Nucleation and epitaxy of gold deposits on sodium chloride substrates during electron bombardment

Abstract

Electron bombardment of cleaved sodium chloride substrates during deposition of gold causes an increase in the nucleation density at early stages of growth, and an improvement in the epitaxial orientation of the deposit nuclei. An experimental study of the variation of nucleation density with temperature, in conjunction with a theoretical analysis of nucleation behaviour on a substrate with both deep and shallow adsorption sites, shows that electron bombardment causes virtually complete coverage by sites of depth 0.47 eV. Without electron bombardment, some small substrate areas contain only shallow adsorption sites of depth approximately 0.1 eV, but most areas contain a high density of deep sites. Competition for incident material by growth of existing nuclei allows nucleation at only a small proportion of the deep adsorption sites. The nature of the deep sites and their significance in epitaxial growth are discussed.