A reaction-diffusion theory of homoepitaxial growth on a stepped surface introduced by Myers-Beaghton and Vvedensky [Phys. Rev. A 44, 2457 (1991)] and Fuenzalida [Phys. Rev. B 44, 10 835 (1991)] is generalized to the case of heteroepitaxy by taking account of misfit strain relief in the growing epilayer. For deposition conditions where two-dimensional (2D) islands nucleate on the terraces before individual adatoms can migrate to vicinal step edges, analysis of the distribution of island sizes resolved in both space and time reveals a strain-driven transition from the familiar layer growth mode dominated by 2D island coalescence to a form of step flow where moving steps engulf very many very small 2D islands. The latter mode of growth is predicted to persist until three-dimensional island formation disrupts layer growth altogether. Both with and without strain, it is found that the island size distribution averaged over a terrace very rapidly approaches a steady-state form, even when kinematic theory predicts oscillations in the signal from diffraction measurements.

Static simulation techniques have been used to examine the defect chemistry in heteroepitaxial ceramic interfaces. Reduced ion density at the interface is seen to enhance the interfacial stability. The energetics of defect formation are shown to be substantially modified at the interface. In particular, we find that the energy of oxygen vacancy formation is lower at the interface between ${\mathrm{CeO}}_2$ thin films on α-${\mathrm{Al}}_2$${\mathrm{O}}_3$ compared with its value on the pure ${\mathrm{CeO}}_2$ surface. This effect of the interface may influence the catalytic activity of several systems.

We present the results of picosecond ultrasonic studies of localized acoustic-phonon surface modes in Al/Ag superlattices. By making measurements on a series of superlattices with different periods, we have been able to study surface modes with frequencies in the range from 110 to 670 GHz. The experiment reveals interesting variations in the surface-mode structure as the geometry of the cap layers is varied. We compare these results with the predictions of a transfer-matrix theory of the localized modes. The measured damping rate of the modes varies linearly with frequency and is nearly independent of temperature in the temperature range from 70 to 300 K. This variation of the attenuation with frequency and the order of magnitude of the attenuation are consistent with the assumption that the attenuation rises from an interaction between the phonon mode and the electrons, but the damping rate is about a factor of 5 larger than expected based upon Pippard’s theory for bulk materials. It is likely that the enhancement in the damping rate is primarily due to losses occurring at the free surface of the structure.

Angular distributions of x-ray-excited Na 1s photoelectrons and Na KVV Auger electrons emitted from c(2×2)-Na/Al(001) have been measured over the full 2π solid angle above the Al(001) surface. A detailed study involving single-scattering cluster calculations and an R-factor analysis has been performed to determine the room-temperature adsorption site of Na on Al(001). The best agreement with experiment is obtained for a configuration in which domains of Na atoms adsorbed in the hollow site and in the substitutional site coexist on the surface. This unusual and unexpected behavior has not been observed for an alkali-metal-on-metal adsorption system up to now, but it can be understood on the basis of very recent results from first-principles density-functional theory [C. Stampfl, J. Neugebauer, and M. Scheffler, Surf. Rev. Lett. 1, 222 (1994)].

Statistical methods developed previously for the evaluation of the electrical conductivity of metals and the description of the propagation of waves through random media are applied to the problem of scattering of high-energy electrons from a rough growing surface of a crystal where the roughness is caused by local fluctuations of site occupation numbers occurring during the growth. We derive the relevant Dyson and Bethe-Salpeter equations and define the short-range order correlation functions that determine the behavior of the reflection high-energy electron diffraction (RHEED) intensities. To analyze the temporal evolution of these correlation functions, we employ an exactly solvable model of the local perfect layer growth [A. K. Myers-Beaghton and D. D. Vvedensky, J. Phys. A 22, L467 (1989)]. Our approach makes it possible to separate individual contributions of various processes that give rise to oscillations of the RHEED reflections. We found that provided that the Bragg conditions of incidence are satisfied, it is the diffuse scattering by the disordered surface layer which is largely responsible for oscillations of the RHEED intensities. The temporal evolution of the angular distribution of the diffusely scattered electrons exhibits the effect of enhancement of the intensity of the Kikuchi lines with increasing surface disorder, as was observed experimentally [J. Zhang et al., Appl. Phys. A 42, 317 (1987)]. An explanation of the origin of this phenomenon is given using the concept of the final-state standing wave pattern.

We report the results of a theoretical study of the effect of the interface s-d hybridization on the photoemission spectral distribution in a one-monolayer Co on Cu(001) structure. The single-particle electronic structure and many-body interactions are treated on an equal footing in a numerical scheme that incorporates both band-structure and interaction effects. Using exact diagonalization method on small clusters with periodic boundary conditions, spin- and angle-resolved photoemission spectra are calculated. We study the effect of the interface hybridization on the spectral distribution by first calculating the spectra of an unsupported Co(001) monolayer in the absence of the substrate. Then we calculate the spectra with the substrate included. In the latter case, the s-d hybridization is first turned off to isolate the contribution from the crystal-field effect. Eventually, the one-monolayer Co on Cu(001) with full interface s-d hybridization, the realistic system, is studied. The calculated spectra are analyzed in a many-body picture and compared to available experimental data. Further experimental measurements are called for to test some theoretically predicted features.

