Microstructural-induced anisotropy in thin films for optical applications

Materials in thin-film form are much more interesting or much more trouble than their bulk counterparts, depending on your point of view. Most coatings are deposited at substrate temperatures considerably lower than the melting points of the evaporant materials, and the trend is generally toward even lower processing temperatures. In these films, the solid material is distributed in an array of fairly closely packed columns that run perpendicular to the substrate, and it is the columnar microstructure that has substantial influence over the physical behavior of the films. The microstructure is anisotropic and so are most thin film properties.