OPTICAL CHARACTERIZATION OF NITROGENATED CARBON OVERCOATS

Protective wear coatings for disks that incorporate a layer of nitroge nated carbon (CNx) have recently attracted attention. The thickness an d nitrogen content of such a layer affects the electrical resistivity, mechanical wear behavior, as well as lubricity and hydroscopic affini ty of a disk. An optical methodology will be presented that can measur e the thickness and optical constants of such CNx overcoats. The metho dology relies on broad-band spectrophotometry and the Forouhi-Bloomer dispersion equations for refractive index (n) and extinction coefficie nt (k). A trend in the optical constants of CNx films will be describe d that allows rapid quantitative determination of nitrogen content. Me asurements of nitrogen content ranging from about 4% to 25% will be pr esented. Results obtained with this methodology are compared to result s from X-ray photoelectron spectroscopy (XPS). Additional outputs of o ptical spectra are utilized to further elucidate chemical structure. ( C) 1997 Elsevier Science S.A.