The microstructure and orientation of silver on NaCl: The influence of surface conditions

Silver films up to 1000 Å thick (coalescence stage and continuous films) were evaporated onto vacuum-cleaved NaCl at constant temperature and constant deposition rate but under various vacuum conditions (ultrahigh vacuum (UHV), high vacuum (oil pumped and ion pumped), a partial pressure of contaminant (10^-10–10^-6 Torr) etc.). The films were characterized by low energy electron diffraction, Auger electron spectroscopy, transmission electron microscopy and transmission electron diffraction to determine their orientation, microstructure and cleanliness. The UHV-grown films were always polycrystalline. In contrast with previous observations, however, an increase in the partial pressure of H₂O alone did not improve the epitaxy. Hence the influence of other materials such as O₂, H₂O + O₂, hydrocarbons etc. was investigated. In addition, films were grown in UHV after pre-irradiation of the substrate with electrons and prenucleation at room temperature. If the prenucleated silver clusters were small and if their orientation was improved by annealing, continuous films were perfectly epitaxial even when the deposition of silver was carried out at room temperature after prenucleation. This indicates a post-nucleation mechanism of epitaxy.