Defect and Diffusion Forum Vols. 237-240

Abstract: The diffusion coefficient of In in TiAl has been measured using ion implantation technique and secondary ion mass spectrometry. The diffusion coefficients of Fe and Pd in FePt have been measured at two compositions by radioactive tracer method. In order to clarify diffusion anisotropy, single crystal of each alloy was used. The In diffusion perpendicular to the [001] axis is faster than that parallel to the [001] axis. Such trend is similar to Ti diffusion previously measured in our group. The diffusion of Fe in FePt perpendicular to the [001] axis is faster than that parallel to the [001] axis at each composition, while the anisotropy of the Pd diffusion is different with composition. The predominant process of the diffusion in perpendicular to the [001] has been discussed on the basis of the expressions of the diffusion coefficients.

Abstract: Ultra-strong gravitational field (Mega-gravity field) causes the sedimentation of even atoms (diffusion), and is expected to create a nonequilibrium crystal-chemical state in multi-component condensed matter. However, the materials science research under mega-gravity field has now remained as an unexploited field, while the sedimentation of molecules or polymer had been used in biochemistory. We presented a self-consistent diffusion equation for sedimentation of atoms in condensed matter. Next, we developed an ultracentrifuge apparatus to generate strong acceleration field of over 1 million (1x106) g at temperature range up to 〜300 °C, and, recently, succeeded in realization of the sedimentation of substitutional solute atoms in some alloys of Bi-Sb, In-Pb, Bi-Pb systems, etc. The diffusion coefficients in sedimentation on Bi-Sb alloy were estimated to be much greater than those at normal conditions by a factor of >20. It is suggested that the sedimentation of substitutional atoms in solids or liquids can be explained in a new type of diffusion, where the diffusion mechanism for substitutional solute atoms was yet unknown. In this article, the recent progress in the investigation of sedimentation of atoms under mega-gravity field is reviewed, and the diffusion mechanism is discussed. The application of the mega-gravity field is also discussed.

Abstract: We present a unified simulation of diffusion in silicon (Si) and silicon dioxide (SiO2) that is based on the diffusing dopant species and point defects that primarily contribute to the diffusion. We first present the simulation of phosphorus (P) diffusion in Si based on the integrated diffusion model that we have developed and elucidate the mechanism of the appearance of the anomalous P in-diffusion profile. The vacancy mechanism governs P diffusion in the plateau region, while the kick-out mechanism governs it in the deeper region, where Si self-interstitials dominate in the kink region and P interstitials dominate in the tail region. Next, we present the simulation of boron (B) diffusion and Si self-diffusion in SiO2. We examined the co-diffusion of implanted B and 30Si in thermally grown 28SiO2, which shows increasing diffusivities with decreasing distance between the diffusers and Si/SiO2 interface and with higher B concentration in SiO2. We propose a model in which SiO molecules generated at the interface and diffusing into SiO2 enhance both B diffusion and Si self-diffusion. The simulation showed that the SiO diffusion is so slow that the SiO concentration at the B and 30Si region critically depends on the distance from the interface. In addition, the simulation predicts the possibility of time-dependent diffusivities for B and Si because more SiO molecules should be arriving from the interface with time, and this time dependence was experimentally observed. Moreover, based on the B concentration dependence, the simulation result indicates that B and Si atoms in SiO2 diffuse correlatively via SiO; namely, the enhanced SiO diffusion by the existence of B enhances B diffusion and Si self-diffusion.