DIFFUSION BEHAVIOR OF LEAD IMPLANTED INTO ALUMINUM

Rutherford backscattering spectrometry (RBS) was used to analyse the depth distributions of 150 keV lead ions implanted into aluminium single crystals at room temperature to fluences in the range from 1 x 10(15) to 1.8 x 10(16) Pb cm-2. Changes in the distributions during isothermal annealing sequences were studied as a function of time and annealing temperature in the range from 250 to 560-degrees-C. During implantation lead was found to segregate into crystalline lead inclusions. Significant changes in the lead distributions, seen by RBS analysis as an asymmetrical broadening of the profiles towards the surface, are only observed after annealing to temperatures above 380-degrees-C, i.e. somewhat higher than the bulk melting point of lead. Above 480-degrees-C lead diffusing to the surface is lost by evaporation into the vacuum. The RBS results support the idea that atomic diffusion plays a minor role in the mobility of lead in aluminium. Substantial changes in the lead profiles are more associated with "Brownian-like motion" of the molten lead inclusions modified by an intensive flow of thermal vacancies to the surface.