bluuebunny/crossref_metadata_2025 huggingface dataset:
Equivalent Dispersion Dependence: A Concept to Characterize the Cardiac Myocardium in the Normal State and Before Fibrillation
Authors: Anosov O. , Berdyshev S. , Khassanov I. , Hensel B.
Published: August 2003

We use the formalism of wave-packet propagation in passive media to characterize the spread of the electrical excitation in excitable media, namely the cardiac myocardium. We introduce equivalent concepts of group and phase velocities, attenuation coefficient and refraction index to describe the myocardial excitation wave and apply the wavelet approach to construct an analogue of the classical dispersion dependence for active media — the "equivalent dispersion dependence". Using the wavelet decomposition we develop a method for the reconstruction of the equivalent dispersion dependence for the myocardium on the basis of electrical intracardiac signals that are measured in two spatially separated points. The novel method is applied to two different sets of experimental data and to data obtained from a numerical simulation of the atrial myocardium. We show that the introduced equivalent dispersion dependence under physiological conditions is similar to the one that is obtained for resonant wave-medium interaction. The analysis of both experimental data sets clearly shows that the number of cardiac cycles with a resonant form of the equivalent dispersion dependence predominates in the normal state of the myocardium while it decreases early before the onset of atrial fibrillation. We set up the hypothesis that an increasing number of non-resonant cardiac cycles is a precursor of atrial fibrillation and thus can serve to predict fibrillation already at an early stage before its onset. The proposed conception can be applied to investigate the properties of the atrial as well as the ventricular myocardium.
Elliptic Partial Differential-Algebraic Multiphysics Models in Electrical Network Design
Authors: Alì G. , Bartel A. , Günther M. , Tischendorf C.
Published: August 2003

In refined network analysis, a compact network model is combined with distributed models for semiconductor devices in a multiphysics approach. For linear RLC networks containing diodes as distributed devices, we construct a mathematical model that combines the differential-algebraic network equations of the circuit with elliptic boundary value problems modeling the diodes. For this mixed initial-boundary value problem of partial differential-algebraic equations a first existence result is given.
Asymptotic Energy Behavior of Two Classical Intermediate Benchmark Shell Problems
Authors: Beirão da Veiga L.
Published: August 2003

We consider two classical problems which are widely used as benchmark tests for shell numerical methods: the Scordelis–Lo roof and the pinched roof. Due to the particular load and boundary conditions applied, neither belongs to the well-known classes of purely bending or purely membrane dominated shells. Consequently the asymptotic energy norm behavior, which is useful not only because it represents the structure stiffness, but also for numerical comparison purposes, is not a priori known. In this work, using space interpolation techniques and a recently developed "intermediate" shell theory, the asymptotic energy behavior of both problems is found analytically. The results are in agreement with the numerical estimates obtained in other papers.
Strong Steady Solutions for a Generalized Oldroyd-B Model with Shear-Dependent Viscosity in a Bounded Domain
Authors: Arada N. , Sequeira A.
Published: August 2003

We study a system of nonlinear partial differential equations governing the motion of an incompressible viscoelastic fluid of Oldroyd type in a bounded domain, with a non-Newtonian viscosity depending on the second invariant of the rate of deformation tensor. Considering the equations in a suitably decomposed form, we establish, for small and suitably regular data, existence of a unique solution using a fixed point argument in an appropriate functional setting. This model includes the classical Oldroyd-B fluid as a particular case.
Asymptotic Estimates of Hierarchical Modeling
Authors: Arnold Douglas N. , Madureira Alexandre L.
Published: August 2003

In this paper we propose a way to analyze certain classes of dimension reduction models for elliptic problems in thin domains. We develop asymptotic expansions for the exact and model solutions, having the thickness as small parameter. The modeling error is then estimated by comparing the respective expansions, and the upper bounds obtained make clear the influence of the order of the model and the thickness on the convergence rates. The techniques developed here allows for estimates in several norms and semi-norms, and also interior estimates (which disregards boundary layers).
An Elliptic Equation with Blowing-Up Diffusion and Data in L1: Existence and Uniqueness
Authors: García Vázquez Concepción , Ortegón Gallego Francisco
Published: August 2003

We establish some existence and uniqueness results for a nonlinear elliptic equation. The problem has a diffusion matrix A(x, u) such that A(x, s)ξξ ≥ β(s)|ξ|2, with β : (s0, + ∞) ↦ ℝ a continuous, strictly positive function which goes to infinity when s is near s0. On the other hand, [Formula: see text]. Also, the right-hand side f belongs to L1(Ω). We make use of the concept of renormalized solutions adapted to our problem.
Atomic Structure of Si(100) Surfaces
Authors: Koo Ja-Yong , Yi Jae-Yel , Hwang Chanyong , Kim Dal-Hyun , Lee Sekyung , Ko Young-Jo , Chang K. J. , Shin Dong-Hyuk
Published: August 2003

The structure of a clean Si(100) and a Ni-contaminated si(100) was investigated using scanning tunneling microscopy. The clean Si (100) shows the 2 × 1 reconstruction with a surface dimer vacancy density less than 2%. The major defects on the clean surface are a single dimer vacancy and the C defect. A small amount of Ni on the surface drastically changes the surface structure and produces 2 × n reconstructions. The formation of vacancy clusters is favored. A rebonded SB step is preferred on the clean Si(100) while a nonrebonded SB step with a split-off dimer is mainly observed on the Ni-contaminated Si(100) and in the vicinity of dimer vacancies of the lower terrace on the clean Si(100).
AR-PES Study of the Single Domain Si(100)-(2 × 1)Pb Surface
Authors: Odasso S. , Göthelid M. , Yu. Aristov V. , Le Lay G. , Kim H. J. , Buslaps T. , Johnson R. L.
Published: August 2003

