Using the linear muffin-tin orbitals in the atomic-sphere approximation with the local-density approximation (LDA), we studied the electronic structure and Schottky-barrier height (SBH) of the Si interface with metal silicides: ${\mathrm{CoSi}}_2$, ${\mathrm{NiSi}}_2$, and ${\mathrm{YSi}}_2$. We used large supercells with 9 ${\mathrm{Si}}_2$ and 8–10 silicide (${\mathrm{CoSi}}_2$, ${\mathrm{YSi}}_2$) layers for the (111) interface and with 11 ${\mathrm{Si}}_2$ and 11 silicide (${\mathrm{NiSi}}_2$, ${\mathrm{CoSi}}_2$) layers for the (001) interface. Together with our previous calculations on the two types of ${\mathrm{NiSi}}_2$/Si(111) interfaces, we demonstrate that the LDA calculation with a large supercell correctly reproduces the dependence of experimental SBH’s on the interface structure and type of metal silicide. Electron transfer at the silicide-Si interface depends significantly on the atomic structure of the interface, especially the interfacial space, whether atoms are crowded or not. The energy distribution of interfacial gap states varies significantly with interface atomic structures. These electronic structures directly depend on the interface atomic structure; in contrast the calculated SBH’s do not always depend on the interface structure. We discuss the underlying mechanisms for the formation of Schottky barriers.

The electronic subband structure of periodically n-type δ-doped silicon is calculated self-consistently within the local-density approximation. Two types of energy levels are distinguished, one due to valleys transverse to the superlattice axis, and the other due to longitudinal valleys. Minibands, potential profiles, miniband occupancies, and Fermi-level positions are studied and their dependence on the spacing d between δ layers and the doping concentration ${\mathit{N}}_{\mathit{D}}$ is obtained. Pronounced changes with increasing ${\mathit{N}}_{\mathit{D}}$ and decreasing d are observed. For d>150 Å, and ${10}^{13}$≤${\mathit{N}}_{\mathit{D}}$<${10}^{15}$ ${\mathrm{cm}}^{\mathrm{-}2}$, the system behaves as a set of practically independent isolated δ-doped wells. Significant dispersion of the higher subbands takes place for d lower than 150 Å. The transition from a multiple-δ-doped-well behavior to a superlattice regime is observed for doping concentrations >2.0×${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ and periods d<50 Å. The twofold degeneracy of longitudinal levels and the fourfold degeneracy of transverse levels are removed by the many-valley coupling. The corresponding splitting energies are calculated.

Low-voltage breakdown of the quantum Hall effect is considered in narrow quasi-two-dimensional channels subjected to a strong perpendicular magnetic field. The interaction of electrons with acoustical (deformation or piezoelectric) phonons leads to a substantial dissipation at the edges of the channel, due to electron transitions between the edges states. It is the main dissipation if the channel width W is not too large. Nonheating negative differential conduction, ${\mathit{dj}}_{\mathit{x}}$/${\mathit{dE}}_{\mathit{x}}$<0, when an electric field ${\mathit{E}}_{\mathit{x}}$ is applied along the channel, is possible for drift velocities ${\mathit{v}}_{\mathit{D}}$ smaller (${\mathit{v}}_{\mathit{D}}$<s) or much smaller (${\mathit{v}}_{\mathit{D}}$≪s) than the speed of sound s as well for ${\mathit{v}}_{\mathit{D}}$>s. The current-voltage characteristic (CVC) ${\mathit{j}}_{\mathit{x}}$=${\mathit{j}}_{\mathit{x}}$(${\mathit{E}}_{\mathit{x}}$), evaluated numerically for a number of qualitatively different cases, is substantially nonlinear if ${\mathit{v}}_{\mathit{D}}$ is not too small. The results are in good agreement with the experimental results by von Klitzing et al. for low breakdown velocities (${\mathit{v}}_{\mathit{D}}$∼s/20) in metal-oxide-semiconductor (MOS) structures. An increase by orders of magnitude in the dissipation, before breakdown, as observed, e.g., by Komiyama et al. is explained as well. The anisotropy of the electron-phonon interaction in MOS structures and its substantial influence on the CVC and breakdown velocities is also considered. The dissipation depends very strongly on the frequency Ω of the confining potential if ${\mathit{v}}_{\mathit{D}}$ is not too large. In contrast with Martin and Feng [Phys. Rev. Lett. 64, 1971 (1990)], for sufficiently small Ω, an exponential suppression of the dissipation occurs due to intralevel-intraedge acoustic-phonon-assisted transitions.

