Opal Films Made by the Capillary Deposition Method: Crystal Orientation and Defects

Opal films fabricated by the CDM (capillary deposition method, a special flow induced technique) have been studied with respect to their lattice alignment and defect distribution in the film. The substrate plane as well as the growth direction controls the orientation of the lattice. Both together allow two possible densely packed sphere arrangements in the film, very likely occurring simultaneously and interconnected either by stacking faults or by disordered regions. Parallel oriented cracks are formed randomly near open edges and propagate stepwise inward the cell. The distance between two adjacent cracks was found to be nearly proportional to the thickness of opal film. The UV/vis transmission spectra of the opal films indicate a homogeneous defect distribution and a very broad scattering background. The background has a 1/lambda behavior pointing to a Mie-like scattering phenomenon. The investigations show indications for possible defect- control and reveal differences in opals fabricated by other methods.