Optical characterization of nitrogenated carbon overcoats

Protective wear coatings for disks that incorporate a layer of nitrogenated carbon (CNx) have recently attracted attention. The thickness and nitrogen content of such a layer affects the electrical resistivity, mechanical wear behavior, as well as lubricity and hydroscopic affinity of a disk. An optical methodology will be presented that can measure the thickness and optical constants of such CNx overcoats. The methodology relies on broad-band spectrophotometry and the Forouhi-Bloomer dispersion equations for refractive index (n) and extinction coefficient (k). A trend in the optical constants of CNx films will be described that allows rapid quantitative determination of nitrogen content. Measurements of nitrogen content ranging from about 4% to 25% will be presented. Results obtained with this methodology are compared to results from X-ray photoelectron spectroscopy (XPS). Additional outputs of optical spectra are utilized to further elucidate chemical structure. (C) 1997 Elsevier Science S.A.