The surface-impedance (SI) expression that was recently obtained for a corrugated metal surface, up to second order in the penetration depth, is reconsidered in connection with the extinction-theorem equations for the electromagnetic field. Instead of using a coordinate transformation, which stretches the corrugated surface, we obtain here the same SI expression from Green’s theorem in a more natural and easy way. In addition, this method allows us to evaluate SI corrections of the third order in the penetration depth. We also show that for a one-dimensional corrugation our result reduces to the SI expression given recently by Maradudin.

The 1.681-eV luminescence center characteristically observed in chemical-vapor-deposited diamond films is studied in a homoepitaxially grown diamond film. Homoepitaxial growth relaxes the strain typical for films grown on heterosubstrates with lattice mismatch, thus reducing dramatically the optical linewidths down to 0.2 meV. The no-phonon luminescence transition that we observe exhibits fine structure consisting of a fully resolved doublet with line components at 1.6820 and 1.6828 eV. The doublet thermalizes with an activation energy of (0.80±0.04) meV equal to the spectroscopic spacing of 0.8 meV. In addition, either doublet component has itself an associated close satellite in a mirrorlike arrangement. Three other partly resolved lines enhance the total number of components in the no-phonon transition to at least seven. Photoluminescence and photoluminescence excitation measurements under uniaxial stress along the 〈001〉 crystal direction reveal a splitting of the no-phonon structure into four main components. These are studied at varying temperatures and stress values for their thermalization behavior. We deduce an electronic level scheme of two excited states from which electrons radiatively relax to two lower states. The data are not consistent with excitonic recombination or electron-to-hole recombination. They indicate that the optical center is under uniaxial internal overpressure of approximately 0.06 GPa, probably due to its large size. The luminescence decay time of the optical center was measured to be 4 ns (5 K) through 2.7 ns (300 K) in the homoepitaxial film and ≊1 ns nearly independent of temperature in a polycrystalline diamond film.

The behavior with the irradiation energy and with the magnetic field of the thermomagnetic response induced by laser pulses in 5.5-μm Bi films at room temperature is reported in this paper. The Nernst-Ettingshausen coefficient at an applied magnetic field of 1 T is estimated: ${\mathit{Q}}_{\mathrm{NE}}$≃1.0×${10}^{\mathrm{-}5}$ V/T K. A good agreement is found when these results are compared with those reported earlier in polycrystalline bulk samples obtained by a conventional method. This supports the reliability of the pulsed laser technique in the measurement of weak transport effects and indicates that the optically pumped carriers hardly influence the transport properties of bismuth.

Angular distribution, time-of-flight, retarding field, and effective positive-ion cross-section measurements are presented for positive ions produced by electron-stimulated desorption from physisorbed monolayers of ${\mathrm{H}}_2$, HD, and ${\mathrm{D}}_2$ on graphite and from ${\mathrm{D}}_2$ on Kr-plated graphite. The electron energy was 60–63 eV, except as noted. The angular distributions are isotropic in the range of 140°–170° from the forward direction of the normally incident electron beam. Diatomic and triatomic ions are each less than 1% of the positive ions detected; the rest are monatomic ions (${\mathrm{H}}^{+}$ and/or ${\mathrm{D}}^{+}$). The proportion of higher energy ${\mathrm{H}}^{+}$ ions from ${\mathrm{H}}_2$ increases as the electron energy is raised above 30 eV, the threshold for dissociative ionization from the ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$(2pσ) antibonding state of the diatomic positive ion. The proportion of low-energy ${\mathrm{D}}^{+}$ ions is larger for ${\mathrm{D}}_2$ on Kr-plated graphite than for ${\mathrm{D}}_2$ on bare graphite. Retarding field measurements were fit assuming one or two Gaussian components of monatomic-ion kinetic-energy distributions; the most probable monatomic-ion kinetic energies (without contact-potential corrections) were 5.7 eV for ${\mathrm{H}}^{+}$ from ${\mathrm{H}}_2$; 5.4 eV for ${\mathrm{D}}^{+}$ from ${\mathrm{D}}_2$; 7.9 eV for ${\mathrm{H}}^{+}$ from HD; 2.6 eV for ${\mathrm{D}}^{+}$ from HD; and 1.2 eV for ${\mathrm{D}}^{+}$ from ${\mathrm{D}}_2$ on Kr-plated graphite. The ratio of the number of ${\mathrm{H}}^{+}$ ions to the number of ${\mathrm{D}}^{+}$ ions from HD decreases from 3.1 to 2.9 as the coverage is increased from commensurate to incommensurate. The effective positive-ion cross sections are estimated within a factor of 2 to be 1×${10}^{\mathrm{-}5}$, 3×${10}^{\mathrm{-}6}$, and 1×${10}^{\mathrm{-}6}$ ${\mathrm{nm}}^2$ for ${\mathrm{H}}_2$, HD, and ${\mathrm{D}}_2$.

