Neon atoms are captured by helium clusters in a crossed-beam experiment. The capture process depends strongly on the cluster beam source conditions. We identify a sharply defined region corresponding to expansions passing near the critical point for which the capture probability is anomalously large.

Domain-shape instabilities are investigated in a two-dimensional binary mixture of near-critical composition, a monomolecular film confined to an air-water interface and composed of a phospholipid and cholesterol. We apply the methodology of spectral analysis to the quantitative description of domain-wall configurations. This permits us to identify an elliptic instability and a branching instability leading into a ‘‘melted’’ stripe phase in the vicinity of the consolute point. In between, a regime exists in which domain-wall fluctuations exhibit a capillary-wave spectrum.

The director-field configuration of a nematic liquid crystal confined to a spherical cavity within a urethane polymer is observed to transform from a radial- to axial-type structure as the radius of the cavity, temperature, or strength of an applied electric field are varied. The phase diagram, anchoring strength at the droplet wall, and a value of the reduced field inside the droplet are determined for different polymer/liquid crystal interfaces.

The adsorption of water onto a crystal surface can result in a first-order transition in the orientation of the director of a nematic liquid crystal spread on top of the surface. Here, we show that coadsorption of two or three chemicals can lead to a phase diagram having first-order transition boundaries, critical lines, and critical points. A simple Landau theory accounts for most of the phenomena we observe. This experiment gives the first direct optical visualization of a two-dimensional system near its critical point.

A cellular-automaton-based model that simulates flexible polymers in good solvents is constructed. Excluded-volume effects as well as hydrodynamic interactions are incorporated in this model in a very natural way. The center-of-mass velocity autocorrelation function of a single polymer chain in a 2D solution is found to obey a dynamic scaling relation which violates the nondraining concept.

${}_{}{}^3{}_{}{}^{}\mathrm{He}$ films on Grafoil at areal density n≳0.25 atom/A${\mathrm{̊}}^2$ have unusual magnetic properties. This system is modeled as a two-dimensional solid in interaction with a two-dimensional Fermi liquid. A calculation of the magnetic behavior of this model leads to a Ruderman-Kittel-Kasuya-Yosida exchange interaction that has several features in reasonable accord with experiment.

A new ‘‘mapping technique’’ is introduced which allows the study of epitaxy in systems that are commensurate or incommensurate. This method is applied to the epitaxy of fcc(111)/bcc(110) which is commensurate in one direction and incommensurate in the other. The mapping technique predicts a new epitaxial orientation, in good agreement with recent experimental results. The use of second-order perturbation theory in conjunction with the mapping technique predicts a change in epitaxial orientations as a function of island size and stiffness of overlayer lattice.

It is argued in the context of noisy, nonequilibrium Langevin models that systems with conserving deterministic dynamics and noise which violates the conservation law always exhibit self-organized criticality—spatial and temporal correlations that decay algebraically under generic conditions. Systems with both conserving deterministic dynamics and conserving noise require spatial anisotropy to exhibit self-organized criticality.

Using an atomic force microscope (AFM), we have studied the attractive and adhesive forces between a cantilever tip and sample surfaces as a function of sample surface energy. The measured forces systematically increased with surface energy. The AFM is very sensitive; changes in the surface forces (i.e., attraction and adhesion) of monolayer covered samples could be clearly discerned when only the surface group of the monolayer film was changed from -${\mathrm{CH}}_3$ to -${\mathrm{CF}}_3$.

A phase diffusion equation valid at arbitrary distances above the Mullins-Sekerka threshold is derived from the front integral equation. The steady-state solutions and the associated adjoint functions are computed numerically. As a first exploitation of the phase equation we determine the range of the phase-stable band of steady solutions. Even very close to threshold we find a strong deviation from the Landau-Ginzburg theory. Far from threshold we find that the wavelength ${\lambda }_{\mathrm{Eck}}$ on the long-wavelength edge of the Eckhaus band scales with the growth velocity V as ${\lambda }_{\mathrm{Eck}}$≊${\mathit{V}}^{\mathrm{-}1/2}$, as does the experimentally observed wavelength.

We have studied solid molecular hydrogen in various ortho-para concentrations at megabar pressures and down to liquid-helium temperatures. From changes of Raman spectra of rotational and vibrational modes we have identified three new phases. We show evidence for the orientationally ordered phase of parahydrogen at a pressure of 110 GPa (1.1 Mbar) and 8 K and for molecular orientational ordering within the newly discovered hydrogen-A phase.

