The de Haas–van Alphen (dHvA) effect of the stage-1 compound intercalated with ${\mathrm{CdCl}}_2$ has been investigated with magnetic fields up to 14 T and for temperatures between 50 mK and 1.87 K. There are two dominant oscillations with values of 1144 and 1190 T with the magnetic field parallel to the c axis. The average value of the mass for these two frequencies is (0.26±0.01)${\mathit{m}}_0$, where ${\mathit{m}}_0$ is the mass of the electron. The change of the frequencies with magnetic-field direction shows that the Fermi surface is an undulating cylinder directed along the c axis with a 4% difference between the minimum and maximum cross-sectional areas. The Fermi energy determined from the Holzwarth band model is -1.113 eV. There is also a dHvA frequency of 334 T with the magnetic field parallel to the c axis from a minority carrier.

The damping of collective electron resonances in clusters which develop into plasmon polaritons at larger sizes is investigated for free, supported, and embedded neutral metal clusters. Embedding of free 2 nm Ag clusters of 2-nm diameter into a ${\mathrm{SiO}}_2$ matrix leads to an increase of the width of the resonances by more than a factor of 3. The optical spectra are compared with the Mie theory using size-effect-modified dielectric functions of the solid state. The results corroborate the assumption that the widths of the resonances strongly depend on chemical interface effects. The results are briefly discussed with regard to limited-mean-free-path and quantum-size-effect theories and a recent approach by Persson. It is demonstrated that the widths of the spectra of supported and embedded clusters have to be interpreted with care since true intrinsic size effects of the clusters appear to be less effective than previously believed and can be obscured by the chemical interface damping.

Results of scanning-tunneling-microscopy (STM) and molecular-dynamics (MD) annealing studies based on quantum-mechanically derived interatomic forces using a semiempirical density-functional approach are combined for analyzing diamond surface structures. Experimentally obtained STM images of diamond (100) and (111) faces on polycrystalline films reveal (1×1),(√3 × √3 ) R30°, and possible (2×1) structures. The (100) faces show stable (2×1) reconstruction with dimer formation. Surface structures with and without adsorbed hydrogen are determined and their stability is obtained by MD simulated annealing techniques. The bulklike and (√3 × √3 ) R30° structures, as they are observed on grown (111) facets, are attributed to the two different single atomic (111) layers, which support growth mechanisms, in which the two alternating single atomic layers grow in turn and not simultaneously. The equilibrium surface modifications which have been realized are electronically characterized by investigating the local electronic density of states at selected surface atoms. This information is compared and related to the features seen in the STM images.

Strained island growth in lattice-mismatched epitaxial systems differs from relaxed island growth. The total elastic energy of a strained island changes its chemical potential and growth rate. This effect is investigated for an ensemble of misfitting coplanar hemispherical caps interacting through surface diffusion alone. A general expression for the growth rate of strained islands is obtained by including elastic energies in the driving force for Ostwald ripening. For the first time, to our knowledge, a coherent-to-incoherent transition is shown to dramatically affect ripening kinetics. Coherent islands are shown to grow more slowly than incoherent islands of the same radius. Consequently, the growth rate of an island accelerates when it dislocates at the coherent-to-incoherent transition in agreement with recent experimental observations.

A boson-expansion method is used to study one- and two-boson states in metallic clusters. A jellium model and local-density-approximation energy-density-functional theory are the starting point for obtaining the basic bosons describing electron excitations. A boson mapping allows one to diagonalize the residual interaction between bosons. For the example of the ${\mathrm{Na}}_{21}^{+}$ cluster, it is found that strong anharmonic effects appear in the electronic excitation spectrum.

We calculate wetting behavior for the adsorption of Ne, Ar, Kr, and Xe for temperatures above their triple point. Experimental observations of wetting transitions of these simple liquids are predicted. We also report a nearly universal trend in the physical interaction parameters for Ar, Kr, and Xe on various substrates. With a simple model, we show that the classical ‘‘law of corresponding states’’ can be extended to predict approximately universal behavior in the wetting transitions of these films. We then demonstrate, by comparison with Ne, ${\mathrm{H}}_2$, and He films, that quantum effects enhance wetting in that there is a larger range of adsorption parameters leading to wetting when zero-point motion is included.

