46 results on '"Matthew J, Highland"'
Search Results
2. Operando Nanoscale Imaging of Electrochemically Induced Strain in a Locally Polarized Pt Grain
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Dina Sheyfer, Ruperto G. Mariano, Tomoya Kawaguchi, Wonsuk Cha, Ross J. Harder, Matthew W. Kanan, Stephan O. Hruszkewycz, Hoydoo You, and Matthew J. Highland
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Mechanical Engineering ,General Materials Science ,Bioengineering ,General Chemistry ,Condensed Matter Physics - Abstract
Developing new methods that reveal the structure of electrode materials under polarization is key to constructing robust structure-property relationships. However, many existing methods lack the spatial resolution in structural changes and fidelity to electrochemical operating conditions that are needed to probe catalytically relevant structures. Here, we combine a nanopipette electrochemical cell with three-dimensional X-ray Bragg coherent diffractive imaging to study how strain in a single Pt grain evolves in response to applied potential. During polarization, marked changes in surface strain arise from the Coulombic attraction between the surface charge on the electrode and the electrolyte ions in the electrochemical double layers, while the strain in the bulk of the crystal remains unchanged. The concurrent surface redox reactions have a strong influence on the magnitude and nature of the strain changes under polarization. Our studies provide a powerful blueprint to understand how structural evolution influences electrochemical performance at the nanoscale.
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- 2022
3. In situ microbeam surface X-ray scattering reveals alternating step kinetics during crystal growth
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Matthew J. Highland, G. Brian Stephenson, Weronika Walkosz, Carol Thompson, Jeffrey A. Eastman, Dongwei Xu, Peter Zapol, and Guangxu Ju
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Materials science ,Solid-phase synthesis ,Science ,Kinetics ,Stacking ,General Physics and Astronomy ,FOS: Physical sciences ,Crystal growth ,02 engineering and technology ,Epitaxy ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,Surfaces, interfaces and thin films ,0103 physical sciences ,Growth rate ,010306 general physics ,Condensed Matter - Materials Science ,Multidisciplinary ,Scattering ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,Microbeam ,021001 nanoscience & nanotechnology ,Applied physics ,Chemical physics ,0210 nano-technology ,Vicinal - Abstract
The stacking sequence of hexagonal close-packed and related crystals typically results in steps on vicinal {0001} surfaces that have alternating A and B structures with different growth kinetics. However, because it is difficult to experimentally identify which step has the A or B structure, it has not been possible to determine which has faster adatom attachment kinetics. Here we show that in situ microbeam surface X-ray scattering can determine whether A or B steps have faster kinetics under specific growth conditions. We demonstrate this for organo-metallic vapor phase epitaxy of (0001) GaN. X-ray measurements performed during growth find that the average width of terraces above A steps increases with growth rate, indicating that attachment rate constants are higher for A steps, in contrast to most predictions. Our results have direct implications for understanding the atomic-scale mechanisms of GaN growth and can be applied to a wide variety of related crystals., The basal-plane surfaces of hexagonal close-packed crystals typically exhibit an alternating sequence of A and B steps with different atomic structures and growth kinetics. Here the authors demonstrate a method to determine whether A or B steps have faster kinetics under specific growth conditions.
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- 2021
4. Sub-pixel high-resolution imaging of high-energy x-rays inspired by sub-wavelength optical imaging
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Matthew J. Highland, J. Weizeorick, N. Bertaux, Jonathan Almer, Marc Allain, Siddharth Maddali, Sarvjit Shastri, Stephan O. Hruszkewycz, Peter Kenesei, Jun-Sang Park, Coherent Optical Microscopy and X-rays (COMiX), Institut FRESNEL (FRESNEL), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), PhyTI (PhyTI), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), and Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)
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Physics ,Point spread function ,Diffraction ,0303 health sciences ,[STAT.AP]Statistics [stat]/Applications [stat.AP] ,Photon ,Pixel ,business.industry ,030303 biophysics ,Detector ,Bragg's law ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Dot pitch ,Upsampling ,03 medical and health sciences ,[SPI.ELEC]Engineering Sciences [physics]/Electromagnetism ,Optics ,0103 physical sciences ,[SPI.OPTI]Engineering Sciences [physics]/Optics / Photonic ,010306 general physics ,business ,[SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing ,ComputingMilieux_MISCELLANEOUS - Abstract
We have developed and demonstrated an image super-resolution method—XR-UNLOC: X-Ray UNsupervised particle LOCalization—for hard x-rays measured with fast-frame-rate detectors that is an adaptation of the principle of photo-activated localization microscopy (PALM) and stochastic optical reconstruction microscopy (STORM), which enabled biological fluorescence imaging at sub-optical-wavelength scales. We demonstrate the approach on experimental coherent Bragg diffraction data measured with 52 keV x-rays from a nanocrystalline sample. From this sample, we resolve the fine fringe detail of a high-energy x-ray Bragg coherent diffraction pattern to an upsampling factor of 16 of the native pixel pitch of 30 μm of a charge-integrating fastCCD detector. This was accomplished by analysis of individual photon locations in a series of “nearly-dark” instances of the diffraction pattern that each contain only a handful of photons. Central to our approach was the adaptation of the UNLOC photon fitting routine for PALM/STORM to the hard x-ray regime to handle much smaller point spread functions, which required a different statistical test for photon detection and for sub-pixel localization. A comparison to a photon-localization strategy used in the x-ray community (“droplet analysis”) showed that XR-UNLOC provides significant improvement in super-resolution. We also developed a metric by which to estimate the limit of reliable upsampling with XR-UNLOC under a given set of experimental conditions in terms of the signal-to-noise ratio of a photon detection event and the size of the point spread function for guiding future x-ray experiments in many disciplines where detector pixelation limits must be overcome.
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- 2021
5. Coherent X-ray spectroscopy reveals the persistence of island arrangements during layer-by-layer growth
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Hua Zhou, Hyunjung Kim, Peter Zapol, Guangxu Ju, Paul H. Fuoss, G. Brian Stephenson, Dongwei Xu, Jeffrey A. Eastman, Matthew J. Highland, and Carol Thompson
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Physics ,Crystal ,chemistry.chemical_compound ,X-ray spectroscopy ,chemistry ,Dynamic light scattering ,Chemical physics ,Layer by layer ,General Physics and Astronomy ,Gallium nitride ,Crystal growth ,Spectroscopy ,Epitaxy - Abstract
Understanding surface dynamics during epitaxial film growth is key to growing high-quality materials with controllable properties. X-ray photon correlation spectroscopy (XPCS) using coherent X-rays opens new opportunities for in situ observation of atomic-scale fluctuation dynamics during crystal growth. Here, we present XPCS measurements of two-dimensional island dynamics during homoepitaxial growth in the layer-by-layer mode. Analysis of the results using two-time correlations reveals a new phenomenon—a memory effect in the arrangement of islands formed on successive crystal layers. Simulations indicate that this persistence in the island arrangements arises from communication between islands on different layers via adatoms. With the worldwide advent of new coherent X-ray sources, the experimental and analysis methods pioneered here will enable broad application of XPCS to observe atomic-scale processes on surfaces. In situ measurements based on coherent X-ray spectroscopy are performed during the epitaxial growth of gallium nitride films, revealing a memory effect in the arrangement of islands formed on successive crystal layers.
