A5051008805- Surface and Thin Film Phenomena
- Electron and X-Ray Spectroscopy Techniques
- Advanced Chemical Physics Studies
- 2D Materials and Applications
- Topological Materials and Phenomena
- Semiconductor materials and interfaces
- Graphene research and applications
- Semiconductor materials and devices
- X-ray Diffraction in Crystallography
- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Ga2O3 and related materials
- Magnetic properties of thin films
- Advanced Materials Characterization Techniques
- Quantum and electron transport phenomena
- Silicon and Solar Cell Technologies
- Rare-earth and actinide compounds
- Chemical and Physical Properties of Materials
- Atomic and Molecular Physics
- Chalcogenide Semiconductor Thin Films
- Silicon Nanostructures and Photoluminescence
- Inorganic Chemistry and Materials
- Electronic and Structural Properties of Oxides
- Perovskite Materials and Applications
- Semiconductor Quantum Structures and Devices
University of Arkansas at Fayetteville
2019-2025
Missouri State University
2018-2022
Kyushu Institute of Technology
2001
IBM Research - Thomas J. Watson Research Center
1983-1996
Harvard University
1993
Massachusetts Institute of Technology
1987
IBM (United States)
1977-1983
Nokia (United States)
1976
Columbia University
1974
University of Warwick
1974
Several qualitatively different structural models have been examined in a critical evaluation of spectroscopic and other data for the Si(111)-(2\ifmmode\times\else\texttimes\fi{}1) surface. Within one-electron theory, only novel $\ensuremath{\pi}$-bonded chain model with covalent surface, not generally accepted buckled an ionic is consistent data.
Buckling distortions, widely thought to lower the total energy of semiconductor surfaces, are shown actually raise Si(111)-2\ifmmode\times\else\texttimes\fi{}1. The $\ensuremath{\pi}$-bonded-chain reconstruction, in contrast, stabilizes surface, even relative recently proposed magnetic reconstructions. Calculations for GaAs(110) reveal that large charge transfers associated with buckling can stabilize surface heteropolar semiconductors, by returning ions bulk neutral atoms at surface. These...
Of the relaxed, graphitic, buckled, and $\ensuremath{\pi}$-bonded-chain-type models for diamond (111)-(2 \ifmmode\times\else\texttimes\fi{} 1) surface, only chain model appears to account measured surface-band dispersion. The interaction of dangling orbitals which determines dispersion is large in because this are bonds located on nearest-neighbor atoms. data also suggest a dimerization chains.
The semiempirical tight-binding method is used to construct accurate valence bands for bulk Si and Ge using Hamiltonian parameters through second neighbors. One additional parameter describe surface relaxation (back-bond contraction). density of resonances associated with atomic layers near the calculated. Surprisingly, are found contribute states almost as effectively proper states. Comparison ion-neutralization, electron-energy loss, ultraviolet photoemission data made.
We give semiempirical tight-binding calculations of dangling- and back-bond surface bands resonances for unreconstructed relaxed Si Ge (111) surfaces. For at high-symmetry points these are in very good agreement with those Appelbaum Hamann. Comparison the results energy-loss-spectroscopy data Rowe Ibach suggests that observed associated primarily minima bands.
A methodology is developed for the theoretical study of polar surfaces compound semiconductors. It based on calculation total energy in context density-functional theory pseudopotential approximation. The method used to investigate (2\ifmmode\times\else\texttimes\fi{}2) reconstructions GaAs(111). Emphasis given relative chemical potential, which plays a crucial role determining lowest-energy geometry with different stoichiometries. total-energy versus chemical-potential curves indicate that...
We present a novel concerted exchange mechanism for the diffusion of substitutional atoms in semiconductors that does not involve any defects. For self-diffusion Si we show this is energetically favorable and able to account number experimental observations. Implication dopants discussed.
Extensive first-principles calculations are presented for the formation energies and migration barriers of elementary defects in graphite, as well activation energy atomic exchange. The show that long-held view, diffusion graphite occurs via direct-exchange mechanism, is incorrect, although more complicated exchange processes have not been ruled out. We find most likely mediated by vacancies with an which lower than interstitial mechanisms, reasonable agreement experiment.
Nonlocal pseudopotentials are constructed for Ge and GaAs. Agreement with interband optical edges in the region 0-7 eV is achieved to within 0.05 eV. The by-products of calculation are: an improved fit valence-band as measured by photoemission; critical-point topology energy difference between lowest conduction highest valence bands; more significant local-pseudopotential parameters.
Ab initio total-energy calculations indicate that the formation of a new defect complex, vacancy surrounded by four arsenic atoms, is responsible for electrical deactivation and structural changes seen in measurements extended x-ray-absorption fine structure when heavily arsenic-doped silicon annealed. The $v\ensuremath{-}{\mathrm{As}}_{4}$ complex energetically favored over both substitutional, isolated As Si substitutional $\mathrm{S}\mathrm{i}\ensuremath{-}{\mathrm{As}}_{4}$...
A realistic tight-binding model for chemisorption on semiconductor surfaces is presented. The quantitatively accurate, computationally very simple, free from adjustable parameters, and can be applied to a wide variety of problems. basic assumption underlying the model, which based H\"uckel approximation, that local bond (i.e., bond) at surface similar corresponding in an appropriately chosen molecule. While Hamiltonian matrix elements between substrate atomic orbitals are determined...