The surface plasmon resonance of alkali-metal (potassium) and noble-metal (silver) clusters embedded in different dielectric matrices is studied within the time-dependent density-functional formalism and the jellium model, including dielectric screening for the electron-electron interaction. The calculated redshift of the plasma frequency as the dielectric constant (ε) of the matrix increases is in good agreement with the available experimental data for both potassium and silver clusters. In the case of potassium, the shifts induced by rare-gas matrices are predicted. A tendency to saturation in the polarizability and surface plasmon resonance when ε increases is obtained and is due to the screening of the Coulomb interaction by the dielectric surrounding the cluster. We conclude that the basic effect of the dielectric matrix comes from the direct screening of the electron-electron interaction and not from the modification of the cluster ground state.

We have investigated the fragmentation of ${\mathrm{C}}_{60}$,${\mathrm{C}}_{70}$ carbon clusters using molecular-dynamics simulation combined with the empirical-tight-binding total-energy-calculation method. The fragmentation process is studied by considering the heat capacity, binding energy, and the average number of neighboring atoms in terms of temperature and the relation to the formation process is further discussed.

The changes in resistivity in fullerene (${\mathrm{C}}_{60}$) films subjected to 320-keV Xe ion irradiation are investigated as a function of ion dose. From a comparison of this dependence with similar data on Xe irradiated diamond and with data on C implanted fused quartz, it is concluded that upon ion impact ${\mathrm{C}}_{60}$ clusters completely disintegrate. This disintegration releases about 60 carbon atoms which disperse among the remaining intact ${\mathrm{C}}_{60}$ spheres giving rise to hopping conductivity between isolated C atoms. The present finding may explain the negative results in the search for fullerenes conjectured to exist in instellar dust and may establish limitations on the use of ion implantation to dope fullerenes with the aim of synthesizing new forms of high-${\mathit{T}}_{\mathit{c}}$ superconductors.

The collective modes of coaxial-graphene-tubule systems are calculated using both classical and quantum-mechanical approaches. While the derived results are valid for any number of coaxial tubules, the numerical results for the dispersion relations of the plasmons are presented for a system consisting of four graphene tubules for various values of the azimuthal quantum number m. The lowest modes (m=0) are found to be quasiacoustic, like the one-dimensional plasmons, whereas the higher modes are of optical nature. For each m, the number of observable modes is equal to the number of tubules having a metallic character. The effect of the intertubule interactions is a broadening of the frequency range of the m modes. This broadening remains important so long as the plasmon momentum is significantly smaller than the Fermi momentum.

Adsorbate bonding and preferred adsorption sites and rotational orientations of ${\mathrm{C}}_{60}$ on Au(111) and Ag(111) were studied using scanning tunneling microscopy (STM) and related techniques. Spatially resolved tunneling spectroscopy and barrier height measurements indicated that bonding occurs by charge transfer from the metal to ${\mathrm{C}}_{60}$. The internal structure of adsorbed ${\mathrm{C}}_{60}$ observed by STM was found to be a strong function of the adsorption site, the molecular orientation, and the tunneling bias. Occupied state images were found to reflect the adsorption site symmetry while unoccupied state images reflected the molecular symmetry. In domains where all the molecules were in equivalent adsorption sites, the observed internal structure of adsorbed ${\mathrm{C}}_{60}$ was assigned to an on-top site with the five-membered ring on the surface.

We have used a variety of cw optical and optically detected magnetic-resonance techniques to characterize long-lived photoexcitations in methanofullerene (${\mathrm{C}}_{61}$) as a dispersion in polystyrene glass, at temperatures below 10 K. We identify triplet excitons with zero-field-splitting (ZFS) parameters D=105×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$ and E=9×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$. The triplet excitons are characterized by two photoinduced absorption (PA) bands in the triplet manifold at 1.5 and 1.7 eV, both with a lifetime of 160 μsec, and a phosphorescence emission (PL) band with onset at 1.85 eV and a lifetime of 10 μsec. The difference in lifetimes between PA and PL is explained as being due to different recombination kinetics of the triplet sublevels. This and the finite axial symmetry ZFS parameter E≠0 compared to E=0 for triplets in ${\mathrm{C}}_{60}$ show the lower symmetry of triplets in ${\mathrm{C}}_{61}$, consistent with its postulated distortions from icosahedral symmetry in the ground-state structure.

Input parameters are reported for the theory of ideal metals, a uniform electron-gas model of the elemental transition metals. These input parameters, the electron density, and the ‘‘bonding valence,’’ have been given previously for the 3d and 4d series of transition metals. Here, we extend our work based on recent calculations of Sigalas et al. [Phys. Rev. B 45, 5777 (1992)] to include the 5d series. We have also calculated the cohesive energies of the 5d transition metals using the theory of ideal metals with these parameters. The calculations agree with experiment to within ±25%.

