The logitudinal-optical-phonon effect on the exciton binding energies in a quantum well consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As are studied. By using the Lee-Low-Pine unitary transformation, the Hamiltonian can be separated into two parts which contain the phonon variables and exciton variables, respectively, providing that the virtual phonon-electron and virtual phonon-hole interactions are neglected. A trial wave function, which is able to reproduce the correct exciton binding energy in a quantum well, is obtained by using a perturbative variational technique. The trial wave function consists of a product of the envelope function in the z direction (perpendicular to the layers) for electron and hole and a purely two-dimensional exciton wave function. The dependence of the ground-state binding energy, which includes the effect of electron-phonon interaction on the well width, is investigated. It is found that the correction due to polaron effects on the exciton binding energy is quite significant for a well width of several hundred angstroms and the effects of either surface phonons or bulk phonons on the binding energy of the heavy-hole exciton is always larger than that of the light-hole exciton. Our results are compared with some previous results, and satisfactory agreements are obtained.

Scanning electron microscopy with polarization-analysis (SEMPA) measurements of the dependence of the oscillations of the exchange coupling in Fe/Cr/Fe(100) structures on the Cr growth temperature are correlated with the thickness fluctuations in Cr films measured by scanning tunneling microscopy (STM) at similar growth temperatures. Layer-by-layer growth was observed by STM for Cr deposition on very flat Fe(100) whiskers at deposition temperatures ≥300 °C. The SEMPA measurements of the magnetization of the Fe overlayer as a function of Cr spacer-layer thickness at this temperature could be simulated well by oscillatory coupling with periods 2.105±0.005d and 12±1d, where d is the layer spacing. Rougher Cr growth, limited by diffusion kinetics, occurs at lower growth temperatures giving a distribution of thicknesses in the growth front as determined by STM. We modeled the Fe magnetization for lower-temperature Cr growth by assuming that the exchange coupling at each discrete Cr thickness is the same as found for layer-by-layer growth. The total coupling at each average Cr spacer-layer thickness was determined by adding the weighted contribution to the coupling from each Cr layer thickness contributing to the average thickness. Thus, by taking into account the thickness fluctuations in the Cr spacer layer as determined by STM, very good agreement was obtained between the model and the SEMPA measurement of the Fe overlayer magnetization for Cr growth at lower temperatures without including other consequences of roughness at the interface, such as the breakdown of translational invariance. Important characteristic length scales and the role of biquadratic coupling in the SEMPA measurements are addressed.

We present results for the lattice defects in diamond films and discuss interplay between the defects and growth rate of the films grown by chemical vapor deposition and dc plasma arc jet. We identify the nature of the defects and present defect depth profiles for films grown under different conditions of these two techniques. Defect density and film properties change significantly with growth parameters and the growth rate is related to defects in the film.

We show that the electrical deterministic fractal lattice (DFL) model can provide a good physical and theoretical understanding of the far-infrared anomalous absorption properties of fractal metallic clusters as well as the cluster ‘‘surface’’-plasmon resonances discussed previously by means of numerical methods. Using the analytical properties of the DFL model, it is possible to calculate exactly the power-law exponents of the enhancement factors B, of the crossover localization length ${\mathit{L}}_{\mathrm{\omega }}$ as well as the Cantor structure of the self-similar cluster-plasmon resonance spectrum in terms of the fractal characteristics of the aggregate.

The intra-atomic transitions involving bound states of an ion or an atom moving parallel to a solid surface are analyzed using linear-response theory. Different models have been employed to describe the response of the medium. The velocity dependence of excitation and deexcitation processes is studied. Numerical calculations are presented for transitions involving 1s and 2p hydrogenic states. The highest deexcitation rate is obtained when a 2p orbital is oriented in the direction normal to the surface. Numerical results are given for hydrogen atoms moving near aluminum. The decay of the deexcitation rate, which scales following a power law of the distance to the surface, proves to be almost independent of the velocity when v<2 a.u. The excitation probability is about two orders of magnitude below the deexcitation probability. Finally, the effect of the energy shift and splitting of the atomic states originating in the interaction with the valence-band electrons has been studied in detail.

