OXIDATION OF THIN CHROMIUM NITRIDE FILMS - KINETICS AND MORPHOLOGY

Magnetron-sputtered, 150-500 nm thick chromium nitride films of CrN an d Cr2N stoichiometry were exposed to air at 500-800 degrees C. Oxide s cale growth and morphology and the phase transformations during oxidat ion were investigated by means of Rutherford backscattering spectromet ry, resonant nuclear reaction analysis, scanning force microscopy (SFM ) and x-ray diffraction. A combined logarithmic and parabolic Cr2O3 sc ale growth was found and interpreted as due to inwards diffusion of ox ygen via grain boundaries (logarithmic) and outwards lattice diffusion of Cr (parabolic). Pt-marker experiments confirmed this interpretatio n. The activation energies of the two processes were determined to be Q = 60(20) and 196(17) kJ mol(-1). During oxidation of Cr2N a transfor mation into CrN was observed. A linear increase in the surface roughne ss and surface grain size with the oxide layer thickness was found by SFM.