The formation energies of single- and double-layer steps on Si(001) surfaces were calculated. For each case, two configurations with surface dimerization axes normal or parallel to the step edge were examined. Single-layer steps are found to have the lowest formation energy. Bilayer steps become energetically more favorable on surfaces misoriented towards [110] or [1¯10] axes where low- and high-energy single-layer steps are forced to alternate with each other.

The 2${\mathrm{k}}_{\mathrm{F}}$ modulated structure of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) at 15 K has been analyzed by use of a set of satellite intensities collected at the National Synchrotron Light Source. The analysis in the five-dimensional superspace group P:P$2_1$/c:cmm shows the largest modulation to be a slip of the TTF molecules with an amplitude of about 0.02 Å, in the direction of the long molecular axis of the molecule. The TCNQ translational modulations are similar, but of much smaller magnitude . Rotations about the long molecular axes of both type of molecules are also observed.

We employ a density-functional theory designed to treat polyatomic systems, and use it in an approximate form to describe the freezing of water.

The paper presents for the first time microscopic evidence for the presence of oxygen in thermal donor centers in silicon. The evidence as obtained by electron nuclear double resonance on the magnetic isotope ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ is conclusive.

We report the results of a high-resolution synchrotron x-ray–scattering study of the melting of Xe monolayers adsorbed on Ag(111). We find that at high temperatures (T>100 K) all features of the melting transition are, within errors, the same as those found for xenon on graphite. Specifically, in both cases the xenon solid melts into a ‘‘hexatic phase’’ with essentially identical hexatic stiffness. This strongly suggests that the existence of the hexatic phase is a feature of the two-dimensional melting process rather than the adsorbate-substrate interaction.

The end-to-end vector relaxation time, τ, and center-of-mass diffusion constant, D, of a nonintersecting chain with nearest-neighbor attractive interactions were investigated. Data were obtained by Monte Carlo simulation of motion as a function of temperature in the free-draining approximation. The range of temperatures includes the collapse region. It is found that the expression τ≃N〈${\mathrm{R}}^2$〉 is valid in the collapse region. The diffusion constant in the collapsed state is given by D≃${\mathrm{N}}^{\mathrm{-}2/3}$ which indicates that only the surface beads of the collapsed globule contribute to the motion.

The atomic structure of the NiAl(111) surface has been investigated through a LEED I-V analysis. In order to achieve a unique, consistent agreement between experimental and calculated I-V spectra, this surface is determined to be a 50-50 mixture of two ordered domains, one of which is Al terminated and the other is Ni terminated. The relaxations of the outermost interlayer spacings in each domain have been determined as well, and they are different for the two domains. The NiAl(111) surface is the first reported example of a binary-alloy surface in which a mixture of ordered domains with differing terminations coexists.

The detailed structural changes that occur during the isothermal transition from a glass to a single-phase crystalline solid have been determined for the first time by use of the modern technique of high-performance liquid chromatography. Quantitative measurements of the evolution of the type and relative concentration of individual structural units present during the devitrification process were made on lead pyrophosphate glasses annealed below, at, and above the glass transition temperature.

The mysterious ‘‘fast’’ and ‘‘exotic’’ negative carriers in liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ are interpreted as multielectron bubbles. The fast carrier is shown, by a detailed calculation of mobility, to be a two-electron bubble with a radius of approximately 30 Å. A crucial role is played by the unusual kinematics of rotons, which have not previously been adequately treated. The other exotic carriers are multielectron bubbles with higher charges.

Diffusion-limited reactions A+B→inert, with input A,B, or the black reaction (inert→A+B), are studied. I have found that in equilibrium, segregation phenomena can occur below or in two dimensions, with typical size of A-rich and B-rich clusters ξ∼1/$R^{2/2\mathrm{-}d}$ for d<2 and ξ∼exp(1/$R^2$) for d=2, respectively, where R is the A and B input rate or back-reaction rate.

Energy transport in disordered media by use of a random walks through a new entropylike function ${\mathrm{I}}_{\mathrm{N}}$ which results in an information dimension ${\mathrm{D}}_{\mathrm{I}}$ of a random-walk process is studied. ${\mathrm{D}}_{\mathrm{I}}$ is calculated and compared to the fractal dimension for two-dimensional square lattices. It is found that a fractal lattice has a much broader (by a factor of 5) site-visitation distribution than a perfect lattice. The above parameters contain more information than the usual random-walk parameters, and provide a new picture and characteristic quantities where random walks are used to simulate transport properties.

A planar dc SQUID with integrated pickup loops and field coils has allowed precise ac magnetic susceptibility measurements of ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te-CdTe superlattices as a function of temperature and applied magnetic field. The spin-glass transition in 86-Å-thick magnetic layers broadens and disappears as the thickness is reduced to 18 Å, suggesting the inability of the 2D system to support long-range spin-glass order. Novel hysteretic effects are seen in the thinnest layers.