Having detected two surface states in the valence band spectra of the single domain Si(100) surface covered with an ordered lead monolayer (2 × 1 reconstruction), we follow their dispersions along the ΓJ direction of the surface Brillouin zone. Evidence is also given of the persistence of silicon dimers at the interface.
RHEED Study of the Si(100) Surface Structure with Temperature
Authors: Quentel G. , Müller P. , Gauch M. , Hammadi Z.
Published: August 2003

The structural properties of clean silicon (100) surface have been investigated by RHEED. The clean surface is reconstructed and the RHEED pattern shows superstructures associated to (2×1) and (1×2) domains. We recorded the intensity of the integer, as well as half order rods of the RHEED pattern, as a function of the crystal temperature from room temperature to 1500 K. The (1×2) domain grows at the expense of the others until it predominates. Between 1170 K and 1350 K the RHEED intensity of half order spots varies quickly and passes through a maximum. Such a behavior could be interpreted as originating from step bunching due to the heating mode (Joule effect by using DC current). At around 1350 K the half order spot decreases abruptly. The analysis of the intensity profile change versus temperature shows that the half width increases as the intensity decreases until the spot disappears. Analysis suggests that at arround 1400 K there is a lack of order at the crystal surface, which could originate in an incomplete melting.
Evolution and Degeneration of Dimer-Adatom-Stacking-Fault Structure in Solid-Phase Epitaxy on Si(111) Surface Observed by Scanning Tunneling Microscopy
Authors: Zhang Z. , Kulakov M. A. , Bullemer B.
Published: August 2003

Large unit cells of dimer-adatom-stacking-fault structure and related 2 × 2 and c(4 × 2) reconstructions have been prepared by low-temperature solid-phase epitaxy and observed by scanning tunneling microscopy. The size-different unit cells of the DAS structure are considered to be a structure evolution in which more electron charge transfers in a larger unit cell from the adatom dangling bonds to the rest-atom dangling bonds. In some cases the DAS structure can degenerate into triangular 2 × 2 domains and bundlinke c(4 × 2) domains. The rest atoms are always fully filled by electrons due to the charge transfer. The adatom dangling bonds are partially filled in a c(4 × 2) symmetry and essentially empty in a 2 × 2 symmetry. As a result, the rest atoms in 2 × 2 domains can be imaged without the adatom protrusions while in the c(4 × 2) domains the protrusions of the adatoms and the rest atoms appear in zigzag chains, when the sample is negatively biased.
LEEM Determination of Critical Terrace Widths for Si/Si(111) Step Flow Growth
Authors: Altman M. S. , Chung W. F. , Franz T.
Published: August 2003

The condition for step flow growth of Si on the Si(111)-(7 × 7) surface has been investigated using low energy electron microscopy (LEEM). The critical terrace width for step flow growth was found to be independent of the azimuthal direction. This is consistent with isotropic diffusion and step flow kinetics. The dependence of the critical terrace width upon temperature for fixed incident flux (0.1 monolayer/minute) has also been measured. The square of the critical terrace width exhibits an Arrhenius behavior between 750 and 80 K with prefactor A = 7.0 × 1019  nm 2 and activation energy E = 2.05 eV. These values are significantly larger than those determined by Iwanari et al. [J. Cryst. Growth119, 241 (1992)] at lower temperatures and similar flux. Possible origins of this discrepancy, including the validity of the Arrhenius description, are discussed.
Structured Roughness of Si Surface Obtained by Molecular Beam Epitaxy on Highly Misoriented Si(111) Substrate
Authors: Gay J.-M. , Lapéna L. , Ladevèze M. , Tolan M.
Published: August 2003

We present the results of an X-ray analysis of the surface morphology of a sample obtained by Si MBE onto a higly misoriented Si(111) substrate. X-ray reflectivity and diffuse scattering provide a description of the surface. The amplitude of the surface profile is about 6.6 nm, with a sawtooth shape. Satellites in the diffuse scattering indicate a 215±5 nm periodicity int he miscut direction. The analysis of satellite intensities shows an asymmetry of the surface shape. The results are in agreement with AFM images of the surface.
Formation of Nanoscale Structures on the Ge(111) Surface Under Mechanical Loading
Authors: Korsukov V. , Lukyanenko A. , Obidov B.
Published: August 2003

Surface layers of Ge(111) under external mechanical loading have been investigated by EELS on plasmons and RHEED techniques. The positions of plasmon peaks and the diffraction patters were found to be strongly influenced by the external stress. Lattice dilatation in the layers 1 and 10 nm thick was estimated from the energy shifts of plasmon peaks under the applied load. It has been concluded that under high stress values of the order of 1 GPa the surface layers of Ge(111) undergo a transformation from the single-crystal to nanocrystallin state.
Ab-Initio MD Studies of the Structure of C(111): nH Surfaces
Authors: Kern G. , Hafner J. , Kresse G.
Published: August 2003

We present ab-initio local-density-functional investigations of clean and hudrogen-covered one- (1db) and three-dangling-bond (3db) diamond (111) surfaces, the geometries of the reconstructed surfaces and their stabilities at different values of the hydrogen chemical potential. At low values of the hydrogen chemical potential the clean 1db–(2 × 1) π-bonded Pandey-chain structure forms the ground state. As the hydrogen chemical potential increases, first the hydrogenated 1db–(1 × 1):H structure becomes stable. Then we find a narrow region where a 3db–(2 × 1):2H dihydride surface is stable, until at last a fully hydrogen-saturated 3db–(1 × 1):3H surface has the lowest energy. Then preliminary molecular-dynamics results of reconstruction and graphitization for the 1db surface at elevated temperatures are reported.
Si(111)-(7 × 7) Under Silane UHV-LPCVD: A STM Study
Authors: Masson L. , Albertini D. , Thibaudau F. , Salvan F.
Published: August 2003

