Study of NiO/Ni(100) structural changes under the influence of ion irradiation at different temperatures

Abstract

Thin films of nickel oxide, epitaxially grown on Ni(100), have been exposed to ion irradiation (2 keV Ar + and He + at different temperatures. The changes of the surface were followed by LEED, XPS, UPS and MIES (metastable induced electron spectroscopy). The latter method shows that low irradiation doses cause destruction of oxide and the appearance and growth of surface areas covered with chemisorbed oxygen. At higher doses the MIES signal of chemisorbed oxygen vanishes and that of clean nickel appears. The arising chemisorbed oxygen forms a pronounced c(2 × 2)O/Ni structure at a sample temperature of T= 420 K; at T= 320 K the LEED patterns are weak and at T= 220 K no ordered structure is observed at all. The very surface of the irradiated NiO/Ni(100) film (as observed by MIES) demonstrates qualitatively the same surface structure as the annealed one. Data analysis shows that under ion bombardment the sample undergoes the same stages as during the oxidation process but in reverse order.