By preselecting the appropriate photoelectron energies with the aid of simple model calculations, we show that the main peaks in angular distributions of core-level photoemission from adsorbed species on surfaces, caused by elastic backscattering, can be directly related to adsorbate-substrate interatomic directions, thus permitting direct real-space triangulation of adsorption sites on surfaces. The method is demonstrated with the aid of experimental data from oxygen and CO on Cu(110), and offers comparable spatial resolution to holographic inversion, but requires a much smaller data set.

Optical second-harmonic generation and ellipsometry were used to study molecular alignment in an interfacial region and the deviation of the layer normal from the surface-rubbing axis in the smectic-A phase of a ferroelectric liquid crystal. The results can be well explained by the surface electroclinic effect.

A simple model is developed to describe the intermolecular interactions in solid ${\mathrm{C}}_{60}$. The model correctly predicts the observed ground-state structure Pa3¯ and the first-order transition to the high-temperature fcc phase. The calculated transition temperature ${\mathit{T}}_{\mathit{c}}$∼270 K and its pressure dependence ${\mathit{dT}}_{\mathit{c}}$/dP=11.5 K/kbar agree very well with recent experiments. Below ${\mathit{T}}_{\mathit{c}}$, there exist nearly degenerate orientations that are separated by potential barriers of order ∼300 meV, leading to a glassy behavior with ${\mathit{T}}_{\mathit{g}}$∼90–130 K. It is suggested that similar orientational disorder exists in ${\mathrm{K}}_3$${\mathrm{C}}_{60}$ and other fullerides.

By measuring fracton mode displacements in artificial piezoelectric composities with hierarchical structure, we find direct evidence of their localized and self-similar character. Clear indications of the existence of multiple fracton and phonon regimes are also presented.

The ordering kinetics of a conserved order parameter with O(n) symmetry are studied using the approach of Mazenko. Conventional scaling is obtained for any finite n, while for n strictly infinite the multiscaling form found by Coniglio and Zannetti is recovered. The two different results can be understood in terms of the different orders in which the limits n→∞ and t→∞ are taken. For large, finite n the characteristic scale grows as L(t)∼(t/ln n${)}^{1/4}$ for t→∞.

The Kapitza conductance between isotopically enriched synthetic diamond and Ti, Al, Au, and Pb has been studied using picosecond optical techniques. For Ti and Al, which have Debye temperatures roughly 1/5 of that of diamond, the measured heat flow is in reasonable agreement with calculations of the phonon heat transport based on a simple lattice dynamical model. However, for Au and Pb, which have Debye temperatures 0.07 and 0.04 times that of diamond, the measured Kapitza conductances are as much as 100 times larger than expected, suggesting the existence of a second conductance mechanism.

We measure the activation energy for surface diffusion of isolated Pb adatoms on Ge(111) by observing individual atomic interchanges using a scanning tunneling microscope. The diffusion occurs mainly along one direction of the c(2×8) reconstructed surface with Pb adatoms moving between substitutional Ge adatom sites. Only half of the adatom interchanges are to near-neighbor sites, the rest are ‘‘long jumps.’’ The scanning process does not affect the diffusion. For temperatures from 24 to 79 °C we find the diffusion obeys an Arrhenius law with an activation energy of 0.54±0.03 eV.

The structures of monolayers of Hg atoms underpotentially deposited on Au(111) were resolved with the atomic force microscope. In sulfate, nitrate, and perchlorate electrolytes, a hexagonal overlayer with a 0.58±0.02-nm spacing was seen. In acetate, a hexagonal lattice exhibiting a 0.74±0.05-nm spacing was observed positive of the underpotential-deposition potential, a rhombic lattice with a 0.43±0.02-nm spacing was seen at intermediate potentials, and another hexagonal lattice with a 0.30±0.03-nm spacing was found just positive of bulk deposition.

Ultrathin (≃1000 Å) ordered films of symmetric diblock copolymers deposited on a plane solid substrate exhibit relief domains at their free surface. Their height is equal to the period L of the lamellar stacking (L=310 Å). The thickness profile at the edge of the domains has been investigated using atomic force microscopy. Its shape, independent of the domain size, is close to the theoretical prediction for the free surface of a smectic liquid crystal above a single dislocation. However, its lateral extension appears to be larger than expected by a factor of 20; the effect of the polymer/air surface tension is qualitatively invoked.

On the basis of realistic tight-binding band-structure calculations, we predict that carbon microtubules exhibit striking variations in electronic transport, from metallic to semiconducting with narrow and moderate band gaps, depending on the diameter of the tubule and on the degree of helical arrangement of the carbon hexagons. The origin of this drastic variation in the band structure is explained in terms of the two-dimensional band structure of graphite.

Analysis of the effects of hydrostatic pressure on the electronic emission and capture properties of the (0/+) and (+/++) deep levels of the EL2 defect in GaAs leads to the following conclusions: (1) Both levels move higher in the band gap with pressure; (2) relatively large inward (outward) lattice relaxations accompany electron emission (capture) from (by) these levels; and (3) the magnitudes of the relaxations agree quantitatively with theoretical results which identify EL2 as the As antisite defect. These results which emphasize the antibonding character of the orbitals which describe EL2 are consistent with this identification.