The effect of potassium promoter atoms on Rh(111) on the surface potential has been investigated with photoemission of adsorbed Xe, Kr, and Ar. By using probe atoms of different sizes, we have measured the variation of the surface potential in the vicinity of a potassium atom. The surface potentials have been probed on Rh(111) surfaces, covered with 2.7, 4.1, and 5.0 at. % potassium. At all these coverages, we find a decrease in potential close to the potassium atoms (<4 Å) on the order of 1–2 eV, which depends on the lateral distance from the potassium atom. Further away from the potassium atoms we find a nearly constant potential that is 0.4–1.0 V lower than on unpromoted Rh(111). This implies that all available adsorption sites on the promoted surface are affected by the presence of potassium. The measured potentials depend on the potassium coverage, indicating that the potentials result from a cumulative effect of all potassium atoms on the surface. The observed changes in surface potential agree well with the potential in a hexagonal network of dipoles, indicating that they are of electrostatic origin and do not require long-range changes in electronic structure.

We study the electronic structure of atomic overlayers on semi-infinite jellium in the presence of an ac electric field parallel to the surface within the time-dependent density-functional theory. It is shown that the wind force acting on adatoms and the adsorbate-induced surface resistivity are related in the static limit by exactly the same equation as in the classical theory. Results of our self-consistent calculations performed for Mg, Al, and Si overlayers on jellium with ${\mathit{r}}_{\mathit{s}}$=2 demonstrate that the linear-induced charge and the wind force are highly sensitive to physical parameters such as the local density of states at the Fermi energy, the adatom-substrate bond length, and the adsorbate coverage.

Mechanism of CO chemisorption on a metal surface is discussed on the basis of self-consistent local-density-functional calculations using norm-conserving pseudopotential in the linear-combination-of-atomic-orbitals method. The CO/Pt(111) system is studied by the cluster model for metal surfaces by introducing a model potential intended to pick up surface states by placing dangling bonds around the cluster surface. The CO-2π state is found to lie about 2–4 eV above the Fermi level with weak bonding surface Pt atoms. The donation–back-donation mechanism is found to be unlikely in CO/Pt(111).

Silver segregation on a (100) surface of Al-3 at. % Ag, induced by heat treatment, is studied at temperatures up to 480 °C. The surface concentration of silver is monitored with Auger-electron spectroscopy, while its geometry is determined with low-energy electron diffraction. The measurements show that the segregation results in a Ag concentration of up to 30 at. % at the surface which forms a disordered overlayer. The electronic information about the Ag atoms, obtained both by means of x-ray-photoelectron and electron energy-loss spectroscopy, reveals that ${\mathrm{Ag}}_2$Al-like clusters segregate to the surface at temperatures ranging up to 440 °C. At higher temperatures, the clusters reversibly dissolve, in agreement with the bulk phase diagram, without changing the average Ag concentration at the surface.

Local density-functional calculations show that on Al(331), a S adatom binds preferentially in a step-edge geometry, where it can passivate two relatively undercoordinated surface Al atoms, where it can simultaneously satisfy its own need to complete a closed-shell electronic configuration, and where its nonbonding electrons are minimally repelled by electrons of the substrate. In contrast, on the close-packed Al(111) surface, S optimally resides in a high-coordination site, specifically, a fcc threefold hollow.

We have carried out a back reflection x-ray standing-wave investigation to study the adsorbate-substrate bond length and bonding site for the system Rb/Cu(111). Our low-energy electron diffraction study showed an ordered (2×2) phase for one monolayer of Rb on Cu(111) (θ=0.25). By measuring both the (111) and (111¯) Bragg reflections at this coverage, we determine the Rb adsorption to be in the top site. We observe a high degree of order in the Rb overlayer perpendicular to the surface, with large disorder parallel to the surface.

