[en] The thermal energy flux exchanged between a solid and a liquid, in particular during the quenching process is studied: two-phase transient heat transfer phenomena are analyzed and the conditions in which burnout occurs are defined. A temperature measurement and recording system was developed, in order to determine simultaneously the temperature at several points of a sample during its cooling by quenching. Quenching experiments in liquid nitrogen were carried out and the so-called ''thermal surface resistance'' technique was developed, which allows burnout control. It was shown that it is possible to induce changes in vaporization phenomena by substituting latent and then nucleate boiling to burnout and to adjust the heat flux density transmitted to the liquid. A critical resistance was defined: it corresponds to nucleate boiling and to the fastest cooling. It was shown that an acceleration of the cooling do not necessarily induce an increase of stresses and the formation of quench defects but, on the contrary, reduces or eliminates such defects. Methods were developed to calculate both temperature and thermal stresses distributions. They rely on measurements results and do not involve any hypothesis

[en] We show that the Casimir force (CF) gradient can be measured with no contact involved. Results of the CF measurement with systematic uncertainty of 3% are presented for the distance range of 100 - 600 nm. The statistical uncertainty is shown to be due to the thermal fluctuations of the force probe. The corresponding signal-to-noise ratio equals unity at the distance of 600 nm. Direct contact between surfaces used in most previous studies to determine absolute distance separation is here precluded. Use of direct contact to identify the origin of distances is a severe limitation for studies of the CF on structured surfaces as it deteriorates irreversibly the studied surface and the probe. This force machine uses a dynamical method with an inserted gold sphere probe glued to a lever. The lever is mechanically excited at resonant frequency in front of a chosen sample. The absolute distance determination is achieved to be possible, without any direct probe/sample contact, using an electrostatic method associated to a real time correction of the mechanical drift. The positioning shift uncertainty is as low as 2 nm. Use of this instrument to probe a very thin film of gold (10 nm) reveals important spatial variations in the measurement. (authors)

No abstract available

[en] The in situ combination of Scanning Probe Microscopies with X-ray microbeams adds a variety of new possibilities to the panoply of synchrotron radiation techniques. This paper describes an optics-free Atomic Force Microscope that can be directly installed on most of the synchrotron radiation end-stations for combined X-ray and atomic force microscopy experiments. The instrument can be used for atomic force imaging of the investigated sample or to locally measure the X-ray absorption or diffraction, or it can also be used to mechanically interact with the sample while simultaneously taking spectroscopy or diffraction measurements. The local character of these measurements is intrinsically linked with the use of the Atomic Force Microscope tip. It is the sharp tip that gives the opportunity to measure the photons flux impinging on it, or to locally measure the absorption coefficient or the shape of the diffraction pattern. At the end an estimation of the limits of the various techniques presented is also discussed.

[en] We developed and optimised an optics-free Atomic Force Microscope (AFM) that can be directly installed on most of the synchrotron radiation end-stations. The combination of Scanning Probe Microscopies with X-ray microbeams adds new possibilities to the variety of synchrotron radiation techniques. The instrument can be used for atomic force imaging of the investigated sample or to locally measure the X-ray absorption or diffraction, or it can also be used to mechanically interact with the sample while simultaneously taking spectroscopy or diffraction measurements. The local character of these measurements is intrinsically linked with the use of the Atomic Force Microscope tip. It is the sharpness of the tip that gives the opportunity to measure the photons flux impinging on it giving beam position monitor features, or allows to locally measure the absorption coefficient or the shape of the diffraction pattern. As an example of the possibilities opened by the instrument we will show diffraction measurements performed on a Ge/Si island while being indented with the AFM tip providing local measure of the Young coefficient. Three ESRF beamlines are going to be equipped with this new instrument.