We show that the islands formed in Stranski-Krastanow (SK) growth of Ge on Si(100) are initially dislocation free. Island formation in true SK growth should be driven by strain relaxation in large, dislocated islands. Coherent SK growth is explained in terms of elastic deformation around the islands, which partially accommodates mismatch. The limiting critical thickness, ${\mathit{h}}_{\mathit{c}}$, of coherent SK islands is shown to be higher than that for 2D growth. We demonstrate growth of dislocation-free Ge islands on Si to a thickness of ≊500 Å, 50×higher than ${\mathit{h}}_{\mathit{c}}$ for 2D Ge/Si epitaxy.

Photoelectron spectra from metal overlayers on GaP(110) show that the photoionization light source may induce a surface photovoltage, causing an energy shift of valence- and core-level peaks. We analyze the dependence of this surface photovoltage on metal coverage, substrate doping, and temperature. The presence of a surface photovoltage seriously affects the determination of surface band bending by photoelectron spectroscopy, a technique which is generally thought to reflect the equilibrium electronic structure of metal-semiconductor interfaces.

The free-electron cyclotron resonance in n-GaAs with rather weak impurity doping in a regular sequence of sheets shows a strong dependence of the carrier scattering rate on the direction of the applied magnetic field B. For the case of B directed exactly along the sheets we find a linewidth narrowing of more than a factor of 4. This effect is due to the B aligned trajectory of the circling electrons which extends along, but outside of the doping sheets. Our experiment is the direct observation of an anisotropic distribution of scatterers in an otherwise isotropic semiconductor.

We address the problem of finding interatomic force fields for silicas from ab initio calculations on small clusters. It is shown that the force field cannot be determined from cluster data alone; incorporation of bulk-system information into the force field remains essential. Bearing this in mind, we derive a force field based on both microscopic (ab initio) and macroscopic (experimental) data. This force field combines accuracy with transferability to other polymorphs. The possibility of parametrizing other elements is also demonstrated.

An expression for the off-diagonal component of the acoustoelectric tensor is obtained from the momentum-conservation law. The acoustoelectric current along the direction of sound propagation exhibits plateaus as a function of gate voltage if the circuit in the perpendicular direction is open. The product jB has the same plateaus as a function of magnetic field. The values of jB at the plateaus are equidistant and are separated by deep minima. The ratio of the plateau values of the current to the open-circuit voltage is equal to ${\mathrm{\sigma }}_{\mathit{x}\mathit{y}}$. This effect can be used for measuring the intensity of a surface acoustic wave propagated through the heterojunction.

We discuss a number of potential advantages offered by materials with very narrow energy gaps in the study of quasi-one-dimensional physics. Besides the expectation of quite large subband splittings, we predict several new phenomena which have no analog in wide-gap structures, such as the opening of a confinement-induced energy gap in semimetallic structures, a strong decrease of the gap with magnetic field, and ballistic conductance per channel in fractional units of ${\mathit{c}}^2$/πħ.

Rotation of the plane of polarization following transmission of a synchrotron x-ray beam through a thin sample has been directly observed. Within a few eV of the cobalt K-absorption edge, rotations of up to 2 mrad were obtained in cubic ${\mathrm{Co}}_{0.9}$${\mathrm{Fe}}_{0.1}$, and somewhat less in a cobalt metallic glass and in chiral organometallic samples. These effects were observed using a high-extinction tunable perfect-crystal Bragg-reflection x-ray polarimeter of novel design which can detect optical rotations as small as 70 μrad.

We show that both the elastic and the inelastic phonon-scattering rates among edge-state transport channels in mesoscopic two-dimensional electron-gas systems can be dramatically suppressed by a large magnetic field. This results in an increase in the carrier mean free path allowing the observation of anomalously quantized integer Hall conductance in macroscopic dimensions. Relations of theoretical results with recent experiments are discussed.

We have measured the magnetostriction L(H) of a single crystal of the heavy-fermion superconductor ${\mathrm{UBe}}_{13}$ using an all-silicon high-precision capacitance dilatometer. We find clear evidence for a transition to an antiferromagnetic state at ${\mathit{T}}_{\mathit{N}}$∼8.8 K, which is suppressed in a field by ${\mathit{dT}}_{\mathit{N}}$/dH∼0.36 K/T. At low temperatures we observe pronounced magnetostrictive oscillations, which we believe are de Haas–van Alphen oscillations due to an unusual aspect of the Fermi surface.