Nickel evaporation in high vacuum and formation of nickel oxide nanoparticles on highly oriented pyrolytic graphite. X-ray photoelectron spectroscopy and atomic force microscopy study

Abstract

Nickel was evaporated in high vacuum (0.8–1.3 · 10 − 4 Pa) onto highly oriented pyrolytic graphite substrate kept at room temperature. Nanoparticles produced in this way were subsequently oxidized in air. The dependence of the nickel atoms impinging rate on the input power was determined for the used sources. Impinging rates ranging from 1.2 · 10 11 to 1.8 · 10 16 nickel atoms/cm 2s were achieved. The composition of the prepared nanoparticles, their size distribution and structure were examined by X-ray photoelectron spectroscopy and atomic force microscopy. Nanoparticles composed of nickel oxide and oxyhydroxide formed flat islands with fine structure. Average island areas increased linearly with increasing amount of deposited nickel at a constant impinging rate. The increase in the impinging rate of more than three orders of magnitude shifted the average island size to lower values. Fine structure of islands was composed of particles with average diameter 20 nm. The mean surface-diffusion length of Ni atoms equal to 50 nm and the difference between the desorption energy and the activation energy of surface diffusion 0.17 eV were estimated. The condensation threshold on basal planes at room temperature was found at an impinging rate of 5.5 · 10 11 nickel atoms/cm 2s while on the step areas the deposit occurred at an impinging rate five times lower. The knowledge of the condensation threshold and of impinging rate effect on island size distribution made it possible to control the size and number of islands per unit surface area.