Superconductivity in silicon nanostructures

We present the findings of the superconductivity observed in the silicon nanostructures prepared by short time diffusion of boron on the n-type Si(100) surface. These Si-based nanostructures represent the p-type ultra-narrow self-assembled silicon quantum wells, 2nm, confined by the delta - barriers heavily doped with boron, 3nm. The EPR and the thermo-emf studies show that the delta - barriers appear to consist of the trigonal dipole centres, which are caused by the negative-U reconstruction of the shallow boron acceptors. Using the CV and thermo-emf techniques, the transport of two-dimensional holes inside SQW is demonstrated to be accompanied by single-hole tunneling through these negative-U centres that results in the superconductivity of the delta - barriers. The values of the correlation gaps obtained from these measurements are in a good agreement with the data derived from the temperature and magnetic field dependencies of the magnetic susceptibility, which reveal a strong diamagnetism and additionally identify the superconductor gap value.Comment: 4 pages, 6 figures, presented at the 4th International Conference on Vortex Matter in Superconductors, Crete, Greece, September 3-9, 200

Some remarks on the damage unilateral effect modelling for microcracked materials

This study deals with the macroscopic modelling of the mechanical behaviour of microcracked materials and particularly with the unilateral aspect of such damage which leads, at the closure of microcracks, to a partial damage deactivation. By means of a micromechanical analysis, the aim of this article is first to point out the influence of the opening-closure of microdefects on the effective elastic properties of a microcracked medium. According to these considerations, a new elastic moduli recovery condition at damage deactivation is proposed. The introduction of this condition within the anisotropic damage model proposed by Halm and Dragon, 1996 allows to extend its micromechanical background while preserving its main advantages, in particular the continuity of the stress-strain response and the symmetry of the stiffness tensor

Modeling microdefects closure effect with isotropic/anisotropic damage

International audienceContinuum damage mechanics (CDM) for metals is often written in terms of an isotropic (scalar) damage. In this case, solutions have been proposed to represent the differences of behavior in tension and in compression also called quasi-unilateral (QU) conditions or microdefects closure effect. A recent anisotropic damage model has been developed to take into account the damage orthotropy induced by plasticity (Lemaitre, J., Demorat R. and Sauzay, M. (2000). Anisotropic Damage Law of Evolution, Eur. J. Mech. A/Solids, 19: 513--524). The purposes here are then two. First, a unified framework for isotropic and anisotropic damage is proposed. Then, it is to extend Ladevèze and Lemaitre's framework (Ladevèze, P. and Lemaitre, J. (1984). Damage Effective Stress in Quasi Unilateral Conditions, In: Proceedings of the 16th International Congress of Theoretical and Applied Mechanics, Lyngby, Denmark) for the QU conditions to anisotropic damage induced by plasticity. Yield surfaces and damage versus accumulated plastic strain curves, drawn for different loading, illustrate the effect of the QU conditions on the damage evolution

An alternative 3D model for damage induced anisotropy and unilateral effect in microcracked materials

A three-dimensional model of damage by microcrack growth is proposed to account for the mechanical behavior of quasi brittle materials (especially for concrete and rocks). The emphasis is put on the induced anisotropy and on the elastic moduli dependence on the opening and closure of microcracks (unilateral effect). This formulation is based first on a damage characterization throught the microcracked density distribution, and secondly avoids the use of spectral decompositions generally adopted in literature and which induce some major inconsistencies

Technical progress in silicon sheet growth under DOE/JPL FSA program, 1975-1986

The technical progress made in the Silicon Sheet Growth Program during its 11 years was reviewed. At present, in 1986, only two of the original 9 techniques have survived to the start-up, pilot-plant stage in industry. These two techniques are the edge-defined, film-fed growth (EFG) technique that produces closed shape polygons, and the WEB dendritic technique that produces single ribbons. Both the status and future concerns of the EFG and WEB techniques were discussed