The dynamics of domain growth in intercalation compounds has been investigated using computer simulations. The system has been modeled as sheets of two-dimensional diffusive lattice gas with attractive interactions within the sheets and repulsive interactions between atoms in adjacent sheets. The atoms enter the ‘‘crystal’’ from a reservoir at one edge. For a stage-2 phase with alternate-layer occupancy the results show a fingerlike domain formation which propagates in from the crystal edge. As fingers propagate into the crystal, the length scale increases via a merging mechanism. Finger formation and merging is also seen during simulations of deintercalation of a filled crystal. The results are in qualitative agreement with stage-2 intercalation domains reported previously in Ag-intercalated ${\mathrm{TiS}}_2$.

The scaling of island-size distribution of an epitaxially grown 1×1 Fe film on a Au (001) surface as a function of coverage was observed using high-resolution low-energy electron diffraction. The scaling function extracted from the intensity distribution of integer-diffracted beams is best described by a γ function. The island density is almost a constant in the aggregation growth regime. The forms of the scaling function and the island density are in qualitative agreement with recent simulations of molecular-beam-epitaxy growth.

We present a theory for extended x-ray-absorption fine structures (EXAFS) measured in the x-ray Raman-scattering mode. Spectra of such structures can be obtained by scanning the frequency of the exciting x-ray photons over the EXAFS region while fixing the detector frequency to an emission resonance. It is shown that these spectra in addition to the structure-determining features of ordinary EXAFS allow us to obtain orientational information, that is, to obtain data on both bond lengths and on orientations of bonds. We derive the explicit dependence of spectral features on the angles between the bond direction and the dipole moment direction of an x-ray-emission transition. Since each resonance frequency is associated with a specific direction of the transition dipole, rich possibilities prevail for orientational information within a molecular framework. We show that measurements of extended x-ray-absorption fine structures in the x-ray Raman-scattering mode also allow us to obtain bond angles of disordered systems such as glasses or free molecules, for which conventional x-ray-diffraction methods do not apply. A comparative discussion is given on the prospects of EXAFS experiments in the nonradiative (Auger) scattering mode.

Medium-energy ion-scattering measurements and Monte Carlo simulations have been used to study the Al(001) surface as a function of temperature. Surface melting does not occur and the surface stays well ordered up to the bulk melting point ${\mathit{T}}_{\mathit{m}}$=933.52 K. The combination of the effective-medium potential, used to simulate the interacting Al atoms, and ion-scattering calculations on the simulated Al(001) surface, reproduces the ion-scattering intensities very well. The Monte Carlo simulations show that the surface relaxations and the vibration amplitudes both display strongly anharmonic behavior which extends several layers into the crystal and increases with increasing temperature.

We have calculated the ${\mathbf{k}}_{\mathrm{\parallel }}$-, symmetry-, and layer-resolved density of states (DOS) at ${\mathbf{k}}_{\mathrm{\parallel }}$=0 for Pd and Rh (001) surfaces. For the xy and ${\mathit{x}}^2$-${\mathit{y}}^2$ subbands, which do not hybridize with any other low-lying orbitals, the resulting DOS closely resembles that of a one-dimensional semi-infinite chain of nondegenerate tight-binding atomic orbitals perturbed by a repulsive potential at the terminal site. It displays interference induced oscillations and bound states or resonances of particular simplicity.

We have studied the surface behavior of the Blume-Emery-Griffiths model within the mean-field approximation, interpreting the model as a lattice gas. The solid surface exhibits a series of first-order layering transitions, and wetting phenomena are found all along the first-order part of the solid-liquid bulk coexistence line. We present a complete phase diagram of the solid surface and discuss the various kinds of surface behavior observed near bulk melting.

The model of a semi-infinite uniaxial crystal with a flat surface is reexamined. The surface-energy-loss function for uniaxial crystals, which generalizes the conventional expression Im-1/[1+ɛ(ω)], is derived. We demonstrate that in uniaxial crystals the three-dimensional charge-density oscillations can be excited by incident electrons, which do not penetrate into the bulk but are reflected at or above the surface plane. This effect is altogether due to the system anisotropy and it is inhibited in cubic crystals or homogeneous isotropic media. The implications of the theory are compared with the electron-energy-loss data for graphite.

