Stochastic simulation results, appropriate for molecular-beam epitaxy, involving ballistic deposition and thermally activated Arrhenius diffusion of adatoms, are presented for one- and two-dimensional substrates, allowing for overhangs and bulk vacancies. The asymptotic Kardar-Parisi-Zhang universality is found to be triggered by a sudden nucleation of large-scale defect formation in the growing film that shows a distinct dependence on dimensionality. The prenucleation transient behavior, which may be of experimental relevance due to the low defect content, is associated with standard solid-on-solid univerality classes.

We present a detailed model describing the effects of surface stress on the equilibrium spacing and biaxial modulus of thin metal films. The model predicts that very thin films will equilibrate to a spacing in the plane substantially smaller than the bulk spacing for the material, and that this biaxial strain will vanish as the reciprocal of the film thickness. The model predicts enhancements in the biaxial modulus of thin metal films which also scale with the reciprocal of the film thickness. The magnitude of both the strain and the resulting change in biaxial modulus are proportional to the magnitude of the surface stress. We verified the predictions of the surface-stress model by performing molecular-dynamics computer simulations of thin metal films using an analytic form of the embedded-atom-method potential. The model was found to predict accurately the equilibrium properties of thin metal films.

In the adjoining paper we presented a detailed model describing the effects of surface stress on the equilibrium spacing and biaxial modulus of thin metal films. We extend the model to describe the effects of interface stress on metallic multilayers. The model predicts that very thin layers will equilibrate to a spacing in the plane smaller than the bulk spacing for the material, and that this effect will vanish as the reciprocal of the layer thickness. The model predicts enhancements in the biaxial modulus of metallic multilayers which scale with the reciprocal of the layer thickness. The magnitude of both the strain and the resulting change in biaxial modulus are proportional to the magnitude of the interface stress. In order to verify the predictions of the interface stress model, we performed molecular-dynamics computer simulations of metallic multilayers using the ‘‘universal’’ form of the embedded-atom-method (EAM) potentials, an analytic form of the EAM potential, and a slightly modified version of the analytic form. The model was found to predict accurately the equilibrium properties of metallic multilayers. We discuss the limitations of the EAM potentials and the implications of this work for the supermodulus effect.

The occupied and unoccupied electronic states of ${\mathrm{C}}_{60}$ have been studied for single monolayer and multilayer coverages on Au(110). Only the electronic structure of the first layer, which is chemisorbed, is changed by the interaction with the substrate, due to hybridization with the possibility of charge transfer. There is no measurable bonding interaction with the second layer, which has essentially the same electronic structure as the thick film. The unoccupied electronic states below the ionization level are shown to be largely localized around the ${\mathrm{C}}_{60}$ molecule. The energy levels of the molecules not in direct contact with the substrate are referenced to the vacuum level.

We show that Berry’s phase exists in the Jahn-Teller-distorted anionic and cationic fullerenes, ${\mathrm{C}}_{60}^{\pm }$. Berry’s phase helps recover the ‘‘missing’’ zero-point vibration energy by generating a finite pseudorotational angular momentum, enhances the Jahn-Teller distortion, and restores the ground-state degeneracy back to the value before distortion.

The cubic ${\mathrm{YH}}_{2+\mathit{x}}$ system with an extended hydrogen composition is studied using the pseudopotential method and the local-density-functional approximation with a plane-wave basis. The study focuses on the β phase with the metal atoms forming a face-centered-cubic lattice and the octahedral sites partially occupied by hydrogen for 0<x<1. The self-consistent total-energy calculation is performed by employing the supercell modeling method. The structural property, in particular, the volume contraction with increasing x, is investigated by analyzing the energy changes for different site occupation. It is found that the lattice contracts mainly to increase the interaction of the additional electron and the metal d potential. In addition, the (420)-plane ordering of the x-excess hydrogen is examined for ${\mathrm{YH}}_{2.25}$ and is confirmed by energetics studies.

We report a sharp photoluminescence (PL) emission at 1.356 eV present in InP layers homoepitaxially grown on (111)B substrates by gas-source molecular-beam epitaxy. The PL spectrum consists of a no-phonon line at 1.356-eV and rich phonon-related sidebands involving both lattice and localized vibrational modes (LVM’s). The LVM’s consist of both local and gap modes attributable to the double-donor phosphorus antisite ${\mathrm{P}}_{\mathrm{In}}$. Thus, the 1.356-eV emission is assigned to an exciton bound to the ${\mathrm{P}}_{\mathrm{In}}$. The photoluminescence intensity of the 0.8-eV donor-acceptor (${\mathrm{P}}_{\mathrm{In}}$-acceptor) pair transition is found to correlate with that of the 1.356-eV emission.

A particle may be trapped by a local potential due to the presence of a satellite particle that does not interact with the potential. A physical example is the trapping of an exciton by an isoelectronic impurity that is unable to bind the single electron.

We compute the peak velocity of a broad Gaussian pulse propagating in an absorbing thin film modeled with a one-oscillator dielectric function. The exact numerical calculation is done for a GaP:N film in the frequency region of the bound A exciton. For absorption lengths greater than the film thickness, the pulse velocity essentially coincides with the group velocity, and with the experimental results of S. Chu and S. Wong [Phys. Rev. Lett. 48, 738 (1982)]. However, outside the region of strong absorption the pulse velocity depends sensitively upon the thickness of the slab. Our results give a better account of the Chu and Wong experiment than the calculation based on the group velocity. For film thickness with smaller than one absorption length the pulse velocity disagrees with the group velocity even in the strong absorption region, as a consequence of Fabry-Pérot reflections of the pulse inside the film.

