Experiments were carried out on 3 types of polycrystalline material, at temperatures ranging from 551 to 1265C, by using 195Au radiotracer and serial sectioning techniques (table 1). The 3 materials were termed Siemens (1015B/cm3, 30 grain size, dislocation density of about 107/cm2), Polix (1016B/cm3, 5 to 25mm grain size, dislocation density of between 105 and 107/cm2) and MRC (1016O2/cm3, 1018C/cm3, non-uniform grain size). Depending upon the temperature, material structure, and diffusion time, various types of profile were obtained. Some of these could not be explained, within the framework of classical solutions of Fick’s equations, in the presence of grain boundaries. However, all of the profiles could be successfully analyzed by using a new diffusion model which was applicable to host-impurity systems which involved strong segregation effects and negligible diffusion along extended defects. At temperatures above about 1100C, effective diffusion coefficients that were slightly lower then those previously reported in the literature were measured. Upon decreasing the temperature, the effective Au diffusivity began to depend upon the structure of the sample. This produced various Arrhenius plots which exhibited a downward curvature. A segregation enthalpy, for Au, of about 141kJ/mol was estimated from the observed diffusion behavior.

C.Poisson, A.Rolland, J.Bernardini, N.A.Stolwijk: Journal of Applied Physics, 1996, 80[11], 6179-87

Table 1

Diffusivity of Be in Various Types of Si