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- 2019
6. Crystal Truncation Rods from Miscut Surfaces with Alternating Terminations
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Matthew J. Highland, Weronika Walkosz, Dongwei Xu, Peter Zapol, G. Brian Stephenson, Jeffrey A. Eastman, Carol Thompson, and Guangxu Ju
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Surface (mathematics) ,Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Scattering ,Stacking ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Crystal growth ,02 engineering and technology ,Crystal structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystal ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Vicinal ,Intensity (heat transfer) - Abstract
Miscut surfaces of layered crystals can exhibit a stair-like sequence of terraces having periodic variation in their atomic structure. For hexagonal close-packed and related crystal structures with an {\alpha}{\beta}{\alpha}{\beta} stacking sequence, there have been long-standing questions regarding how the differences in adatom attachment kinetics at the steps separating the terraces affect the fractional coverage of {\alpha} vs. {\beta} termination during crystal growth. To demonstrate how surface X-ray scattering can help address these questions, we develop a general theory for the intensity distributions along crystal truncation rods (CTRs) for miscut surfaces with a combination of two terminations. We consider half-unit-cell-height steps, and variation of the coverages of the terraces above each step. Example calculations are presented for the GaN (0001) surface with various reconstructions. These show which CTR positions are most sensitive to the fractional coverage of the two terminations. We compare the CTR profiles for exactly oriented surfaces to those for vicinal surfaces having a small miscut angle, and investigate the circumstances under which the CTR profile for an exactly oriented surface is equal to the sum of the intensities of the corresponding family of CTRs for a miscut surface., Comment: 15 pages, 15 figures, Supplemental with 9 tables specifying coordinates of the 9 reconstructions examined. v2 has edits for clarity, addition of supplemental. (arXiv admin note: substantial text overlap with arXiv:2007.05083)
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- 2020
7. Tunable side-bounce monochromator
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Hawoong Hong, Jonathan Z. Tischler, Xianbo Shi, and Matthew J. Highland
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Physics ,Nuclear and High Energy Physics ,Radiation ,Offset (computer science) ,business.industry ,Polarization (waves) ,law.invention ,Ray tracing (physics) ,Optics ,law ,Physics::Accelerator Physics ,business ,Instrumentation ,Monochromator - Abstract
Side-bounce beamlines with fixed-exit angles have been intended to operate with only one selected energy. However, a tunable monochromator in a new geometry is presented here that will make side-bounce beamlines energy tunable. It requires the addition of two more rotations. Analytic solutions for the values of these two rotation angles are provided. The validity of the new concept was checked by ray tracing and two-dimensional searches in the additional angles. Operational details on the new scheme, including the exit offset and steering of the beams, were determined. In addition to tunability, the new monochromator will reduce the loss from the polarization factor at low energies.
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- 2020
8. Burton-Cabrera-Frank theory for surfaces with alternating step types
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Guangxu Ju, Dongwei Xu, Carol Thompson, Matthew J. Highland, Jeffrey A. Eastman, Weronika Walkosz, Peter Zapol, and G. Brian Stephenson
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Condensed Matter - Materials Science ,Condensed Matter::Materials Science ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
Burton-Cabrera-Frank (BCF) theory has proven to be a versatile framework to relate surface morphology and dynamics during crystal growth to the underlying mechanisms of adatom diffusion and attachment at steps. For an important class of crystal surfaces, including the basal planes of hexagonal close-packed and related systems, the steps in a sequence on a vicinal surface can exhibit properties that alternate from step to step. Here we develop BCF theory for such surfaces, relating observables such as alternating terrace widths as a function of growth conditions to the kinetic coefficients for adatom attachment at steps. We include the effects of step transparency and step-step repulsion. A general solution is obtained for the dynamics of the terrace widths, assuming quasi-steady-state adatom distributions on the terraces. An explicit simplified analytical solution is obtained under widely applicable approximations. From this we obtain expressions for the full-steady-state terrace fraction as a function of growth rate. Fits of the theoretical predictions to recent experimental determinations of the steady-state and dynamics of terrace fractions on GaN (0001) surfaces during organo-metallic vapor phase epitaxy give values of the kinetic coefficients for this system. In Appendices, we also connect a model for diffusion between kinks on steps to the model for diffusion between steps on terraces, which quantitatively relates step transparency to the kinetics of atom attachment at kinks, and consider limiting cases of diffusion-limited, attachment-limited, and mixed kinetics., Comment: 22 pages, 11 fig, 5 tables, 3 appendices, and Supplemental. For clarity, arXiv:2007.05083 was split into two distinct papers focusing on separate subtopics. This paper focuses on developing BCF theory in presence of non-identical step-edges. The other paper arXiv:2010.06166, on the scattering experiments whose interpretations required the extensions to BCF
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- 2020
- Full Text
- View/download PDF
9. Instrument for in situ hard x-ray nanobeam characterization during epitaxial crystallization and materials transformations
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Samuel D. Marks, Matthew J. Highland, Thomas F. Kuech, G. Brian Stephenson, Peiyu Quan, Rui Liu, Paul G. Evans, and Hua Zhou
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010302 applied physics ,Diffraction ,Condensed Matter - Materials Science ,Materials science ,business.industry ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Sputter deposition ,01 natural sciences ,Evaporation (deposition) ,Coherent diffraction imaging ,010305 fluids & plasmas ,law.invention ,Amorphous solid ,Condensed Matter::Materials Science ,law ,0103 physical sciences ,Optoelectronics ,Deposition (phase transition) ,Crystallization ,Thin film ,business ,Instrumentation - Abstract
Solid-phase epitaxy (SPE) and other three-dimensional epitaxial crystallization processes pose challenging structural and chemical characterization problems. The concentration of defects, the spatial distribution of elastic strain, and the chemical state of ions each vary with nanoscale characteristic length scales and depend sensitively on the gas environment and elastic boundary conditions during growth. The lateral or three-dimensional propagation of crystalline interfaces in SPE has nanoscale or submicron characteristic distances during typical crystallization times. An in situ synchrotron hard x-ray instrument allows these features to be studied during deposition and crystallization using diffraction, resonant scattering, nanobeam and coherent diffraction imaging, and reflectivity. The instrument incorporates a compact deposition system allowing the use of short-working-distance x-ray focusing optics. Layers are deposited using radio-frequency magnetron sputtering and evaporation sources. The deposition system provides control of the gas atmosphere and sample temperature. The sample is positioned using a stable mechanical design to minimize vibration and drift and employs precise translation stages to enable nanobeam experiments. Results of in situ x-ray characterization of the amorphous thin film deposition process for a SrTiO3/BaTiO3 multilayer illustrate implementation of this instrument., Comment: 28 pages, 6 figures
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- 2020
- Full Text
- View/download PDF
10. Stability Limits and Defect Dynamics in Ag Nanoparticles Probed by Bragg Coherent Diffractive Imaging
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Yuzi Liu, G. B. Stephenson, Nenad M. Markovic, Ross Harder, J. Maser, Stephan O. Hruszkewycz, Evan Maxey, Hoydoo You, P. P. Lopes, Wonsuk Cha, Matthew J. Highland, and Andrew Ulvestad
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Materials science ,Mechanical Engineering ,Nanoparticle ,Bioengineering ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Electron ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Silver nanoparticle ,0104 chemical sciences ,Nanomaterials ,General Materials Science ,Rotating disk electrode ,0210 nano-technology ,Nanoscopic scale ,Dissolution ,Inductively coupled plasma mass spectrometry - Abstract
Dissolution is critical to nanomaterial stability, especially for partially dealloyed nanoparticle catalysts. Unfortunately, highly active catalysts are often not stable in their reactive environments, preventing widespread application. Thus, focusing on the structure–stability relationship at the nanoscale is crucial and will likely play an important role in meeting grand challenges. Recent advances in imaging capability have come from electron, X-ray, and other techniques but tend to be limited to specific sample environments and/or two-dimensional images. Here, we report investigations into the defect-stability relationship of silver nanoparticles to voltage-induced electrochemical dissolution imaged in situ in three-dimensional detail by Bragg coherent diffractive imaging. We first determine the average dissolution kinetics by stationary probe rotating disk electrode in combination with inductively coupled plasma mass spectrometry, which allows in situ measurement of Ag+ ion formation. We then observe...
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- 2017
11. Effect of SrO Doping on LaGaO3 Synthesis via Magnetron Sputtering
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Jeffrey A. Eastman, Chad M. Folkman, Paul H. Fuoss, Edith Perret, Dillon D. Fong, Carol Thompson, and Matthew J. Highland
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010302 applied physics ,Materials science ,Scattering ,Doping ,Oxide ,Ionic bonding ,Mineralogy ,02 engineering and technology ,General Chemistry ,Sputter deposition ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Epitaxy ,Microstructure ,01 natural sciences ,chemistry.chemical_compound ,chemistry ,Chemical physics ,0103 physical sciences ,General Materials Science ,Thin film ,0210 nano-technology - Abstract
The high temperature growth behavior of epitaxial LaGaO3 thin films with and without SrO is determined with realtime x-ray scattering. We find SrO alters the thin film growth mode of LaGaO3, both when pre-deposited on a surface as well as when SrO and LaGaO3 are co-deposited. We also find that depositing a small amount of SrO on a LaGaO3 surface induces significant structural rearrangement in the film. We describe possible mechanisms under which these transformations may occur. The strong effect of SrO on the microstructure of La1-xSrxGaO3 likely has wider implications for other ionic conducting oxide materials.
