担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The influence of external fields and electrons or holes injected into surface states on the relative stability of c(4×2) and p(2×2) reconstructed Si(001) surfaces was investigated by performing density-functional calculations. An electric field parallel to the [001] direction or the insertion of electrons into surface states favors the formation of p(2×2) periodicities. The changes of surface reconstruction of Si and Ge(001) surfaces induced by the STM and the occurence of p(2×2) reconstructions on (001) surfaces of n-doped Si were also explained. The external electric fields affect the charge distribution at the surface and the equilibrium positions of the surface atoms.

DOI： 10.1103/PhysRevLett.93.036101

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

We report first-principles total-energy calculations based on real-space density-functional theory that unveil the atom-scale mechanisms of surface diffusion of adatoms on the Si-faced 3C-SiC(111) stepped surface. The quality of the epitaxial layer of SiC affects the device performance. Therefore, fundamental knowledge of the microscopic mechanisms of epitaxial growth is crucial for the improvement of the quality of SiC power devices. However, adatom diffusion on the growing stepped SiC surfaces is still unknown. We identify diffusion pathways for three important adatom species of SiC chemical vapor deposition (CVD), Si, C, and H, and obtain the corresponding energy profiles for both on the surface terraces and near the surface steps, providing a complete picture of the adatom diffusion. We find that the Si adatom is most mobile on the terrace and shows prominent Ehrlich-Schwoebel (ES) effect in the inter-terrace diffusion, whereas the C and H adatoms show less ES effect and in an ascending diffusion even the inverse ES effect appears for the C adatom. The results obtained are fundamentals to explore the microscopic mechanism of the epitaxial growth on 3C-SiC(111) surfaces and equivalently hexagonal SiC(0001) surfaces.

DOI： 10.1016/j.apsusc.2021.149927

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

We have performed density­functional calculations in order to clarify atomic structures and energetics of surface steps on SiC. The obtained energetics of distinct step types on vicinal 3C­ SiC(111) surfaces which correspond to 4H­ and 6H­SiC(0001) surfaces reveals the atom­scale reason for the experimental observation in the past that the step morphology is straight for the SiC(0001) surfaces inclined toward the ‹1100› direction while it is meandering for the ‹1120› inclined surfaces. The calculations clarify the rebonding between upper­ and lower­terrace edge atoms, which is decisive for the energetics of the atomic steps.

DOI： 10.4028/www.scientific.net/MSF.1004.145

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The temperature-dependent energetics of self-assembled Au nanowires on Ge(001) surfaces is studied with the help of density-functional theory (DFT) calculations: By calculating the surface phonon modes within harmonic approximation the surface vibrational free energy is obtained to complement the zero-temperature DFT total energies. We consider several previously suggested structural models for a Au coverage between 0.75 and 1.75 monolayer and investigate a temperature range between 0 and 900 K. The stability of the investigated surface models is found to depend clearly on temperature. We find that the extended Ge bridge dimer model previously predicted to be most stable for a large range of preparation conditions is less prominent in the phase diagrams for finite temperatures. On the other hand, a model derived previously from the giant missing row structure with a higher Au coverage gets stabilized by temperature. These findings explain, at least partially, the discrepancies between experimental data and previous theoretical investigations neglecting temperature effects.

DOI： 10.1016/j.susc.2017.10.005

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Despit e intense research the microscopic atomic structure of Au-induced nanowires on Ge(0 0 1) substrates is still under discussion. We analyse a variety of structural models for Au-induced nanowires on the Ge(0 0 1) surface using first-principles calculations. Here we focus on subridge modifications at higher Au coverages and study geometries based on the giant missing row model with Ge-Ge dimers in the grooves between the nanowires due to replacing them by Ge-Au heterodimers or Au-Au homodimers. Stable geometries are predicted for higher Au coverages, which however have only a minor influence on the electronic structure. The findings are interpreted that the Au coverage and the actual geometry may vary in the various experiments according to the preparation conditions.

