First nucleation steps of nickel nanoparticle growth on Al2O3 (0 0 0 1) studied by XPS inelastic peak shape analysis

A series of Ni nanoparticles has been deposited on sapphire (Al2O3 (0 0 0 1)) substrates using the pulsed laser deposition technique. The amount of material deposited has been controlled by means of the number of laser pulses utilized. The substrate temperature was varied from room temperature to 500 °C. The nanoparticles deposited were characterized in situ by X-ray photoelectron spectroscopy. The inelastic peak shape of O 1s was analyzed to obtain the mode of growth of the Ni nanoparticles. The results show the height of the Ni nanoparticles increases with deposition from ∼1 to 9 nm and the surface coverage increased simultaneously from ∼0.1 to 0.85. For 200 or more laser pulses, as the substrate temperature increased (300-500 °C) the height of the nanoparticles increased. On the other hand, the coverage always decreased as a function of substrate temperature. This implies that the mobility of the deposited Ni increases with substrate temperature thus forming taller islands with corresponding smaller coverage.