B diffusion in ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ strained layers on Si was studied as a function of annealing temperature and Ge content and is shown to be characterized by lower diffusivity as compared to unstrained Si. The influence of the Ge content on the dopant diffusion was also measured, demonstrating that the diffusivity of the B atoms is reduced with increasing Ge fraction in the strained layer. The reduced diffusivity of B in the strained ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ relative to the dopant diffusivity in unstrained Si is attributed to the change in the charged point-defect concentration caused by band-gap narrowing. We find good agreement between the measured and simulated diffusivity using the known band-gap for the strained layers.

The equilibrium crystal shape of lead develops an edge around the (111) orientation in the temperature range where surface melting is observed. In this temperature range, the (111) facet grows with temperature. The thermal behavior of the edge and facet is shown to result from a competition between a localized melting of surface diffusers and vacancies on the (111) facet and a localized step melting. The formation of the edge cannot be explained solely by the surface melting of high-index orientations.

The steady state molecular hydrogen ion yield from a single atomic step site of a [110]-oriented tungsten and of a [100]-oriented rhodium crystal is determined as a function of surface temperature using mass and energy resolved probe hole field ion microscopy. A second order kinetic model is developed to fit the experimental data thus obtaining the hydrogen binding energy. For local fields of about 3 V/Å the data are close to values obtained from thermal desorption spectroscopy. A comparison is made with calculations of the field-adsorption binding energy of atomic hydrogen on a jellium surface based on density functional theory.

It has been reported that the growth mode of Ag on Ag(111), which is usually multilayer (3D), changes to layer-by-layer (2D) growth if Sb is used as a surfactant. In a model study on the clean system Ag/Ag(111) (without any surfactant) we find that two-dimensional layers do grow, if the substrate is prepared with an anomalously high density of Ag nuclei. As an enhanced density of nuclei is also observed in the presence of Sb, this effect may explain the mechanism for surfactant-induced layer-by-layer growth.

The experimental information about magnetic bands and their temperature dependence is distorted by Fermi distribution and apparatus function. The recovery of the spectral density constitutes an ill-posed inversion problem. We have invoked the maximum entropy regularization to deconvolute spin-resolved inverse photoemission data of Ni(110). The effective energy resolution is hereby improved by a factor of 5 and structures below ${\mathit{E}}_{\mathit{F}}$, which are generally lost in inverse photoemission, are recovered. The temperature-dependent data for Ni reveal clearly a pair of spin-split bands. The splitting vanishes on approaching the Curie temperature.

We have discovered an alternate pathway below the usual 1.1 eV threshold for Si photoionization from the DX ground state in AlGaAs. This alternate photpath proceeds via a 0.1 eV wide resonance at 0.65 eV. The ionization rate for this path scales as the square of the resonance photon intensity, not linearly with the intensity as does the usual 1.1 eV threshold path. Photons at 0.5 eV accompanied by weak photon fluxes at 0.65 eV do scale linearly with 0.5 eV intensity showing the 0.65 eV state is a short-lived resonant intermediate level.

A ${\mathrm{Ag}}_8$/${\mathrm{Au}}_3$/${\mathrm{Ag}}_{\mathit{x}}$ double quantum well is grown on Au(111) to form two Ag quantum wells coupled through a thin Au barrier layer, and the electronic structure of this system is examined with angle-resolved photemission. As the thickness of the outer well (x, in monolayers) is varied, the measured binding energies of the quantum-well states show an avoided-crossing behavior, in good agreement with a model calculation based on Bloch wave functions. The results demonstrate the effect of electronic translayer coupling.

Spatially resolved electron energy loss spectroscopy has been performed on single, H-terminated, Si nanocrystals in the size range 25–500 Å. The particles were prepared via the gas-phase photolysis of a dilute ${\mathrm{Si}}_2$${\mathrm{H}}_6$/He mixture in a gas flow cell, and deposited on a holey carbon grid for analysis. Energy loss within a few eV of the core 2p ionization edge reveals information about the conduction band states at ${\mathrm{\Delta }}_1$ and ${\mathit{L}}_1$ in the Brillouin zone. The conduction band edge is observed to shift to higher energy as the inverse square of the particle radius. In addition, a strong increase in the oscillator strength for these transitions is observed for decreasing particle sizes below 60 Å.

Magnetization curves of high quality ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{x}}$ single crystals in fields slightly misaligned with the ab plane show a peak at small fields (6 Oe at 5 K for a misalignment angle of 6°). This is attributed to flux penetration into the Josephson coupling between the ${\mathrm{CuO}}_2$ layers and a resultant three- to two-dimensional crossover of the shielding current path with the increase of the field. A surface barrier model for the interlayer flux penetration yields the anisotropy ratio γ of ≊700.