DOI： 10.1088/0953-8984/28/28/284005

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The Si(111)-5×2-Au surface is increasingly of interest because it is one of the rare atomic chain systems with quasi-one-dimensional properties. For the deposition of 0.7 monolayers of Au, these chains are metallic. Upon the evaporation of an additional submonolayer amount of gold, the surface becomes insulating but keeps the 5×2 symmetry. This metal-to-insulator transition was in situ monitored based on the infrared plasmonic signal change with coverage. The phase transition is theoretically explained by total-energy and band-structure calculations. Accordingly, it can be understood in terms of the occupation of the originally half-filled one-dimensional band at the Fermi level. By annealing the system, the additional gold is removed from the surface and the plasmonic signal is recovered, which underlines the stability of the metallic structure. So, recent results on the infrared plasmonic signals of the Si(111)-5 × 2-Au surface are supported. The understanding of potential one-dimensional electrical interconnects is improved.

DOI： 10.1021/acs.jpclett.5b01530

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The metal-atom chains on the Si(111) - 5 × 2 - Au surface represent an exceedingly interesting system for the understanding of one-dimensional electrical interconnects. While other metal-atom chain structures on silicon suffer from metal-to-insulator transitions, Si(111) - 5 × 2 - Au stays metallic at least down to 20 K as we have proven by the anisotropic absorption from localized plasmon polaritons in the infrared. A quantitative analysis of the infrared plasmonic signal done here for the first time yields valuable band structure information in agreement with the theoretically derived data. The experimental and theoretical results are consistently explained in the framework of the atomic geometry, electronic structure, and IR spectra of the recent Kwon-Kang model. (Graph Presented).

DOI： 10.1021/acs.nanolett.5b01279

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

We report results of ab initio calculations with various exchange-correlation functionals for the Si(111) surface with a 0.6-monolayer Au decoration. Seven different variations of the recently developed Erwin-Barke-Himpsel and Abukawa-Nishigaya models are studied in detail. Atomic geometries are determined by total-energy minimizations. We find the Erwin-Barke-Himpsel model of the Si(111)-(5×4)-Au surface with one Si adatom per unit cell to be the most favorable structure. Seven-member rings and undercoordinated Si atoms of the Abukawa-Nishigaya model are unstable. Scanning tunneling images and band structures are calculated for the controversial geometries. For the (5×4) adatom geometry the resulting electronic structure agrees with the available experimental data.

DOI： 10.1103/PhysRevB.90.165407

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Based on ab initio density functional calculations of Si nanocrystals (NCs) in a SiO 2 matrix we study the impact of NC size and separation on electronic properties and present consequences for inter-NC carrier transport. The NC size and separation significantly influence the electronic structure of three-dimensional superlattice systems with different NC filling. The energy levels for large NC distances are broadened to minibands for small separations due to the wave-function overlap. Their formation is described in terms of inter-NC hopping and carrier tunneling. We find that electron transport in conduction minibands is more likely than hole transport. © 2012 American Physical Society.

DOI： 10.1103/PhysRevB.86.075312

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The influence of the nanocrystal separation of Si nanocrystals embedded in an amorphous SiO 2 matrix is investigated using ab initio density functional theory. We consider different structural models of Si nanocrystals embedded in a SiO 2 matrix with the same nominal nanocrystal diameter but different nanocrystal separations. We demonstrate that the nanocrystal distance influences electronic, optical and dielectric properties. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mseb.2012.05.016

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Using a density-functional approach, we study the effective density of states and the effective masses of Si(00 1)/SiO2 superlattices. We apply four models of the Si/SiO2 interface and vary the Si layer thickness. The role of the confinement and the interface geometry on the effective density of states and effective masses is discussed in detail. Averages over the k-space in three and one dimensions are compared. The critical influence of the SiO2 barriers on the transport of electrons and holes is investigated. © 2011 IOP Publishing Ltd.