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- 2016
12. Strain annealing of SiC nanoparticles revealed through Bragg coherent diffraction imaging for quantum technologies
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Wonsuk Cha, David D. Awschalom, Matthew J. Highland, Kevin C. Miao, Andrew Ulvestad, Christopher P. Anderson, F. J. Heremans, Siddharth Maddali, and Stephan O. Hruszkewycz
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Diffraction ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Annealing (metallurgy) ,Quantum sensor ,02 engineering and technology ,Crystal structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystallographic defect ,Coherent diffraction imaging ,Synchrotron ,law.invention ,Quantum technology ,law ,0103 physical sciences ,General Materials Science ,010306 general physics ,0210 nano-technology - Abstract
The crystalline strain properties of nanoparticles have broad implications in a number of emerging fields, including quantum and biological sensing in which heterogeneous internal strain fields are detrimental to performance. Here we used synchrotron-based Bragg coherent x-ray diffraction imaging (BCDI) to measure three-dimensional lattice strain fields within individual 3C-SiC nanoparticles, a candidate host material for quantum sensing, as a function of temperature during and after annealing up to ${900}^{\phantom{\rule{0.16em}{0ex}}\ensuremath{\circ}}\mathrm{C}$. We observed pronounced homogenization of the initial strain field at temperatures above ${500}^{\phantom{\rule{0.16em}{0ex}}\ensuremath{\circ}}\mathrm{C}$, and we find that the surface layers and central volumes of the nanoparticles reduce strain at similar rates, suggesting a uniform healing mechanism. Thus, we attribute the observed strain homogenization to activation of mobile point defects that annihilate and improve the overall quality of the crystal lattice. This work also establishes the feasibility of performing BCDI at high temperatures (up to ${900}^{\phantom{\rule{0.16em}{0ex}}\ensuremath{\circ}}\mathrm{C}$) to map structural hystereses relevant to the processing of quantum nanomaterials.
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- 2018
13. Reply to 'Comment on ‘Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO3 ' '
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Jörgen Larsson, Yubo Qi, Frank W. Chen, Il Woong Jung, Diling Zhu, Meng-Ju Sher, Lane W. Martin, Y. Zhu, Henrik Enquist, Jian Lu, Arturas Vailionis, John W. Freeland, Anoop R. Damodaran, Andrew M. Rappe, Henrik T. Lemke, Harold Y. Hwang, Jin-Seong Park, J. Goodfellow, Peter Zalden, Matthew J. Highland, M. Chollet, Te Hu, Aaron M. Lindenberg, James M. Glownia, Z. Cai, Klaus Sokolowski-Tinten, Donald A. Walko, F. Quirin, Keith A. Nelson, M. C. Hoffmann, Nathaniel C. Brandt, Shi Liu, Haidan Wen, and Paul G. Evans
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Diffraction ,Physics ,Field (physics) ,Condensed matter physics ,Terahertz radiation ,Ionic bonding ,02 engineering and technology ,Function (mathematics) ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Displacement (vector) ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Ultrashort pulse - Abstract
In this reply to S. Durbin's comment on our original paper "Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO3," we concur that his final equations 8 and 9 more accurately describe the change in diffracted intensity as a function of Ti displacement. We also provide an alternative derivation based on an ensemble average over unit cells. The conclusions of the paper are unaffected by this correction.
- Published
- 2018
14. Characterization of the X-ray Coherence Properties of an Undulator Beamline at the Advanced Photon Source
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Guangxu Ju, Carol Thompson, Jeffrey A. Eastman, Hua Zhou, G. Brian Stephenson, Paul H. Fuoss, Roger J. Dejus, and Matthew J. Highland
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Diffraction ,Accelerator Physics (physics.acc-ph) ,Nuclear and High Energy Physics ,genetic structures ,Physics::Instrumentation and Detectors ,Astrophysics::High Energy Astrophysical Phenomena ,brightness ,FOS: Physical sciences ,Physics::Optics ,Advanced Photon Source ,02 engineering and technology ,01 natural sciences ,law.invention ,Optics ,law ,0103 physical sciences ,Instrumentation ,Monochromator ,010302 applied physics ,Physics ,Radiation ,business.industry ,Astrophysics::Instrumentation and Methods for Astrophysics ,Undulator ,021001 nanoscience & nanotechnology ,Research Papers ,eye diseases ,Coherence length ,coherence ,Beamline ,Physics::Accelerator Physics ,Physics - Accelerator Physics ,sense organs ,0210 nano-technology ,business ,divergence ,Coherence (physics) ,Beam divergence - Abstract
Methods are described to measure divergence by imaging the apparent source size using either slits to form a pinhole camera or a compound refractive lens. The values of brightness and coherent flux obtained are compared with those calculated for the undulator source, to evaluate the effects of beamline optics., In anticipation of the increased use of coherent X-ray methods and the need to upgrade beamlines to match improved source quality, here the coherence properties of the X-rays delivered by beamline 12ID-D at the Advanced Photon Source have been characterized. The measured X-ray divergence, beam size, brightness and coherent flux at energies up to 26 keV are compared with the calculated values from the undulator source, and the effects of beamline optics such as a mirror, monochromator and compound refractive lenses are evaluated. Diffraction patterns from slits as a function of slit width are analyzed using wave propagation theory to obtain the beam divergence and thus coherence length. Imaging of the source using a compound refractive lens was found to be the most accurate method for determining the vertical divergence. While the brightness and coherent flux obtained without a monochromator (‘pink beam’) agree well with those calculated for the source, those measured with the monochromator were a factor of three to six lower than the source, primarily because of vertical divergence introduced by the monochromator. The methods described herein should be widely applicable for measuring the X-ray coherence properties of synchrotron beamlines.
- Published
- 2018
15. Island dynamics and anisotropy during vapor phase epitaxy of m-plane GaN
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Edith Perret, G. B. Stephenson, Carol Thompson, Anneli Munkholm, Paul H. Fuoss, Matthew J. Highland, Dongwei Xu, and Peter Zapol
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Surface diffusion ,Condensed Matter - Materials Science ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Scattering ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Reciprocal lattice ,0103 physical sciences ,Monolayer ,Growth rate ,Kinetic Monte Carlo ,010306 general physics ,0210 nano-technology ,Anisotropy - Abstract
Using in situ grazing-incidence x-ray scattering, we have measured the diffuse scattering from islands that form during layer-by-layer growth of GaN by metal-organic vapor phase epitaxy on the (1010) m-plane surface. The diffuse scattering is extended in the (0001) in-plane direction in reciprocal space, indicating a strong anisotropy with islands elongated along [1 $\overline{2}$ 10] and closely spaced along [0001]. This is confirmed by atomic force microscopy of a quenched sample. Islands were characterized as a function of growth rate G and temperature. The island spacing along [0001] observed during the growth of the first monolayer obeys a power-law dependence on growth rate G$^{-n}$, with an exponent $n = 0.25 \pm 0.02$. Results are in agreement with recent kinetic Monte Carlo simulations, indicating that elongated islands result from the dominant anisotropy in step edge energy and not from surface diffusion anisotropy. The observed power-law exponent can be explained using a simple steady-state model, which gives n = 1/4., Comment: 4 pages, 5 figures, ancillary material includes Supplement material (pdf) of 4 pages, 5 figures with details of analysis
- Published
- 2018
16. Structural imaging of nanoscale phonon transport in ferroelectrics excited by metamaterial-enhanced terahertz fields
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Frank W. Chen, Subramanian K. R. S. Sankaranarayanan, Matthew J. Highland, Lane W. Martin, Bin Hu, John W. Freeland, Joonkyu Park, Anoop R. Damodaran, Paul G. Evans, Il Woong Jung, Haidan Wen, Kiran Sasikumar, Aaron M. Lindenberg, Yi Zhu, Donald A. Walko, I-Cheng Tung, and Zhonghou Cai
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Diffraction ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Phonon ,Terahertz radiation ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Thermal conduction ,01 natural sciences ,Ferroelectricity ,Condensed Matter::Materials Science ,Excited state ,0103 physical sciences ,General Materials Science ,010306 general physics ,0210 nano-technology ,Excitation ,Order of magnitude - Abstract
Nanoscale phonon transport is a key process that governs thermal conduction in a wide range of materials and devices. Creating controlled phonon populations by resonant excitation at terahertz (THz) frequencies can drastically change the characteristics of nanoscale thermal transport and allow a direct real-space characterization of phonon mean-free paths. Using metamaterial-enhanced terahertz excitation, we tailored a phononic excitation by selectively populating low-frequency phonons within a nanoscale volume in a ferroelectric $\mathrm{BaTi}{\mathrm{O}}_{3}$ thin film. Real-space time-resolved x-ray diffraction microscopy following THz excitation reveals ballistic phonon transport over a distance of hundreds of nm, two orders of magnitude longer than the averaged phonon mean-free path in $\mathrm{BaTi}{\mathrm{O}}_{3}$. On longer length scales, diffusive phonon transport dominates the recovery of the transient strain response, largely due to heat conduction into the substrate. The measured real-space phonon transport can be directly compared with the phonon mean-free path as predicted by molecular dynamics modeling. This time-resolved real-space visualization of THz-matter interactions opens up opportunities to engineer and image nanoscale transient structural states with new functionalities.
