This paper investigates the interaction of a surface state with a one-dimensional scattering object on the surface of a metal. Examples are straight rows of regularly spaced adsorbed atoms, and straight step edges. The layer–Korringa-Kohn-Rostoker method is employed to investigate the electronic structure of periodic arrays of rows of adatoms on the Cu(111) surface in a 6×2 geometry, as well as periodic arrays of missing rows to simulate step edges. From these band structures, the behavior of one individual scatterer is extracted by means of a one-dimensional model. Thus we obtain the rates of reflection, transmission, and scattering into the substrate. Rows of adsorbed Cu, Fe, S, and C are considered as well as single and double missing rows. It is found that none of these scatterers comes close to total reflectivity (R=1). Most cases lead to R around 0.3–0.4. The rest of the incoming electrons are mainly transmitted into the surface state on the other side, if the scatterer is a row of Cu or Fe atoms, while they are mainly scattered into the bulk by S and C. The behavior of missing rows is found to lie in between. By counting the number of outgoing states that a surface state can scatter into, qualitative information is obtained for two important situations. First, it is shown that for less than close-packed rows of adsorbed atoms, the ratio of the scattering rate into the bulk to that into the surface state is enhanced because of Bragg scattering. On Cu(111), this enhancement starts at an adatom spacing of M≥2. Second, it is argued that replacing the semi-infinite substrate by a thin film is unlikely to reduce the loss of electrons into the bulk. While it is found that surface states interact strongly with most adsorbates, our results suggest that the total confinement of surface states within artificially made structures may not be feasible.

We report on sharp and intense features that appear in the electron-energy-loss spectra of Ag(001) and Ag(110) for kinematical conditions corresponding to low-energy electron diffraction resonance. In accord with previous literature we assign the in-specular-reflection features to inelastic processes occurring prior to the impact of the electron with the surface, whereby electron-hole pairs are excited and the loss intensity is eventually modulated by the energy-dependent elastic reflectivity. Shape and intensity of the energy losses are strongly affected when moving the monochromator off-specular reflection. The phenomenon is due in general to the interference between inelastic processes corresponding to loss before and loss after reflection. For Ag(001) strong inelastic intensity is observed off-specular reflection for resonant conditions of the impinging electrons. Such losses are attributed to selective adsorption, followed by energy loss and selective desorption of electrons off the image-potential states.

We describe a technique for simultaneously treating the dynamics of electrons and ions. The key features are a generalized Hellmann-Feynman theorem, a standard time-dependent self-consistent-field (TDSCF) description, and use of the interaction picture to separate fast electronic oscillations from slower processes. The technique can be used in tight-binding or first-principles simulations, with either a ground-state or TDSCF Hamiltonian.

The effect of electron correlation on the band gap of the halogen-bridged transition-metal compounds (MX complexes) with charge-density waves is studied by using the projection technique. It is found that the band gap of an MX complex is reduced by the electron correlation. This effect in an MX complex is contrary to that in polyacetylene, where the band gap of the bond-order wave is enhanced by the electron correlation, and the origin for this contrast is discussed.

The optical reflectance spectra of various wurtzite-BN (w-BN) specimens prepared by the shock-wave method have been measured in the vacuum-ultraviolet region with synchrotron radiation. The optical constants have been determined by applying the Kramers-Kronig relation. The optical band gap was found to be 8.7±0.5 eV, which compares favorably with the latest calculations. The effect of the nanoscale particle size on the reflectance spectra and optical properties is also discussed.

An exact formula for the nondiagonal part of the one-particle temperature Green’s function is obtained within the framework of the nonperturbative canonical formulation of the finite-temperature generalized Ward-Takahashi relation. It is shown that the Landau-level Green’s function for two-dimensional electrons has a nonvanishing nondiagonal part if the electron-electron interaction is included.

We have calculated the frequencies of zone-center optical phonons in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As as well as ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As by using a modified random-element-isodisplacement model and obtained good agreement with experimental values. The optical phonons in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As exhibit two-mode behavior as in the case of ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As. The force constants in terms of the alloy compositions were discussed.

We present an analysis of the magnetic-susceptibility data on polyaniline, poly(m-toluidine), poly(o-ethylaniline), and poly(o-propylaniline) in terms of thermally excited triplet bipolarons. Implications of the conclusions are discussed with reference to the dc conductivity, thermoelectric power, and electron-spin-resonance results.

The phase diagram of a two-dimensional (2D) Coulomb-gas model is studied in the framework of quantum sine-Gordon theory in 2D Euclidean space. The core structures of the Coulomb charge are considered by evaluating some distribution functions, and the phase diagrams related to the different distributions are compared.

Picosecond decay and temperature-dependence measurements of violet and blue-light emissions from nanocrystalline-silicon thin films were carried out. The luminescence band exhibits separated peaks at a wavelength region from 350 to 500 nm and shows no intensity degradation. The emission energies of the peaks shift towards the high-energy side at low temperatures by a temperature coefficient similar to single-crystalline silicon. The photoluminescence decays of these emissions can be completely fitted by a double-exponential equation. The two components of the lifetime ${\mathrm{\tau }}_1$ and ${\mathrm{\tau }}_2$ determined from the decay curves are 170 and 600 ps, respectively. All the optical events finish within 5 ns. The short lifetimes are suggested to be caused by an enhancement effect on the oscillator strength of the confined levels in zero-dimensionally confined silicon nanometer-sized crystallites.