DOI： 10.1088/0268-1242/26/1/014024

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The interfacial electronic properties of silicon nanocrystals embedded in a silica matrix are studied using ab initio density-functional theory. We aim to obtain local band edges for a typical nanostructured system, nanocrystals embedded in a surrounding matrix. We compute the spatial variation in the electronic structure for realistic Si nanocrystals with nominal diameters ranging between 0.8 and 1.6 nm, i.e., up to systems with more than 1000 atoms. The evolution of the valence and conduction band edges between Si nanocrystals and amorphous silica along radial directions versus size is presented. Significant differences are found comparing embedded Si nanocrystals and planar Si/ SiO2 interfaces. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevB.82.085320

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記述言語：英語   掲載種別：研究論文（学術雑誌）

In order to investigate the applicability of new photovoltaic absorber materials, we show how to use first-principles calculations combined with device simulations to determine the efficiency limits of solar cells made from SiO2 /Si superlattices and from coaxial ZnO/ZnS nanowires. Efficiency limits are calculated for ideal systems according to the Shockley-Queisser theory but also for more realistic devices with finite mobilities, nonradiative lifetimes, and absorption coefficients. Thereby, we identify the critical values for mobility and lifetime that are required for efficient single junction as well as tandem solar cells. © 2009 American Institute of Physics.

DOI： 10.1063/1.3132093

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Using first-principles calculations we investigate the influence of interface modification and layer thicknesses on the optical properties of Si/SiO 2 superlattices. Four interface models with different dangling-bond passivation are considered. The results demonstrate confinement effects not only for the fundamental band gaps but also for the optical properties. While for a large Si layer thickness of the Si/SiO 2 superlattices the interface dependence is small, the calculations show a significant structure dependence for thin Si layers. © 2007 Elsevier Science. All rights reserved. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2008.07.028

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記述言語：英語   掲載種別：研究論文（学術雑誌）

We investigate the influence of layer thicknesses and interface modifications on the fundamental electronic gap of Si/SiO2 multilayers by a combined ab initio calculation and photoluminescence (PL) analysis. For the band gap calculations different Si/SiO2 interface models are studied. Experimentally investigated multiple quantum wells are prepared by remote plasma-enhanced chemical vapor deposition and rapid thermal annealing. The well-width dependence of the band gap obtained from PL measurements is much weaker than found in previous studies. This sublinear variation is in accordance with simulated electronic band gaps for hydrogen-free Si/SiO2 interfaces. The presence of hydrogen at the interfaces enforces the confinement effect for the band gap. Materials involved: nanocrystalline silicon, amorphous silica, β-cristobalite silica, and Si/SiO2 interface. ©2007 American Vacuum Society.

DOI： 10.1116/1.2779040

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The quantum conductance of the paradigmatic quasi-one-dimensional In/Si(1 1 1) surface system is calculated for 4 × 1, 4 × 2 and 8 × 2 surface reconstructions. In agreement with experiment, we find the recently suggested formation of hexagons within the In nanowires [C. Gonzalez, F. Flores, J. Ortega, Phys. Rev. Lett. 96 (2006) 136101] to drastically modify the electron transport along the In chains. In contrast, the formation of trimers barely changes the quantum conductance. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.053

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Based on ab initio density functional theory the influence of many-body excitation effects on band structures of Si/SiO2 multilayers with nanometer thickness is studied. The quasiparticle band structures are calculated within the GW approximation to the exchange-correlation self-energy. The resulting fundamental energy gaps are discussed and compared with experimental data. © 2007 American Institute of Physics.

DOI： 10.1063/1.2750526

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The structural and electronic properties of the quasi-one-dimensional In/Si(111) surface system are calculated from first principles. It is found that the symmetry lowering of the In chains is energetically favorable, provided neighboring nanowires are correlated, giving rise to a doubling of the surface unit cell both along and perpendicular to the chain direction. The recently suggested formation of hexagons within the In nanowires â€"in clear contrast to the trimer formation proposed earlierâ€" drastically modifies the electron transport along the In chains, in agreement with experiment. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevLett.98.026105

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The optical spectrum of water is not well-understood. For example, the main absorption peak shifts upwards by 1.3 eV upon condensation of gas-phase water monomers, which is contrary to the behaviour expected from aggregationinduced broadening of molecular levels. We investigate theoretically the effects of electron-electron and electron-hole correlation, finding that condensation leads to delocalisation of the exciton onto nearby hydrogen-bonded molecules. This reduces its binding energy and has a dramatic impact on the line shape. The calculated spectrum is in excellent agreement with experiment.