- Published
- 2017
17. An instrument for in situ coherent x-ray studies of metal-organic vapor phase epitaxy of III-nitrides
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Carol Thompson, Angel Yanguas-Gil, Sean M. Brennan, G. Brian Stephenson, Jeffrey A. Eastman, Hua Zhou, Guangxu Ju, Paul H. Fuoss, and Matthew J. Highland
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010302 applied physics ,Diffraction ,Materials science ,business.industry ,Detector ,Phase (waves) ,02 engineering and technology ,Microbeam ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Coherent diffraction imaging ,Synchrotron ,law.invention ,Optics ,law ,0103 physical sciences ,Metalorganic vapour phase epitaxy ,0210 nano-technology ,business ,Instrumentation - Abstract
We describe an instrument that exploits the ongoing revolution in synchrotron sources, optics, and detectors to enable in situ studies of metal-organic vapor phase epitaxy (MOVPE) growth of III-nitride materials using coherent x-ray methods. The system includes high-resolution positioning of the sample and detector including full rotations, an x-ray transparent chamber wall for incident and diffracted beam access over a wide angular range, and minimal thermal sample motion, giving the sub-micron positional stability and reproducibility needed for coherent x-ray studies. The instrument enables surface x-ray photon correlation spectroscopy, microbeam diffraction, and coherent diffraction imaging of atomic-scale surface and film structure and dynamics during growth, to provide fundamental understanding of MOVPE processes.
- Published
- 2017
18. Surface diffraction on a ψ-circle diffractometer using the χ-axis geometry
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Tim T. Fister, Jeffrey A. Eastman, Dillon D. Fong, Matthew J. Highland, Stephan O. Hruszkewycz, Chad M. Folkman, Paul H. Fuoss, Paul Fenter, and Hua Zhou
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Diffraction ,Crystal ,Surface (mathematics) ,Physics ,Optics ,business.industry ,Instrumentation ,Truncation (statistics) ,Specular reflection ,business ,Sample (graphics) ,General Biochemistry, Genetics and Molecular Biology ,Diffractometer - Abstract
The restricted volume above and below the sample on a six-circle diffractometer can limit the size and complexity of sample environments used in surface diffraction studies. An alternative configuration of the diffractometer, where the sample normal is aligned parallel to the χ axis, allows for ample space above and below the χ circle for instrumentation. The merits of this approach are outlined and angles are derived for the diffraction condition for constant-incident-angle, constant-sample-azimuthal-angle and specular geometries. Using a version of this code written forSPEC(http://www.certif.com/content/spec/), sample specular and nonspecular crystal truncation rods measured from a 5 nm-thick thin film are presented.
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- 2013
19. Structural sensitivity of x-ray Bragg projection ptychography to domain patterns in epitaxial thin films
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Qingteng Zhang, Stephan O. Hruszkewycz, Paul G. Evans, Matthew J. Highland, Paul H. Fuoss, and Martin V. Holt
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Physics ,Diffraction ,business.industry ,Bragg's law ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Coherent diffraction imaging ,Ptychography ,Orientation (vector space) ,Condensed Matter::Materials Science ,Projection (relational algebra) ,Optics ,Condensed Matter::Superconductivity ,0103 physical sciences ,X-ray crystallography ,Sensitivity (control systems) ,010306 general physics ,0210 nano-technology ,business - Abstract
Bragg projection ptychography (BPP) is a coherent diffraction imaging technique capable of mapping the spatial distribution of the Bragg structure factor in nanostructured thin films. Here, we show that, because these images are projections, the structural sensitivity of the resulting images depends on the film thickness and the aspect ratio and orientation of the features of interest and that image interpretation depends on these factors. We model changes in contrast in the BPP reconstructions of simulated ${\mathrm{PbTiO}}_{3}$ ferroelectric thin films with meandering ${180}^{\ensuremath{\circ}}$ stripe domains as a function of film thickness, discuss their origin, and comment on the implication of these factors on the design of BPP experiments of general nanostructured films.
- Published
- 2016
20. Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO$_3$
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Henrik Enquist, M. Chollet, Nathaniel C. Brandt, Y. Zhu, James M. Glownia, Matthias C. Hoffmann, Te Hu, F. Quirin, Aaron M. Lindenberg, Jörgen Larsson, Keith A. Nelson, Donald A. Walko, Haidan Wen, Klaus Sokolowski-Tinten, Yubo Qi, Diling Zhu, Henrik T. Lemke, Il Woong Jung, Arturas Vailionis, Frank W. Chen, Z. Cai, Anoop R. Damodaran, Shi Liu, Jian Lu, J. Goodfellow, Jin-Seong Park, Meng-Ju Sher, Lane W. Martin, Peter Zalden, Andrew M. Rappe, Harold Y. Hwang, Paul G. Evans, Matthew J. Highland, and John W. Freeland
- Subjects
Materials science ,Terahertz radiation ,Fluids & Plasmas ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,Condensed Matter::Materials Science ,Optics ,Engineering ,Electric field ,0103 physical sciences ,010306 general physics ,Condensed Matter - Materials Science ,Condensed matter physics ,business.industry ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,Polarization (waves) ,Ferroelectricity ,Picosecond ,Femtosecond ,Physical Sciences ,Chemical Sciences ,0210 nano-technology ,business ,Ultrashort pulse ,Excitation - Abstract
© 2016 American Physical Society. The dynamical processes associated with electric field manipulation of the polarization in a ferroelectric remain largely unknown but fundamentally determine the speed and functionality of ferroelectric materials and devices. Here we apply subpicosecond duration, single-cycle terahertz pulses as an ultrafast electric field bias to prototypical BaTiO3 ferroelectric thin films with the atomic-scale response probed by femtosecond x-ray-scattering techniques. We show that electric fields applied perpendicular to the ferroelectric polarization drive large-amplitude displacements of the titanium atoms along the ferroelectric polarization axis, comparable to that of the built-in displacements associated with the intrinsic polarization and incoherent across unit cells. This effect is associated with a dynamic rotation of the ferroelectric polarization switching on and then off on picosecond time scales. These transient polarization modulations are followed by long-lived vibrational heating effects driven by resonant excitation of the ferroelectric soft mode, as reflected in changes in the c-axis tetragonality. The ultrafast structural characterization described here enables a direct comparison with first-principles-based molecular-dynamics simulations, with good agreement obtained.
