Film Formation and Influence of Ions on Crystal Growth Using Ionized Cluster Beams

Abstract

Film growth using ion-based techniques has become an useful method of preparing films at lower substrate temperatures. In various ion-based techniques, it is characteristics of the ionized cluster beam (ICB) technique that macro-aggregates of atoms (clusters)formed from deposited material vapor are utilized instead of atomic or molecular state particles, and that the structural properties of films are artificially controlled by adjusting the acceleration voltage and the content of ions. The roles of ions in film formation are to enhance the chemical activity of vaporized materials and to promote film growth along a particular crystal axis at lower substrate temperatures compared with conventional vacuum evaporation system, but the elementary mechanisms of nucleus and film growth at the initial stages have remained obscure. Therefore, an attempt to investigate the effects of cluster ions on film growth was made for Bi and Te films, which were deposited simultaneously on a glass (insulating) and an Al coated glass (conducting) substrate. The major results obtained ar e as follows: (1) the presence of ions, even though the content of ions is only -a few per cent in the total flux, brings about a marked change in the condensation process of the deposited materials. (2) The structural parameters of nuclei at the initial stage can be modified by adjuisting the total ionic charge and their kinetic energies. (3) The effect of ions on film growth along a particular crystal axis is qualitatively explained by using a valence bond orbital model.