In this work, we present a scanning tunneling microscopy (STM) study of the LPCVD (low pressure chemical vapor deposition) growth of Si on Si(111)-(7 × 7) using silane ( SiH 4) decomposition. Surface reactivities have been studied at room and high temperature (700 < T < 800  K ), and the major chemical mechanisms have been identified at an atomic scale on the basis of room temperature STM images of the reacted surfaces. The study provides a better understanding of nucleation and initial stages of growth. More particularly, we show that the growth kinetics and the final structure of the film are different from what is observed by molecular beam epitaxial (MBE) growth.
Surface Structures of Phosphorus and Indium on Si(111)
Authors: Netzer F. P. , Vitali L. , Kraft J. , Ramesy M. G.
Published: August 2003

The interaction of vapor phase P2 with the [Formula: see text] monolayer surface at room temperature and elevated temperature has been monitored by scanning tunneling microscopy (STM) and spectroscopy (STS) in conjunction with Auger electron spectroscopy and low-energy electron diffraction (LEED). The surface rection can be readily followed by STM because of the very different contrast of the reacted areas in the STM images. The reaction develops around overlayer defects at room temperature and appears to be diffusion-limited, whereas at 300°C the reaction is initiated at the step edges, from which the reaction front progresses onto the lower terrace areas. At elevated temperature several ordered surface reconstructions, showing different STS fingerprints, are detected on the P–In/Si(111) surfaces, which are associated tentatively with P- and Si-terminated structures and an ordered InP phase.
First-Principles Study of the As-Mediated Growths of Si and Ge on Si(100)
Authors: Ko Young-Jo , Chang K. J. , Yi Jae-Yel , Park Seong-Ju , Lee El-Hang
Published: August 2003

We study the mechanism of the As-mediated epitaxial growths of Ge and Si on Si(100) surfaces through first-principles pseudopotential calculations. On an As-monolayer-covered Si(100) surface, individual Ge or Si adatoms are found to incorporate rapidly into subsurface As sites with minimum surface diffusion. The segregation of As is initiated by the substitutional adsorptions of individual Ge or Si adatoms. Because of the rapid adatom incorporation, adatom mobility is drastically reduced, compared with the growth without surfactants, resulting in a high density of two-dimensional islands. The inclusion of gradient corrections to the LDA energies does not change our results.
The Behavior of Cs on S-Covered Si(100)-(2 × 1) and Si(100)-(1 × 1) Surfaces
Authors: Papageorgopoulos Aris , Mosby Dwight , Papageorgopoulos C. A.
Published: August 2003

In this work we study the adsoption of Cs on (a) clean Si(100)-(2 × 1), (b) 0.5 ML of S-covered Si(100)-(2 × 1) and (c) 1 ML of S-covered Si(100)-(1 × 1) in ultrahigh vacuum (UHV). LEED and AES measurements suggest that the array of a Cs monolayer on clean and S-covered Si(100)-(2 × 1) surfaces was that of the double layer model, according to which, half of the Cs atoms reside on the raised sites of the dimers and the other half in the troughs. However, Cs on 1 ML of S-covered Si(100)-covered Si(100)-(1 × 1) forms initially a coplanar monolayer with the Cs atoms residing only on the same kind of sites. The presence of S on the Si surfaces increases the subsequently deposited (at RT) coverage of Cs to more than 1 ML. Structural models of Cs on clean and S-covered Si(100) surfaces are proposed.
Electronic Structure of the Ultrathin Cs/Si(100)-(2 × 1) and Cs/Si(111)-(7 × 7) Interfaces in the Threshold Energy Region
Authors: Benemanskaya G. V. , Daineka D. V. , Frank-Kamenetskaya G. E.
Published: August 2003

The electronic band structure of the Cs/Si(100)-(2 × 1) and Cs/Si(111)-(7 × 7) interfaces has been studied near the Fermi level at submonolayer coverages. The technique of threshold photoemission spectroscopy with linearly polarized light excitation has been employed. Surface photoemission spectra reveal on Cs-induced band which can be either below the VBM or at the Fermi level, depending on the substrate. Parameters of the Cs band and the change in ionization energy and work function are obtained as a function of Cs coverage. Experimental data provide direct evidence that the Cs/Si(100)-(2 × 1) interface exhibits semiconducting charcter in a great part of the submonolayer range, in contrast to the metallic-like Cs/Si(111)-(7 × 7) interface.
Atomic Structure of a Monolayer of Ge on Si(001)(2 × 1)
Authors: Jenkins S. J. , Srivastava G. P.
Published: August 2003

We present results of first-principles pseudopotential calculations for an ordered monolayer growth of Ge on Si(001)(2 × 1). Our results strongly support the asymmetric Ge–Ge dimer model. We also provide a detailed discussion on the nature of the bonding within the overlayer and between the overlayer and the substrate.
First-Principles Investigations of the Atomic and Electronic Structure of Pb, Sn and Ge Adsorbed on the ${\rm Ge}(111)\mbox{-}(\sqrt{3}\times\sqrt{3})$ Surface
Authors: Würde K. , Krüger P. , Mazur A. , Pollmann J.
Published: August 2003

