge mediated lattice distortions in complex oxide solid solutions
- Author
-
Everett D. Grimley, Douglas L. Irving, Xiahan Sang, Changning Niu, and James M. LeBeau
- Subjects
Condensed Matter - Materials Science ,Physics and Astronomy (miscellaneous) ,Scanning electron microscope ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Charge density ,Molecular physics ,3. Good health ,law.invention ,Transmission electron microscopy ,law ,Atom ,Scanning transmission electron microscopy ,Density functional theory ,Electron microscope ,Solid solution - Abstract
Material properties depend sensitively on picometer scale atomic displacements introduced by local chemical fluctuations. Direct real-space, high spatial-resolution measurements of this compositional variation and corresponding distortion can provide new insights into materials behavior at the atomic scale. Using aberration corrected scanning transmission electron microscopy combined with advanced imaging methods, we observed atom column specific, picometer-scale displacements induced by local chemistry in a complex oxide solid solution. Displacements predicted from density functional theory were found to correlate with the observed experimental trends. Further analysis of bonding and charge distribution were used to clarify the mechanisms responsible for the detected structural behavior. By extending the experimental electron microscopy measurements to previously inaccessible length scales, we identified correlated atomic displacements linked to bond differences within the complex oxide structure., Comment: 11 pages, 3 figures
- Published
- 2015
182. Large area strain analysis using scanning transmission electron microscopy across multiple images
- Author
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Krishna Rajan, Surendra K. Saxena, S. V. Raju, Scott Broderick, Aakash Kumar, Susan B. Sinnott, James M. LeBeau, Xiahan Sang, Santoshrupa Dumpala, and A. A. Oni
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Strain (chemistry) ,Scanning electron microscope ,business.industry ,Resolution (electron density) ,Phase (waves) ,Analytical chemistry ,Optics ,Transmission electron microscopy ,Distortion ,Microscopy ,Scanning transmission electron microscopy ,business - Abstract
Here, we apply revolving scanning transmission electron microscopy to measure lattice strain across a sample using a single reference area. To do so, we remove image distortion introduced by sample drift, which usually restricts strain analysis to a single image. Overcoming this challenge, we show that it is possible to use strain reference areas elsewhere in the sample, thereby enabling reliable strain mapping across large areas. As a prototypical example, we determine the strain present within the microstructure of a Ni-based superalloy directly from atom column positions as well as geometric phase analysis. While maintaining atomic resolution, we quantify strain within nanoscale regions and demonstrate that large, unit-cell level strain fluctuations are present within the intermetallic phase.
- Published
- 2015
183. Chemical Analysis of Airbrushed Nickel Nanoparticles for Large-Area Growth of Vertically Aligned Carbon Nanofibers on Metal Surfaces
- Author
-
Ryan C. Pearce, Anatoli V. Melechko, Dale K. Hensley, Bryan D. Anderson, Justin G. Railsback, Mehmet Fahri Saraç, Ryan M. White, James M. LeBeau, Joseph B. Tracy, and A. A. Oni
- Subjects
Metal ,Nickel ,Materials science ,chemistry ,Carbon nanofiber ,visual_art ,visual_art.visual_art_medium ,chemistry.chemical_element ,Nanoparticle ,Nanotechnology ,Instrumentation - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.
- Published
- 2013
184. Addressing Detector Non-Uniformity in Scanning Transmission Electron Microscopy
- Author
-
Scott D. Findlay and James M. LeBeau
- Subjects
Conventional transmission electron microscope ,Materials science ,Optics ,Electron tomography ,business.industry ,Detector ,Scanning transmission electron microscopy ,Scanning confocal electron microscopy ,Energy filtered transmission electron microscopy ,business ,Instrumentation ,Dark field microscopy - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.
- Published
- 2013
185. Multi-detector STEM-EDS mapping of ion-irradiated nanostructured ferritic alloys
- Author
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Yanwen Zhang, Michael K Miller, Ryan M. White, Chad M. Parish, and James M. LeBeau
- Subjects
Ferritic alloy ,Materials science ,business.industry ,Optoelectronics ,Irradiation ,business ,Instrumentation ,Multi detector ,Ion - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.
