A kinetic study of the initial oxidation of the Ni(110) surface by RHEED and X-ray emission

Nickel (110) surfaces, prepared by a combination of high temperature oxidation, argon ion bombardment and hydrogen reduction, were oxidized in pure O₂. The structural aspects of this interaction were studied by reflection high energy electron diffraction (RHEED) and the corresponding kinetics determined by electron excited X-ray emission spectroscopy. On exposure to oxygen the surface was observed to go through three ordered two-dimensional structures. These were a (2 × 1), a (3 × 1) and finally a (9 × 4) structure containing 0.015 microg/cm² of oxygen. From this surface NiO was produced in a (001) epitaxy which was compressed 4.5% in the plane of the surface. With oxidation beyond 0.060 microg/cm² the oxide strain was relieved and a complex oxide epitaxy developed which has been tentatively identified as a (117) oxide parallel to the nickel (110) surface. The kinetics have been explained on the basis of three distinct processes. (i) An initial chemisorption stage (0 to 0.015 microg/cm²) associated with the two-dimensional structures, (ii) Oxide nucleation and spreading to cover the surface, associated with the (001)-NiO epitaxy (0.015 to 0.06 microg/cm²), (iii) Logarithmic film thickening above 0.060 0.06 microg/cm² associated with the development of (117) epitaxy.