We present a theoretical study of the dielectric response and collective excitations of a two-dimensional system of bosons interacting via a dipolar interaction. The model is designed to simulate the situation occurring in semiconductor double quantum well systems under strong electric fields perpendicular to the layers. The field produces a net polarization of photoexcited electron and hole carriers and favors the appearance of long-lived polarized excitons. This gas of interacting point dipoles shows interesting features and we study the effects of low dimensionality and statistics. Well-defined density-fluctuation excitations appear at low temperatures with a linear dispersion relation at long wavelengths. The low dimensionality of the system gives rise to an effective long-ranged potential with only a faster power-law decay.

Electronic structures of short-period GaAs/AlAs superlattices in a uniform electric field along the growth axis are studied by a second-neighbor tight-binding method. Minibands of the X-band edge in AlAs show discrete energy levels, the so-called Stark ladder, as do the Γ minibands in GaAs. Electric-field-induced mixing between a Stark ladder of the Γ miniband and one of the X miniband is studied and found to depend strongly on miniband indices and superlattice structures. The optical transition probability between the Stark ladder of valence states and that of the X miniband is strongly enhanced due to the Γ-X mixing.

It is shown that in a degenerate two-dimensional electron gas (2DEG), intralevel intracenter electron transitions due to a strong impurity potential, for not too low temperatures, can lead to the observed activated behavior of the resistivity in micrometer-, or submicrometer-width parabolic channels. This contribution is exponentially suppressed if the Fermi level is not too close to the bottom of the nearest Landau level. As the temperature decreases, at fixed confining potential, this activated behavior is changed to a temperature-independent behavior that is usual for elastic scattering of the degenerate 2DEG. The latter is related with intralevel interedge electron transitions. The asymmetry of the Shubnikov–de Haas oscillations and their dependence on confinement and temperature are obtained in agreement with experimental observations.

In the vicinity of the Coulomb-blockade threshold, quantum fluctuations of the charge strongly influence the energy spectrum of small metallic junctions. We develop a nonperturbative calculation of the junction ground-state energy and evaluate the junction charge in the limit of a small junction conductance. Close to the Coulomb-blockade threshold this charge is effectively screened due to intensive virtual electron tunneling. We also describe level splitting close to the edges of the Brillouin zone and show that the electron tunneling rate can be substantially suppressed due to quantum fluctuations of the charge. As a result the junction current-voltage characteristic becomes non-Ohmic near the Coulomb gap.

The optical anisotropy in the layer plane of (100) InAs/AlSb superlattices was investigated by ellipsometry and by reflection difference spectroscopy. The superlattices are anisotropic in the (100) plane with the dielectric function along the [011] and [011¯] axes differing by as much as ∼5% in the energy range from 2 to 4 eV. The anisotropy in superlattices with either only AlAs or only InSb interface bonds is attributed to a reduction of the ${\mathit{D}}_{2\mathit{d}}$ symmetry of a perfect structure due to differences between the interfaces where InAs is grown on AlSb and those where AlSb is deposited on InAs. Different mechanisms for the interface-related anisotropy are discussed.

The first stages of oxidation of thin Li films (leading to the formation of ${\mathrm{Li}}_2$O) were found to be accompanied by emission of ${\mathrm{O}}^{\mathrm{-}}$ ions as well as electrons, reflecting the participation of electronically highly excited states in this reaction. A model is proposed and supported by the results of local-spin-density-approximation cluster calculations whereby electron transfer from the metal onto the impinging ${\mathrm{O}}_2$ molecule leads to formation of a transient ${\mathrm{O}}_2$ ${}_{}{}^{2\mathrm{-}}{}_{}{}^{}$ species. This species dissociates without a noticeable activation barrier and there is a finite (but rather low) probability that one of the ${\mathrm{O}}^{\mathrm{-}}$ fragments formed near the surface is ejected into the gas phase. The ${\mathrm{O}}^{\mathrm{-}}$ species at the Li surface forms, on the other hand, a hole state, which subsequently transforms into the ${\mathrm{O}}^{2\mathrm{-}}$ ground state. For excitations larger than the work function, the energy associated with its decay (>2 eV) may be released in an Auger process associated with electron emission. The yield of light emission was found to be below the detection limit of about ${10}^{\mathrm{-}10}$ photons per reacting ${\mathrm{O}}_2$ molecule and indicates a short lifetime (<100 fs) of the ${\mathrm{O}}^{\mathrm{-}}$ species at a Li surface.