[en] We present detailed studies of electronic properties of Al-Si alloys prepared in a nonequilibrium state by means of rapid solidification. The quenched alloys exhibit an enhanced superconducting transition temperature up to 6.2 K in an Al--Si 30 at. % alloy as well as an increased thermal slope of resistivity. Using differential scanning calorimetry, a large enthalpy variation (ΔH = 4.1 kJ/mole for Al--Si 30 at. %) has been measured during the irreversible transition from the non- equilibrium state to the equilibrium one. This is mainly attributed to the energy difference between the metallic state of silicon atoms trapped in fcc aluminum matrix during quenching and the usual covalent state of silicon precipitates in an equilibrium state. This large energy difference is presented as the origin of a lattice instability which softens the phonon spectrum and gives rise to a stronger electron-phonon coupling. This appears to be a characteristic property of nonequilibrium Al-Si solid solutions, which is associated with the metallic state of silicon atoms. An interpretation of the T/sub c/ enhancement is proposed for both Al-Si and Al-Ge alloys based on the phonon softening in these nonequilibrium crystalline alloys

[en] In a molecular beam epitaxy chamber (MBE), we have performed epitaxial growths of iron on silicon (111) surface and homoepitaxial growths of silicon on silicon (111) surface. The thicknesses of the grown films were typically 500.10^-10 - 1000.10^-10. We have observed a continuous and irreversible change of the Reflection High Energy Electron Diffraction (RHEED) patterns during the growth of iron at room temperature and of silicon at temperature below 400 C. This effect can be satisfactory explained by an increasing roughness of the surface during the growth. Annealing after growth leads in both cases to an irreversible flattening of the rough surface. These are experimental evidences for the occurrence of a kinetic roughness during epitaxial growth. In this article, a quantitative analysis of these RHEED pattern changes during epitaxial growth of silicon and of iron is presented. In both cases, the surface with deduced from the RHEED patterns closely follows a power law σαh^β. However the most reasonable values for β are around 0.25 for the growth of iron on silicon and β≅1 for the homoepitaxial growth of silicon (111). These results indicate that marked differences are found in the occurrence of kinetic roughening for these two different systems: iron on Si(111) or Si/Si(111)

[en] Cold neutron scattering was used to study the initial steps of the ion beam mixing process for NiPd and NiAg multilayers. The mixing rate was deduced from the observed changes in the first-order Bragg peak intensities. The authors show that the previously found correlation between the mixing rate and the thermodynamic heat of mixing holds even when the deposited energy density is low, and when the diffusion length is only a few A. 12 refs.; 3 figs

[en] The low temperature homoepitaxial growth of silicon has been probed in situ by Reflection High Energy Electron Diffraction (RHEED) in a Molecular Beam Epitaxy (MBE) chamber in the temperature range 250 C-400 C. The continuous change in the RHEED patterns during the growth of thick films (several hundred angstroms) shows the progressive appearance of a surface roughness during and after the decay of RHEED oscillations. This is a clear evidence for kinetic roughening in the case of silicon epitaxial growth at low temperatures on the Si(111) face. The surface width, σ, measured as the film thickness, h, is increased, can be described by: σ(h, T) ∼ Ah exp (E_f/kT) with E_f ∼ 0.65 eV. This is in marked difference with the kinetic roughening behavior measured during the growth of a metal like iron by means of the same RHEED technique (see Chevrier et al., Europhys. Lett. 8 (1991) 737). Furthermore, an extrapolation of this behavior to epitaxial growths at higher temperatures (T ∼ 600 C-800 C) suggests an effective influence of kinetic roughening in the determination of growth temperatures generally used for silicon MBE (i.e. the empirical usual growth temperatures T_epi∼ 650 C). During growth at substrate temperatures between 250 C and 400 C, the nucleation of misoriented silicon islands takes place following the occurrence of kinetic roughening at the surface. In this range of temperatures, this suggests that the loss of epitaxy occurs on a rough surface through the proliferation of defects and of misoriented crystals. (orig.)

[en] The elastic diffuse neutron scattering of an NbC_0.73 single crystal has been measured at room temperautre on two different spectrometers, the four-circle D10 at the HFR-ILL (Grenoble), and the two-axis G44 with time-of-flight analysis at the Laboratoire Leon Brillouin (Saclay). The data were treated either by Fourier transformations or by least-squares fit. The short-range-order parameters and the interatomic static displacements obtained by the various experiments and/or data treatment are in good agreement: carbon vacancies tend to be third neighbours in the f.c.c. metalloid sublattice and metal atoms relax away from the vacancy first neighbours by ∝0.05 A. It is shown that the treatment of diffuse scattering data limited to two reciprocal planes [(001) and (1anti 10)] gives satisfactory results. (orig.)