VAPORIZATION OF SOLID SILVER .I. KINETIC INFLUENCE OF SURFACE ORIENTATION, DEGREE OF VAPOR PHASE UNDERSATURATION, AND GASEOUS CONTAMINANTS

A vaporization experiment is described in which both vaporization and condensation coefficients can be accurately determined. The technique involves rate measurements under various degrees of undersaturation and supersaturation and shows that for silver both the vaporization and growth processes are ideal and independent of surface orientations. Low pressures of vapor phase reactants, p<10-5 Torr of O2, CO2, N2, H2S, Cl2, acetone vapor, or CH4, were found to have no influence upon the kinetics of the process. Through the process of adsorption several of these gases markedly influenced the surface morphology of the specimens without appreciably disturbing the concentration of the desorbing silver species. Mechanistically, these results imply that there is a free interchange of silver between surface and bulk sites and that the desorption of silver from the surface is the controlling step in the vaporization process. In a similar way, the gas results show that the absorption or desorption of surface impurities characteristic of normal vacuum environments maintains the surface concentration of all impurities below a value where they could impede the vaporization process. © 1969 The American Institute of Physics.