- Published
- 2016
21. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy
- Author
-
Haidan Wen, Donald A. Walko, John W. Freeland, Stuart S. P. Parkin, Il Woong Jung, Matthew J. Highland, Pice Chen, Jaewoo Jeong, Paul G. Evans, Qingteng Zhang, Mahesh G. Samant, Zhonghou Cai, Eric M. Dufresne, and Yi Zhu
- Subjects
Diffraction ,Mesoscopic physics ,Phase transition ,Multidisciplinary ,Materials science ,Condensed Matter - Mesoscale and Nanoscale Physics ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,Photoexcitation ,Chemical physics ,Phase (matter) ,Excited state ,0103 physical sciences ,X-ray crystallography ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,010306 general physics ,0210 nano-technology ,Excitation - Abstract
Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.
- Published
- 2016
22. Structural phase progression in photo-excited VO2
- Author
-
Paul G. Evans, Haidan Wen, Pice Chen, Z. Cai, Donald A. Walko, Stuart S. P. Parkin, Yi Zhu, Qingteng Zhang, John W. Freeland, Mahesh G. Samant, Eric M. Dufresne, Jaewoo Jeong, Il Woong Jung, and Matthew J. Highland
- Subjects
0301 basic medicine ,Diffraction ,Structural phase ,Materials science ,Condensed matter physics ,business.industry ,Wave propagation ,01 natural sciences ,Pulsed laser deposition ,03 medical and health sciences ,030104 developmental biology ,Optics ,Lattice (order) ,Excited state ,0103 physical sciences ,Microscopy ,Thin film ,010306 general physics ,business - Abstract
We reveal inhomogeneous structural phase transformation in photo-excited VO 2 thin films by time-resolved x-ray diffraction microscopy. The in-plane plane phase progression is a result of displacive lattice transformation rather than driven by thermal transport.
- Published
- 2016
23. In-situ synchrotron x-ray studies of the microstructure and stability of In2O3 epitaxial films
- Author
-
Irene Calvo-Almazán, Jeffrey A. Eastman, Peter M. Baldo, Dillon D. Fong, Matthew J. Highland, Siddharth Maddali, Paul H. Fuoss, Xiaojing Huang, Andrew Ulvestad, Evgeny Nazaretski, Carol Thompson, Hua Zhou, Stephan O. Hruszkewycz, Hanfei Yan, and Yong S. Chu
- Subjects
010302 applied physics ,Materials science ,Nanostructure ,Physics and Astronomy (miscellaneous) ,business.industry ,02 engineering and technology ,Sputter deposition ,021001 nanoscience & nanotechnology ,Epitaxy ,Microstructure ,01 natural sciences ,Crystallography ,Sputtering ,0103 physical sciences ,X-ray crystallography ,Optoelectronics ,Thin film ,0210 nano-technology ,business ,Single crystal - Abstract
We report on the synthesis, stability, and local structure of In2O3 thin films grown via rf-magnetron sputtering and characterized by in-situ x-ray scattering and focused x-ray nanodiffraction. We find that In2O3 deposited onto (0 0 1)-oriented single crystal yttria-stabilized zirconia substrates adopts a Stranski–Krastanov growth mode at a temperature of 850 °C, resulting in epitaxial, truncated square pyramids with (1 1 1) side walls. We find that at this temperature, the pyramids evaporate unless they are stabilized by a low flux of In2O3 from the magnetron source. We also find that the internal lattice structure of one such pyramid is made up of differently strained volumes, revealing local structural heterogeneity that may impact the properties of In2O3 nanostructures and films.
- Published
- 2017
24. Functional links between stability and reactivity of strontium ruthenate single crystals during oxygen evolution
- Author
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Nenad M. Markovic, Matthew J. Highland, Peter M. Baldo, John W. Freeland, Nemanja Danilovic, Vojislav R. Stamenkovic, Arvydas P. Paulikas, Ram Subbaraman, Jeffrey A. Eastman, Kee-Chul Chang, Seo Hyoung Chang, and Dillon D. Fong
- Subjects
inorganic chemicals ,Multidisciplinary ,Oxygen evolution ,General Physics and Astronomy ,Mineralogy ,General Chemistry ,Conductivity ,General Biochemistry, Genetics and Molecular Biology ,Catalysis ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Reactivity (chemistry) ,Strontium ruthenate - Abstract
In developing cost-effective complex oxide materials for the oxygen evolution reaction, it is critical to establish the missing links between structure and function at the atomic level. The fundamental and practical implications of the relationship on any oxide surface are prerequisite to the design of new stable and active materials. Here we report an intimate relationship between the stability and reactivity of oxide catalysts in exploring the reaction on strontium ruthenate single-crystal thin films in alkaline environments. We determine that for strontium ruthenate films with the same conductance, the degree of stability, decreasing in the order (001)(110)(111), is inversely proportional to the activity. Both stability and reactivity are governed by the potential-induced transformation of stable Ru(4+) to unstable Ru(n4+). This ordered(Ru(4+))-to-disordered(Ru(n4+)) transition and the development of active sites for the reaction are determined by a synergy between electronic and morphological effects.
- Published
- 2014
25. Full-field X-ray reflection microscopy of epitaxial thin-films
- Author
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Christian M. Schlepütz, Zhan Zhang, Joan Vila-Comamala, Paul Fenter, Nouamane Laanait, and Matthew J. Highland
- Subjects
Diffraction ,Nuclear and High Energy Physics ,Radiation ,Microscope ,Materials science ,Scattering ,business.industry ,Resolution (electron density) ,law.invention ,Reflection (mathematics) ,Optics ,law ,Microscopy ,Near-field scanning optical microscope ,business ,Instrumentation ,Image resolution - Abstract
Novel X-ray imaging of structural domains in a ferroelectric epitaxial thin film using diffraction contrast is presented. The full-field hard X-ray microscope uses the surface scattering signal, in a reflectivity or diffraction experiment, to spatially resolve the local structure with 70 nm lateral spatial resolution and sub-nanometer height sensitivity. Sub-second X-ray exposures can be used to acquire a 14 µm × 14 µm image with an effective pixel size of 20 nm on the sample. The optical configuration and various engineering considerations that are necessary to achieve optimal imaging resolution and contrast in this type of microscopy are discussed.
- Published
- 2014
26. Coherent Bragg nanodiffraction at the hard X-ray Nanoprobe beamline
- Author
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Jörg Maser, Martin V. Holt, Conal E. Murray, Stephan O. Hruszkewycz, Paul H. Fuoss, Matthew J. Highland, and Chad M. Folkman
- Subjects
Diffraction ,X-ray nanoprobe ,Materials science ,business.industry ,General Mathematics ,General Engineering ,General Physics and Astronomy ,Bragg's law ,Physics::Optics ,Advanced Photon Source ,Articles ,Coherent diffraction imaging ,Ptychography ,Optics ,Beamline ,Diffraction topography ,business - Abstract
Bragg coherent diffraction with nanofocused hard X-ray beams provides unique opportunities for quantitative in situ studies of crystalline structure in nanoscale regions of complex materials and devices by a variety of diffraction-based techniques. In the case of coherent diffraction imaging, a major experimental challenge in using nanoscale coherent beams is maintaining a constant scattering volume such that coherent fringe visibility is maximized and maintained over the course of an exposure lasting several seconds. Here, we present coherent Bragg diffraction patterns measured from different nanostructured thin films at the Sector 26 Nanoprobe beamline at the Advanced Photon Source and demonstrate that with nanoscale positional control, coherent diffraction patterns can be measured with source-limited fringe visibilities more than 50% suitable for imaging by coherent Bragg ptychography techniques.
