Surface Self-Diffusion of Ag+ on AgBr by a New Radiotracer Technique

Abstract

The tracer diffusion coefficient of radioactive silver 110 on thin epitaxial layers of silver bromide has been determined for temperatures in the range 95–160 °C. These layers were formed by vacuum deposition of AgBr onto mica substrates which resulted in epitaxial layers having a 〈111〉 surface and a thickness ranging from 0.1 to over 1.0 μ. At each temperature, the diffusion coefficient along the surface of layers having different thicknesses was determined by autoradiography. The results for different layers were then extrapolated towards zero thickness to give a surface diffusion coefficient. An activation energy for surface diffusion of 0.34 eV was obtained. This technique makes possible, for the first time, a determination of the surface self-diffusion coefficient of ionic solids without the need for assuming an arbitrary surface layer thickness as required by other tracer diffusion methods.