The growth and structure of thin oxide films on cerium ion-implanted nickel

Cerium ions were implanted into a high purity polycrystalline Ni to a dose of 2 x 10(16) Ce+/cm(2). The radiation damage and distribution of Ce in Ni substrate were modified by postimplantation vacuum annealing. The Ce implants significantly decreased the NiO growth rate at 973 K. Thin oxide films formed on implanted Ni were composed of three well-defined sublayers, each with an essentially different microstructure. Cerium was present in the near surface region of the oxide in the form of CeO2 particles, randomly distributed in NiO matrix, and Ce ion segregants at NiO grain boundaries. The size of CeO2 particles, formed during the initial stages of exposure to oxygen, affected the inhibition of oxide growth. Vacuum annealing following implantation decreased the beneficial effect of Ce implants by increasing the size of CeO2 particles. The role of Ce implants in inhibiting grain boundary diffusion in NiO is analysed. As a result of this study, the growth mechanism of thin NiO films on Ce-implanted Ni is proposed.