Submonolayer adsorption of group-IV elements (Ge, Sn, Pb) on the Ge(111) surface has been investigated using first-principles pseudopotential total-energy and force calculations. The most prominent adsorption geometries, namely T4 and H3, are compared with respect to their atomic and electronic structure. As the most striking result, our calculations favor adsorption of adatoms in thresfold-symmetric T4 sites for all three different adatom species in agreement with earlier predictions and experiment.
Charge Transfer and Surface Diffusion of Lead on Ge(111)
Authors: Seehofer L. , Falkenbeng G. , Johnson R. L.
Published: August 2003

Small amounts of Pb significantly enhance the surface diffusion on the Ge(111)c(2 × 8) surface. Scanning tunneling microscopy at different sample bias polarities has been used to study the local geometric and electronic properties of the mixed Pb and Ge adatom structure. It was found that all Ge adatoms transfer charge to the Ge rest atoms whereas the Pb atoms exist in two different electronic configurations. Pb atoms which do not transfer charge to Ge rest atoms allow the existence of various characteristic Pb-induced defects in the c(2 × 8) reconstruction. During the formation of these defects vacancies are created which facilitate the diffusion of adatoms over large distances on the surface.
Halogen Interaction with the Ge(111) and Ge(100) Surfaces
Authors: Göthelid M. , Le Lay G. , Wigren C. , Björkqvist M. , Karlsson U. O.
Published: August 2003

A comparative study of the interaction of iodine and chlorine with Ge(1111) and Ge(100) has been performed using photoelectron spectroscopy. On the Ge(111) surface both adsorbates preferentially occupy the on-top T 1 site. In addition small amounts of GeX 2 species are found in bridge sites (X=I or Cl). On Ge(100)–I only Ge is formed at room temperature with one iodine atom on each dimer atom dangling bond. The halogen coverage at saturation has been estimated from survey spectra including both the Ge 3d and the I 4d or Cl 2p levels and from detailed Ge 3d spectra. These two approaches yield significantly different values; this discrepancy is interpreted as reflecting the presence of molecular species on top of the chemisorbed adlayer.
Growth of Aluminum on Silicon: Comparison of the Si(111)7 × 7 and Si(111)δ7 × 7–D Surfaces
Authors: Kharamtsova E. A. , Gołek F. , Bauer E.
Published: August 2003

The initial stages of Al film formation on the clean Si(111)7 × 7 and deuterium-induced Si(111)δ7 × 7–D surfaces have been investigated using AES, LEED and TDS. Our experimental data show that epitaxial Al films form on both surfaces though the growth mode depends strongly on the substrate temperature and surface conditions. At about 90 K Al grows on the (7 × 7) surface in the quasi-Frank–van der Merwe mode forming crystallites of size 10–15 Å with Al(111)‖Si(111) and predominantly [Formula: see text]. The azimuthal disorder of about 10° is considerably reduced by annealing at room temperature. At and above 300 K the films grow in the Stranski–Krastanov mode with epitaxial Al(111) and Al(100) orientations. On the δ7 × 7–D surface Al grows at room temperature in the Volmer–Weber mode with epitaxial Al(111) and Al(100) islands. The film does not become continuous even at 30 ML Al, the largest Al coverage studied.
Elastic Strain Relaxation in Si1-xGex Layers Epitaxially Grown on Si Substrates
Authors: Berbezier I. , Gallas B. , Derrien J.
Published: August 2003

We have investigated the elastic strain relaxation in Si 1-x Ge x layers grown by the molecular beam epitaxy (MBE) technique and in situ controlled with RHEED. Up to ≈0.8% critical lattice mismatch (about 20% Ge) uniform strained and flat layers were grown both on (111) and on (001) Si substrates. Calculations of the elastic constants evidenced a tetragonal distortion about 50% higher on (001) than on (111) in the same experimental conditions. At higher misfits (and/or thicknesses) a growth instability was evidenced only on (001) Si substrates. Si 1-x Ge x layers there displayed a surface layer undulation. On the contrary, Si 1-x Ge x layers grown on (111) Si substrates remained smooth throughout the growth up to the plastic relaxation of the layers. To determine stress fields in the Si 1-x Ge x layers, a high spatial resolution convergent beam electron diffraction (CBED) experiment was performed with a field effect analytical microscope. The CBED technique was applied to two typical cases: totally strained layer and undulated dislocation-free layer. In the latter case, CBED patterns recorded on nanometer scale areas of an undulation crest (cross-section sample) showed a gradual elastic relaxation mainly directed along the growth axis (z). Moreover a triclinic distortion of the unit cell was pointed out. These results were confirmed on a plane view sample. In conclusion, our results show that the driving force for the undulation is not the in-plane elastic relaxation since CBED experiments proved an important elastic relaxation of the (001) Si 1-x Ge x layers along the z axis. This was in agreement with the calculations of the elastic constants. We think that this could be at the origin of the undulation.
X-Ray Characterization of Buried δ Layers
Authors: Falta J. , Bahr D. , Materlik G. , Müller B. H. , Horn-Von Hoegen M.
Published: August 2003

A combination of measurements of crystal truncation roda and X-ray standing waves has been used for a detailed characterization of buried Ge δ layers on Si(001). Measurements of crystal truncation rods reveal the interface roughness, the δ layer lattice constant and the δ layer concentration. From measurements with X-ray standing waves the dopant lattice position and crystallinity of the δ layer are determined. We find a linear dependence of the local tetragonal distortion of the Ge bonding in the δ layer on the Ge concentration in the layer.
Epitaxial Growth of Sb/Ge/Si(111) Studied by Photoelectron Diffraction
Authors: Westphal C. , Sökeland F. , Dreiner S. , Zacharias H.
Published: August 2003

