Chemical shift photoelectron diffraction has been applied to the model system of coadsorbed ${\mathrm{PF}}_{\mathit{x}}$(x=1,2,3) species on Ni(111), produced by electron beam fragmentation of a ${\mathrm{PF}}_3$ overlayer, to determine quantitatively and independently the local adsorption site of each species. ${\mathrm{PF}}_3$ is found to occupy atop adsorption sites above the outermost Ni layer atoms at a P-Ni bond length of (2.07±0.05) Å, ${\mathrm{PF}}_2$ occupies bridge sites at a spacing of (1.70±0.05) Å, while the PF species occupy both types of threefold coordinated hollow sites, maintaining a constant P coordination throughout the fragmentation.

We present first-principles calculations which support a dimer exchange mechanism for substitutional As adsorption on Si(100) surfaces. In contrast to the prevailing picture, we find that the origin of the substitution of the underlying Si atoms by As is the flexible reconstructions of the Si atoms in the resulting geometries, including the newly discovered π bonded reconstruction between the top-layer and the second-layer Si atoms. Calculated scanning tunneling microscopy images of the resulting As-Si heterodimer and the As dimer differ prominently from that of the Si dimer.

We study the selection of the shape and growth velocity of three-dimensional dendritic crystals in cubically anisotropic materials. In the framework of asymptotics beyond all orders we derive the inner boundary-layer equation for the nonaxisymmetric shape correction to the Ivantsov paraboloid shape. The solvability condition for this equation provides selection for both the velocity and the shape. The comparison with available numerical and experimental results is reasonably good.

We discuss a class of similarity solutions to the hydrodynamic equations that describe droplets spreading under capillarity. The spreading time scale of these solutions exhibits a subtle dependence on the microscopic length scale around the contact line. We show that such solutions are linearly stable to small perturbations away from the contact line, justifying the universality of experimental spreading laws. We discuss the transition between the two macroscopic spreading regimes. Our prediction for the transition time is consistent with experimental data.

The density of states in the upper half of the mobility gap of both intrinsic and n-type a-Si:H samples was determined by the modulated photocurrent (MPC) and junction capacitance methods. We conclude that the narrow defect band revealed by the MPC measurements reflects the distribution of relaxed ${\mathit{D}}^0$ states, while the broader and deeper defect band obtained by capacitance measurements corresponds to relaxed ${\mathit{D}}^{\mathrm{-}}$ states. Both distributions are correctly predicted by a calculation that takes into account the relaxation dynamics of deep defects in these different charge states.

Spin-dependent dynamics of polarized carriers in a series of ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$SeZnSe superlattice structures are directly observed by time-resolved upconversion photoluminescence spectroscopy at low temperatures. Polarization measurements in small magnetic fields reveal spin-flip scattering of carriers confined within a magnetic quantum well. A marked change in the dynamics is observed with increasing field and subsequent spin superlattice formation. Exciton lifetimes and spin relaxation are seen to be strongly dependent on both the energy and location of spin states in the heterostructure.

It is found that the thermally activated behavior of nonlinear conduction below the threshold field in thin samples of orthorhombic ${\mathrm{TaS}}_3$ vanishes at temperatures below 10 K. Current noise appearing in the low-temperature region indicates that the electric current is transferred by portions of charge which correspond to displacement of the charge-density waves (CDW) by a distance of the order of their wavelength. This phenomenon can be accounted for as a transition from thermally activated to quantum creep of the CDW.

Spatially resolved electron energy loss spectra of the Si 2p core excitation are obtained in transmission through a single cross section of a 3 nm thick ${\mathrm{Ge}}_{40}$${\mathrm{Si}}_{60}$ quantum well. The spectra yield the positions of the ${\mathit{L}}_1$ and ${\mathrm{\Delta }}_1$ conduction band minima, and the biaxial strain splitting of ${\mathrm{\Delta }}_1$. From annular dark field images, the well composition appears to be graded over three to four layers on the cap side. The conduction band offset varies from 0 eV at the well edge to +25 meV in the well center, relative to the Si substrate and cap. The biaxial strain splitting is 0.28 eV in the well center and shows an asymmetry with position that is consistent with the annular dark field data.

Using single-electron capacitance spectroscopy, we map the magnetic field dependence of the ground state energies of a single quantum dot containing from 0 to 50 electrons. The experimental spectra reproduce many features of a noninteracting electron model with an added fixed charging energy. However, in detailed observations deviations are apparent: Exchange induces a two-electron singlet-triplet transition, self-consistency of the confinement potential causes the dot to assume a quasi-two-dimensional character, and features develop which are suggestive of the fractional quantum Hall effect.

The Hall resistivity ${\mathrm{\rho }}_{\mathit{H}}$ and the longitudinal resistivity ρ of single crystalline ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{x}}$ are measured in the thermally activated flux flow regime. It is shown that ${\mathrm{\rho }}_{\mathit{H}}$ scales to a universal function of ρ: ${\mathrm{\rho }}_{\mathit{H}}$(T)=A[ρ(T)${]}^{\mathrm{\beta }}$, where β=2±0.1 and A is a positive and magnetic field independent coefficient for magnetic fields from 1 to 5 T. A resistivity-squared dependence of ${\mathrm{\rho }}_{\mathit{H}}$ can be explained by the recent theory of Vinokur, Geshkenbein, Feigel’man, and Blatter in terms of weak pinning of a vortex liquid.