Mode locking in ac-driven charge-density waves is studied numerically in two and three dimensions, using both continuous equations of motion and a cellular automaton model. As the system size is increased, a complete devil’s staircase of steps is approached. The fractal dimension of the set of gaps in the staircase is found to be ${\mathit{D}}_0$=0.75±0.04 (0.88±0.05) in two (three) dimensions in the automaton model. The spectrum of singularities f(α) is calculated and is related to the dynamic critical exponent ζ for the charge-density-wave depinning transition.

The low-frequency conductivity ${\mathrm{\sigma }}_1$(ω) of ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ has a Drude-like component below ${\mathit{T}}_{\mathit{c}}$. Interpreting the width of this component as the quasiparticle relaxation rate (${\mathrm{\tau }}^{\mathrm{-}1}$), we find that ${\mathrm{\tau }}^{\mathrm{-}1}$ decreases dramatically just below ${\mathit{T}}_{\mathit{c}}$, in sharp contrast with the T-linear ${\mathrm{\tau }}^{\mathrm{-}1}$ above ${\mathit{T}}_{\mathit{c}}$ and ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CuO}}_6$. This decrease causes a peak in ${\mathrm{\sigma }}_1$(ω→0,T) for T just below ${\mathit{T}}_{\mathit{c}}$, a peak which is due to the scattering rate and not to pair coherence effects, consistent with the lack of a coherence peak in the NMR relaxation rate. This result implies that the excitations which scatter the carriers are suppressed below ${\mathit{T}}_{\mathit{c}}$.

It has been proposed that the Abrikosov flux lattice in high-${\mathit{T}}_{\mathit{c}}$ superconductors is melted over a significant fraction of the phase diagram. We provide a thermodynamic argument which establishes that the angular dependence of the melting temperature is controlled by the superconducting mass anisotropy. Using a low-frequency torsional-oscillator technique, this relationship has been tested in untwinned single-crystal ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. The results offer decisive support for the melting proposal.

We study the specific heat of single-crystal ${\mathrm{UPt}}_3$ for uniaxial stress 0≤S≤4 kbar. For S∥c^, the lower and upper superconducting transitions move towards each other in temperature and merge by S=2 kbar and T=485 mK. In the normal state, the Sommerfeld constant γ increases 12% by 2 kbar and then plateaus. By contrast, for S∥a^, γ decreases steadily and the onset ${\mathit{T}}_{\mathit{c}}$’s of the two superconducting transitions remain essentially unchanged, although the specific-heat peaks broaden markedly. Residual strain in the basal plane may account for some crystals of ${\mathrm{UPt}}_3$ showing only one broad superconducting transition.

We perform a general symmetry analysis of optical experiments on samples in the ‘‘scrPscrT state,’’ that is, samples for which 3D inversion symmetry scrP and time inversion symmetry scrT are each broken, but which are invariant under the product scrPscrT. We show that scrPscrT symmetry is compatible with all known results on optical rotation in the high-temperature superconductors. We also find a o/Iunique and accessible experimental signature for the scrPscrT state.

A simple model is proposed for the photoluminescent emission spectrum in the fractional quantum Hall system. In this model we show that the expression for the emission intensity I(ω) can be factorized into an excitonlike part and a portion which depends explicitly on the dynamical structure factor S(q,ω) for the unperturbed quantum Hall state. For the observed ${\mathit{E}}_0$ line the model explains a series of intensity minima which occur at the onset of each plateau in ${\mathrm{\sigma }}_{\mathit{x}\mathit{y}}$ for ν=2/3, 7/11, 3/5, and 4/7, superimposed on a general rising trend versus applied magnetic field B.

Multielectron excitations involving deep and shallow core levels have been identified for the first time in the x-ray-absorption fine-structure (XAFS) energy range for crystalline samples, RbBr and β-${\mathrm{PbO}}_2$. The XAFS oscillations have been fitted and subtracted from the experimental data using theoretical standards. The positions of steps in the extracted background are in excellent agreement with the Z+1 approximation. The ability to determine this structure has important implications for XAFS and multiexcitation studies.

Core excitation in Al atoms following the impact of pure Al clusters and composite Al-Au clusters on Au surfaces has been investigated by molecular-dynamics simulation. Core excitation was found to be most probable during the early, compressional phase of cluster impacts. Our simulations predict that a significant fraction of the core-excited Al cluster atoms will decay by atomiclike Auger emission following ejection from the surface, providing a useful diagnostic tool to investigate collisions of cluster ions with surfaces.

A growth model is presented to simulate the corrosion pattern in pitting corrosion in three dimensions. The pitting corrosion is controlled by diffusion of anions toward the metal surface. The computer simulation is performed to study the scaling structure of pit-size distribution in the corrosion pattern. It is shown that a transition occurs in the overall corrosion pattern from disconnected pits to a percolating structure at the percolation threshold. Below the percolation threshold, it is found that the pit-size distribution ${\mathit{n}}_{\mathit{s}}$(t) obeys the dynamic scaling ${\mathit{n}}_{\mathit{s}}$(t)≊${\mathit{t}}^{\mathrm{-}\mathit{w}}$${\mathit{s}}^{\mathrm{-}\mathrm{\tau }}$f(s/${\mathit{t}}^{\mathit{z}}$) (τ=0.93±0.03, z=1.43±0.02, and w=0.66±0.02), where the cutoff function f(x) is a constant for x≪1.