X-ray photoelectron diffraction is used to investigate the epitaxial growth of thin high quality Ge films on Si(111). Several Ge films have been prepared with varying coverages with and without Sb terminating the interface towards the vacuum. The measured photoelectron pattern for monolayer Ge films exhibits only intralayer diffraction maxima due to the double layers formed by the Ge diamond structure. For thicker films interlayer scattering between two adjacent layers can be observed as well.
The Atomic Structure of the Si(111)-Pb Buried Interface Grown on the ${\rm Si}(111)\mbox{-}(\sqrt{3}\times\sqrt{3})\mbox{-}{\rm Pb}$ Reconstruction
Authors: Howes P. B. , Edwards K. A. , Macdonald J. E. , Hibma T. , Bootsman T. , James M. A. , Nicklin C. L.
Published: August 2003

The Si(111)-Pb interface is a prototypical metal-semiconductor interface and has been the subject of a number of experimental studies. The Schottky barrier height is known to depend on the initial reconstruction formed by the first monolayer of Pb atoms and we have previously shown that there are structural differences between the buried interfaces.

We present surface X-ray diffraction measurements of the interface grown from the incommensurate [Formula: see text] reconstruction and show that, in contrast to the starting surface, the interface comprises the junction between unreconstructed, bulk-like Si(111) and disordered, bulk-like Pb(111). This interface is contrasted with the interface formed by growth on the Si(111)-(7 × 7)-Pb reconstruction at which the starting reconstruction is preserved.
Monolayer Nitrogen Atom Incorporation at Buried Si-SiO2 Interfaces: Preparation by Remote Plasma Oxidation/Nitridation and Characterization by On-Line Auger Electron Spectroscopy
Authors: Lucovsky G. , Niimi H , Koh K. , Green M. L.
Published: August 2003

This paper presents experimental studies in which N-atoms have been incorporated at Si-SiO 2 interfaces by forming the interface and oxide film by a 300°C remote-plasma-assisted nitridation/oxidation process using N 2 O . Process dynamics have been studied by on-line Auger electron spectroscopy (AES) by interrupted plasma processing. Based on AES studies using N 2 O , O 2 and sequenced N 2 O and O 2 source gases, reaction pathways for (i) N-atom incorporation at and/or (ii) removal from buried Si-SiO 2 interfaces have been identified, and contrasted with reaction pathways for nitridation using conventional furnace processing.
Atomic Structure of the Domain Walls of the Discommensurate Phases in Ge(111)/Ga
Authors: Gai Zheng , Gao Bo , Ji Hang , Zhao R. G. , Yang W. S.
Published: August 2003

We have studied the γ and β discommensurate phases of the Ge(111)/Ga system with scanning tunneling microscopy (STM). On the basis of the features of these phases known from our STM images as well as from previous papers, models of domain-wall structure of both phases have been proposed for further investigations.
Atomic Structure of Hexagonal 6H– and 3C–SiC Surfaces
Authors: Schardt J. , Bernhardt J. , Starke U. , Heinz K.
Published: August 2003

The crystallography of hexagonal SiC surfaces prepared ex situ by chemical methods was investigated by low energy electron diffraction (LEED) structure analysis. The surface morphology was analyzed by considering mixtures of domains with different surface layer stacking geometries. On the 6H–SiC(0001) surface ABCACB stacking is the dominating termination, covering about 80% of the surface. On [Formula: see text] all three possible surface stacking sequences are present. The (111) surface of a 3C–SiC film sample shows linear stacking of layers with only one domain orientation present. In contrast to the carbon-terminated 6H sample, the silicon-terminated surfaces are covered by an oxygen layer with the adatoms bound on top of silicon.
Electronic and Structural Properties of the 6H–SiC(0001) Surfaces
Authors: Gunnella R. , Veuillen J. Y. , Berthet A. , Nguyen Tan T. A.
Published: August 2003

The atomic and electronic structures of clean 6H–SiC(0001) surfaces have been investigated by means of LEED and photoelectron spectroscopies (XPS, XAES and UPS). First a clean surface having the (3 × 3) structure has been obtained by heating the sample at 800°C under a low Si flux. Successive annealings in UHV have produced two other stable reconstructions, namely the [Formula: see text] and the [Formula: see text]. The various surface structures show distinctive core-level and Auger line shapes, which are characteristic of the composition of the surface layer, as checked by the XPS intensities by two different excitation sources (Mg Kα and Zr Mζ), while UPS spectra show sizeable differences in the character of the valence bands. The evaluation of the atomic composition is able to sort between different models proposed in the literature.
Structure of 6H–SiC(0001) Surfaces from AB-Initio Calculations
Authors: Sabisch M. , Krüger P. , Mazur A. , Pollmann J.
Published: August 2003

We report the results of ab-initio calculations of structural properties of hexagonal 6H–SiC(0001) surfaces. The calculations have been carried out self-consistently within local density approximation employing supercell geometries, smooth norm-conserving pseudopotentials in separable form and Gaussian orbital basis sets. We have investigated several structural models for adatom-induced [Formula: see text] reconstructions with adsorbed Si or C adatoms or trimers residing in threefold-symmetric T 4 or H 3 positions above Si- or C-terminated substrate surfaces, respectively. In the case of the Si-terminated substrate surface our results favor Si adatoms in T 4 sites as optimal configuration in very good agreement with experimental data. For the C-terminated substrate surface our results indicate that none of the investigated [Formula: see text] adatom or trimer configurations is the optimal surface structure.
Scanning Tunneling Microscopy Study of Single Domain β-SiC(100) Surfaces: Growth and Morphology
Authors: Semond F. , Douillard L. , Soukiassian P. , Mayne A. , Dujardin G. , Di Cioccio L. , Jaussaud C.
Published: August 2003