A p-doped resonant-tunneling device with tunnel barriers having different transmission coefficients is investigated. The magneto-oscillations observed in the tunnel current when a quantizing magnetic field is applied along the direction of current flow are used to measure the resonant space-charge buildup in the quantum well. For one bias direction, intrinsic bistability is observed on one of the resonant peaks in the current-voltage characteristics.

The electronic structure of (GaAs${)}_{\mathit{m}}$(AlAs${)}_{\mathit{n}}$ superlattices, with 1≤(m,n)≤10, grown in the [113] direction is calculated by employing the local empirical pseudopotential approach within the S-matrix implementation. Short period (n,n) superlattices are predicted to have a marginally direct (indirect) band gap for even (odd) values of n. The calculated results are compared against those for the more conventional growth directions.

We have studied the effect of hydrogen in the ${\mathrm{CoSi}}_2$/Si(100) interface on the Schottky-barrier height of ${\mathrm{CoSi}}_2$ on n-type and p-type Si(100). It was found that hydrogenation results in an increase of 120 meV in the barrier height to n-type Si(100). Measurements of the hydrogen concentration in the interface, using quantitative ion-beam techniques, were used to establish the correlation between the change in barrier height and hydrogen concentration; other hydrogen effects such as passivation of shallow donor and acceptor impurities in silicon were ruled out. The results demonstrate that 8×${10}^{15}$ hydrogen atoms/${\mathrm{cm}}^2$ can alter an interface layer and thereby change the pinning position of the Fermi level.

We present an ab initio study of the diffusion of Ge adatoms and the disordering of Ge(111)-c(2×8) at ∼300 °C. In the absence of adatom vacancies, we find that the most likely diffusion mechanism is an anisotropic correlated process in which several adatoms of a [11¯0] row hop concertedly along the same row. When surface vacancies are present, adatoms can instead hop one by one along [11¯0] in an uncorrelated way. Anisotropy arises from the special bonding topology of the c(2×8) structure. Calculated scanning tunneling microscopy images of the diffusion process show that adatom jumps are accompanied by an important electron backflow.

Using a combined scanning-tunnel-microscopy (STM)/atomic-force microscopy (AFM) setup, we have measured simultaneously the apparent barrier height and the tip-sample force gradient for various tip-sample distances of an STM configuration in air. Our results reconfirm the existence of repulsive tip-sample forces during the STM operation with inert metal systems in air. Also, the gradient of such forces is of the correct sign that is necessary to cause the lowering of the apparent barrier heights through elastic deformations. However, our results indicate that the model that is based on the elastic deformation due to the tip-sample forces does not provide a satisfactory explanation of the lowering of the barrier heights for the case of gold in air.

A full matrix random-phase-approximation calculation is performed to analyze surface plasmon excitations in spheroidal alkali-metal clusters, described in the jellium model. The single-particle levels are obtained in the local-density approximation to density-functional theory by solving the Kohn-Sham equations for deformed systems, making use of a one-center expansion method for the different potential terms. Numerical results are shown for the prolate ${\mathrm{Na}}_{10}$ and the oblate ${\mathrm{Na}}_6$ clusters.

The solution of the linearized kinetic equation used by Mamun et al. [Phys. Rev. B 44, 8685 (1991)] is incorrect, since it is derived using an unjustified approximation that conflicts with the ordering given in the paper itself. This solution, in contrast with the standard gyrokinetic one, exhibits no features essential for a magnetized plasma. Therefore, it cannot be employed as a basis for the construction of the nonlinear response as well as for obtaining the linear dispersion relation.

The electronic structure and magneto-optical spectra of CeSb have been calculated using the self-consistent local-density approximation with explicit on-site Coulomb parameters for the correlated f state of cerium. The essential electronic structure of cerium antimonide consists of one occupied f band, predominantly with orbital m=-3 character and spin σ=1 located 2 eV below the Fermi level and interacting with broad Sb p bands crossing ${\mathit{E}}_{\mathit{F}}$. The m-dependent p-f hybridization leads to large magnetic anisotropy and magneto-optical spectra in better agreement with experiment than obtained with the standard local-spin-density approximation.

The spectra of the diffracted wave in femtosecond-four-wave mixing and their dependence on the polarization of the driving fields are shown to be a very sensitive probe for the fundamental scattering processes that govern the coherent dynamics in a semiconductor. We demonstrate that the total dephasing rate is the result of a delicate balance between self-energies and vertex corrections. Particle interactions of the polarization scattering type are shown to be important contributions to the nonlinear optical response in the coherent regime.

We report the experimental observation of strongly localized edge collective excitations propagating around each individual wire in a modulation-doped GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum-wire array. The excitations have been observed in radio-frequency experiments at magnetic fields in the vicinities of the filling factors ν=2 and 4. For other magnetic-field strengths or with rising temperature the high-finesse edge wave transforms abruptly into a very different type of excitation, i.e., into a strongly damped relaxation mode distributed all over the wire.

Population dynamics of excitons and biexcitons in nanometer-sized CuCl microcrystallites (nanocrystals) was studied with a time-resolved luminescence measurement. A recurring process between excitons and biexcitons was clearly observed as a function of the second decay component of the biexciton luminescence and with an increase of the exciton luminescence. They become prominent with an increase in the excitation intensity. The biexciton luminescence is broadened asymmetrically to higher energy with an increase in the biexciton density. These temporal as well as spectral characteristics of biexciton luminescence are inherent to CuCl nanocrystals but are not observed in a CuCl bulk crystal, which shows that biexcitons are much more efficiently formed from excitons in a CuCl nanocrystal than in a CuCl bulk crystal.