- Published
- 2013
186. Atomic Structure and Chemistry of Defects in non-stoichiometric SrVO3 Thin Films
- Author
-
R. Engel-Herbret, Jarrett A. Moyer, James M. LeBeau, H. Mohammad Alipour, Craig Eaton, and Ryan M. White
- Subjects
Carbon film ,Chemical engineering ,Chemistry ,Thin film ,Instrumentation ,Stoichiometry - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.
- Published
- 2013
187. Modelling thermal scattering and solving structures usingZ-contrast imaging
- Author
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Susanne Stemmer, Leslie J. Allen, Nathan R Lugg, Andrew V. Martin, B.D. Forbes, Adrian J. D’Alfonso, James M. LeBeau, and Scott D. Findlay
- Subjects
Optics ,Materials science ,Structural Biology ,business.industry ,Thermal scattering ,Contrast imaging ,business - Published
- 2011
188. Exploring the Strain Sensitivity of Image Contrast in Quantitative STEM of SrTiO3
- Author
-
Jack Y. Zhang, Susanne Stemmer, L. Allen, James M. LeBeau, and Adrian J. D’Alfonso
- Subjects
Materials science ,Strain (chemistry) ,Sensitivity (control systems) ,Instrumentation ,Image contrast ,Biomedical engineering - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.
- Published
- 2011
189. Ferroelectric phenomena in Si-doped HfO2thin films with TiN and Ir electrodes
- Author
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Matthew A. Nelson, Chris M. Fancher, Jacob L. Jones, Patrick D. Lomenzo, Toshikazu Nishida, Everett D. Grimley, Xiahan Sang, James M. LeBeau, Saeed Moghaddam, Qanit Takmeel, and Peng Zhao
- Subjects
Materials science ,business.industry ,Annealing (metallurgy) ,Process Chemistry and Technology ,chemistry.chemical_element ,Ferroelectricity ,Ferroelectric capacitor ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Tetragonal crystal system ,Atomic layer deposition ,chemistry ,Materials Chemistry ,Optoelectronics ,Electrical and Electronic Engineering ,Thin film ,business ,Tin ,Instrumentation ,Monoclinic crystal system - Abstract
Ferroelectric HfO2 is an attractive candidate for future ferroelectric random access memory devices due to its compatibility with the complementary metal-oxide-semiconductor process, conformal deposition, and scaling ability. Crystallization of HfO2 with different dopants and annealing conditions can produce the stabilization of the monoclinic, tetragonal, cubic, or orthorhombic crystal phases. In this work, the authors observe ferroelectric behavior in Si-doped hafnium oxide with TiN and Ir electrodes. Atomic layer deposited 10 nm HfO2 capacitors doped with varying concentrations of SiO2 have been fabricated in the metal–ferroelectric–insulator–semiconductor (MFIS) structure. The ferroelectric characteristics of thin film HfO2 are compared in the MFIS and metal–ferroelectric–metal configurations. Post-metallization anneals were applied to all thin film ferroelectric HfO2 capacitors, resulting in a remanent polarization of up to 22 μC/cm2 and a range of observed coercive voltages, emphasizing the importance of the annealing conditions, electrode materials, and device structure on the ferroelectric properties of thin film HfO2.
- Published
- 2014
190. Smooth cubic commensurate oxides on gallium nitride
- Author
-
Elizabeth A. Paisley, Jon Paul Maria, Ramon Collazo, Christopher T. Shelton, James M. LeBeau, Mark D. Losego, Zlatko Sitar, Hans M. Christen, Michael D. Biegalski, Douglas L. Irving, Benjamin E. Gaddy, and Seiji Mita
- Subjects
Materials science ,Condensed matter physics ,Wide-bandgap semiconductor ,General Physics and Astronomy ,Heterojunction ,Gallium nitride ,02 engineering and technology ,Nitride ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystallographic defect ,Pulsed laser deposition ,chemistry.chemical_compound ,chemistry ,0103 physical sciences ,Thin film ,010306 general physics ,0210 nano-technology ,Molecular beam epitaxy - Abstract
Smooth, commensurate alloys of ⟨111⟩-oriented Mg0.52Ca0.48O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals ...