We investigate single domain β-SiC(100) thin film surfaces epitaxially grown on a vicinal (4°) Si(100) surface by atom-resolved (filled and empty states) scanning tunneling microscopy (STM). Contrary to previous beliefs, we observe high quality surfaces having a low density of defects. The β-SiC(100)-(3×2) surface, which is a Si-rich surface, is achieved by sequences of Si deposition and surface annealings. This results in the growth and coalescence of large Si islands and/or vacancies islands having the 3×2 array. Our results indicate the formation of asymmetric Si-Si dimers all tilted in the same direction and forming rows in a 3×2 arrangement at a 1/3 Si mon/layer coverage.
Composition and Structure of β-SiC(100)-(2 × 2) Surfaces Monitored by Photoemission Spectroscopy using Synchrotron Radiation
Authors: Douillard L. , Semond F. , Soukiassian P. , Dunham D. , Amy F. , Rivillon S. , Hurych Z.
Published: August 2003

We investigate the single domain β-SiC(100)-(2 × 1) surface reconstruction by core level and valence band photoemission spectroscopies using synchrotron radiation. Specific spectral features at the Si 2p and C 1s core levels including bulk and surface core level shifts, and in the valence band, bring experimental evidence of reproducible β-SiC(100)-(2 × 1) structures having different Si/C compositions ranging from Si-terminated to Si- + C-containing surfaces.
An ISS Study of Ga-Dimer Arrangement in the GaP(001)-(4 × 2) Surface
Authors: Oishi N. , Shoji F. , Konishi A. , Naitoh M. , Nishigaki S.
Published: August 2003

A GaP(001) Ga-rich surface produced by ion sputtering followed by annealing exhibited a 4 × 2 LEED pattern with half streaks in the [110] direction. We have studied the structure of this surface by low-energy ion-scattering spectroscopy (ISS) using alkali ions ( Na +) .We have found a unit cell of the 4 × 2 structure consisting of two Ga dimers plus two dimer vacancies from the measured incidence-angle dependence of the scattered-ion intensity in the [Formula: see text] surface azimuth and an atomic separation in the Ga dimer being about 0.27 nm from that in the [110] surface azimuth. Evidence is presented showing the unit structures being arranged irregularly in the [Formula: see text] direction around the twofold positions.
Structural and Spectroscopic Investigation of the In-Terminated InAs(100) (4 × 2)/c(8 × 2) Reconstruction
Authors: Kendrick C. , Kahn A. , Le Lay G.
Published: August 2003

We investigate the In-rich (4 × 2)/c(8 × 2) reconstruction of InAs(100) via low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). LEED shows a highly ordered surface with a mixture of (4 × 2) and c(8 × 2) phases. Atomic-resolution STM images are consistent with a previously proposed model for the (4 × 2) surface where the unit cell contains one In dimer in the first layer and two In dimers in the third layer. A defect identified at the transition between (4 × 2) and c(8 × 2) phases appears as two bright spots located in the middle of the top In-dimer rows in filled-state images. The spots are absent in empty-state images but are replaced by intensity due to empty In dangling bonds. We discuss possible origins of this defect based on either the presence of excess In or a sulfur dopant atom.
TED Study of Si(113) Surfaces
Authors: Suzuki T. , Minoda H. , Tanishiro Y. , Yagi K.
Published: August 2003

A TED study of Si(113) surfaces was carried out. Reflections from the 3 × 2 reconstruction were seen at room temperature, while half-order reflections were very faint. The surface showed the phase transition between the 3 × 1 and the disordered (rough) structures at about 930°C. The (113) surface structure at room temperature was analyzed using TED intensity. Four kinds of structure models proposed previously, including both the 3 × 1 and the 3 × 2 reconstructed structures, were examined. The R-factors calculated using the energy-optimized atomic coordinates are not sufficiently small. After minimization of the R-factors, Dabrowski's 3 × 2 structure model is most agreeable, while Ranke's 3 × 1 and 3 × 2 structure models are not to be excluded. STM observation showed that the surface is composed of small domains of the 3 × 2 structure.
Cs and Oxygen Adsorption on Ge(001) and GaAs(001) Surfaces Studied by Metastable De-Excitation Spectroscopy
Authors: Yamada K. , Nishigaki S. , Naitoh M.
Published: August 2003

Metastable de-excitation spectroscopy (MDS) has been employed to elucidate the local electronic structure of oxygen plus alkali metal (Cs) coadsorbed layers on Ge(001)-(2×1) and GaAs(001)-(4×2) surfaces. Upon admission of oxygen at about 0.05–0.6 L, the MDS emission intensity due to Cs 6s-induced states [Formula: see text] mostly decreased, indicating direct transfer of [Formula: see text] electrons to oxygen. This initial step is followed by a steady process of substrate oxidation irrelevant to alkali charge transfer. Alkali-promoted oxygen uptake processes are discussed in connection with substrate-dependent variations in the [Formula: see text] charge states measured by MDS.
Surface Reconstruction of (123) and (111) Ge(Sn) Solid Solutions Induced by Tin Segregation
Authors: Rolland A. , Rouabah A. , Cabané F.
Published: August 2003

We present a comparative study of tin segregation onto the (123) and (111) surfaces of a Ge(Sn)- 0.5 at. % bicrystal using the AES technique. Between 350°C and 450°C, the maximum segregated tin amount, about 1.25 monolayer, does not vary with the orientation of the surface or the temperature. This indicates that attractive Sn-Sn forces are involved in the segregated phase which is in fair agreement with the Ge-Sn phase diagram. The shape of the kinetic curves depends on the orientation. On the (111) surface, the formation of various structures in equilibrium with the bulk is correlated with surface reconstructions. First, Sn atoms take the place of Ge adatoms to form a 2D phase; then, Sn segregates in other superficial sites, which leads to the nucleation of denser 2D phases, such as (7 × 7) structure. On the (123) surface, Sn atoms take the place of Ge atoms in quasisubstitutional sites of the superficial layers; the kinetics of surface segregation is not sensitive to sub monolayer structures.
Epitaxy of 3d Metals on Semiconductors
Authors: Jin Xiaofeng
Published: August 2003

