Enhanced Control of Morphology in Thin Film Nanostructure Arrays

Glancing angle deposition (GLAD) was used to grow thin films of silicon and titanium dioxide slanted post nanostructures onto periodically patterned substrates. The patterned substrates consisted of tetragonal arrays of small hillocks with periodicities of 100, 200, and 300 nm. An advanced substrate rotation algorithm called PhiSweep was used during the deposition. The PhiSweep algorithm consists of rotating the substrate back and forth such that the arriving vapour flux direction alternates from either side of desired column tilt direction. This reduces the anisotropy of the shadowing conditions, which diminishes column fanning. The tilt angle of the columns is affected by the PhiSweep parameters, which is important in applications such as square spiral photonic crystals. This relation is derived and confirmed with tilt angle measurements of the slanted post films. The films grown using the PhiSweep method were compared with similar films grown using traditional GLAD. The PhiSweep technique produced films which conformed to the initial periodic pattern much better than the films grown with traditional GLAD, enabling the growth of nanostructure arrays with smaller periodicities.