Optical properties of nano- and ultrananocrystalline diamond thin layers in the UV and visible spectral range

Abstract

The potential application of nano- and ultrananocrystalline diamond thin films in nanotechnology demands a detailed knowledge of the optical properties and their relation to the structure. By varying the atomic bonding structure and morphological properties of nanodiamond layers we have explored a relation between the structure and the spectral dependence of the refractive index and extinction coefficient in nanodiamond. For this purpose nanodiamond layers were prepared from CH4, H2 and Ar gas mixture in a chemical vapor deposition process with different Ar-content of the feed gas and self-bias of the substrate material. Optical parameters were determined by using a three-layer model in the evaluation of the spectral ellipsometric data. Surface topography was monitored and the average grain size was obtained from scanning electron microscopy images. Bonding characteristics of diamond and non-diamond phases were analyzed by Raman spectroscopy.