The structure of the Cu(110) surface is studied at high temperatures using a combination of lattice-gas Monte Carlo and molecular-dynamics methods with identical many-atom interactions derived from the effective-medium theory. The anisotropic six-vertex model is used in the interpretation of the lattice-gas results. We find a clear roughening transition around ${\mathit{T}}_{\mathit{R}}$=1000 K, and ${\mathit{T}}_{\mathit{R}}$/${\mathit{T}}_{\mathit{M}}$=0.81. Molecular dynamics reveals the clustering of surface defects as the atomistic mechanism of the transition and allows us to estimate characteristic time scales. For the system of size 50×50, the time scale of the local roughening at 1150 K of an initially smooth surface is of the order of 100 ps.

We present theoretical studies of various hydrocarbon radicals and molecules on the (100) surface of diamond. We use molecular dynamics and a dynamical quenching algorithm to calculate the energetics of different adsorption configurations, allowing for full relaxation of the underlying lattice. We use a parametrized many-body potential function that has been used for energetics calculations with a great deal of success [D. Brenner, Phys. Rev. B 42, 9458 (1990)]. Our calculations show that adsorption of hydrocarbons on either the flat terraces or near different types of step edges give small variations of binding energies and equilibrium configurations. This reflects the strong covalent bonding pervasive in the carbon systems, which forces the strain fields and bonding energetics to be determined to a great extent by the local environments. We analyze the consequences of these results for the dynamics of growth under typical conditions.

We study the effects of relativity on the electronic structure of Hg as it evolves from an atom to a cluster, and then to the bulk. A comparison of nonrelativistic and scalar-relativistic results for bulk Hg, obtained self-consistently, clearly shows the importance of including the relativistic terms as well as treating the 5d electrons as valencelike. Our cluster calculations show that the relativistic effects are equally important for clusters, and that the differences in many electronic properties such as the size dependence of the gap energy and the l character of Hg clusters with respect to other divalent-metal clusters, for example, Be and Mg, arise due to the relativistic terms, thus providing further insight into the electronic origins of these properties.

A detailed low energy electron diffraction analysis has been performed to investigate the adsorption of potassium on Al(111) at 90 K and at 300 K. At each temperature a (√3 × √3 )R30° structure is formed, however, the adsorbate positions are different. For absorption at 90 K the adatoms occupy on-top sites and at 300 K they occupy substitutional sites, both geometries have hitherto been regarded as very unusual. An irreversible phase transition from the former to the latter stable structure occurs on warming to 300 K. The obtained interatomic distances and surface relaxations are discussed in terms of an interplay of the electrostatic repulsion between adatoms and substrate screening as well as coordination number. An approximate scheme for including the effect of anisotropic atomic motions under the influence of thermal excitation was applied. It is found that the R factors for the on-top site are significantly improved whereas no improvement is found for the substitutional site.

We have calculated the quasiparticle energy of the occupied surface states of the H-Si(111)1×1 surface. The electron self-energy operator is expanded to first-order in the screened Coulomb interaction in the GW approximation. The results explain the data from recent high-resolution angle-resolved photoemission spectroscopy. Comparison of the quasiparticle surface-state energies with those from local-density-functional eigenvalues shows that the self-energy corrections are very large, typically two to three times larger than the corrections found in previous calculations on other semiconductor surface systems. We have also performed a frozen-phonon study of the stretching mode of the Si-H bond. As observed in several recent experiments and theoretical studies, a large anharmonicity is found.

We report the dark conductivity and photoconductivity (σ and Δσ) in sublimed films of ${\mathrm{C}}_{70}$, ${\mathrm{C}}_{60}$, and ${\mathrm{K}}_{\mathit{x}}$${\mathrm{C}}_{70}$. In comparison with ${\mathrm{C}}_{60}$, the maximum quantum efficiency of ${\mathrm{C}}_{70}$ in air (∼5×${10}^{\mathrm{-}3}$) is two orders of magnitude higher. The frequency-response range of the photoconductivity of ${\mathrm{C}}_{70}$ is wider than that of ${\mathrm{C}}_{60}$ as well. The disorder and charge localization are important for the charge transport in ${\mathrm{C}}_{70}$, reflected in a bimolecularlike recombination and a large temperature dependence of the dark conductivity. The Fowler plot suggests that the energy gap of ${\mathrm{C}}_{70}$ is smaller (1.5 eV) than that of ${\mathrm{C}}_{60}$ (1.7 eV). The temperature dependence of Δσ for ${\mathrm{C}}_{70}$ has a local peak between 260 and 270 K, which is possibly related to the freezing of the orientational disorder in ${\mathrm{C}}_{70}$ below 270 K. The photoconductivity in ${\mathrm{K}}_{\mathit{x}}$${\mathrm{C}}_{70}$ is extremely small, probably due to the charge delocalization which increases the recombination rate.