Scanning-tunneling-microscopy methods are presented, which allow us to determine the adatom yield, the number of adatoms created per primary ion, and the sputtering yield. The reliability and the possible errors of the scanning-tunneling-microscope yield-determination methods are analyzed. For noble-gas ions normally incident on Pt(111), the dependence of adatom and sputtering yields on ion energy and ion mass are determined. The dependence of the adatom yield on these quantities is not in agreement with previous theoretical predictions. Possible mechanisms for the observed ion-energy and ion-mass dependence of the adatom yield are suggested. The observation of the damage patterns of single keV ion impacts and the lateral distribution of the damage features gives additional information on the damage mechanism.

Molecular-dynamics simulations are presented of defect formation in rare-gas ion bombardment of a Pt(111) surface with energies between 100 and 3000 eV, with a particular emphasis on adatom formation. Formation and equilibration of adatoms take considerably more time than sputtering, namely, between 1 and 10 ps for the systems studied. Adatoms have a considerable probability of originating from deeper than the first layer, e.g., 40% for 3-keV Xe bombardment. For energies above several hundred eV, a factor of 2–4 more adatoms than sputtered particles are found; at smaller energies this ratio is even higher. This behavior can be explained by assuming a lower barrier for adatom formation than for sputtering. The trends of adatom formation with bombarding energy and bombarding particle species coincide with recent experiments by Michely and Teichert [Phys. Rev. B 50, 11 156 (1994)].

Using an approximate kinetic-energy functional, we have performed total-energy calculations on bulk and surface Si. The scheme is based on the Thomas–Fermi–von Weizsäcker approximation of the kinetic-energy functional. The method is applied to the ground-state configuration of c-Si and H/Si(100) surfaces. The results are compared with those of experiments and detailed Kohn-Sham-Car-Parrinello type calculations. Encouraging agreement is found. We also compare our results with those obtained using the simpler Thomas-Fermi form of the kinetic-energy functional. In general, the von Weizsäcker correction improves the results.

One-electron spectral functions for a one-dimensional continuum model including electron-phonon coupling are calculated exactly. The electrons coupled to the phonons represent a Luttinger liquid. Results are presented for an Einstein model for spinless electrons and for the model including spin. Apart from Luttinger-liquid features, the spectra show a rich satellite structure with peak separations partially determined by matrix-element effects. The use of Migdal’s approximation neglecting vertex corrections fails to reproduce the exact spectra even for an effective bandwidth large compared to the phonon frequency. The relevance to high-resolution valence photoemission from quasi-one-dimensional conductors is discussed.

The Fermi surface (FS) of the noble metals has been studied theoretically in order to compare calculations based on a full-potential technique to calculations based on atomic-sphere approximation (ASA). Also, the effect of replacing the local-density approximation (LDA) with the generalized gradient approximation (GGA) for the exchange-correlation potential has been studied here. In the present work we have used the generalized gradient approximation derived by Perdew and Wang (PW91). We find that replacing the ASA with a full potential causes a larger modification of the calculated FS, compared to replacing the LDA with the GGA. Our calculations demonstrate that full-potential calculations combined with the LDA improve the FS of Cu and Ag relative to the results of the atomic-sphere approximation. If the full-potential method is combined with PW91 one obtains further improvements for these two metals. For Au, the full-potential calculations, based on LDA or GGA, do not give any improvement over results obtained from the atomic-sphere approximation.

Magnetoplasma modes localized near the edge of a two-dimensional electron gas with a nonabrupt edge density profile are investigated within a simple classical approximation. Two distinct groups of edge magnetoplasmons are found. The high-frequency modes occur only for finite values of the wave vector q along the edge; they are the higher multipole edge modes that occur when the magnetic field B=0. The low-frequency modes have frequencies ω(q) that approach zero as q approaches zero. They exist only for finite values of B and propagate in only one direction along the edge for a given direction of B.

In a recent paper [Phys. Rev. B 48, 18 031 (1993)], Patel and co-workers described hydrostatic-pressure-dependent photoluminescence measurements performed on ${\mathrm{Ga}}_{0.47}$${\mathrm{In}}_{0.53}$P/${\mathrm{Al}}_{0.5}$${\mathrm{In}}_{0.5}$P multiple quantum wells. They determined directly a valence-band offset of 0.24±0.05 eV from the energy difference between the indirect transition in the barrier and the transition from X states in the barrier to hh1 valence-band states in the quantum well, when extrapolated to zero pressure. The conduction-band offset was then indirectly determined to be 0.26 eV from the total-band discontinuity of the system, assuming a value of 2.45 eV for the (low temperature) lowest-energy direct gap of ${\mathrm{Al}}_{0.5}$${\mathrm{In}}_{0.5}$P. This yields a band-offset ratio, Δ${\mathit{E}}_{\mathit{c}}$:Δ${\mathit{E}}_{\mathit{v}}$, of 52:48. Here, we present evidence that the (5 K) direct gap of the ${\mathrm{Al}}_{0.5}$${\mathrm{In}}_{0.5}$P barrier is ∼2.685 eV, which results in a revised band-offset ratio of 67:33, similar to recent values determined for ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{In}}_{\mathit{x}}$P/(${\mathrm{Al}}_{\mathit{y}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$${)}_{0.5}$${\mathrm{In}}_{0.5}$P heterojunctions.