The second-harmonic-generation (SHG) efficiency from a monolayer of oriented chiral molecules (R- or S-2,2’-dihydroxyl-1,1’binaphthyl) has a strong dependence upon the handedness of the circularly polarized excitation beam. The SHG circular-dichroism (CD) effect is much larger than in ordinary CD spectroscopy because SHG-CD is electric dipole allowed. The technique allows the study of chiral surfaces. The preference for left or right circularly polarized light is dependent on both the chirality (R or S) and the absolute orientation of the molecules (pointed up or down).

We extend a model proposed for explaining multiplicity and oscillations of concentrations and temperature in catalyzed oxidation of carbon monoxide; the importance of the dimension of the system and the closure approximation applied to the results, and, especially to the oscillatory behavior, is analyzed. Kinetic phase transitions, namely, single state⇆ multiplicity, single state⇆ oscillations, and multiplicity⇆ oscillations are found, depending on the reaction heat and the temperature relaxation parameter. Also, the role played by desorption of reactants is considered. When there is no desorption, temperature oscillations take place around room temperature, but if desorption is operative, oscillations occur about a higher temperature. For the one-dimensional case a spurious kinetic phase transition is obtained when the singlet closure approximation is applied.

Surface states induced by the C(2×2) phase of oxygen on a Pd(100) surface were studied by means of surface core-level-shift (SCLS) spectroscopy and photoelectron angular distributions that were obtained by using forward-scattering spectroscopy. This combination of the two powerful techniques proved to be very useful in that surface and bulk states were observed to have two distinct energies as determined by the SCLS spectroscopy applied to the Pd 3${\mathit{d}}_{5/2}$ and 3${\mathit{d}}_{3/2}$ core levels. Angular distributions of the surface and bulk components of the Pd 3${\mathit{d}}_{5/2}$ core level were studied separately. Photoelectron angular distributions were found to be consistent with the forward-scattering mechanism in which the same Pd atom residing in its lattice site gives raise to two distinct 3${\mathit{d}}_{5/2}$ photoemission peaks separated by 0.55 eV. Forward-scattering results obtained along the 〈001〉 and the 〈011〉 directions also suggest that surface states extend four to five layers into the bulk and they can be characterized by a wave function whose amplitude decays in the direction of the inward normal. Coefficients of the atomic orbitals that represent oxygen-induced surface states were mapped experimentally. Structural and mechanistic implications of the long-range nature of the O-Pd interaction are discussed.

We have performed ab initio calculations of the stability of one-dimensional long-period superstructures in ${\mathrm{Cu}}_3$Pd, ${\mathrm{Cu}}_3$Al, and ${\mathrm{Ag}}_3$Mg by means of an interface Green’s function technique based on the linear-muffin-tin-orbitals method within the tight-binding and atomic-sphere approximations. The energies of the superstructures relative to the L$1_2$ structure are found by an expansion based on the calculated energy of a single (001) antiphase boundary and the calculated interaction energy between two and three antiphase boundaries of varying distance. The expansion agrees with standard band-structure calculations of the structural energy differences for the two short-period superstructures ${\mathit{DO}}_{22}$ and ${\mathit{DO}}_{23}$. We find that at zero temperature the ground states of ${\mathrm{Cu}}_3$Pd, ${\mathrm{Cu}}_3$Al, and ${\mathrm{Ag}}_3$Mg are one-dimensional superstructures with antiphase boundary separations of 2–5 unit cells of the underlying L$1_2$ structure.

The growth and the structure of thin Au films on Ag(111) were studied by measuring the angular distribution of core-level photoelectrons emitted at high kinetic energy using a two-dimensional display-type electron spectrometer. Additional information was obtained by angle-integrated photoelectron spectroscopy and by thermal desorption spectrometry of NO. We find, even at room temperature, intermixing induced by surface diffusion. This conclusion is corroborated by the study of Au films deposited on (1–3)-monolayer-high Ag films grown on Pd(111).

