Evolution of microstructure and crack pattern in NiO thin films under 200 MeV Au ion irradiation

Abstract

NiO thin films grown on Si (100) substrate by electron beam evaporation method and sintered at 700°C were irradiated with 200MeV Au15+ ions. The fcc structure of the sintered films was retained up to the highest fluence (1×1013ionscm−2) of irradiation. However the microstructure of the pristine film underwent a considerable modification with increasing ion fluence. 200MeV Au ion irradiation led to compressive stress generation in NiO medium. The diameter of the stressed region created by 200MeV Au ions along the ion path was estimated from the variation of stress with ion fluence and found to be ∼11.6nm. The film surface started cracking when irradiated at and above the fluence of 3×1012ionscm−2. Ratio of the fractal dimension of the cracked surface obtained at 200MeV and 120MeV (Mallick et al., 2010a) Au ions was compared with the ratio of the radii of ion tracks calculated based on Coulomb explosion and thermal spike models. This comparison indicated applicability of thermal spike model for crack formation.