- Published
- 2014
27. Nucleation and growth of epitaxial metal-oxide films based on polymer-assisted deposition
- Author
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Peter M. Baldo, Zhenxing Bi, Paul H. Fuoss, P. Shi, Q. X. Jia, W. Ren, Brian L. Scott, Matthew J. Highland, Thomas M. McCleskey, Anthony K. Burrell, Eve Bauer, and Jeffrey A. Eastman
- Subjects
chemistry.chemical_classification ,Materials science ,Nucleation ,Oxide ,General Chemistry ,Polymer ,Thermal treatment ,Epitaxy ,Chemical reaction ,law.invention ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,law ,Deposition (phase transition) ,Filtration - Abstract
Polymer-assisted deposition (PAD) is one of the chemical solution deposition methods which have been successfully used to grow films, form coatings, and synthesize nanostructured materials. In comparison with other conventional solution-based deposition techniques, PAD differs in its use of water-soluble polymers in the solution that prevent the metal ions from unwanted chemical reactions and keep the solution stable. Furthermore, filtration to remove non-coordinated cations and anions in the PAD process ensures well controlled nucleation, which enables the growth of high quality epitaxial films with desired structural and physical properties. The precursor solution is prepared by mixing water-soluble polymer(s) with salt(s). Thermal treatment of the precursor films in a controlled environment leads to the formation of desired materials. Using BaTiO3 grown on SrTiO3 and LaMnO3 on LaAlO3 as model systems, we show the effect of filtration on the nucleation and growth of epitaxial complex metal-oxide films based on the PAD process.
- Published
- 2013
28. Nanosession: Ferroelectric Interfaces
- Author
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Bryan D. Huey, S. Farokhipoor, Dillon D. Fong, Quentin M. Ramasse, J. A. Eastman, Pablo García-Fernández, Ramamoorthy Ramesh, T. Menke, Regina Dittmann, J. X. Zhang, G. B. Stephenson, Javier Junquera, Sui Yang, Matthew J. Highland, Marta D. Rossell, Carol Thompson, Stephen J. Pennycook, G. Singh‐Bhalla, Joachim Mayer, Daesung Park, Sokrates T. Pantelides, Paul H. Fuoss, Lane W. Martin, Beatriz Noheda, Timothy T. Fister, Pablo Aguado-Puente, Chan-Ho Yang, Weidong Luo, Qing He, Di Yi, Ying-Hao Chu, Stephen K. Streiffer, Anja Herpers, Rolf Erni, and Peter Y. Yu
- Subjects
Materials science ,Optics ,business.industry ,business ,Ferroelectricity ,Engineering physics - Published
- 2013
29. Imaging local polarization in ferroelectric thin films by coherent x-ray Bragg projection ptychography
- Author
-
Dong Jin Kim, Stephan O. Hruszkewycz, Seungbum Hong, G. B. Stephenson, Ashish Tripathi, Paul H. Fuoss, Chad M. Folkman, Matthew J. Highland, Martin V. Holt, and Carol Thompson
- Subjects
Diffraction ,Materials science ,Optics ,business.industry ,X-ray crystallography ,General Physics and Astronomy ,Thin film ,Polarization (waves) ,business ,Phase retrieval ,Image resolution ,Ferroelectricity ,Ptychography - Abstract
We used x-ray Bragg projection ptychography (BPP) to map spatial variations of ferroelectric polarization in thin film PbTiO3, which exhibited a striped nanoscale domain pattern on a high-miscut (001) SrTiO3 substrate. By converting the reconstructed BPP phase image to picometer-scale ionic displacements in the polar unit cell, a quantitative polarization map was made that was consistent with other characterization. The spatial resolution of 5.7 nm demonstrated here establishes BPP as an important tool for nanoscale ferroelectric domain imaging, especially in complex environments accessible with hard x rays.
- Published
- 2013
30. Quantitative nanoscale imaging of lattice distortions in epitaxial semiconductor heterostructures using nanofocused X-ray Bragg projection ptychography
- Author
-
Matthew J. Highland, Judson R. Holt, Paul H. Fuoss, John Bruley, Stephan O. Hruszkewycz, Martin V. Holt, Conal E. Murray, Oleg Shpyrko, Ian McNulty, and Ashish Tripathi
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,X-ray ,Physics::Optics ,Bioengineering ,General Chemistry ,Semiconductor device ,Condensed Matter Physics ,Epitaxy ,Ptychography ,Lattice strain ,Condensed Matter::Materials Science ,Optics ,Lattice (order) ,General Materials Science ,business ,Nanoscopic scale ,Semiconductor heterostructures - Abstract
We imaged nanoscale lattice strain in a multilayer semiconductor device prototype with a new X-ray technique, nanofocused Bragg projection ptychography. Applying this technique to the epitaxial stressor layer of a SiGe-on-SOI structure, we measured the internal lattice behavior in a targeted region of a single device and demonstrated that its internal strain profile consisted of two competing lattice distortions. These results provide the strongest nondestructive test to date of continuum modeling predictions of nanoscale strain distributions.
- Published
- 2012
31. Ultrafast Photovoltaic Response in Ferroelectric Nanolayers
- Author
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Donald A. Walko, David A. Reis, Klaus Sokolowski-Tinten, Haidan Wen, David Fritz, Harold Y. Hwang, Andrew M. Rappe, Henrik T. Lemke, Diling Zhu, Tingting Qi, Yuelin Li, Dan Daranciang, Matthieu Nicoul, Michael Vattilana, G. Brian Stephenson, Paul H. Fuoss, Jörgen Larsson, F. Quirin, Keith A. Nelson, Marco Cammarata, John Goodfellow, Steve M. Young, Eric M. Dufresne, Nathaniel C. Brandt, Matthew J. Highland, Aaron M. Lindenberg, and Ilya Grinberg
- Subjects
Physics ,Condensed matter physics ,Scattering ,Atom and Molecular Physics and Optics ,Femtosecond ,General Physics and Astronomy ,Direct coupling ,Electron ,Photovoltaic effect ,Thin film ,Physik (inkl. Astronomie) ,Polarization (waves) ,Ferroelectricity - Abstract
We show that light drives large-amplitude structural changes in thin films of the prototypical ferroelectric PbTiO3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved x-ray scattering to visualize atomic displacements on femtosecond time scales, photoinduced changes in the unit-cell tetragonality are observed. These are driven by the motion of photogenerated free charges within the ferroelectric and can be simply explained by a model including both shift and screening currents, associated with the displacement of electrons first antiparallel to and then parallel to the ferroelectric polarization direction.
- Published
- 2012
32. Equilibrium Polarization of UltrathinPbTiO3with Surface Compensation Controlled by Oxygen Partial Pressure
- Author
-
Carol Thompson, Matthew J. Highland, G. B. Stephenson, Stephen K. Streiffer, Timothy T. Fister, Dillon D. Fong, Paul H. Fuoss, and J. A. Eastman
- Subjects
Phase transition ,Materials science ,Analytical chemistry ,General Physics and Astronomy ,Curie temperature ,Surface charge ,Dielectric ,Partial pressure ,Polarization (waves) ,Ferroelectricity ,Landau theory - Abstract
We present a synchrotron x-ray study of the equilibrium polarization structure of ultrathin PbTiO(3) films on SrRuO(3) electrodes epitaxially grown on SrTiO(3) (001) substrates, as a function of temperature and the external oxygen partial pressure (pO(2)) controlling their surface charge compensation. We find that the ferroelectric Curie temperature (T(C)) varies with pO(2) and has a minimum at the intermediate pO(2), where the polarization below T(C) changes sign. The experiments are in qualitative agreement with a model based on Landau theory that takes into account the interaction of the phase transition with the electrochemical equilibria for charged surface species. The paraelectric phase is stabilized at intermediate pO(2) when the concentrations of surface species are insufficient to compensate either polar orientation.
