A meshlike energy structure of collective intersubband excitations and damped collective energy level crossings are predicted for electrons confined on a cylindrical graphitic nanotube. Unusual Kohn anomalies, besides 2${\mathit{k}}_{\mathit{F}}$, are found for nanotubes. Multipole collective excitations are obtained for ${\mathrm{C}}_{60}$ and related quasispherical fullerenes, and the results are in excellent agreement with available experimental measurements.

Analytic results for Mott-Hubbard metal-insulator transitions in N-fold degenerate Hubbard models are obtained using the Gutzwiller approximation. It is found that for any commensurate filling with integer (x) electrons per site, there exists a metal-insulator transition at the critical correlation energy ${\mathit{U}}_{\mathit{c}}$(N,x)={[ √x(2N-x+1) + √(x+1)(2N-x) ${]}^2$/(2N-x)}‖ε¯(x)‖, where ε¯ is the energy per particle in the absence of correlation. ${\mathit{U}}_{\mathit{c}}$ increases with x reaching the maximum at the half filling x=N. Therefore, it is possible for a system to be metallic at half filling and insulating away from half filling. This provides an explanation for the unusual metal-insulator transitions observed in fullerides ${\mathit{A}}_{\mathit{x}}$${\mathrm{C}}_{60}$.

In the absence of a magnetic field, two formally equivalent expressions for the conductivity contribute different sets of Feynman diagrams, due to cancellations. We use this result to calculate the magnetoconductivity of the N-orbital model to O(1/N) and we show that it coincides with the result for a single-level system.

Using capacitance-voltage and deep-level transient spectroscopy measurements of electron-trap concentrations, we have compared for n-type ${\mathrm{Al}}_{0.22}$${\mathrm{Ga}}_{0.78}$As and n-type GaAs the thermal annealing at 85–500 K of lattice defects produced by irradiation (by 1.0-MeV protons) at 85 K. The isochronal annealing data indicate defect removal of similar magnitudes in each material in annealing stage I (near 235 K) and in annealing stage III (at 450–500 K), but that the magnitude of the defect removal in stage II (near 280 K) in the ${\mathrm{Al}}_{0.22}$${\mathrm{Ga}}_{0.78}$As is only about a half of the corresponding value in the GaAs. These results show that defects involving gallium atoms are removed in annealing stage II in these materials.

Using Adachi’s expression [S. Adachi, Phys. Rev. B 43, 12 316 (1991)] for the complex dielectric function of amorphous semiconductors, we fit out experimental results [M. Fried et al., J. Appl. Phys. 71, 5260 (1992)] for two different types (self-implanted and implanted-annealed or relaxed) of amorphous silicon. The complex dielectric functions were determined by spectroscopic ellipsometric measurements in the visible wavelength region. The fit resulted in different optical band gap (${\mathit{E}}_{\mathit{g}}$) and damping (or broadening, Γ) energies. ${\mathit{E}}_{\mathit{g}}$ is lower and Γ is higher in implanted a-Si. Both changes can be interpreted by the presence of more structural disorder point defects in implanted a-Si compared with relaxed a-Si.

We have used scanning tunneling microscopy to study molecular-beam epitaxial growth on Si(111)7×7 surface. On the homoepitaxially grown surface at 500 °C, we find the small domains of non-DAS (dimer adatom stacking fault) rowlike ordered structures, the periodic rows of which run along the [011¯] and [1¯10] directions. The atomic configuration of these structures seems to be consistent with Pandey’s π-bonded chain model for Si(111)2×1 structure. We discuss two kinds of π-bonded chains, and the boundaries along the atomic rows between the 2×1 and DAS domains.

We have carried out photoluminescence-excitation spectroscopy (PLE) of porous silicon at different temperatures (90–300 K) for various photoluminescence emission (PL) energies (1.65–2.48 eV). Temperature-dependent PLE results indicate that there are two different processes which contribute to the PL emission. Emission at energies >2.0 eV is mainly due to a homogeneously broadened intrinsic mechanism while the lower-energy emission is from carriers confined in disorder-induced states in nanometer-sized silicon structures.

The possibilities of frequency-resolved phonon detection and generation given by a three-barrier tunneling heterostructure tuned by voltage applied to a gate are considered. It is shown that if the dominant channel for charge transfer corresponds to inelastic phonon-stimulated (or assisted) tunneling such a structure may exhibit rather good parameters as a phonon-spectroscopy device.

In this paper, we report on the iron silicide formation when annealing 3–7-Å-thick Fe films deposited on Si(111) between 250 and 550 °C. The growing films are characterized by Auger-electron spectroscopy, electron-energy-loss spectroscopy, low-energy electron diffraction, and surface-extended energy-loss fine structure in order to investigate the film composition, crystallography, and local atomic environment. We show that, upon annealing at 500 °C, ${\mathrm{FeSi}}_2$ in the ${\mathrm{CaF}}_2$ phase is formed when the initial Fe coverage is less than 7 Å whereas β-${\mathrm{FeSi}}_2$ is formed when the Fe coverage lies above 10 Å.