- Published
- 2014
191. Quantitative HAADF Imaging of Crystals Containing Heavy Elements: A Comparison with Theory
- Author
-
Allan J. Jacobson, Xiqu Wang, James M. LeBeau, Leslie J. Allen, Susanne Stemmer, and Scott D. Findlay
- Subjects
Materials science ,Microscopy ,Nanotechnology ,Instrumentation - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009
- Published
- 2009
192. Position Averaged Convergent Beam Electron Diffraction
- Author
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Leslie J. Allen, James M. LeBeau, Susanne Stemmer, and Scott D. Findlay
- Subjects
Reflection high-energy electron diffraction ,Materials science ,Low-energy electron diffraction ,Electron diffraction ,Gas electron diffraction ,Position (vector) ,Microscopy ,Convergent beam ,Atomic physics ,Instrumentation - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009
- Published
- 2009
193. Quantitative HAADF-STEM and EELS
- Author
-
James M. LeBeau, Susanne Stemmer, Scott D. Findlay, and Leslie J. Allen
- Subjects
Materials science ,Analytical chemistry ,Microscopy and Microanalysis ,Instrumentation - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008
- Published
- 2008
194. Simulation of Atomic Resolution Images in STEM
- Author
-
James M. LeBeau, Scott D. Findlay, Michel Bosman, Vicki J. Keast, Mark P. Oxley, Susanne Stemmer, Adrian J. D’Alfonso, and Leslie J. Allen
- Subjects
Materials science ,Optics ,Atomic resolution ,business.industry ,business ,Instrumentation - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008
- Published
- 2008
195. Thermal Stability of Hf-Based Gate Dielectric Stacks with Rare-Earth Oxide Capping Layers
- Author
-
Angus I. Kingon, James M. LeBeau, Daniel J. Lichtenwalner, Susanne Stemmer, Dmitri O. Klenov, and Jesse S. Jur
- Subjects
chemistry.chemical_compound ,Materials science ,chemistry ,business.industry ,Gate oxide ,Rare earth ,Gate dielectric ,Oxide ,Optoelectronics ,Thermal stability ,business ,Instrumentation - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008
- Published
- 2008
196. Carrier concentration modulation by hot pressing pressure in n-type nanostructured Bi(Se)Te alloy
- Author
-
Judy Stuart, Peter Thomas, James M. LeBeau, Carl C. Koch, Tsung-Ta Chan, and Rama Venkatasubramanian
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Band gap ,Metallurgy ,Alloy ,Power factor ,engineering.material ,Hot pressing ,High pressure ,Seebeck coefficient ,Lattice (order) ,Thermoelectric effect ,engineering - Abstract
We demonstrate experimentally that an optimal hot pressing pressure is required for high thermoelectric power factor in different n-type Bi(Se)Te alloys for a given processing temperature. This phenomenon is attributed to the variations in carrier concentration, which changes the Seebeck coefficient and therefore the power factor. The variations could arise from the difference in the concentration of charged antisite defects as their formation energy changes with pressures. Furthermore, modifications of the energy gap resulting from the lattice distortions at high pressure also likely play a role.