We present magnetic neutron scattering and specific heat data on the high-${\mathit{T}}_{\mathit{c}}$ superconductor ${\mathrm{La}}_{1.86}$${\mathrm{Sr}}_{0.14}$${\mathrm{CuO}}_4$. Both types of measurements show that even when the samples are superconducting, there are excitations with energies well below 3.5${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$. These excitations coincide with a magnetic response, χ’’, whose amplitude is considerably below that observed at ${\mathit{T}}_{\mathit{c}}$=35±1 K. At the same time, the wave-vector dependence of χ’’ is identical to that for the normal state, which implies that the low frequency excitations in our crystals are not those associated with the nodes of a clean d-wave superconductor. However, the data are consistent with gapless superconductivity of the type induced by localized magnetic impurities, clearly observed in the specific heat measurements.

We have observed giant magnetic moments in clusters of rhodium, ${\mathrm{Rh}}_{\mathit{n}}$(n=12–32), consistent with ferromagnetic ordering of the 4d electrons. Ferromagnetic behavior has not been reported previously in pure 4d transition metals. Rhodium clusters are superparamagnetic at 93 K, with magnetic moments of between 0.3 and 1.1${\mathrm{\mu }}_{\mathit{B}}$ per atom. We find that ${\mathrm{Rh}}_{15}$, ${\mathrm{Rh}}_{16}$, and ${\mathrm{Rh}}_{19}$ have magnetic moments per atom that are significantly larger than those of adjacent cluster sizes.

The interlayer exchange coupling in Fe(110)/Ag(111) multilayer structures with parallel alignment of the Fe layer magnetizations has been investigated with a zero-field Mössbauer spectroscopy technique that is sensitive only to the spin-wave spectrum at the Fe/Ag interface. Model spin-wave calculations are presented to connect the coupling strength to the observed interfacial spin-wave behavior. As the Ag thickness was varied from 0 to 40 ML (monolayers), the interfacial spectra of the films showed oscillations in the coupling strength with a period of 6 ML, in close agreement with recent predictions.

The photodissociation of HCl in the Ar-HCl cluster is studied theoretically, with the focus on the angular distribution of the H atom photofragments. Excited state resonances, in which the H atom rattles between the heavy atoms, contribute to the process. It is found that for excitation into a resonance state, the measurable angular distribution of H atoms from Ar-HCl clusters oriented in space provides a mapping of the resonance wave function. This predicts the possibility of imaging resonance wave functions in such processes.

The transition from a spatially uniformly oscillating surface to the formation of chemical wave patterns has been investigated in the NO+CO reaction on Pt(100) using photoemission electron microscopy. This transition is associated with a discontinuous jump in the local oscillation frequency and can be described as a breakdown of global coupling caused by the presence of defects in the oscillating medium.

Certain viscoelastic surfactant solutions show unusual nonlinear rheology: In steady shear, the shear stress saturates to a constant value while the first normal stess increases roughly linearly with shear rate over several decades. Here we explain this behavior in terms of the ‘‘reptation-reaction’’ model for the dynamics of reversibly breakable, polymerlike micelles. The constitutive equation for this model leads to a flow instability of shear-banding type. The limiting shear stress is predicted to be ${\mathrm{\sigma }}^{\mathrm{*}}$=0.67${\mathit{G}}_0$ (with ${\mathit{G}}_0$ the plateau modulus), in quantitative agreement with experiment.

The time evolution operator for any quantum-mechanical computer is diagonalizable, but to obtain the diagonal decomposition of a program state of the computer is as hard as actually performing the computation corresponding to the program. In particular, if a quantum-mechanical system is capable of universal computation, then the diagonal decomposition of program states is uncomputable. As a result, in a universe in which local variables support universal computation, a quantum-mechanical theory for that universe that supplies its spectrum cannot supply the spectral decomposition of the computational variables. A ‘‘theory of everything’’ can be simultaneously correct and fundamentally incomplete.

We consider a topological transition which is an abrupt variation from π to zero of Berry’s phase, in the case when it is a phase difference of interfering waves. It manifests itself in a steplike current–magnetic field and current–gate voltage characteristics predicted for in-plane magnetoresistance of rings in noncentrosymmetric materials. Transition points occur at external magnetic fields equal to momentum-dependent effective magnetic fields for different tunneling channels of a quasi-one-dimensional ring. Similar effects due to the angular anisotropy of electron g factor are considered.

Bogomolny’s formula for energy-smoothed scars is applied to a nonspecific, nonscalable Hamiltonian, a two-dimensional anharmonic oscillator. The semiclassical theory reproduces well the exact quantal results over a large spatial and energy range.

The ground-state density matrix for a massless free field is traced over the degrees of freedom residing inside an imaginary sphere; the resulting entropy is shown to be proportional to the area (and not the volume) of the sphere. Possible connections with the physics of black holes are discussed.

Nonextreme walls (bubbles with two insides) and ultraextreme walls (bubbles of false vacuum decay) are discussed. Their respective energy densities are higher and lower than that of the corresponding extreme (supersymmetric), planar domain wall. These singularity-free space-times exhibit nontrivial causal structure analogous to certain nonextreme black holes. We focus on anti-de Sitter-Minkowski walls and comment on Minkowski-Minkowski walls with trivial extreme limit, as well as walls adjacent to de Sitter space-times with no extreme limit.