A new scheme of calculation avoiding the muffin-tin approximation is presented for low-energy-electron diffraction. The finite-difference method is then used to solve the Schrödinger equation. A simple superposition potential and a nonuniform three-dimensional grid of points yields satisfactory experiment-theory agreement for the Cr(100)-(1×1)N surface, with geometrical parameter values close to the ones found in a standard study. An optimization of the charge exchange gives a 1.3 electron transfer from chromium to nitrogen.

While the effectiveness of surfactants in suppressing islanding in Si/Ge heteroepitaxial growth has been demonstrated in previous studies, the atomic scale growth processes have remained unknown. Here we present images of the growing Si(001)/Ge surface obtained with in situ low-energy electron microscopy. From our previous we conclude that surfactant-mediated growth of Ge on Si(001) proceeds by highly local Ge incorporation with minimum surface diffusion. We propose a new two-dimer correlated exchange mechanism to explain this unusual growth mode, as well as the absence of islanding at high Ge coverage.

We study a continuous ballistic deposition process in which disks are incident vertically on an infinite line in random positions. If an incoming disk 1 falls on top of an already adsorbed disk 2, it will, unless prevented by a neighboring disk, roll over the surface of disk 2 until it contacts the line. The kinetics of formation of the first layer, when formulated in terms of a gap distribution function, may be solved exactly. We find in particular that the saturation density is ρ(∞)=0.808 65 . . . . The results are compared with the simpler random sequential adsorption process.

We have measured the autocorrelations for the Swendsen-Wang and the Wolff cluster update algorithms for the Ising model in two, three, and four dimensions. The data for the Wolff algorithm suggest that the autocorrelations are linearly related to the specific heat, in which case the dynamic critical exponent is ${\mathit{z}}_{\mathrm{i}\mathrm{n}\mathrm{t},}$${\mathit{E}}^{\mathrm{W}}$=α/ν. For the Swendsen-Wang algorithm, scaling the autocorrelations by the average maximum cluster size gives either a constant or a logarithm, which implies that ${\mathit{z}}_{\mathrm{i}\mathrm{n}\mathrm{t},}$${\mathit{E}}^{\mathrm{SW}}$=β/ν for the Ising model.

By modeling the process of water erosion we found that river patterns on a surface become invariant after the whole surface is covered by self-organized percolated rivers. Fractal scalings are confirmed in the distribution of basin size and in the contours’ geometrical irregularity.

Sintering of compacted metal powders is investigated by small-angle neutron-scattering techniques. The results evaluated in terms of the total pore surface area F and the total pore volume V give evidence for a universal relation between F and V thus indicating that both coarsening and pore elimination contribute to the surface reduction during the sintering process.

The special configuration and dynamics known for interstitialcies in face-centered-cubic metals are exploited to construct a model giving all the thermodynamic properties of crystalline, liquid, and amorphous states in a unified way. A large diaelastic softening of the shear modulus with defect concentration is derived. This leads to a softening of the interstitialcy formation energy, which, taken together with a large entropy contribution from the interstitialcy resonance modes, makes the model, which contains Lindemann’s law, viable for quantitative calculations of thermodynamic properties.

The behavior of iron in silicon during low-temperature annealing was studied. The influence of electric fields on the underlying defect reactions is detailed. The depth profiles reveal ${\mathrm{Fe}}_{\mathit{i}}$ outdiffusion and no precipitation in the bulk up to 470 K. In the presence of electric fields, the kinetics differ considerably and can be understood in terms of carrier-emission-limited iron drift. Consequences of this mechanism are discussed. The outdiffusion and drift data indicate a charge-state-dependent diffusion mechanism, in contrast to the generally accepted lack of any charge-state effect.

We report high-resolution core- and valence-level photoemission and core-to-valence x-ray absorption spectra of ${\mathrm{O}}_2$ physisorbed on graphite. The submonolayer δ-ζ2 orientational phase transition is manifest in the core-level spectrum as an extra broadening of each component of the paramegnetically split O 1s doublet. This phase transition is not visible in the 1${\mathrm{\Pi }}_{\mathit{g}}$ valence spectrum or the 1s→1${\mathrm{\Pi }}_{\mathit{g}}$ absorption line. The results reflect the detailed shape of the charge distribution in the final state of the molecule. We suggest that the population of low-frequency librational modes makes an important contribution to the core-level linewidths.

We present a high-resolution electron-energy-loss-spectroscopy investigation of the GaAs(110)-Bi(1×1) interface system. Exploiting p- and n-type doped substrates, the Fermi-level pinning position could be related to the electronic surface states produced by the misfit dislocations of the semiconducting Bi epitaxial monolayer. For the first time electronic transitions involving one-dimensional dislocation-related states are brought into evidence, in particular after an adequate thermal treatment of the interfaces that produces a long-range ordering of the dislocations.

