My introduction in the November MRS BULLETIN to this two-part series on deposition processes discussed the extensive use of thin films in science and technology. That it takes two issues and nine articles to cover this topic — and by no means exhaustively — is testimony to the manifold ways thin films are prepared.
If all deposition processes resulted in the same product, then such extensive coverage would be redundant and unnecessary. Thin films, however, cover a virtual infinity of free energy states — and related crystal structures, micro-structures, defects, defect densities, impurities, compositions, composition modulations, etc. — that are sensitive to the particular deposition process and its conditions. It is this richness of choice that makes thin film science and technology both exciting and, at times, frustrating.
Along with the freedom to extensively vary thin film characteristics, resulting properties and applications comes the difficulty in understanding preparation-characterization-property relations in enough detail to control and reproduce deposition processes.
The November articles covered molecular dynamics computer modeling of nucleation and growth processes, molecular beam epitaxy, organometallic vapor phase epitaxy, and chemical vapor deposition. This month's articles continue the sequence of ways to deposit films, the general direction being toward lower substrate temperatures. Plasmas, which offer both increased flexibility and complexity, are primarily considered. The last article covers thermal plasmas, not to control the vapor deposition but to melt powders which result in a multiple splat-quenched array of particles that form coatings important to industry.