Adsorption and Growth of Cadmium on Polycrystalline Tungsten

The multilayer adsorption and growth of cadmium on clean polycrystalline tungsten ribbons (with strong preferred orientation) has been investigated with a molecular-beam and mass-spectrometric technique. The adsorption and desorption kinetics have been studied as a function of temperature, supersaturation, and coverage. Five distinct adsorption states have been found between 100 and 600°C. Growth of bulk cadmium occurs only after multilayer adsorption is complete. No measurable supersaturation or critical nucleation event is observed for the growth of cadmium. However, even at high supersaturation and heavy coverage, the condensation coefficient is still smaller than unity. The kinetic and structural data are explained by the evolution of faceted, crystallographic, and epitaxial cadmium islands on the cadmium multilayer adsorbate.