DOI： 10.1007/978-3-540-36183-1_4

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

We discuss some of the most relevant bonding scenarios for the adsorption of organic molecules on solid surfaces from the perspective of first-principles calculations. The adsorption of uracil and phenanthrenequinone on Si(001) and the adsorption of adenine on Cu(110) and graphite(0001) surfaces serve as prototypical examples to highlight relevant molecule-substrate interactions and their consequences for the properties of the adsystem. Covalent bonds formed during organic reactions with semiconductor surfaces significantly modify the structural and electronic properties of both the adsorbed molecules and the substrate. Organic molecule adsorption on metals may be driven by mutual polarisation that leads to substantial charge transfer and rehybridisation, despite small adsorption energies. Subtle effects related to the lowering of the kinetic energy of the valence electrons as well as dispersion forces, finally, govern the interaction between the organic molecules and chemically inert substrates such as graphite. © Springer-Verlag 2006.

DOI： 10.1007/s00339-006-3691-0

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Density functional calculations on the relative stability of c(4 × 2) and p(2 × 2) reconstructed Si(0 0 1) surfaces exposed to external electric fields and charge injection are presented. Electric fields parallel to the [0 0 1] direction or electrons inserted into surface states are found to favor the p(2 × 2) over the c(4 × 2) reconstruction. This explains recent experimental findings for Si and Ge(0 0 1). © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cap.2005.11.012

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Total-energy calculations for a series of GaAs(001)(4x6) and (6x6) surfaces are presented. For the Ga-rich limit, we confirm the GaAs(001)(4x6) surface model proposed by Ohtake [Phys. Rev. Lett. 93, 266101 (2004)]. The calculations indicate that the bright chains along the [1 1̄ 0] direction observed experimentally for (4x6) and (6x6) surfaces are derived from surface Ga-As heterodimers. The near energetic degeneracy of different arrangements of these mixed dimers explains naturally the disorder of bright chains. A long-range correlation between (6x6) surface units proposed by Kocán [Phys. Rev. B 70, 201303(R) (2004)] allows for fulfilling the electron counting rule and renders a surface based on (6x6) units more favorable. © 2006 The American Physical Society.

DOI： 10.1103/PhysRevB.73.035317

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Based on the ab initio density functional theory we study the influence of many-body effects on the quasiparticle (QP) band structures and optical absorption spectra of highly ionic crystals. Quasiparticle shifts and electron-hole interaction are studied within the GW approximation. In addition to the electronic screening the effect of the lattice polarizability is discussed in detail. Substantial effects are observed for QP bands of AlN and NaCl that have large polaron constants of 1-2. The effect of electronic and lattice polarization on the optical spectra is discussed in terms of dynamical screening and vertex corrections. The results are critically discussed in the light of experimental data available. We find that measured peak positions can be reproduced without lattice polarizability in the screening of the electron-hole interaction and a reduced lattice contribution to the QP shifts. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.72.245114

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

We demonstrate the potential of recently developed electronic-structure methods for the calculation of the optical properties of solids. As prototypical examples semiconductors crystallizing in diamond or zinc-blende structure are studied. The many-body effects are fully taken into account by a solution of the combined Dyson and Bethe-Salpeter equations. We show that an initial-value formulation of the polarization function allows for an efficient numerical calculation of the optical susceptibility. The effect of the renormalization of electrons and holes to quasiparticles is shown for both the band structure and the optical spectrum. In addition, excitonic effects are identified to remarkably influence the optical absorption. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/pssb.200541128

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The adsorption of 2,3-butanediol on the Si(0 0 1) surface is studied by means of first-principles pseudopotential calculations. Molecular adsorption on top of the Si dimers resulting in a 6-membered ring of the O-C-C-O segment with the dimer atoms is energetically favored, in agreement with the interpretation of recent experiments. The adsorption energy difference for butanediol adsorbed in either gauche or anti conformation is nearly one order of magnitude larger than the energy difference between the respective conformers in gas phase, pointing to a conformation-selective adsorption. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2005.04.029

