A digital tracer scanner for studies of longitudinal self-diffusion in thin films

Abstract

A digital tracer scanner, which was constructed to measure the distribution of radio tracers along the surface of thin films in a nondestructive manner, is described. The radiation is measured through a stationary slit as the tracer source is scanned back and forth utilizing a stepping motor; simultaneously, the sweep of a multichannel analyzer operating in the multiscaling mode is synchronized to this motion, such that a given channel corresponds exactly to a given position on the film (to better than 3 μ after many days of scanning). The tracer distribution can then be viewed on an oscilloscope or read out on a teletypewriter. An analysis is presented indicating the distortion of a profile when observed through a slit of finite width, and a method of unfolding the value of the diffusion coefficient, D, from the measured tracer distribution is given. During a typical measurement on a polycrystallineAu film, the value of D was determined to be 3.14±0.3 × 10−11 cm2/sec at 500 °C and the ultimate resolution attainable for a 50 μ slit and a 40 h anneal corresponds to ∼ 6 × 10−12 cm2/sec.