- Published
- 2011
33. Bragg Coherent Diffraction Imaging of Epitaxial Nanostructures Using Focused Hard X‐ray Ptychography
- Author
-
Stephan O. Hruszkewycz, D. L. Proffit, Matthew J. Highland, Martin V. Holt, Alexandra Imre, Paul H. Fuoss, Jeffrey A. Eastman, G. R. Bai, and J. Maser
- Subjects
Diffraction ,Optics ,Materials science ,Nanocrystal ,business.industry ,X-ray crystallography ,Resolution (electron density) ,X-ray ,Phase (waves) ,business ,Coherent diffraction imaging ,Ptychography - Abstract
We present a data collection approach for nanofocused Bragg coherent x‐ray diffraction imaging (CXDI), a technique that can extend the resolution of x‐ray nanoprobes and isolate individual nanostructures for study. Nanofocused Bragg CXDI uses hard x‐rays focused to
- Published
- 2011
34. Equilibrium and Stability of Polarization in Ultrathin Ferroelectric Films with Ionic Surface Compensation
- Author
-
Matthew J. Highland and G. Brian Stephenson
- Subjects
Phase transition ,Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Ionic bonding ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter Physics ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,Phase (matter) ,Metastability ,Chemical equilibrium ,Polarization (electrochemistry) ,Phase diagram - Abstract
Thermodynamic theory is developed for the ferroelectric phase transition of an ultrathin film in equilibrium with a chemical environment that supplies ionic species to compensate its surface. Equations of state and free energy expressions are developed based on Landau-Ginzburg-Devonshire theory, using electrochemical equilibria to provide ionic compensation boundary conditions. Calculations are presented for a monodomain PbTiO$_3$ (001) film coherently strained to SrTiO$_3$ with its exposed surface and its electronically conducting bottom electrode in equilibrium with a controlled oxygen partial pressure. The stability and metastability boundaries of phases of different polarization are determined as a function of temperature, oxygen partial pressure, and film thickness. Phase diagrams showing polarization and internal electric field are presented. At temperatures below a thickness-dependent Curie point, high or low oxygen partial pressure stabilizes positive or negative polarization, respectively. Results are compared to the standard cases of electronic compensation controlled by either an applied voltage or charge across two electrodes. Ionic surface compensation through chemical equilibrium with an environment introduces new features into the phase diagram. In ultrathin films, a stable non-polar phase can occur between the positive and negative polar phases when varying the external chemical potential at fixed temperature, under conditions where charged surface species are not present in sufficient concentration to stabilize a polar phase., 53 pages, 24 figures
- Published
- 2010
35. Polarization Switching without Domain Formation at the Intrinsic Coercive Field in Ultrathin FerroelectricPbTiO3
- Author
-
Paul H. Fuoss, Carol Thompson, Stephen K. Streiffer, Timothy T. Fister, Marie-Ingrid Richard, Dillon D. Fong, Matthew J. Highland, Jeffrey A. Eastman, and G. Brian Stephenson
- Subjects
Materials science ,Condensed matter physics ,Scattering ,Nucleation ,General Physics and Astronomy ,Coercivity ,Polarization (waves) ,Ferroelectricity ,Synchrotron ,law.invention ,Condensed Matter::Materials Science ,Lattice constant ,Nuclear magnetic resonance ,law ,Electric field - Abstract
Polarization switching in ferroelectrics has been thought to occur only through the nucleation and growth of new domains. Here we use in situ synchrotron x-ray scattering to monitor switching controlled by applied chemical potential. In sufficiently thin ${\mathrm{PbTiO}}_{3}$ films, nucleation is suppressed and switching occurs by a continuous mechanism, i.e., by uniform decrease and inversion of the polarization without domain formation. The observed lattice parameter shows that the electric field in the film during switching reaches the theoretical intrinsic coercive field.
- Published
- 2010
36. Polarization switching without domain formation at the intrinsic coercive field in ultrathin ferroelectric PbTiO₃
- Author
-
Matthew J, Highland, Timothy T, Fister, Marie-Ingrid, Richard, Dillon D, Fong, Paul H, Fuoss, Carol, Thompson, Jeffrey A, Eastman, Stephen K, Streiffer, and G Brian, Stephenson
- Abstract
Polarization switching in ferroelectrics has been thought to occur only through the nucleation and growth of new domains. Here we use in situ synchrotron x-ray scattering to monitor switching controlled by applied chemical potential. In sufficiently thin PbTiO₃ films, nucleation is suppressed and switching occurs by a continuous mechanism, i.e., by uniform decrease and inversion of the polarization without domain formation. The observed lattice parameter shows that the electric field in the film during switching reaches the theoretical intrinsic coercive field.
- Published
- 2010
37. Reversible chemical switching of a ferroelectric film
- Author
-
Andrew M. Rappe, G. B. Stephenson, Carol Thompson, Paul H. Fuoss, Jeffrey A. Eastman, Stephen K. Streiffer, Rui Wang, Matthew J. Highland, Alexie M. Kolpak, Dillon D. Fong, and F. Jiang
- Subjects
Condensed matter physics ,Scattering ,General Physics and Astronomy ,chemistry.chemical_element ,Particle accelerator ,Partial pressure ,Polarization (waves) ,Oxygen ,Ferroelectricity ,Synchrotron ,law.invention ,Condensed Matter::Materials Science ,chemistry ,Ab initio quantum chemistry methods ,law - Abstract
According to recent experiments and predictions, the orientation of the polarization at the surface of a ferroelectric material can affect its surface chemistry. Here we demonstrate the converse effect: the chemical environment can control the polarization orientation in a ferroelectric film. In situ synchrotron x-ray scattering measurements show that high or low oxygen partial pressure induces outward or inward polarization, respectively, in an ultrathin PbTiO3 film. Ab initio calculations provide insight into surface structure changes observed during chemical switching.
- Published
- 2008
38. In-situ x-ray studies of compositional control during synthesis of LaGaO3 by radio frequency-magnetron sputtering
- Author
-
Peter M. Baldo, Dillon D. Fong, Carol Thompson, Guangxu Ju, Matthew J. Highland, Jeffrey A. Eastman, and Paul H. Fuoss
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Sputtering ,law ,Scattering ,Analytical chemistry ,X-ray ,Deposition (phase transition) ,Sputter deposition ,Epitaxy ,Synchrotron ,Stoichiometry ,law.invention - Abstract
In-situ synchrotron x-ray scattering has been used to monitor and control the synthesis of LaGaO3 epitaxial thin films by 90° off-axis RF-magnetron sputtering. Films deposited from a single LaGaO3 source were compared with those prepared by alternating deposition from separate La2O3 and Ga2O3 sources. The conditions for growth of stoichiometric films were determined by real-time monitoring of secondary phase formation as well as from features in the diffuse scatter from island formation during synthesis. These results provide atomic-scale insight into the mechanisms taking place during reactive epitaxial growth and demonstrate how in-situ techniques can be utilized to achieve stoichiometric control in ultrathin films.
- Published
- 2015
39. Real-time x-ray studies of crystal growth modes during metal-organic vapor phase epitaxy of GaN on c- and m-plane single crystals
- Author
-
Peter Zapol, Stephen K. Streiffer, Carol Thompson, Matthew J. Highland, Edith Perret, Anneli Munkholm, G. B. Stephenson, and Paul H. Fuoss
- Subjects
Crystallography ,Materials science ,Physics and Astronomy (miscellaneous) ,Scattering ,Phase (matter) ,Analytical chemistry ,Crystal growth ,Metalorganic vapour phase epitaxy ,Activation energy ,Growth rate ,Epitaxy ,Single crystal - Abstract
Non-polar orientations of III-nitride semiconductors have attracted significant interest due to their potential application in optoelectronic devices with enhanced efficiency. Using in situ surface x-ray scattering during metal-organic vapor phase epitaxy (MOVPE) of GaN on non-polar (m-plane) and polar (c-plane) orientations of single crystal substrates, we have observed the homoepitaxial growth modes as a function of temperature and growth rate. On the m-plane surface, we observe all three growth modes (step-flow, layer-by-layer, and three-dimensional) as conditions are varied. In contrast, the +c-plane surface exhibits a direct crossover between step-flow and 3D growth, with no layer-by-layer regime. The apparent activation energy of 2.8 ± 0.2 eV observed for the growth rate at the layer-by-layer to step-flow boundary on the m-plane surface is consistent with those observed for MOVPE growth of other III-V compounds, indicating a large critical nucleus size for islands.