A spontaneous self-healing mechanism, called dislocation-mediated healing (DMH), is demonstrated by molecular-dynamics simulation in ideal (i.e., constrained in two dimensions) and adsorbed monolayers. The self-healing involves a rapid condensation of the vacancies into dislocation dipoles. It is complete at temperatures above the self-diffusion temperature. An associated collapse of the shear modulus similar to the Kosterlitz-Thouless dipole dissociation is observed for high vacancy concentrations. The phenomenon is observed in monolayers with a long-range interparticle interaction and is more effective as the mobility of the vacancies increases. In Lennard-Jones monolayers (LJM’s) a small compressive pressure is required to observe the effect. In a system with a longer-range potential it has been observed even with the monolayer under expansion. It also occurs in monolayers with nearest-neighbor piecewise-linear force interactions (PLFM’s) under pressure provided that a third degree of freedom is present. But in general, in PLFM’s vacancies agglomerate into clusters (voids). The same applies to LJM’s below a critical pressure which decreases with temperature and vacancy concentration. The annealing of the vacancies by the formation of voids is a slower process than DMH, usually by at least an order of magnitude.

Electron-impact-induced Auger spectra at energies below 30 eV were measured from epitaxial sodium films on Cu(001) from a submonolayer up to several layers and assigned to sodium LVV transitions. According to well established deconvolution and background-correction techniques, the line shape of the Na ${\mathit{L}}_{2/3}$VV transition could be used to determine the sodium valence-band density of states. In agreement with photoemission investigations of the Na density of states, our results also suggest a strong narrowing of the valence band with respect to the calculated density of states for a nearly-free-electron metal. Since CVV Auger transitions cannot occur in isolated alkali-metal atoms due to the lack of a second valence s-shell electron, the onset of the Na LVV signal during the growth of the first monolayer unambiguously marks the first stage of an alkali s-level-derived valence-band-like state. Thus, the present model study of Na/Cu(001) demonstrates that CVV Auger spectroscopy can be used as a powerful method to investigate the intriguing electronic behavior during alkali-metal adsorption.

The results of a detailed study of the evolution, scaling, and percolation of islands in a model of submonolayer molecular-beam epitaxy appropriate for the case of dendritic island growth are presented. The scaling of the island density, monomer density, island-size distribution, structure factor, and pair-correlation function are studied as a function of the coverage θ and the ratio R=D/F of the diffusion rate D to the deposition rate F. Our results span the full range of coverage starting from very low coverage all the way through the coalescence and percolation regimes. For small coverages the islands are fractal while at higher coverages they become compact, similar to what has been observed in Au/Ru(0001). For large R, four distinct scaling regimes are found: a low-coverage nucleation regime, an intermediate-coverage regime, an aggregation regime in which the island density remains constant, and a coalescence and percolation regime. The scaling behavior in the first three regimes is compared with results obtained using a generalized rate-equation approach. An anomalous fractal scaling form for the structure factor in the aggregation regime is also derived. The dependence of the percolation threshold on R is also studied and found to show interesting nonmonotonic behavior.