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The optical spectrum of water is not well understood. For example, the main absorption peak shifts upwards by 1.3 eV upon condensation, which is contrary to the behavior expected from aggregation-induced broadening of molecular levels. We investigate theoretically the effects of electron-electron and electron-hole correlations, finding that condensation leads to delocalization of the exciton onto nearby hydrogen-bonded molecules. This reduces its binding energy and has a dramatic impact on the line shape. The calculated spectrum is in excellent agreement with experiment. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevLett.94.037404

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The Ga-rich limit of the surface reconstructions on GaAs(001) was investigated. Scanning tunneling microscopy and reflection high energy electron diffraction (RHEED) analysis were used for the study. The existence of a well-ordered (4 × 6) reconstruction was observed under extreme Ga-rich conditions. A structure model was developed for the (4 × 6) surface that consist of surface Ga-As dimers and subsurface Ga-Ga dimers. It was observed that the structure model was energetically stable at the extremely Ga-rich condition.

DOI： 10.1103/PhysRevLett.93.266101

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Reflectance anisotropy spectra (RAS) for water covered Si(001) surfaces have been calculated within the independent-particle approximation. For low coverages we find essentially an attenuation of the features typical for clean Si surfaces. For the saturation coverage of one molecule per dimer, however, dissociative adsorption and oxygen insertion into the Si dimer give rise to clearly different optical anisotropies. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2004.08.012

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記述言語：英語   掲載種別：研究論文（学術雑誌）

In the last couple of years there has been much methodological and computational progress in the modelling of optical properties from first principles. Reflectance anisotropy spectra (RAS) can now be calculated with true predictive power and can thus be used to draw conclusions directly on the surface geometry. In the present work we study two potentially very interesting applications for RAS: the oxidation of Si(001) and the functionalization of the Si surface with organic molecules. Our calculations confirm experimental indications that the polarity of the interface-induced optical anisotropy is reversed layer by layer with increasing oxide thickness. The oscillation of the RAS amplitude should thus allow for the quantitative monitoring of the vertical progression of the oxidation. Our results for Si(001) surfaces modified by cyclopentene and 9, 10-phenanthrenequinone adsorption show a strong sensitivity of the RAS signal with respect to the adsorption geometry. Comparison with experimental data shows that cyclopentene most probably adsorbs via a cycloaddition reaction with the Si surface dimers, while phenanthrenequinone seems to adsorb across two Si dimers.

DOI： 10.1088/0953-8984/16/39/007

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

We present ab initio calculations of the adsorption of methylchloride (CH 3 Cl) on Si(001). Among multiple plausible adsorption geometries, we find five thermodynamically favorable configurations. These lead to strong geometrical changes in the Si surface structure as well as to significant charge transfer processes. The stability of the adsorption structures is discussed in terms of electrostatics. The results are compared to recent experimental and theoretical findings. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2004.05.041

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The electronic properties of the uracil-covered Si(001) surface have been studied by density-functional calculations. Dative-bonded configurations are characterized by a high density of surface states in the energy region of the fundamental gap, whereas the surface is perfectly passivated when covalent bonds form between the molecule and the substrate. A remarkable influence of the adsorption configuration on the ionization energy is predicted. The results show that semiconductor surface electronic properties can be tuned within a very wide range by organic functionalization even with only one molecular species.

DOI： 10.1103/PhysRevB.69.245309

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

In the last couple of years there has been much methodological and computational progress in the modeling of optical properties from first principles. While the calculation of non-linear optical coefficients is still hampered by numerical limitations - demonstrated here for the case of bulk GaAs - linear optical spectra can now be calculated accurately and with true predictive power, even for large and complex surface structures. This allows on one hand for a much better understanding of the origin of specific features such as surface optical anisotropies. We find that in particular microscopic electric fields at the surface induce slight deformations of bulk-like wavefunctions and thus give rise to optical anisotropies even from sub-surface layers. On the other hand, from the comparison of measured and calculated spectra, one can now confidently reach conclusions on the surface geometry. This short review focuses on the simulation of reflectance anisotropy spectroscopy. The clean, hydrogenated and uracil-covered Si(001) surface is used to illustrate the microscopic origin of surface optical anisotropies and the present state-of-the-art in computational modeling of optical spectra. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2003.11.263