Growth of fcc Mn on GaAs(001), as an example of the lattice-mismatched epitaxy of 3d metals on semiconductors, has been studied using reflection high energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) and the high resolution transmission electron microscope (HRTEM). The result shows that the interface structure plays a critical role in the epitaxial growth of 3d metals on semiconductors. A new recipe is proposed to search for more epitaxially grown 3d metal phases.
Growth of Cobalt on GaAs(001) Studied by Photoemission and Photoelectron Diffraction
Authors: Ababou S. , Lépine B. , Pingel R. , Godefroy A. , Quémerais A. , Guivarch A. , Jézéquel G.
Published: August 2003

Co ultrathin films of increasing thickness (1–40 ML) are deposited on MBE grown GaAs(001) (As 2×4) substrates at RT and 200°C and studied by integrated photoemission and photoelectron diffraction. Co appears to grow on a reocted layer whose thickness strongly depends on deposition temperature (up to 4 nm at 200°C). This interfacial reacted layer appears to exhibit a layered structure composed of two compounds.
Band Bending and Surface States of Cs/GaAs Studied by XPS
Authors: Fujii J. , Tamura K. , Ishizuka S. , Sato T. , Mizoguchi T.
Published: August 2003

Photocurrent and work function of Cs/GaAs and band denging at the interface are measured at room temperature for p-type GaAs clean surfaces with different surface treatments [cleaved GaAs(110); sulfur-passivated GaAs(001); GaAs(001) cleaned by Ar + ion bombardment and annealing]. The photoemission intensity depends on the initial surface treatments of GaAs. Both work function and band bending which influence the photoemission intensity also depend on the surface treatments and the behavior of photoemission intensity is qualitatively explained by them.
The Atomic Structure of the UO2 (111) Surface and the Effects of Additional Surface Oxygen Studied by Elevated Temperature STM
Authors: Muggelberg C. , Castell M. R. , Briggs G. A. D. , Goddard D. T.
Published: August 2003

The structure of the UO 2+x (111) surface has been investigated by elevated temperature STM. Images of atomic terraces reveal two different types of surface termination. One of them corresponds to the stoichiometric UO 2 (111) surface and can be resolved atomically in empty state images above ~ 1.6 V sample bias. The observed (1 × 1) ordering is thought to be due to uranium states because its occurrence corresponds to the bottom of the empty uranium 5f band. On these terraces mobile oxygen forms a local [Formula: see text] superstructure. The other terrace type observed on top of the UO 2+x (111) surface is thought to be a phase of a higher uranium oxide which has grown epitaxially.
Determination of the α-Ai2O3(0001) Surface Relaxation and Termination by Measurements of Crystal Truncation Rods
Authors: Guénard P. , Renaud G. , Barbier A. , Gautier-Soyer M.
Published: August 2003

We have investigated the unreconstructed (0001) surface structure of sapphire (α- Al 2 O 3) by grazing incidence X-ray scattering. Modulations along the crystal truncation rods were analyzed in order to determine the chemical nature of the terminating plane, and the structural relaxations of the first few atomic planes below the surfoce. The most likely model yields a single Al layer termination with relaxations of the first four planes of -51%, +16%, -29% and +20% respectively. These results compare well with the most recent theoretical calculations on this surface.
One-Dimension Chains of Structural Defects on the Surface of Sapphire and their Role in Adsorption of Alkali Atoms
Authors: Bonch-Bruevich A. M. , Vartanyan T. A. , Maksimov Yu. N. , Przhibelskii S. G. , Khromov V. V.
Published: August 2003

Alkali adsorption on the (0001) surface of the monocrystalline α- Al 2 O 3 was studied by means of laser-simulated desorption. It was found that alkali atoms are adsorbed mostly on the centers with the surface concentration of about 1013  cm -2. Although the temperature dependence of surface coverage is consistent with the conventional Langmuir model for adsorption on the isolated centers, the estimated adsorption energy of about 1 eV is too large to account for the quantum yield of the photodesorption process, which is as high as 5 ×10-5. To resolve this contradiction we assumed that adsorption centers make up chains along the steps on the surface. Lateral interactions between neighboring adatoms were accounted for by means of methods developed for the Ising model. Theoretical results are in agreement with the experiment.
[001] Surface Structure in SrTiO3 — Atomistic Study
Authors: Heifets Eugene , Dorfman Simon , Fuks David , Kotomin Eugene , Gordon Alex
Published: August 2003

Thin superconducting films attract great attention as a promising material for plenty of applications. The surface determines most of the physical properties of these films. We studied the polarization effect for the [001] surface of perovskite ABO 3 superconducting crystals on the example of SrTiO 3. Optimization of the ion positions in several surface layers is provided. These ions are placed in the external field of the rest crystal. The interaction between ions is described by means of the shell model technique. We show that Ti +4, Sr 2+ and O -2 ions displace differently from their crystalline sites, which leads to the creation of a dipole moment in the near-surface region.
X-Ray Photoelectron Study of Surface of Superconductive Y-Ba-Cu-O as Dependent on Cleaning, Temperature, Composition and Doping
Authors: Shabanova I. N. , Popova O. V. , Kukuev V. I. , Kormilets V. I.
Published: August 2003