This study utilizes Auger-electron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM) to examine sulfur coverages above ${\mathrm{\Theta }}_{\mathit{S}}$=0.25 on the Cu(100) surface. These large sulfur coverages are observed to induce a restructuring of the copper surface through the removal of copper atoms from terrace sites. The layer produced at room temperature by ${\mathrm{H}}_2$S exposures is composed of small Cu-S aggregates which do not exhibit long-range order, but which orient in the [001] and [010] directions. Heating above 873 K causes tetramer sulfur unit cells to form in a poorly ordered overlayer. Annealing to 1173 K produces a well-ordered (√17 × √17 )R14° structure which shows four sulfur atoms per unit cell in the STM images. Since the sulfur coverage of the (√17 × √17 )R14° structure has been previously measured to contain a total of eight sulfur atoms per unit cell, a structural model is proposed that is consistent with the coverage and STM measurements.

The evolution of surface structures following NO dissociative adsorption on Rh(110) has been studied as a function of N+O coverage and reaction temperature using scanning tunneling microscopy (STM) and low-energy electron diffraction. Static and dynamic STM measurements were performed at different stages of the reaction in order to examine (i) the growth mode of the N- and O-related structural units, (ii) the surface morphology of flat terraces and areas with a high step density, (iii) the kind and concentration of structural defects characteristic for the islands of (n×1)N and (1×n)O reconstructions, (iv) the nucleation and growth mechanisms in the initial stages of the reaction when the (1×n)N reconstruction dominates, and (v) the elementary steps involved in the conversion to a (1×2) reconstructed surface at high N+O coverages.

Na deposited onto the (0001) cleavage plane of 1T-${\mathrm{TaS}}_2$ is intercalated into the van der Waals gap of the layered compound. The amount of intercalated Na is dependent on such experimental conditions as deposition flux and sample temperature. The charge-density-wave related superstructure of the clean sample exhibits several phase transitions due to the electron transfer associated with the intercalation process. A metal-to-semiconductor transition is observed as a consequence of intercalation.

The electronic properties of fcc Cu(100) and Co(100) surfaces and of the Co/Cu (100) interface are studied by the surface Green function matching method and an empirical tight-binding model. The band structures and layer densities of states allow us to establish the short-range character of surface and interface-induced effects. The Co surface exhibits a slightly reduced magnetic moment. At the interface, the spin polarizations and magnetic moments for both localized d electrons and nearly free sp electrons are induced at the Cu layer.

We calculate the optical absorption of the ${\mathrm{C}}_{60}$ molecule using the singlet single-excitation approximation, which should be valid for systems such as π-conjugated polymers and fullerenes with large gaps between occupied and unoccupied bands. The low-energy part of the optical absorption of the ${\mathrm{C}}_{60}$ molecule is satisfactorily explained by our calculation. In Appendix B we show the details of how to calculate the coordinates of carbon atoms in a dimerized ${\mathrm{C}}_{60}$ molecule, since these coordinates are important in the calculation of optical absorption.

Using bosonization and renormalization-group techniques, we classify the correlation properties, ground states, and associated phase transitions for a one-dimensional translationally invariant system of interacting fermions or repulsive bosons having an arbitrary number of nontranslational degrees of freedom. Depending on the interactions, the system realizes one of several ground states: a noncorrelated gapless quantum fluid, a correlated quantum fluid of clusters formed from the original particles, or a correlated fluid of evenly distributed particles with periodic repeats of all possible permutations of the different kinds.

We exhibit a variational wave function for the orbitally nondegenerate Anderson lattice model, which incorporates the effects of onsite Coulomb interaction to deal with essentially metallic systems. The average occupation in the correlated orbitals, the renormalized hybridization matrix element, and the mass enhancement are calculated as a function of Coulomb interaction U and the hybridization matrix element V. Our results for the U→∞ limit are in agreement with the existing results for the infinite-U problem. We show that the infinite-U approximation is a good approximation for a class of materials with U>${\mathit{U}}_{\mathit{c}}$ and V<${\mathit{V}}_{\mathit{c}}$. The calculation of the effective mass ${\mathit{m}}^{\mathrm{*}}$ in the heavy-fermion regime shows that it becomes large mainly because of the small hybridization of f electrons with the conduction band rather than because of large Coulomb correlations. The advantages of our approach are briefly discussed.

The force formula of Soler and Williams is implemented in the full-potential linearized-augmented-plane-wave program wien93. The feasibility and accuracy of the method is demonstrated by calculations for the H-point phonon in Mo and Li and for the Γ-point phonon in Si and diamond.