Photoemission spectra show that atomic hydrogen reacts near room temperature with Si(111)1\ifmmode\times\else\texttimes\fi{}1 to form a trihydride phase, Si(111): Si${\mathrm{H}}_{3}$. The new clearly be distinguished from the monohydride H obtained Si(111)7\ifmmode\times\else\texttimes\fi{}7, has been identified by theoretical calculation of photoemission spectrum. Formation Si${\mathrm{H}}_{3}$ suggests vacancies exist on clean Si(111)7\ifmmode\times\else\texttimes\fi{}7 are disordered...
We report independent-electron model calculations of the ${L}_{2,3}VV$ and ${L}_{1}{L}_{2,3}V$ Auger line shapes for ideal Si (111), (100), (110) surfaces compare results to data Houston, Lagally, Moore. For transitions, agreement between experiment theory is excellent, in contrast poor self-fold occupied density states; this result shows that matrix-element angular momentum dependence not many-electron effects cause latter discrepancy. lines our calculated are less satisfactory. suggest...
Coordinates of atoms in the first and second layers Si(111) 2\ifmmode\times\else\texttimes\fi{}1 have been determined which yield surface energy bands good agreement with experiment. Two resonances angular photoemission data previously assigned to dangling-bond states are identified as arising from maximum lower band a saddle point upper back-bonding band.
Recent developments in two-dimensional (2D) magnetism have motivated the search for van der Waals (vdW) magnetic materials to explore phenomena 2D limit. Metal thiophosphates, $M\mathrm{P}{X}_{3}$, are a class of vdW with antiferromagnetic ordering persisting down atomically thin The this material family has been found be highly dependent on choice transition metal $M$. In work, we synthesized intermediate compounds...
Scanning-tunneling-microscopy images of the Si(111) \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} -Sb surface show a trigonal lattice protrusions, with characteristic dependence on bias voltage. When probing filled states, protrusions consist three topographic maxima, while empty states gives single maximum. These observations are interpreted in terms an Sb-trimer model, structure which is obtained through first-principles calculations. Charge-density contours that maxima seen when...
A \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} surface reconstruction is obtained on Si(111) when B diffuses from the bulk to in heavily doped Si samples. First-principles total-energy calculations show that lowest-energy atomic configuration for this consists of a atom at subsurface substitutional site, directly underneath adatom. Surface electronic states observed by photoemission and inverse experiments are analyzed through structure shown be related back-bond dangling-bond
A new measurement of the Compton profile graphite is reported. These results, along with previously reported results for diamond, are compared pseudopotential- and localized-bond-model calculations profile. Qualitative but not quantitative agreement experiment obtained. We conclude that better band needed to achieve a localized-bond model reasonable graphite.
The physics of phase transitions in two-dimensional (2D) systems underpins research diverse fields including statistical mechanics, nanomagnetism, and soft condensed matter. However, many aspects 2D are still not well understood, the effects interparticle potential, polydispersity, particle shape. Magnetic skyrmions chiral spin-structure quasi-particles that form lattices. Here, we show, by real-space imaging using situ cryo-Lorentz transmission electron microscopy coupled with machine...
Magnetic van der Waals (vdW) materials offer an opportunity to design heterostructures that will lead exotic functionalities arise from interfacial interaction. In addition coupling different vdW materials, the naturally oxidized surface layer of a material also forms heterostructure with its bulk film, giving rise intriguing phenomena. Here, we directly observe impact oxidation on magnetic domains, namely, stripe domain and skyrmions, in nanoscale Fe3GeTe2 flake using cryo Lorentz...
Using ultraviolet photoemission spectroscopy (UPS) in conjunction with theoretical calculations, we have studied the reaction of gaseous chlorine Si(111) 7 \ifmmode\times\else\texttimes\fi{} and 1 surfaces. The UPS spectra two saturated surfaces are very similar consist four peaks, a sharp main peak at -10.7 eV smaller ones -7.5, -13.0, -15.7 relative to vacuum level. Both positions their intensities quantitative agreement calculation for structural model which single atom sits on top each...
We have studied the electronic and geometrical structure of cleaved GaAs(110) surface, using experimental ultraviolet photoemission spectroscopy (UPS) both filled empty surface states together with tight-binding calculations. considered several different types structural models, including relaxation model in which Ga atoms move into, As out of, by an amount such that plane through nearest-neighbor makes a tilt angle, ϑT, corresponding ideal while bond lengths remain constant. show this angle...
Abstract Magnetotransport, the response of electrical conduction to external magnetic field, acts as an important tool reveal fundamental concepts behind exotic phenomena and plays a key role in enabling spintronic applications. Magnetotransport is generally sensitive field orientations. In contrast, efficient isotropic modulation electronic transport, which useful technology applications such omnidirectional sensing, rarely seen, especially for pristine crystals. Here strategy proposed...
Magnetic topological materials LnSbTe (Ln = lanthanide) have attracted intensive attention because of the presence interplay between magnetism, topological, and electron correlations depending on choices magnetic Ln elements. Varying Sb Te composition is an efficient approach to control structural, magnetic, electronic properties. Here, we report composition-dependent properties in PrSbxTe2−x. We identified tetragonal-to-orthorhombic structure transitions this material system very large...