We have performed an ab initio pseudopotential total-energy study of hydrogen adsorption on the Ru(0001) surface. It is found that the surface threefold hollow sites have the lowest energy, as expected for close-packed metal surfaces. However, at higher coverage, the occupation of the subsurface octahedral sites is made possible by the repulsive interaction between nearest-neighbor surface hollow sites. Our results resolve the previous controversy of two hydrogen-binding states observed in the measurements of work-function changes and sticking coefficients.

Multiple-scattering Xα results are reported which show that spin polarization must be included to obtain a detailed understanding of the hyperfine spectra of the Si dangling-bond ${\mathrm{P}}_{\mathrm{b}}$ defect at the ${\mathrm{SiO}}_2$/Si(111) interface. The largest superhyperfine interaction is found to be produced not by the trivalent Si atom’s nearest neighbors as has been commonly assumed, but by three second-nearest neighbors located behind the defect in bulk c-Si. Our ${\mathrm{P}}_{\mathrm{b}}$ center results support the threefold-coordinated Si model for this defect; they also suggest a straightforward interpretation of recent ESR data on the dominant paramagnetic center in a-Si:H.

The short coherence length of high-${\mathrm{T}}_{\mathrm{c}}$ oxides is shown to induce considerable weakening of the pair potential at surfaces and interfaces. It is argued that this effect is responsible for the existence of internal Josephson junctions at twin boundaries, which are at the origin of the superconductive glassy state, as well as for gapless tunneling characteristics.

The dynamical coupling of the first two conduction-band sublevels in an 84.5-Å GaAs multiple-quantum-well structure by an intense ${\mathrm{CO}}_2$ laser pulse leads to drastic changes in the absorption spectrum of the lowest excitons. In order to observe this new effect, the polarization of the pump laser has to be perpendicular to the plane of the layers. From the analysis of the experimental results in terms of a three-level nonlinear susceptibility the energy difference of the first two conduction-band sublevels and their transition dipole moment are determined to be 110.3 meV and 14 e⋅Å, respectively.

We consider the dynamics of an electron in a finite one-dimensional system, subject to a uniform electric field (or an electron in a ring; subject to an emf induced by a time-dependent magnetic flux). In the presence of elastic scattering due to localized potentials the driving source does not supply energy to the system in the steady state. The dissipation in the presence of inelastic scattering is evaluated. The Ohmic resistance of the system depends crucially on the inelastic rate even in the weak-localization limit.

Studies of ferromagnetic resonance lines at ≃73 and ≃36 GHz yield the static and dynamic parameters of ultrathin layers of bcc Fe(100) grown on fcc Ag(100) substrates and covered by fcc Au(100). Results for layer thicknesses of 28, 17, 5, and 3 monolayers when extrapolated to 2 monolayers indicate that the magnetization of bilayers of Fe should be perpendicular to the film. This indicates a large unexplained contribution to the magnetic anisotropy at or near the surfaces. A rapid increase in the Gilbert damping coefficient with decreasing film thickness reflects an enhanced role of spin-orbit coupling.

The temperature-dependent dielectric response and conductivity at ≃${10}^{10}$ Hz is reported for the title compound, (NMP${)}_{\mathrm{x}}$(Phen${)}_{1\mathrm{-}\mathrm{x}}$(TCNQ), in the regime 0.50≤x≤0.59, spanning commensurate, bipolaron, and incommensurate regimes. The large and strongly temperature-dependent dieelectric constant and σ${(10\mathrm{}}^{10}$ Hz) are accounted for by a model based on the dynamics of pinned charge-density waves and the presence of relatively mobile charged bipolarons (confined soliton pairs) in the commensurate phase.

We report the first simultaneous observation of two of the quadrupole-split components of the nuclear magnetic resonance in oriented nuclei. Perturbation of the gamma-ray anisotropy from 72-d ${}_{}{}^{160}{}_{}{}^{}\mathrm{Tb}$ implanted and oriented at low temperatures in a Tb single crystal was used to detect the resonance signal. From the resonance frequencies, ${\nu }_1$=480.0(4) MHz and ${\nu }_2$=842.3(3) MHz, we derive the magnetic dipole and electric quadrupole interaction frequencies independently. They are ${\nu }_M$=1385.8(1.6) MHz and ${\nu }_P$=181.2(4) MHz; ${\nu }_M$ is about 5% higher than expected from the NMR of stable Tb${:}^{159}$Tb combined with an ESR determination of the g-factor ratio, but is in agreement with bulk nuclear orientation results.