Induced absorption from the exciton state to the biexciton state was clearly observed under the site-selective excitation of the inhomogeneously broadened ${\mathit{Z}}_3$ exciton band in CuCl microcrystallites embedded in NaCl crystals. This allows us to obtain the size-dependent biexciton binding energy in CuCl quantum dots. The binding energy of biexcitons increases with the decrease in their size and its size dependence and bulk value are well represented by the expression 78/${\mathit{a}}^{\mathrm{*}2}$+52/${\mathit{a}}^{\mathrm{*}}$+33 (meV), where ${\mathit{a}}^{\mathrm{*}}$ is the effective radius of microcrystallites in a unit of nm. The experimental results are compared with an available theoretical result. The enhanced Coulomb interaction in microcrystallites still increases the biexciton binding energy in the large-size regime, where the quantum confinement energy of excitons is not considerable. The size-dependent biexciton binding energy cannot be explained by the weak-confinement model of biexcitons.

Using time-resolved photoluminescence to study ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se/ZnSe multiple quantum wells, we show that the formation and decay kinetics of exciton magnetic polarons (EMP’s) depend strongly upon the Mn concentration. We suggest that as the Mn ion concentration in the barrier is increased, three different types of EMP may form: (i) both the electron and hole are confined to the magnetic material (type-I EMP), (ii) the electron and hole are spatially separated (type-II EMP), or (iii) confined at the interface. In agreement with previous results in thick epilayers, we find that both the formation time and recombination lifetime of the type-I EMP are approximately 400 ps, so that the majority of the EMP’s never fully achieve their equilibrium configuration. In contrast, the recombination lifetime of the spatially indirect type-II EMP observed here is greater than 20 ns (nearly forty times the formation time), so that the EMP’s in quantun wells may be studied in thermal equilibrium.

Charge distributions in lithium clusters ${\mathrm{Li}}_{\mathit{n}}$ (n=3,4,5) embedded into a matrix of argon atoms have been computed by means of a combined Hartree-Fock and density-functional-theory approach. The positions of the argon atoms, found using molecular-dynamics techniques, points to the origins of pseudopotential locations. We show that charge alterations in ${\mathrm{Li}}_{\mathit{n}}$ may be as high as 0.2e, reflecting local changes in the environment.

The propagation of a sound wave along a statistically rough solid-vacuum interface is investigated for the case of self-affine fractals. The wave-number relation ω=ω(k) is examined for the transverse polarized surface wave. The range of existence of this wave is analyzed as a function of the degree of surface irregularity or fractal dimension.

The temperature-dependent surface structural behavior of Pb(100) is studied using reflection high-energy electron diffraction. Anomalous surface expansion for temperatures between room temperature to about 500 K is observed. A high density of surface vacancies appears at temperatures above ∼500 K.

We report on detailed studies of the low-field magnetoconductance fluctuations observed in ballistic GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum dots. The main finding of our study is that the temperature-dependent scaling of the fluctuations is very different from that in disordered systems. In particular, the amplitude of the fluctuations decays exponentially with increasing temperature while the correlation field remains unaltered. We suggest that these results are consistent with the scattering of electrons via geometrical features, and so demonstrate the different nature of electron interference in disordered and ballistic systems. Finally, we discuss our results in relation to recent theoretical predictions for ballistic dots with chaotic geometries, in order to obtain information on the distribution of electronic trajectories in the square dots we study.

We report the pressure dependence up to 95 kbar of Raman-active stretching modes in the quasi-one-dimensional MX chain solid ${\mathrm{Pt}}_2$${\mathrm{Br}}_6$(${\mathrm{NH}}_3$${)}_4$. The data indicate that a predicted pressure-induced insulator-to-metal transition does not occur, but are consistent with the solid undergoing either a three-dimensional structural distortion or a transition from a charge-density wave to another broken-symmetry ground state. We show that such a transition can be well modeled within a Peierls-Hubbard Hamiltonian.

The Si(111)-7×7 reconstruction is investigated by high-resolution core-level spectroscopy. A detailed line-shape analysis of spectra recorded over a wide photon energy range demonstrates the presence of four surface-derived components in the Si 2p line. These are attributed to the structural building blocks of the (7×7) structure through their relative intensities, evaluated for different photon energies in order to take photoelectron-diffraction effects into account, and on the basis of temperature-dependent changes in line shape that occur in the (7×7)-(1×1) phase transition at around 1130 K.

We present a quantum theory of interaction between quantum-well excitons and electromagnetic eigenmodes of a multilayer dielectric cavity. The coupled exciton-photon modes are obtained by analyzing the exciton spectral function. The design of the cavity allows us to obtain enhanced spontaneous emission or a normal-mode splitting. We find very good agreement with the normal-mode splitting data of Weisbuch et al. [Phys. Rev. Lett. 69, 3314 (1992)].

We show that even in the absence of the ordinary drag effect (e.g., in thin impure metallic films and semiconductor heterostructures), the quantum corrections to the transport equation result in an electron current under a phonon temperature gradient. In accordance with the Onsager principle there is also a phonon heat current under an electric field. As a result, the measured thermoelectric voltage depends on whether the phonons experience the same temperature gradient as electrons. In an optically heated thin film only the electrons feel the thermal gradient. The difference between this case and an experiment where the electrons and phonons are in a local equilibrium permits an independent measurement of the electron-phonon coupling.