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記述言語：英語   掲載種別：研究論文（学術雑誌）

We present equilibrium geometries, vibrational modes, dipole moments, ionization energies, electron affinities, and optical absorption spectra of the DNA base molecules adenine, thymine, guanine, and cytosine calculated from first principles. The comparison of our results with experimental data and results obtained by using quantum chemistry methods show that in specific cases gradient-corrected density-functional theory (DFT-GGA) calculations using ultrasoft pseudopotentials and a plane-wave basis may be a numerically efficient and accurate alternative to methods employing localized orbitals for the expansion of the electron wave functions.

DOI： 10.1002/jcc.10372

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The reflectance anisotropy properties of uracil covered Si(001) surfaces were studied. Scanning tunneling microscopy (STM) and high-resolution electron energy-loss spectroscopy were used to investigate the system. The reflectance anisotropy spectra (RAS) for the energetically favored models of uracil covered Si(001) surfaces was calculated within the independent particle approximation. The calculations predict the appearance of new peaks for higher coverages, suggesting the usage of RAS for the analysis of organic/inorganic interfaces.

DOI： 10.1016/j.susc.2003.11.002

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

First-principles pseudopotential calculations for a large number of C4H4NH/Si(0 0 1) adsorption configurations possibly resulting from reactions such as [2 + 2] or [4 + 2] cycloadditions are presented. Energetically most favorable are dissociative reactions, leading to the partial fragmentation of the molecule. The lowest energy configuration for monolayer coverage is characterized by pyrrole rings bonded to the surface via Si-N linkage. In co-existence with adsorption geometries where both N and C are bonded to the surface, this structure accounts very well for the available experimental data. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0039-6028(03)00159-6

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The adsorption of uracil on the Si(OOl) surface has been investigated by density-functional theory calculations using a plane-wave basis in conjunction with ultrasoft pseudopotentials. A large number of possible interface structures are studied. Electrostatic effects and the keto-enol tautomerism play an important role for the surface reaction. There exists a pronounced tendency for molecular fragmentation, leading to the dissociation of hydrogen from the molecules and possibly to oxygen insertion into Si dimers.

DOI： 10.1021/jp0342531

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The functionalization of the Si(001) surface by pyrrole and polypyrrole is investigated by means of first-principles pseudopotential calculations. We find dissociative reactions, leading to the partial fragmentation of the molecule, to be energetically most favored for pyrrole adsorption. The lowest-energy configuration for monolayer coverage is characterized by pyrrole rings bonded to the surface via Si-N linkage. In coexistence with adsorption geometries where both N and C are bonded to the surface, this structure accounts very well for the available experimental data. Chemisorption of pyrrole is found to effectively passivate the Si(001) surface, irrespective of the details of the adsorption geometry. The formation of well-ordered polypyrrole structures on Si(001) may require chemical modifications of the polypyrrole chains in order to account for the lattice mismatch.

DOI： 10.1142/s0218625x03004901

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The atomic structures and energies of Ga-rich GaAs(0 0 1) surface reconstructions are examined by means of first-principles total-energy calculations based on a real-space multigrid method. Our calculations confirm the existence of the novel ζ(4 × 2) structure suggested by Lee et al. [Phys. Rev. Lett. 85 (2000) 3890]. (4 × 6) surface reconstructions suggested to explain STM experiments are found to be unstable. The calculations indicate that the adsorption of Ga adatoms in the trenches of the ζ(4 × 2) surface could possibly explain the observed structures. The diffusion of Ga/As adatoms on the Ga-rich GaAs surface is predicted to be anisotropic and should preferably take place parallel to the [1 1 0]/[1 1̄ 0] direction, respectively. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0039-6028(02)01278-5

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The microscopic migration of group V adatoms on a Ga-terminated GaAs(0 0 1) surface is investigated by performing first-principle calculations using density functional theory and a slab model of the surface. It is found that the hopping barrier energies of the As and P adatoms on Ga-terminated GaAs(0 0 1) surface are anisotropic and that the hopping barrier energies of those are lower than that of the Ga adatom. Comparing the hopping barrier energies of the As and P adatoms, the migration of the As adatom is easier than that of the P adatom. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-0248(01)01870-X

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Role of As2 molecules on Ga-terminated GaAs surfaces was investigated during molecular beam epitaxy (MBE). The calculations were based on the density functional theory (DFT) within the local density approximation (LDA). The migration of the two As atom pair on the Ga-terminated GaAs (0 0 1)-β2(2×4) surface was calculated. It was suggested that Ga dimers will play an important role to incorporate As2 molecule into the surface, during the MBE growth.