We have calculated magnetoresistances of an H-shaped quantum-wire structure by using the mode-matching technique. We have observed that anomalous Hall-resistance plateaus with accompanying anomalous longitudinal-resistance plateaus exist in relatively low magnetic fields as precursors of integer Hall plateaus. We attribute the appearance of the anomalous magnetoresistance plateaus to the unique scattering mechanisms at t junctions of the H-shaped structure together with the symmetrical geometry of the structure. We have also identified different resonance patterns on the anomalous plateaus and the integer plateaus.

The hierarchy theory of the fractional quantum Hall effect (FQHE) is formulated in two structurally identical ways, where two sets of trial wave functions are written hierarchically for the incompressible FQHE states as well as other low-energy states. In one formulation, the hierarchical trial wave functions for ν=n/[n(${\mathit{m}}_{\mathit{L}}$-1)+1] FQHE states are shown to be the same as those given by the nonhierarchical composite fermion theory. A state-to-state comparison shows that the two formulations presented in this paper are physically equivalent.

We report an oxygen-induced metastable ordered structure on a Si(001) surface. The c(4×4) structure is obtained after extensive annealing of a clean Si(001)-2×1 surface dosed with oxygen at room temperature. This c(4×4) structure appears only after the completion of the 2×1 structure, which disappears in the early annealing stage. The c(4×4) structure reverts back irreversibly to the 2×1 structure after the surface is heated to above 720 °C. Possible structural models for the c(4×4) reconstruction are discussed.

We have observed several reconstructions on a Si(100) surface with different annealing procedures. The observed reconstructed phases are the coexistence of the (2×2) phase and the (2×8) phase after high-temperature (≳950 K) annealing followed by quenching, and the half-order streak with the presence of the (2×1) phase after low-temperature (≲950 K) annealing. The phase transition from the metastable (2×2) and (2×8) phases to the stable half-order streak is reversible upon annealing temperature and cooling rate. The distribution of kinks and missing dimer defects is expected to be the main cause of these reconstructions.

Second-harmonic generation (SHG) from ${\mathrm{SiO}}_2$/Si(111) interfaces was studied. The SHG intensity was measured as a function of azimuthal rotation angle for a 45° incident, s-polarized YAG laser beam (where YAG denotes yttrium aluminum garnet). An interface with a 500-Å thermal-oxide film showed an asymmetric rotational dependence. However, the asymmetry disappeared after hydrogen annealing, whereas the asymmetry did not change for nitrogen annealing. The asymmetry is caused by the nonlinear susceptibility ${\mathrm{\chi }}_{\mathit{z}\mathit{x}\mathit{x}}^{\mathrm{}\left(2\right)\mathrm{}}$. Hence, the difference between hydrogen and nitrogen annealing shows that ${\mathrm{\chi }}_{\mathit{z}\mathit{x}\mathit{x}}^{\mathrm{}\left(2\right)\mathrm{}}$ decreases by annealing with hydrogen. Because ${\mathrm{\chi }}_{\mathit{z}\mathit{x}\mathit{x}}^{\mathrm{}\left(2\right)\mathrm{}}$ reflects the local potential asymmetry along the interface normal direction, the decrease of the asymmetry is related to the passivation by hydrogen of interfacial dangling bonds in this direction. This means that the ${\mathrm{SiO}}_2$/Si(111) interface has an intrinsic interface dangling bond normal to the interface which is detectable as a ${\mathrm{\chi }}_{\mathit{z}\mathit{x}\mathit{x}}$ contribution to the interface SHG.

Using the first-principle ab initio pseudopotential method and the Bardeen transfer Hamiltonian approximation, we have calculated scanning-tunneling-microscopy images of the fully relaxed GaAs(001) β(2×4) and β(4×2) surfaces. Our calculation included a four-atom Al cluster to represent the tip. We present the results that we obtained for these two different surfaces at different tip-surface bias voltages and discuss the relationship between the simulated scanning-tunneling-microscopy images and the surface charge density within the given energy range with respect to the Fermi level.