The core level X-ray photoelectron spectra of the high-temperature superconductor system YBa 2 Cu 3 O x are studied in dependence on the oxygen composition x, temperature of the sample, doping by Ag and quality of cleaning the sample surface. Nowadays there are many X-ray photoelectron investigations, but comparative investigations of electron structure in superconductive and unsuperconductive states are absent in the majority of them. The X-ray electron magnetic spectrometer used in our work allows one to obtain spectra in the temperature range from room temperature to the temperature of liquid nitrogen with simultaneous mechanical cleaning of the sample surface from the contaminations and degraded layers. Thus the obtained results are unique and allow one to obtain for the first time the following conclusions. Three charge states of copper atoms are shown to exist in this system — Cu 1+, Cu 2+ and Cu 3+ — but only the Cu 2+ state plays the main role in the transition of the system to the superconductive state. New peaks arise in O1s, Ba3d and Ba4d spectra after the transition of the system to the superconductive state, which implies the changes in the surroundings of O and Ba atoms in this state. In Ag-doped samples similar changes in X-ray photoelectron spectra are observed and they are even more pronounced than in the undoped ones.
Acetylene C2H2 Adsorbed onto MgO(001): Structure and Thermodynamics
Authors: Ferry D. , Suzanne J. , Hoang P. N. M. , Girardet C.
Published: August 2003

Structural and thermodynamical LEED experiments were performed on MgO(001) single crystal cleaved in situ under ultrahigh vacuum conditions within the temperature range of 40–94 K. We observe a commensurate (2 × 2) herringbone structure containing two molecules and having two glide planes. The isosteric heat of adsorption Qst = 6.9 ± 0.4   kcal · mole -1 and lateral interoction energy Q// = 3.1 ± 0.4  kcal · mole -1 have been measured and compared with semiempirical potential calculations. The influence of the molecular motions on the calculated isosteric heat of adsorption is evaluated to take into account temperature effects.
Variation of the Local Work Function of MgO(001) Surface by Palladium Deposition
Authors: Di Salvo J.-P. , Gillet E.
Published: August 2003

A study of ultrathin palladium films deposited on MgO(100) is reported. The early studies of the growth are in situ investigated at 300 K and 600 K by secondary ion mass spectrometry used in static mode (SSIMS). The variation of ion species typical of the metal deposit ( Pd +, [Formula: see text]) and of the substrate ( MgO +) is analyzed as a function of the deposit mean thickness. The results show that Pd films grow initially by sticking of isolated adatoms on sites leading to the formation of 2D islands until a critical coverage which depends on the temperature. Thereafter a second layer begins to grow that leads to 3D flat clusters at high temperatures. The SSIMS method enables us to determine quantitatively the local work function of both palladium and MgO surfaces. Changes in the electronic structure of these systems during deposition of the two first Pd layers suggest a strong influence of the oxide support.
Comparison of Cu-MgO Interfaces Studied by EXES and XPS
Authors: Jonnard P. , Hombourger C. , Vergand F. , Bonnelle C. , Ealet B. , Renou A. , Gillet E.
Published: August 2003

With the aim of studying the physicochemical interactions in metal-ceramic interfaces, we have investigated the Cu-MgO system. Two kinds of interfaces prepared at room temperature have been studied: interfaces during their formation (studied by X-ray photoelectron and Auger spectroscopies — XPS, AES) and buried interfaces (studied by electron-induced X-ray emission spectroscopy — EXES). Auger parameter results reveal a Cu(I) state for copper and point out, by comparison with the Cu-NaCl interface, that the oxidation comes from an interaction at the interface. EXES studies of the oxygen and copper valence densities of states evidence that the same kind of interaction exists at the interface between thick films of Cu and MgO and it does not exceed one interatomic distance.
SSIMS and XPS Studies of Reconstruction of Alumina-Supported Rh Particles
Authors: Stará I. , Di Salvo J.-P. , Nehasil V. , Matolín V. , Gillet E.
Published: August 2003

Rhodium particles were vapor-deposited on (-1012) α-alumina and polycrystalline γ-alumina substrates. Variations of morphological parameters during the growth and/or thermal annealing in vacuum, oxygen and CO atmosphere have been investigated by means of static SIMS and XPS. The ratios of Rh/substrate ion species and the Rh 3d electron binding energy variations indicated changes in metal coverage given by particle size and dispersion variations. The heating of as-deposited particles in vacuum led to the particle coalescence. On the other hand the oxygen interactions with particles gave an increase of particle dispersion.
Chemisorption Geometry, Vibrational Spectra, and Thermal Desorption of Formic Acid on TiO2(110)
Authors: Chambers S. A. , Henderson M. A. , Kim Y. J. , Thevuthasan S.
Published: August 2003

We have used high-energy X-ray photoelectron spectroscopy and diffraction (XPS/XPD), low-energy electron diffraction (LEED), high-resolution electron energy loss spectroscopy (HREELS) and temperature-programmed desorption (TPD) to determine the molecular orientation, long-range order, vibrational frequencies, and desorption temperatures for formic acid and its decomposition products on TiO 2(110). Molecular adsorption occurs at coverages approaching one monolayer, producing a weakly ordered (2 × 1) surface structure. High-energy XPD reveals that the formate binds rigidly in a bidentate fashion through the oxygens to Ti cation rows along the [001] direction with an O–C–O bond angle of 126 ± 4°. During TPD some surface protons and formate anions recombine and desorb as formic acid above 250 K. However, most of the decomposition products follow reaction pathways leading to H 2 O , CO and H 2 CO desorption. Water is formed in TPD below 500 K via the abstraction of lattice oxygen by deposited acid protons.