Columnar microstructure in vapor-deposited thin films

The columnar microstructures commonly observed in crystalline and amorphous thin films possess many morphological features in common. The structure consists of a low density or void network that surrounds an array of parallel uniform-sized rods of higher density. The column orientation in films deposited at oblique incidence is always more nearly perpendicular to the substrate than the vapor beam direction. The structure is observed only in film materials that exhibit a limited atomic mobility. A simple geometric argument based upon shadowing of the vapor beam by atoms within the growing film is sufficient to explain the gross features of the structure. The shadowing mechanism is demonstrated by means of atomistic simulations of the deposition process, which also yield a columnar structure similar to that observed in vapor-deposited films. In such films, the columns are oriented at an angle β such that tanβ = 1 2 tan α, where α is the angle between the normal and the vapor beam.