The effect of disordered interfaces and bulk impurities on perpendicular transport in metallic multilayers is considered in an effective-mass semiclassical approximation. The transmission matrix is obtained by diagrammatic perturbation theory in terms of the effective-mass and conduction-band profiles at the interface. In the weak-scattering limit specular and diffuse scattering give equally important contributions to the conductance. Predictions for the transport properties of interfaces with low concentrations of strongly scattering defects should be accessible to verification by experiments. The transition from fully ballistic (Sharvin) to diffuse transport (Drude) is described analytically both in two- and three-dimensional systems, where the former case is of relevance for transport in the two-dimensional electron gas in semiconductor heterostructures. The theory is applied to the spin-valve effect in magnetic multilayers. The magnetoconductance is described by a simple formula in terms of the mean free path for the majority- and minority-spin electrons.

The excitation modes of electrons in symmetric, neutral jellium slabs are studied within the time-dependent local density and related approximations, in the regime when there are several bound states below the Fermi level. Unlike most previous calculations, the present ones do not require all single-particle wave functions to vanish at some small distance from the slab. This modification of the boundary conditions significantly affects the excitation spectra, generally reducing the number of peaks that appear. In particular, from our calculations modeling excitation by longitudinal near fields with nonzero surface-parallel wave vector, we do not find resolvable peaks above the bulk plasmon frequency ${\mathrm{\omega }}_{\mathit{p}}$ which could be interpreted as standing plasma waves resonating across the neutral slab. This is in contrast to the case of a symmetric but non-neutral jellium slab (wide parabolic quantum well or embedded electron gas) where we do predict distinct (but weak) standing plasmon resonances above ${\mathrm{\omega }}_{\mathit{p}}$ at nonzero surface-parallel wave vector, even for a well with only a few occupied bound states. Although bulk plasmon resonances seem to be unobservable in the relatively narrow, symmetric, neutral jellium slabs studied here, we do find the following peaks consistently at low surface-parallel wave vector: an ‘‘intraband’’ mode near the two-dimensional-plasmon frequency and a ‘‘multipole surface plasmon’’ near 0.8${\mathrm{\omega }}_{\mathit{p}}$, the latter being amenable also to other interpretations for very thin slabs. Further peaks, including a cluster near ${\mathrm{\omega }}_{\mathit{p}}$, are harder to interpret. They can be related to single-particle transitions in the case of thin slabs. However, in the intermediate-thickness regime it is difficult to assign a unique physical cause to each peak in a spectrum, and various ways to help sort out ambiguities are illustrated. These do not always resolve matters since for neutral jellium slabs one has a relatively wide transition region between quantum and classical size effects.

We have determined the 4f occupation number ${\mathit{n}}_{\mathit{f}}$ of the Kondo insulator ${\mathrm{Ce}}_3$${\mathrm{Bi}}_4$${\mathrm{Pt}}_3$ over the temperature range 10–300 K using x-ray-absorption measurements near the Ce ${\mathit{L}}_{\mathrm{III}}$ edge. The compound is weakly mixed valent: ${\mathit{n}}_{\mathit{f}}$ is approximately 0.9 at 10 K and varies slowly with temperature in a manner similar to that observed in metallic mixed-valent rare-earth compounds.

The quantum dynamics of electrons on the Koch fractal is investigated within the framework of a tight-binding approximation. The invariant sets of an exact real-space renormalization procedure play a crucial role for the mainly analytical methods employed. Inverse iteration of the critical fixed points is the key to the construction of dense spectral subsets. This approach is confirmed by numerical determination of periodic orbits of the decimation map. As a corollary, a classification scheme for the quantum states of the system is proposed. This scheme is directly related to the 4-adic representation of the rotation number of the wave function.