The decay in time of the number of positive ions desorbed by 62-eV electrons incident on ${\mathrm{H}}_2$ and HD submonolayers physisorbed on graphite is used to measure the electron-stimulated desorption (ESD) total-removal cross sections. The nonexponential decay is analyzed by approximating the electron-beam spatial profile as a Gaussian. The total removal rate is found to be linear in electron current density. The total ESD removal cross sections deduced at 62 eV are much larger than the gas-phase total-ionization cross section of 0.01 ${\mathrm{nm}}^2$: 1.2 ${\mathrm{nm}}^2$ for HD and 5.2 ${\mathrm{nm}}^2$ for ${\mathrm{H}}_2$, with a 20% uncertainty.

Employing the stabilized jellium model [J. Perdew et al., Phys. Rev. B 42, 11 627 (1990)] without the bulk stability condition, the bulk cohesive properties and surface energy of a simple metal are calculated. In the calculations the core-radii values are taken from the pseudopotential theory. Good agreement with experimental data is achieved.

A concise variational approach is presented for the calculation of the ground-state energy of the strongly bound exciton-phonon system. By using the phonon coherent state to represent the phonon wave function, which depends on the wave function of the relative motion φ(r), a nonlinear integrodifferential equation satisfied by φ(r) is derived. Numerical calculations are carried out for a few polar materials and the upper bounds to the true ground-state energy of corresponding excitons are obtained. It is found that our method is especially suitable for the case of the strong binding.

We present a fully ab initio calculation of the thermodynamic properties for silicon within the quasiharmonic approximation, making use of volume-dependent phonon frequencies obtained from pseudopotential local-density calculations. The temperature dependence of the thermal-expansion coefficient, specific heat (at constant volume), and other related quantities are studied. We confirm that the thermal-expansion coefficient behaves differently in three temperature regions: positive for temperature below 15 K, negative between 15 and 125 K, and positive again above 125 K. This finding agrees with experiment. The abnormal (negative) thermal-expansion coefficient at low temperatures is explained through a detailed study of mode Grüneisen parameters. Both specific-heat and thermal-expansion-coefficient values calculated are in excellent agreement with experiment up to a few hundred kelvin.

We present an approach which goes beyond the virtual-crystal approximation and the molecular-field approximation in the description of the spin splitting in diluted magnetic semiconductors. The theory explicitly takes into account a chemical and a magnetic disorder due to substitutional ions. The results reproduce the apparent dependence of the p-d exchange integral on x in ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$S observed in experiments for small concentrations of magnetic ions. The asymmetric field and temperature dependence of the spin splitting in this compound are predicted.

A spatial superlattice becomes a spatiotemporal lattice and the minibands (MB’s) change to quasienergy MB’s under intense laser pumping. The width of the quasienergy MB collapses at a particular ratio of the field to frequency of the driving laser. It is shown that both the excitonic binding energy and the absorption oscillator strength reach maxima at this particular critical ratio. Optical studies may, therefore, lead to a verification of the laser-induced miniband collapse.

We use a linear response argument and macroscopic electrostatics to derive the formula 〈σ(x)σ(x’)${\mathrm{〉}}^{\mathit{T}}$∼-(x+x’) /[β2${\mathrm{\pi }}^2$(xx’${)}^{1/2}$(x-x’${)}^2$], where σ(x) denotes the charge density, for general logarithmic-potential Coulomb systems on a half-line x>0.

When a strong magnetic field B is applied perpendicular to the interface of a two-dimensional electron system (2DES), the total electron density in the structure may differ from that at B=0 because the density of states in the Landau quantized system differs from that at B=0. For the 2DES based on modulation-doped ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs structures, the ionized donor density in the ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As layer will vary with the magnetic field, which leads to differing total electron densities. In this paper we observe this effect by self-consistently calculating the electronic structure of selectively doped ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As single quantum wells. In the quantum Hall plateaus, the total electron density increases linearly with magnetic field. The numerical results are presented for the case with one and two occupied electronic subbands.

Three-layered superlattices are formed from a periodic repetition of three different slabs. Closed-form expressions for the study of bulk and surface polaritons in such materials are given in this paper with a few illustrative applications.

We report a current (I)-dependent transport measurement in between two adjacent integer quantum Hall plateaus at different bath temperatures (${\mathit{T}}_{\mathit{b}}$) for 10 nA<I<10 μA. We find the maximum slope in ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$ scales with I when I is larger than a characteristic value. Combined with previous T scaling results, we find the current-dependent effective temperature of the two-dimensional electron gas in the integer quantum Hall effect regime, ${\mathit{T}}_{\mathit{e}}$∼${\mathit{I}}^{0.5}$, independent of Landau levels and the spin degeneracy. This result allows us to deduce that p=2 for the T exponent of the inelastic scattering length (${\mathit{l}}_{\mathrm{in}}$∼${\mathit{T}}_{\mathit{e}}^{\mathrm{-}\mathit{p}/2\mathrm{}}$). Therefore, the values of the localization exponent ν and of the dynamical exponent z can be obtained directly and independently.