Effects of sputtering parameters on optical constant of NiO_x thin films

The effects of sputtering parameters on optical constant of NiO_x thin films prepared by reactive magnetron sputtering were studied by spectroscopic ellipsometry, XRD and XPS methods. The optical constant of the deposited films became smaller with O₂/Ar flow ratios increasing. After annealing, the refractive index shows an increase, especially at a high O₂/Ar flow ratio, while the extinction coefficient reduced by about 50%. The refractive index is greater for a higher sputtering power while smaller for a higher work pressure. It is related to the existence of interstitial oxygen and vacancy of Ni, the decomposition of NiO_x and compactness degree of NiO_x films, respectively.