- Published
- 2014
40. Interfacial charge and strain effects on the ferroelectric behavior of epitaxial (001) PbTiO3 films on (110) DyScO3 substrates
- Author
-
P. H. Fuoss, Matthew J. Highland, Stephen K. Streiffer, J. A. Eastman, G. B. Stephenson, Marie-Ingrid Richard, Dillon D. Fong, Carol Thompson, and Timothy T. Fister
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Strain (chemistry) ,Charge (physics) ,Epitaxy ,Ferroelectricity ,Synchrotron ,law.invention ,Crystallography ,law ,Curie temperature ,Boundary value problem ,Thin film - Abstract
In-situ synchrotron x-ray observations reveal that the ferroelectric behavior of epitaxial (001) PbTiO3 thin films grown on (110) DyScO3 substrates depends on both film thickness and interfacial electrical properties. A 92-nm-thick film was found to exhibit an a/c domain structure with a ferroelectric Curie temperature similar to that theoretically predicted based on the strain state. In contrast, 6-nm-thick films contained only c-oriented domains, and the ferroelectric behavior was found to depend strongly on the nature of the electrical boundary condition at the buried interface.
- Published
- 2014
41. Modular instrument mounting system for variable environment in operando X-ray experiments
- Author
-
S. Seifert, Seong Keun Kim, Hua Zhou, Timothy T. Fister, Matthew J. Highland, Jeffrey A. Eastman, Dillon D. Fong, Peter M. Baldo, P. H. Fuoss, C. M. Folkman, and Edith Perret
- Subjects
Coupling ,Materials science ,business.industry ,Interface (computing) ,Mechanical engineering ,Modular design ,Rotation ,Sample (graphics) ,Bellows ,Optics ,Torr ,business ,Instrumentation ,Diffractometer - Abstract
In the growing field of in operando and in situ X-ray experiments, there exists a large disparity in the types of environments and equipment to control them. This situation makes it challenging to conduct multiple experiments with a single mechanical interface to the diffractometer. Here, we describe the design and implementation of a modular instrument mounting system that can be installed on a standard six-circle diffractometer (e.g., 5021 Huber GmbH). This new system allows for the rapid changeover of different chambers and sample heaters and permits accurate sample positioning (x, y, z, and azimuthal rotation) without rigid coupling to the chamber body. Isolation of the sample motion from the chamber enclosure is accomplished through a combination of custom rotary seals and bellows. Control of the pressure and temperature has been demonstrated in the ranges of 10(-6)-10(3) Torr and 25°C-900°C, respectively. We have utilized the system with several different modular instruments. As an example, we provide in situ sputtering results, where the growth dynamics of epitaxial LaGaO3 thin films on (001) SrTiO3 substrates were investigated.
- Published
- 2013
42. X-ray nanodiffraction of tilted domains in a poled epitaxial BiFeO3 thin film
- Author
-
Chad M. Folkman, Peter M. Baldo, Stephen K. Streiffer, P. H. Fuoss, C. B. Eom, Stephan O. Hruszkewycz, Seung Hyub Baek, Matthew J. Highland, and Martin V. Holt
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Poling ,Ferroelectricity ,Condensed Matter::Materials Science ,Hysteresis ,Optics ,Tilt (optics) ,Condensed Matter::Superconductivity ,Electric field ,Perpendicular ,Multiferroics ,Thin film ,business - Abstract
We present measurements of crystallographic domain tilts in a (001) BiFeO3 thin film using focused beam x-ray nanodiffraction. Films were ferroelectrically pre-poled with an electric field orthogonal and parallel to as-grown tilt domain stripes. The tilt domains, associated with higher energy (010) vertical twin walls, displayed different nanostructural responses based on the poling orientation. Specifically, an electric field applied perpendicular to the as-grown domain stripe allowed the domain tilts and associated vertical twin walls to persist. The result demonstrates that thin film ferroelectric devices can be designed to maintain unexpected domain morphologies in working poled environments.
- Published
- 2011
43. Real-time X-ray studies of the effect of chemical transients on oxide thin-film surface structure
- Author
-
P. H. Fuoss, Carol Thompson, Stephen K. Streiffer, Matthew J. Highland, Timothy T. Fister, J. A. Eastman, Stephan O. Hruszkewycz, Marie-Ingrid Richard, Dillon D. Fong, and G. B. Stephenson
- Subjects
chemistry.chemical_compound ,Materials science ,chemistry ,Structural Biology ,Analytical chemistry ,X-ray ,Oxide ,Surface structure ,Thin film - Published
- 2010
44. In situ synchrotron x-ray studies of strain and composition evolution during metal-organic chemical vapor deposition of InGaN
- Author
-
G. B. Stephenson, Stephen K. Streiffer, J. Mei, Paul H. Fuoss, Marie-Ingrid Richard, Matthew J. Highland, Carol Thompson, Timothy T. Fister, and Anneli Munkholm
- Subjects
Reciprocal lattice ,Materials science ,Physics and Astronomy (miscellaneous) ,Strain (chemistry) ,Chemical physics ,law ,X-ray crystallography ,Relaxation (NMR) ,Stress relaxation ,Metalorganic vapour phase epitaxy ,Chemical vapor deposition ,Synchrotron ,law.invention - Abstract
Composition and strain inhomogeneities strongly affect the optoelectronic properties of InGaN but their origin has been unclear. Here we report real-time x-ray reciprocal space mapping that reveals the development of strain and composition distributions during metal-organic chemical vapor deposition of InxGa1−xN on GaN. Strong, correlated inhomogeneities of the strain state and In fraction x arise during growth in a manner consistent with models for instabilities driven by strain relaxation.
- Published
- 2010
45. Phase stabilization of δ-Bi2O3 nanostructures by epitaxial growth onto single crystal SrTiO3 or DyScO3 substrates
- Author
-
Thomas O. Mason, D. L. Proffit, J. A. Eastman, G. R. Bai, Peter M. Baldo, Stephan O. Hruszkewycz, Matthew J. Highland, Timothy T. Fister, Dillon D. Fong, and Paul H. Fuoss
- Subjects
Materials science ,Nanostructure ,Physics and Astronomy (miscellaneous) ,Scattering ,Annealing (metallurgy) ,chemistry.chemical_element ,Partial pressure ,Epitaxy ,Oxygen ,Synchrotron ,law.invention ,Crystallography ,chemistry ,law ,Single crystal - Abstract
We observe that the high-temperature δ-phase of Bi2O3 is stabilized to room temperature by the epitaxial growth of nanostructures onto either (001)-oriented SrTiO3 or (001)p-oriented DyScO3 single crystal substrates. In addition, the morphology can be controlled by the miscut of the substrate. Synchrotron x-ray scattering observations at controlled temperatures and oxygen partial pressures reveal that the δ-Bi2O3 nanostructures are coherently strained to the substrates at room temperature. Annealing the nanostructures at 600 °C causes gradual conversion of the (001)-oriented δ-phase to an unidentified strain-relaxed phase.
- Published
- 2010
46. In situ characterization of strontium surface segregation in epitaxial La0.7Sr0.3MnO3 thin films as a function of oxygen partial pressure
- Author
-
K. R. Balasubramaniam, Peter M. Baldo, Tim T. Fister, Paul A. Salvador, Jeffrey A. Eastman, Matthew J. Highland, Paul H. Fuoss, Dillon D. Fong, and Joanna C. Meador
- Subjects
inorganic chemicals ,Strontium ,Alkaline earth metal ,Materials science ,Physics and Astronomy (miscellaneous) ,Enthalpy ,Analytical chemistry ,chemistry.chemical_element ,Crystal growth ,Partial pressure ,Oxygen ,Crystallography ,chemistry ,Vacancy defect ,Thin film - Abstract
Using in situ synchrotron measurements of total reflection x-ray fluorescence, we find evidence of strontium surface segregation in (001)-oriented La0.7Sr0.3MnO3 thin films over a wide range of temperatures (25–900 °C) and oxygen partial pressures (pO2=0.15–150 Torr). The strontium surface concentration is observed to increase with decreasing pO2, suggesting that the surface oxygen vacancy concentration plays a significant role in controlling the degree of segregation. Interestingly, the enthalpy of segregation becomes less exothermic with increasing pO2, varying from −9.5 to −2.0 kJ/mol. In contrast, the La0.7Sr0.3MnO3 film thickness and epitaxial strain state have little impact on segregation behavior.
- Published
- 2008
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