The issues of sign reversal of the Hall voltage and scaling between longitudinal (${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$) and Hall (${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$) resistivities are studied in ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{10}$ films in which the vortex dynamics is drastically changed by flux pinning at heavy-ion-irradiation–induced linear defects. While the sign anomaly diminishes with increasing defect concentration, the power law ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$∼${\mathrm{\rho }}_{\mathit{x}\mathit{x}}^{\mathrm{\beta }}$, β=1.85±0.1, holds even after irradiation. This result shows that the scaling is a universal feature of the mixed state in this system. The sign anomaly, on the other hand, is not consistent with a model that invokes pinning-induced backflow in the vortex core as the mechanism for this effect.

We point out that a nonunitary pairing state is realized in the so-called B phase in a low T and H region of ${\mathrm{UPt}}_3$ where time inversion is already known to be broken. This nonunitarity leads us to understand several long-standing puzzles, including the large ‘‘residual’’ T-linear specific heat and thermal conductivity at lower T. The B phase is concluded to be spin-triplet odd parity (so-called β phase), belonging to a one-dimensional representation. A recent muon spin rotation result, detecting the intrinsic moment in the B phase, is consistent with this identification.

We present a systematic study of local spin moments of impurities in alkali-metal hosts, by means of ab initio, local-spin-density electronic structure calculations. Our results predict for the first time that besides the well-known cases of 3d and 4d impurities also 5d and some sp impurities are magnetic in the alkali metals both on substitutional and interstitial positions.

Experiments reveal that the near surface second-order nonlinear optical susceptibility, ${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$(2ω,ω,ω), is significantly affected by band-bending-induced electric fields in the depletion region of GaAs(001). Both n- and p-type GaAs samples exhibit a reduction of the bulk second-order susceptibility ${\mathrm{\chi }}_{\mathit{y}\mathit{x}\mathit{z}}^{\mathrm{}\left(2\right)\mathrm{}}$ independent of electric field direction. A three band theoretical model was used to qualitatively explain these observations.

In this paper, it is reported that the electroluminescence (EL) of porous silicon shows a reversible spectral shift as large as 270 nm for an external bias variation of 0.6 V. This electroluminescence is obtained upon cathodic polarization of lightly doped n-type porous silicon in contact with aqueous persulphate solutions. The study of the EL behavior as a function of the external voltage and the persulphate ion concentration proves that while the amplitude of the EL is proportional to the intensity of the exchanged current, the spectral position is only determined by the applied voltage.

We have investigated a model co-adsorption system using electron energy loss spectroscopy. When the dispersed phase of K graphite is exposed to ${\mathrm{O}}_2$ at 25 K, the charge donated by the alkali is depleted, as evidenced by a reduction of the surface plasmon energy from ∼320 to ∼130 meV. The co-adsorbed ${\mathrm{O}}_2$ species is molecular, with a vibrational frequency consistent with the ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$ ground state of ${\mathrm{O}}_2^{\mathrm{-}}$. The results demonstrate local transfer of charge from alkali to co-adsorbate, consistent with a simple electrostatic model. By contrast, CO perturbs the K-graphite interaction only weakly.

Swollen networks possess permanent elastic constraints that induce static variations 〈δ${\mathit{\phi }}^2$${\mathrm{〉}}_{\mathit{s}}$ at a microscopic scale in the polymer volume fraction φ. It is shown that the concentration polydispersity 〈δ${\mathit{\phi }}^2$${\mathrm{〉}}_{\mathit{s}}$/${\mathit{\phi }}^2$ is related to the macroscopic osmotic and elastic properties of the gel. An expression is derived for the dependence of 〈δ${\mathit{\phi }}^2$${\mathrm{〉}}_{\mathit{s}}$/${\mathit{\phi }}^2$ on swelling. Good agreement is found with previously reported small-angle neutron scattering measurements in randomly cross-linked polyvinyl acetate and end-linked polydimethyl siloxane networks swollen in toluene.

We performed Green’s function calculations on the double ionization of ${\mathrm{SiF}}_4$ in order to interpret its Si 2p Auger spectrum, which has caused controversy for a decade. We provide an accurate interpretation and a model of far wider generality in the Auger study of ionic species. Contrary to the usual self-imaging picture of Auger spectroscopy, the silicon spectrum exhibits eight distinct bands reflecting a complete and precise image of the fluorine ligands, due to strong hole-localization effects. The generality of this foreign-imaging character of Auger spectroscopy is discussed.

An essential signature of the topological nature of all Aharonov-Bohm type phases is that they are nondispersive, i.e., independent of the velocity (wavelength) of the interfering particles. This implies that an Aharonov-Bohm phase shift can greatly exceed the usual limit given by the coherence length of the interfering beams. We report the results of a polarized neutron experiment demonstrating this property for a spin-rotation analog of the scalar Aharonov-Bohm effect.

A general theory of coherent behavior (‘‘locking’’) in a globally coupled ensemble of pulse-emitting units is presented. Each unit is modeled as a dynamic threshold device with arbitrary excitability function and noise. The interaction is described by a general linear-response kernel that includes a transmission delay. In the bulk limit, the dynamics is solved exactly. Two types of solutions are studied, viz., coherent states with synchronous activity of all units and incoherent stationary states, and their stability is analyzed in the low-noise limit.