We have used a Hartree approximation to study the properties of N electrons in a quantum dot in the presence of a magnetic field. Different Landau bands are found to be weakly coupled to each other and an activation energy must be paid for transferring electrons from a Landau band to another. It is only for a discrete set of values of the magnetic field that the Coulomb blockade does not exist and that electrons move freely between two different Landau bands. The chemical potential of the system depends almost linearly on the number of particles and oscillates weakly when the magnetic field is varied in agreement with available experimental information.

Sub-Coulomb-gap leakage currents observed in small-capacitance tunnel junctions have most often been interpreted in terms of cotunneling. We suggest another possible mechanism for this subgap conductance and address related issues on energy conservation in the context of dissipative open junctions. We show that whenever the junction is biased by the chemical-potential difference between the two electron reservoirs, the bias voltage always induces leakage currents, irrespective of other features of the setup. We also discuss the implications of this mechanism for junction arrays.

The surface-plasmon dispersion relation for a statistically rough surface can display a splitting under specific conditions. Calculations of the dispersion-relation splitting are performed in terms of a correlation model for self-affine fractal rough surfaces with analytic form of the associated roughness spectrum, G(K)∝(1+${\mathit{aK}}^2$${\xi }^2$${)}^{\mathrm{-}1\mathrm{-}\mathit{H}}$. The dependence of the splitting on the roughness exponent H is investigated.

Diffraction-intensity oscillations have been observed using molecular-dynamics simulations of vapor deposition. Atoms interacting via modified Lennard-Jones potentials were deposited onto fcc(111) and fcc(100) surfaces with periodic boundary conditions and the diffraction was calculated during growth. The oscillations increased in amplitude with increasing temperature and, in some cases, with reduced deposition rate. Larger oscillations were observed on the fcc(100) surface than the fcc(111) surface. Strong reentrant oscillations, observed earlier experimentally, were not observed.

For submonolayer coverages of Cs on Ru(0001) surfaces, the Cs-Ru vibration is observed at 7.8 meV (63 ${\mathrm{cm}}^{\mathrm{-}1}$) by means of high-resolution electron-energy-loss spectroscopy. At Cs coverages near the complete monolayer the adlayer becomes metallic as indicated by screening of the Cs-Ru vibration and the occurrence of an electronic excitation (plasmon) at 580 meV. Coadsorption of CO as well as of oxygen leads to the reappearance of the Cs-Ru vibration and the disappearance of the electronic excitation which is interpreted as a demetallization through chemical interaction with the coadsorbed species.

Two-photon-absorption spectra of Si, ZnSe, and GaAs are evaluated in a wide photon-energy range by using ab initio full-band-structure and microscopic-nonlinear-susceptibility calculations. It is shown that Si and ZnSe have abundant spectral structures originating from the transitions at both the center and boundary of the Brillouin zone, being in good agreement with recent experimental results. The calculated spectra are analyzed by comparing with those of one-photon absorption and the scaling formula.

The electronic stopping of a fast, charged particle in a lattice-periodic structure is treated by linear response theory. The energy loss in open crystal channels is found to be reduced due to destructive interference of umklapp scattering processes with small momentum transfer. A sum rule for the first reciprocal moment of the velocity-dependent stopping power is derived, which can be expressed in terms of the static inverse dielectric function. Quantitative information about the importance of the crystal potential is obtained by first-principles pseudopotential calculations. The averaged stopping power in the 〈110〉 channel in Si is calculated to be smaller by 30% compared to nonchanneling directions. The sum-rule calculations in the local-density approximation agree with the band-structure results within 20% and are used to discuss the electronic stopping in other semiconductors.

The acceptor concentration of two type-IIb natural diamonds has been measured by Hall effect (to 1300 K), capacitance-voltage (CV), and secondary-ion mass-spectroscopy measurements. Reduction of contact effects in both Hall and CV measurements resulted in excellent agreement between the three techniques. Hall contact size and placement effects were measured and corrected. The capacitance and resistance of the Ohmic contact for CV measurements were minimized with a large-area ion-implanted contact. The long-standing discrepancy between Hall-effect and CV results in diamond is shown to be primarily due to nonideal CV contacts.

We report excess longitudinal resistivity of a high-mobility two-dimensional electron gas (2DEG) in a random distribution of submicrometer magnetic-flux tubes (vortices) which are formed at the 2DEG by a superconducting gate layer. The results are explained in terms of small-angle scattering of ballistic electrons by the magnetic-field inhomogeneities.

Barrier-modulated ${\mathrm{In}}_{0.09}$${\mathrm{Ga}}_{0.91}$As/GaAs quantum wires with widths down to 18 nm have been studied by photoluminescence and photoluminescence excitation spectroscopy. Up to three transitions arising from different laterally confined electron and hole subbands were observed for varying wire widths in photoluminescence excitation experiments. The experimentally determined dependence of the transitions of the three subbands on the wire width is described well by detailed calculations made using the geometrical dimensions of the wires.

Fano resonances are observed in the photoluminescence excitation spectra of GaAs-AlAs quantum wells. They originate from the Coulomb interaction that couples a discrete state and a continuum of excitonic states belonging to different pairs of conduction and valence subbands. This interpretation is supported by our calculations and by the behavior of the excitonic line shape in the presence of a magnetic field applied perpendicular to the layers.