Fine structures near the Si K-absorption edges of single-crystal Si and amorphous ${\mathrm{SiO}}_2$ were measured for well-characterized films by a transmission method with a high-resolution double-crystal spectrometer. The spectrum of single-crystal Si was not affected by the changes of the angle between the polarization vector and the crystal axis. Both single-crystal Si and amorphous ${\mathrm{SiO}}_2$ showed strong absorption lines near the edges. Energies of the K-absorption edges were determined to be 1840.3 and 1846.1 eV for single-crystal Si and amorphous ${\mathrm{SiO}}_2$, respectively. The edge structure of single-crystal Si shows features related to the theoretical empty-conduction-band structure of Si. In amorphous ${\mathrm{SiO}}_2$, the strong absorption line can be interpreted in terms of the excitonic state.

The dielectric constants and the refractive index of n-type GaAs are obtained by a second-order many-body-perturbation-theory calculation of the transition energy of the donor-triad molecules. The imaginary part of the dielectric constant, which is associated with the optical conductivity, exhibits a peak at an energy in relatively good agreement with the observed line ‘‘X.’’ This result supports the interpretation of this peak as due to the electronic ${\mathrm{H}}_3$→${\mathrm{H}}_3^{+}$ transition from their impurity ground state.

We report ab initio calculations of the lattice constants and the electronic structure of the hexagonal wurtzite semiconductors CdS and CdSe. The calculations have been carried out self-consistently in the local-density approximation employing nonlocal, separable, and norm-conserving pseudopotentials. We use ${\mathrm{Cd}}^{12+}$ ionic pseudopotentials so that the Cd 4d electrons are explicitly taken into account as valence electrons. The calculated electronic structure is compared with photoemission data. Calculated and measured bands show good agreement in the energy region of the mostly anion-derived s-p valence bands. The calculated Cd 4d bands result for both compounds roughly 3 eV too high in energy as compared to the measured data. This rigid shift of the narrow 4d bands is related to correlation effects which are not fully taken into account in the local-density approximation.

The acoustic scattering rate of the carriers in a two-dimensional electron gas is calculated here under the condition of low temperature when the approximations of the well-known traditional theory are not valid. The results of numerical calculations are presented for GaAs and Si. The results are interesting in that they are significantly different from those that follow from the traditional theory.

We report the study of a mixed-spin multiple-quantum-well system consisting of alternating ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se and ${\mathrm{Zn}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Fe}}_{\mathit{y}}$Se layers, grown by molecular-beam epitaxy. The two spin components of the heavy-hole exciton are each dominated by different exchange interactions as revealed by their temperature and magnetic-field dependence. We find that the energy of the spin-down ${\mathrm{\sigma }}_{+}$ component (-3/2,-1/2) is well described by exchange interactions of the electrons and holes with ${\mathrm{Mn}}^{2+}$ ions (Brillouin paramagnet), while the energy of the spin-up ${\mathrm{\sigma }}_{\mathrm{-}}$ component (+3/2,+1/2) is determined by the interactions of carriers with ${\mathrm{Fe}}^{2+}$ ions (Van Vleck paramagnet). Thus, these tailored heterostructures permit simultaneous study of Brillouin and Van Vleck paramagnetism as well as associated carrier dynamics in a single structure.

Photoluminescence studies on ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ layers exceeding the critical thickness show not only dislocation-related D1, . . ., D4, but also in addition a broad band (T band), centered at ∼110 meV below the strained alloy band gap. Depth profiling studies show that the T band is due to centers in the ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$. The excitation power dependence and high quantum efficiency of the T band can be explained by assuming that it is due to an isoelectronically trapped exciton. T-band line shapes were fitted by a model based on statistical fluctuations of the Ge content and their effect on the local gap energy.

A study of the magnetoplasmons of a cylindrical quasi-one-dimensional electron system is given in the presence of an axial magnetic field B. A two-subband system is considered and the dispersion relations for both intrasubband and intersubband magnetoplasmons are obtained using the exact infinite wall eigenfunctions. It is demonstrated that the application of a longitudinal B changes the mode frequencies for both types of excitations. The model includes both local-field corrections, which are shown to be important, and the Hartree potential, which is given in closed form.