The electronic and transport properties of a perfect amorphous graphitic carbon model constructed by Townsend et al. [Phys. Rev. Lett. 69, 921 (1992)] are studied by first-principles calculations within the local-density approximation. It is shown that such a random system with two-dimensional interaction in a three-dimensional structure is a high-resistivity metal. A zero-temperature resistivity of about 1160 μΩ cm and a positive thermopower at low temperature are obtained. Localized states near the Fermi level are induced by subtle difference in the π bonding of different ring structures. Relaxation time due to elastic electron-electron scattering and the Fermi velocity are estimated to be 2.4×${10}^{\mathrm{-}15}$ s and 2.61×${10}^4$ m/s, respectively.

Two-dimensional ‘‘separation of interactions’’ ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR spectra of powdered ${\mathrm{C}}_{60}$ have been measured between 13.8 and 280 K and the results are compared with various theoretical models. The data show that above ${\mathit{T}}_{\mathit{c}}$=260 K the ${\mathrm{C}}_{60}$ molecules reorient nearly isotropically and that at least two different motional processes are involved below ${\mathit{T}}_{\mathit{c}}$: A relatively slow process corresponding to the flipping of the axis of rotation and a fast one corresponding to uniaxial rotation of the ${\mathrm{C}}_{60}$ molecules around this axis. The spectra below ${\mathit{T}}_{\mathit{c}}$ are compatible with a pseudorandom sequence of small amplitude uniaxial reorientations around at least three different axes separated by 60° leading to the same two nearly degenerate states as originally suggested. The spectra definitely rule out any uniaxial reorientations around a single axis. A linewidth transition was observed around 150 K in the homogeneous line shape reflecting the freezing in of the flipping of the rotational axis. Below 90 K also the uniaxial rotation slowly freezes out and the spectra gradually change into a static powder pattern as T→0.

In the first part of this work we develop a model describing the influence of many-electron effects in ${\mathrm{C}}_{60}$ K-shell photoemission (only the π valence electrons are taken into account). Then we extend this model to the calculation of the ${\mathrm{C}}_{60}$ K-shell absorption spectrum. We first determine a one-electron spectrum obtained by considering only direct transitions from the 1s to the unoccupied valence levels. This spectrum exhibits three main peaks. Then, following a previous Friedel’s analysis, we add two kinds of many-electron effects. In the first step, we include the transitions with shake-off excitations. The obtained spectrum is similar to the one-electron spectrum for the positions and the relative intensities of the three peaks, however, a high-energy tail appears. In a second step we also include replacement transitions. Then the relative intensities of the three peaks vary and are in better agreement with experiment than in the one-electron spectrum. The differences with experiment which still remain are discussed.

Lattice dynamics of solid ${\mathrm{C}}_{60}$ is studied using a unified interaction model which consists of a tight-binding potential for the intramolecular interaction and a Lennard-Jones and bond-charge model for the intermolecular interaction. Phonon dispersion and density of states of solid ${\mathrm{C}}_{60}$ are calculated in the energy range from 0 to 210 meV. The intermolecular-phonon density of states shows peaks around 2.3 and 3.7 meV, and extends to 7.6 meV. Intermolecular phonons and intramolecular vibrational modes are well separated by a gap of nearly 22 meV. The intermolecular-phonon modes show strong dispersion, so do the intramolecular modes, especially those with energy below 70 meV. The calculated phonon spectrum agrees very well with recent inelastic neutron-scattering experiments. The effects of orientational disorder and pressure on the intermolecular and intramolecular phonons of solid ${\mathrm{C}}_{60}$ are investigated. Intermolecular-phonon modes are sensitive to orientational disordering, and orientational disordering softens libron modes. The pressure dependence of the phonon dispersion and density of states is studied for solid ${\mathrm{C}}_{60}$ in the range of pressures from 0 to 56 kbar. The intermolecular-phonon spectrum shows strong broadening when pressure is applied. The libron modes shift to higher frequencies with a rate of about 0.4 ${\mathrm{cm}}^{\mathrm{-}1}$/kbar. Intramolecular modes broaden or split, and shift toward higher frequencies at a rate of up to 0.88 ${\mathrm{cm}}^{\mathrm{-}1}$/kbar. Most Raman and infrared active modes show strong pressure dependence. Intermolecular- and intramolecular-phonon spectra at various pressures are presented and results are compared with the available experiments.

We study the electronic states of giant single-shell and the recently discovered nested multiple-shell carbon fullerenes within the tight-binding approximation. We use two different approaches, one based on iterations and the other on symmetry, to obtain the π-state energy spectra of large fullerene cages: ${\mathrm{C}}_{240}$, ${\mathrm{C}}_{540}$, ${\mathrm{C}}_{960}$, ${\mathrm{C}}_{1500}$, ${\mathrm{C}}_{2160}$, and ${\mathrm{C}}_{2940}$. Our iteration technique reduces the size of the problem by more than one order of magnitude (factors of ∼12 and 20), while the symmetry-based approach reduces it by a factor of 10. We also find formulas for the highest occupied and lowest unoccupied molecular orbital energies of ${\mathrm{C}}_{60\mathit{n}}^2$ fullerenes as a function of n, demonstrating a tendency towards a metallic regime for increasing n. For multiple-shell fullerenes, we analytically obtain the eigenvalues of the intershell interaction.