- Published
- 2013
197. Interface properties of Ga(As,P)/(In,Ga)As strained multiple quantum well structures
- Author
-
Salah M. Bedair, Joshua P. Samberg, Geoffrey K. Bradshaw, Peter C. Colter, Hamideh M. Alipour, C. Zachary Carlin, Nadia A. El-Masry, and James M. LeBeau
- Subjects
Materials science ,Photoluminescence ,Physics and Astronomy (miscellaneous) ,business.industry ,Chemical vapor deposition ,Gallium arsenide ,chemistry.chemical_compound ,Absorption edge ,chemistry ,Scanning transmission electron microscopy ,Optoelectronics ,Metalorganic vapour phase epitaxy ,business ,Spectroscopy ,Quantum well - Abstract
(In,Ga)As/Ga(As,P) multiple quantum wells (MQWs) with GaAs interface layers have been characterized with photoluminescence (PL) and high resolution scanning transmission electron microscopy (STEM). By growing (In,Ga)As/Ga(As,P) MQWs with asymmetric GaAs interfacial layers, we found that phosphorus carry-over had a profound effect on the absorption edge of the (In,Ga)As wells. Evidence for this phosphorus was initially determined via PL and then definitively proven through STEM and energy dispersive x-ray spectroscopy. We show that the phosphorus carry-over can be prevented with sufficiently thick GaAs transition layers. Preliminary results for GaAs p-i-n solar cells utilizing the improved MQWs are presented.
- Published
- 2013
198. Atomic scale structure and chemistry of Bi2Te3/GaAs interfaces grown by metallorganic van der Waals epitaxy
- Author
-
Jonathan Pierce, Ryan M. White, J. Houston Dycus, Rama Venkatasubramanian, and James M. LeBeau
- Subjects
Crystallography ,Physics and Astronomy (miscellaneous) ,Chemical physics ,Scanning transmission electron microscopy ,Dangling bond ,Chemical vapor deposition ,Metalorganic vapour phase epitaxy ,Thin film ,Spectroscopy ,Epitaxy ,Atomic units - Abstract
Here, we report the atomic scale structure and chemistry of epitaxial Bi2Te3 thin films grown via metallorganic chemical vapor deposition on (001) GaAs substrates. Using aberration corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), we report an atomically abrupt interface spanned by a second phase. Further, we demonstrate that interpretation of HAADF STEM image intensities does not provide an unambiguous interface structure. Combining atomic resolution imaging and spectroscopy, we determine the identity of the interfacial species is found to be consistent with that of a bilayer of Ga–Te that terminates GaAs dangling bonds.
- Published
- 2013
199. Quantitative transmission electron microscopy at atomic resolution
- Author
-
Adrian J. D’Alfonso, Leslie J. Allen, James M. LeBeau, B.D. Forbes, Scott D. Findlay, and Susanne Stemmer
- Subjects
Conventional transmission electron microscope ,History ,Microscope ,business.industry ,Chemistry ,Analytical chemistry ,Scanning confocal electron microscopy ,Dark field microscopy ,Computer Science Applications ,Education ,law.invention ,Optics ,Electron tomography ,law ,Scanning transmission electron microscopy ,Energy filtered transmission electron microscopy ,business ,High-resolution transmission electron microscopy - Abstract
In scanning transmission electron microscopy (STEM) it is possible to operate the microscope in bright-field mode under conditions which, by the quantum mechanical principle of reciprocity, are equivalent to those in conventional transmission electron microscopy (CTEM). The results of such an experiment will be presented which are in excellent quantitative agreement with theory for specimens up to 25 nm thick. This is at variance with the large contrast mismatch (typically between two and five) noted in equivalent CTEM experiments. The implications of this will be discussed.
- Published
- 2012
200. Quantitative STEM: Experimental Methods and Applications
- Author
-
James M. LeBeau, Scott D. Findlay, Susanne Stemmer, and Leslie J. Allen
- Subjects
Diffraction ,History ,Materials science ,business.industry ,Quantitative Biology::Tissues and Organs ,Dark field microscopy ,Image contrast ,Computer Science Applications ,Education ,Optics ,Annular dark-field imaging ,Microscopy ,Scanning transmission electron microscopy ,Atomic number ,Experimental methods ,business - Abstract
High-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy (STEM) is highly sensitive to both the atomic number and the Debye-Waller factor of the atom columns. We will discuss the experimental requirements for a quantitative understanding of STEM image contrast, in particular the determination of the precise specimen thickness. We show that near perfect agreement can be achieved between theory and experiment and demonstrate that quantitative STEM allows for column-by-column counting of all the atoms in an arbitrarily shaped specimen.
- Published
- 2012
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