Papers by Author: Patrick Gas

Abstract: Experiments of niobium diffusion at infinite dilution and Nb reaction-diffusion in pure iron and in ferrites with different amounts of carbon were performed, for comparison, in order to understand the influence of carbon on the diffusion process in the Nb-Fe system. A proportional decrease of the diffusion coefficient with the increasing amount of carbon was found. This effect seems to be stronger than in the self-diffusion analyzing the literature; moreover SIMS measurements in niobium- implanted samples show a redistribution of carbon during the first steps of the diffusion process. For those reasons, a stronger effect of carbon-niobium interaction over the carbon-vacancy interaction seems to be responsible for the decrease in the diffusion coefficient.

Abstract: We have investigated the lattice diffusion of B and Sb by means of molecular beam epitaxy in Si1−xGex (x < 0.2) layers grown on Si(001) substrate. Using Si1−xGex relaxed buffers we were able to differentiate the chemical effect (change in the Ge composition) as opposite to the biaxial stress effect (due to the epitaxy on Si) on dopant diffusion. B diffusion follows a behavior opposite to Sb diffusion versus Ge composition and biaxial stress. These results are explained in view of the difference of diffusion mechanism between B (interstitials) and Sb (vacancies). We also show that dopant diffusion follows contrasting behaviors under biaxial pressure and hydrostatic pressure, and that the activation volume of dopant diffusion is of opposite sign for biaxial pressure and for hydrostatic pressure. This is explained using a formalism based on the extra work done by the system for diffusion under pressure, concluding that for biaxial stress the activation volume depends mainly on the relaxation volume linked to the defect formation.