We present the results of a tight-binding calculation of the soft-x-ray emission spectra obtained in an earlier study of resonant inelastic scattering of x rays at the carbon k edge of diamond. The close agreement between the calculated spectra and the experimental observations lends support to a picture of momentum conservation restricting the emission process to the same point in the Brillouin zone sampled by the initial excitation. We thus demonstrate qualitatively the feasibility of band-structure determinations with this technique.

A general method is presented for evaluating shape truncation functions of arbitrary Voronoi polyhedra. Unlike some other methods developed in recent years, the method described here does not demand any particular knowledge about a Voronoi pohyhedron other than the position of the set of possible boundary planes. Besides its generality, the accuracy and efficiency of our method are also demonstrated.

Based on data for insulating n-type CdSe at temperatures between 0.05 and 4.2 K and magnetic fields above 3 T (up to the highest measured field of 9 T), we demonstrate an empirical relation between the longitudinal and transverse conductivities given by ${\mathrm{\sigma }}_{\mathit{x}\mathit{y}}$=scrAH${\mathrm{\sigma }}_{\mathit{x}\mathit{x}}^{3/2}$.

We present strong experimental evidence suggesting that we have synthesized the β-${\mathrm{C}}_3$${\mathrm{N}}_4$ phase. This is a material predicted by theory to have bulk moduli comparable to diamond. Thin films containing small crystals were deposited on Si and Ge wafers by rf diode sputtering of a pure graphite target with pure ${\mathrm{N}}_2$. The crystal structure of these phases was investigated using x-ray and electron-beam diffractometry as well as transmission electron microscopy. Our results indicate that the β-${\mathrm{C}}_3$${\mathrm{N}}_4$ particles with typical dimensions of ∼0.5 μm are embedded in a 1-μm-thick layer of a C-N polymer. These particles are believed to crystallize preferentially on Si (100) wafers.

The differential resistance of wires defined in the two-dimensional electron gas in an (Al,Ga)As heterostructure is observed to first increase and then decrease with increasing current. It is demonstrated that this behavior results from the interplay of an enhanced electron-electron-scattering rate (due to current heating of the electron gas), and the partly diffusive nature of boundary scattering in the wire. The data are identified as an experimental observation of the Knudsen maximum and the Poiseuille flow regime in electron transport, and confirm an analogy between electron and gas flow that has been anticipated since the 1950s.

The vibrational density of states associated with the in-plane dynamics of intercalants in graphite intercalation compounds obtained from inelastic-neutron-scattering (INS) measurements shows a characteristic two-peak structure. Using molecular-dynamics simulations of screened Coulomb systems on a strongly corrugated substrate we show that the high-frequency peak is due to two-phonon response, thus providing a correct understanding of the INS experiments. The temperature and q dependence of the incoherent dynamic structure factor confirms our picture.

Another defect center has been observed in micro-Raman and photoluminescence (PL) studies of diamond films deposited on silicon substrates by microwave plasma and hot filament chemical-vapor deposition (HFCVD). The strong, to our knowledge, previously unreported PL emission at 775 nm (1.60 eV) is observed from the HFCVD film only. This impurity/defect center is shown to be distinct from the well-known Si-related defect at 735 nm (1.69 eV) which was observed in both films. The possibility of an interfacial SiC layer being the source of the PL emission is also investigated. Possible impurity/defect complexes responsible for this optical defect center are discussed.

Intercalant-pair and corrugation potentials for stage-1 and stage-2 Rb and K graphite intercalation compounds (GIC’s) were calculated within the local-density-functional-theory framework. The predicted corrugation potential for the stage-2 Rb GIC is in excellent agreement with potentials derived from x-ray experiments, although some discrepancy was found for the stage-2 K GIC. The potentials for stage-2 Rb GIC’s were tested by molecular-dynamics simulations of the wave-vector-dependent neutron-scattering quasielastic linewidth for the Rb GIC, which is found to be in close accord with experiment.

Transmission electron-energy-loss spectra of crystalline ${\mathrm{C}}_{84}$ have been measured and compared with those of ${\mathrm{C}}_{60}$, ${\mathrm{C}}_{70}$, and graphite. Two peaks due to the π plasmon and the π+σ plasmon have been observed at 6.1 and 25.5 eV, respectively. The structures due to π→${\mathrm{\pi }}^{\mathrm{*}}$ transitions of ${\mathrm{C}}_{84}$ are much broader than those of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ because of the lower molecular symmetry of ${\mathrm{C}}_{84}$. The energy of the interband transition between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (band gap) was found to be 1.2 eV from the onset energy in the imaginary part ${\mathrm{\epsilon }}_2$ of the dielectric function.