DOI： 10.1016/S0022-0248(01)02226-6

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The functionalization of the Si(001) surface by pyrrole and polypyrrole is investigated by means of first-principles pseudopotential calculations. We find dissociative reactions, leading to the partial fragmentation of the molecule, to be energetically most favored for pyrrole adsorption. The lowest energy configuration for monolayer coverage is characterized by pyrrole rings bonded to the surface via Si-N linkage. In co-existence with alternative adsorption geometries where both N and C are bonded to the surface, this structure accounts very well for the available experimental data. Chemisorption of pyrrole is found to effectively passivate the Si(001) surface, irrespective of the details of the adsorption geometry. The formation of well-ordered polypyrrole structures on Si(001) may require chemical modifications of the polypyrrole chains in order to accommodate the lattice mismatch-induced strain. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.235323

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

We present theoretical results of the density functional calculations on the adsorption of Ag on Ge(0 0 1) surface. The scanning tunneling microscopy (STM) images of each stable or metastable sites for the adsorption of a low coverage of Ag adatom are calculated. We suggested that the unit element of Ag islands in the STM is the Ag ad-dimer structures which are composed by the two coupling Ag atoms on Ge substrate. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0039-6028(01)01248-1

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The adsorption of Ag on the Ge(001) surface has been studied with first-principles calculations for a range of coverages from an isolated Ag adatom up to a second Ag atom on the surface. Two-dimensional islands of Ag, observed by scanning tunneling microscopy (STM) experiments, consist of the Ag ad-dimers which lie on the trenches between two Ge dimer rows. The Ag ad-dimer is parallel to the underlying Ge dimer direction. We found that the Ag ad-dimers reside stably at the position between Ge dimer rows.

DOI： 10.1016/S0039-6028(00)00752-4

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The microscopic migration of an As adatom on a Ga-terminated GaAs(001) surface is investigated by performing first-principle calculations using density functional theory and a slab model of the surface, because the importance of As adatom migration has been reported. The obtained values of barrier energy are compared with those to hopping in the kinetic Monte Carlo simulation. The anisotropic migration of the As adatom is clarified, which agrees with the result of the kinetic Monte Carlo simulation as well as the properties obtained by the scanning tunneling microscopy observation. It is shown that an As adatom is more mobile than a Ga adatom, and the kinetics of both As and Ga atoms on the growing surface are important during molecular beam epitaxial growth. © 2000 The Japan Society of Applied Physics.

DOI： 10.1143/jjap.39.4285

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The hopping barrier energies of As adatoms on smooth GaAs(001) surfaces have been investigated using the first-principle pseudopotential density functional approach. The hopping barrier energies were calculated for a few surface structures. We found that the migration of As adatom exhibits anisotropy as well as that of Ga adatom and the hopping barrier energy for As adatom is smaller than that for Ga adatom. These results agree with the results of recent Monte Carlo simulations.

DOI： 10.1143/PTPS.138.164

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The hopping barrier energy of the As adatom on the Ga-terminated GaAs(100) surface has been studied by using a first-principles calculation. It has been assumed that there are As adatoms on the Ga-terminated surface and each single As adatom is moved on it during epitaxial growth. The simple straight-line paths were applied to estimate the hopping barrier energy. It is found that the hopping barrier energy of the As adatom on the Ga-terminated GaAs(100) surface is anisotropic and that the hopping barrier energy of the As adatom is lower than that of the Ga adatom. The calculated results agree with the results from the Monte Carlo simulation.

DOI： 10.1016/S0039-6028(99)00550-6

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