[en] Senftleben-Beenakker experiments are reported on the thermal conductivity and visosity of polyatomic gases. Polar molecules of linear and symmetric top structure have been investigated in a magnetic field. NH₃-noble gas mixtures and CH₃CN mixtures have been studied. The results indicate the concentration dependence of the various non-equilibrium polarizations for these specific systems. (C.F.)

[en] Molecular dynamics simulations of Si(0 0 1) targets subject to uninterrupted Ar bombardment of various energies and angles of incidence were performed, in order to study the atomic processes that take place during the transient and steady state sputtering regimes. Silicon interactions were described with the Modified Embedded Atom Method potential and the Stillinger-Weber potential. Detailed information is extracted and briefly discussed. It is found that these potentials lead to significant differences in sputter behavior. By testing these potentials (and two others) against newly calculated DFT data for Si energies in a wide variety of atomic environments, we demonstrate that they all have severe shortcomings. Therefore, the Modified Embedded Atom Method potential was re-fitted to the DFT data, leading to a new parametrization and a greatly improved fit. However, a spurious 'amorphous phase' energy minimum was detected during molecular dynamics simulations at room temperature. Roads to dealing with this problem are discussed

[en] The isothermal change of the electrical resistivity during structural relaxation in the temperature range 500 to 600 K is measured for amorphous Fe₄₀Ni₄₀B₂₀. The resistivity changes are measured both, at the annealing temperature T_a and at 77 K. In both the cases the resistivity of as-quenched samples decreases continuously with time, but the decrease is smaller by about a factor of two when measured at 77 K. The size of the effect measured at 77 K increases with increasing T_a, whereas the reverse is true when the effect is measured at T_a. Analysis of the data shows that structural relaxation can be separated into two parts: 1) Topological short range ordering (TSRO), the annealing out of free volume, which can be quantitatively described in terms of a free volume model with a single activation energy (E_f = 250 kJ/mol). 2) A 'non TSRO' part, which can be separated in an irreversible and a reversible contribution, which occur simultaneously and cover the same wide range of activation energies (130 to 250 kJ/mol). The reversible part is ascribed to chemical short range ordering (CSRO). An increase of chemical order yields an increase respectively decrease of the resistivity when measured at 77 K and T_a, respectively. In particular, the result that CSRO is accompanied by an irreversible process is new. (author)

[en] The Reverse Monte Carlo method (RMC) is tested in various ways to study the influence of erroneous or insufficient experimental input data. It is found that normalization errors can be overcome, and that large density errors are detected by RMC. For Ti₆₇ Ni₃₃, acceptable results could be obtained from two (instead of three) diffraction experiments, but not from one. Even in case of a very good fit, the final atomic configuration may still contain traces of the starting configuration. An RMC-fit of the first peak of the Ni Ni partial radial distribution function of Ni₈₁ B₁₉ shows that Ni Ni nearest-neighbour correlations alone set up a medium-range structure. (authors) 4 figs., 8 refs

[en] The diffusion process at a temperature just below the glass-transition temperature is studied in a computer model of amorphous Ni₈₁B₁₉. The observed diffusion events cause structural changes that are highly localized and are correlated with low-frequency localized vibrational modes. The excitation of such a mode can result in a jump, which is identical to the diffusion event. The jump has a cooperative character involving some tens of atoms and can be of a reversible or of an irreversible nature

[en] The magnetic field effect on the viscosity has been measured for several polyatomic gases with the emphasis on symmetric top molecules with strong electric dipoles. Theoretical expressions are given for the field dependent viscosity coefficients for various types of angular momentum polarizations, both for linear and symmetric top molecules. For CO₂, OCS, N₂O, SF₆, CH₃F, CHF₃, PF₃ and NF₃ a decrease of the viscosity in a magnetic field was observed, which can be well described on the basis of a single angular momentum tensor polarization of the type JJ. For NH₃ and ND₃, however, an increase in the viscosity was observed. In this case, a single polarization of the type WWJ is involved. For HCl, DCl, AsH₃ and PH₃ no effects could be observed (mod(Δeta/eta)<=2x10^-5). No simple correlation is found between the magnitude of the effect and the strength of the molecular electric dipole moment. The experimental results are expressed in terms of effective cross sections. (Auth.)

[en] We have performed defect studies on Ti₁N_1.07 by means of thermal helium desorption spectrometry (THDS), a technique which uses helium as an inert atomic probe. First, the defects in the solid are decorated with helium by ion implantation. The helium is subsequently released as the sample is heated. For low ion implantation energy (100 eV) one desorption peak is dominant, which represents structural vacancies on the Ti sublattice due to the off-stoichiometry. For implantation energies of 400 eV and higher, the ion beam induces new, strongly binding trapping sites for helium, which become increasingly prominent in the spectra. These spectra can be well understood on the basis of a trapping and retrapping theory of helium in two types of defects. (orig.)

[en] Thermal helium desorption spectrometry (THDS) has been used for the investigation of defects and thermal stability of thin Cu films (5-200 A ) deposited on a polycrystalline Mo substrate in ultrahigh vacuum. These films are metastable at room temperature. On heating, the films transform into islands, giving rise to a relatively broad peak in the helium desorption spectra. The temperature of this island formation is dependent on film thickness, being 417 K for 10 A and 1100 K for a 200 A film. The activation energy for island formation was found to be 0.3±0.1 eV for 75 A film. Grain boundaries have a strong effect on island formation. The defect concentration in the as-deposited films is ∼5x10^-4, for films thicker than 50 A and more for thinner films. Helium release from monovacancies was identified in the case of a 200 A film. Helium release was also seen during sublimation of the Cu film (∼1350 K). Overlayer experiments were used to identify helium trapped close to the film surface. An increase of the substrate temperature during deposition resulted in a film that had already formed islands. Argon-ion assistance (250 eV) during film deposition with an ion/atom ratio of ∼0.1 resulted in a significant enhancement of helium trapping in the films. The argon concentration in the films was found to be 10^-3. The temperature of island formation was increased due to argon-ion assistance. The helium and argon desorption spectra are found to be similar, which is due to most of the helium becoming trapped in the defects created by the argon beam. The role of the Mo surface in affecting the defects at the film-substrate interface is investigated. The effect of variation of helium fluence and helium implantation energy is also considered. The present THDS results of Cu/poly-Mo are compared to those of Cu/Mo(100) and Cu/Mo(100) reported earlier

[en] We describe an UHV apparatus for the investigation of in-situ grown thin films by thermal desorption spectrometry (TDS). In the design the demands imposed by TDS are combined with those imposed by ion-beam assisted deposition (IBAD). The films are deposited onto a substrate by electron-beam evaporation of the source material. A broad-beam ion source provides the low-energy ions (0.1-1.5 keV) which are used as probes for TDS and as active agents in the deposition process. The ion and atom fluxes can be controlled independently. The ion-to-atom arrival ratio will be in the range 0.01-1.0. We plan to study the effect of ion assistance in IBAD layers with the TDS technique. (orig.)

[en] Implantation and trapping effects of helium and neon are studied by thermal desorption spectrometry (TDS) in single-crystalline Ti₁C_0.924, which has a structural defect concentration on the order of percents on the carbon sublattice. For neon a first-order surface-related release peak and a very broad diffusional bulk-related release peak are found. For helium only the bulk peak has significant magnitude. The bulk diffusion mechanism can be explained by either a hopping or a vacancy assisted mechanism. In addition, neon is capable of displacing titanium atoms, and hence of creating vacancy clusters which have a stronger binding energy for neon than the structural defects; this is clearly visible in the spectra. (orig.)