We have observed the thermalization of conduction electrons in GaAs from a Gaussian to a Maxwell-Boltzmann distribution, by time-resolved observation of the band-to-acceptor luminescence folllowing a short (5 ps) near-resonant laser pulse of very low excitation power. At electron density less than ${10}^{14}$/${\mathrm{cm}}^3$ the thermalization of the electron density distribution occurs on a time scale of 50 ps with a rate independent of density. At higher density, thermalization occurs via electron-electron scattering with a total cross section of approximately 6×${10}^{\mathrm{-}12}$ ${\mathrm{cm}}^2$.

We report the first measurements of the optical functions of polycrystalline metal films throughout nucleation and growth. The dielectric function of aluminum, evaporated onto ${\mathrm{SiO}}_2$, was determined versus thickness d by real-time multichannel ellipsometry (1.3≤hν≤4.1 eV). We find that the electron relaxation time for the (200) parallel-band transition is independent of particle size during nucleation (d<50 Å) and increases abruptly only after coalescence. This behavior is not consistent with a classical size effect and suggests that the atomic structure of the particles dominates their optical properties.

The transition rates of individual two-state systems in a mesoscopic disordered metal (Bi) are studied via time-dependent conductance fluctuations. A striking increase in the transition rates is observed as the temperature T is decreased below 1 K for defects with energy splitting ɛ<${\mathit{k}}_{\mathit{B}}$T. In contrast, the transition rates decrease monotonically as T is lowered if ɛ>${\mathit{k}}_{\mathit{B}}$T. We show that these phenomena are a manifestation of dissipative quantum tunneling and estimate, for one particular defect, the defect–conduction-electron coupling parameter, α≊0.24.

For a particular choice of vertex weights, the two-dimensional six-vertex model can be viewed as a probabilistic cellular automaton. Physically it describes then the surface slope of a two-dimensional solid which grows through deposition. Based on this analogy we predict the large-scale asymptotic behavior of the vertical polarization correlations. The transfer matrix commutes with a nonsymmetric spin Hamiltonian. We diagonalize it using the Bethe ansatz and prove that the dynamical scaling exponent for kinetic roughening is z=3/2 in 1+1 dimensions.

The probability distribution of the largest local Liapunov exponent is evaluated for a classical ${\mathrm{Ar}}_3$ cluster at different values of the internal energy E, for a set of increasing values of the length in which the trajectory is partitioned. These distributions can be directly related to the evolution of ergodic behavior, particularly to how it exhibits distinctive, separable time scales which depend strongly on the energy of the system. Therefore, even though the inequivalence of ergodicity and chaos prohibits a Liapunov exponent itself from being a quantitative index of ergodicity, we find that 2 the sample distributions used to evaluate Liapunov exponents nevertheless can be used for this purpose.

We use a new technique to compute the correlation function for large-angle cosmic microwave background anisotropies resulting from both the space and time variations in the gravitational potential in flat, vacuum-dominated, cold dark matter cosmological models. Such models with ${\mathrm{\Omega }}_0$∼0.2 fit the excess power, relative to the standard cold-dark matter model, observed in the large-scale galaxy distribution and allow a high value for the Hubble constant. The low-order multipoles and quadrupole anisotropy that are potentially observable by COBE and other ongoing experiments should definitively test these models.

At high temperatures, in the presence of quarks, QCD has one stable and two metastable Z(3) vacua. We propose a scenario in which the Universe, after inflationary expansion for example at the grand unified scale, lies in one of these metastable vacua. We estimate that the metastable vacuum decayed at T∼10 TeV. The inhomogeneities caused by this phase transition are over one-tenth of the horizon radius. As a result of a large pressure difference between stable and metastable vacua their density contrast is also large.

It is shown that in a general class of models in which the baryon number of the Universe is created by electroweak anomalies, the energy density in dark matter may be related to the energy density in baryons as ${\mathrm{\Omega }}_{\mathit{b}}$/${\mathrm{\Omega }}_{\mathrm{dm}}$=c times )(proton mass)/(weak scale), where the number c is order unity and calculable from the anomaly equation. The scenario unambiguously predicts charged and neutral particles with weak-scale masses which carry a new conserved quantum number and can be pair produced via the weak interactions.

We study the cosmological consequences of an inert 17-keV state mixing with the electron neutrino. We find that the nucleosynthesis upper bound on the primordial helium abundance prohibits the existence of such a state, unless its lifetime falls into the range 6×${10}^{\mathrm{-}4}$≲${\mathrm{\tau }}_{\mathrm{vac}}$≲2×${10}^{\mathrm{-}2}$ s. In this range the decay occurs after the chemical decoupling of the electron neutrinos and before the beginning of the nucleosynthesis, with the result that the predicted helium abundance can be lower than what it would be in the standard scenario.

The energy dependence of ν-e scattering of solar neutrinos is investigated in the framework of neutrino oscillations and the nonadiabatic Mikheyev-Smirnov-Wolfenstein effect. It is shown that, with sufficient data, it will be possible to establish unambiguously whether neutrino oscillations are actually occurring and whether the electron neutrino oscillates into active or inactive (sterile) neutrino flavors.