OXIDATION OF MOLYBDENUM SURFACES BY REACTIVE OXYGEN PLASMA AND O-2(- AN AUGER AND XPS STUDY() BOMBARDMENT )

The oxidation of molybdenum at room temperature with oxygen plasma or a beam of O-2(+) ions has been studied with Auger electron spectroscop y (AES) and x-ray photoelectron spectroscopy (XPS). Auger electron spe ctroscopy shows a progressive modification of the N2,3VV lineshape and the development of new features close to the intense M4,5NN Auger tra nsitions of metallic Mo at 160, 186 and 221 eV. The effects are greate r with the oxygen plasma than with the O-2(+) bombardment. X-ray photo electron spectroscopy shows that the incorporation of oxygen into the molybdenum gives rise to the formation of Mo6+, Mo4+ and a form of Mon + (n<4). The (Mo4+-Mon+)/MO6+)/Mo6+ ratio was higher after O-2(+) ion bombardment than by treatment with the oxygen plasma, in which case th e concentration of the Mo4+ and Mo6+ oxidation states was very similar . The analysis of the O 1s and O KLL Auger spectra under the different conditions showed that whenever a high concentration of the Mo6+ spec ies is present, the O-Mo bond is more covalent in character. To evalua te the influence of chemical and ballistic effects in the two oxidatio n processes, additional experiments were carried out with MoO3. This o xide was bombarded with Ar+ and O-2(+) until a steady-state surface co mposition was reached. In both cases, the formation of a considerable amount of Mo4+ + Mon+ (n < 4) and Mo-0 species (i.e. reduction of Mo6 initially present in the sample) was detected. These results suggest that the high concentration of Mo4+ + Mon+ found upon bombardment of M o-0 with O-2(+) is rather produced by ballistic effects, which cause t he reduction of the initially formed Mo6+. (C) 1998 John Wiley & Sons, Ltd.