Determination of the optical constants of diamond films with a rough growth surface

The determination of the optical constants n and k for polycrystalline diamond films with typical growth surface roughness a of the order of tens to hundreds of nanometers is both an important and a difficult procedure. A method for determining n, k and a for rough diamond films is presented here. It is based on theoretical expressions for the optical reflectance R and transmittance T for a free-standing thin film incorporating the effects of surface scattering at one surface. The usefulness and validity of this approach are illustrated using experimental R and T data for diamond films. Simplified expressions for R and T are also presented which are valid when scattering or absorption are sufficiently strong to cause interference effects in the films to be averaged out. Prime novelty: Simple expressions for n, k and sigma are presented which will enable researchers to extract this important information about the optical constants and surface roughness of their CVD diamond films.