XPS studies on surface reduction of tungsten oxide nanowire film by Ar+ bombardment

• DOI: 10.1016/j.elspec.2012.01.004
• Publication Date: 2012-02-06T18:04:34Z
• Authors: F.Y. Xie; L. Gong; X. Liu; Y.T. Tao; W.H. Zhang; S.H. Chen; H. Meng; J. Chen
• Keywords: Chemical state

Abstract WO 3 nanowire film was bombarded by Ar ion beam in the analysis chamber of an X-ray photoelectron spectroscopy (XPS) system to produce uniform tungsten cone arrays. The WO 3 nanowire film itself served as an etching mask during the Ar + bombardment. The changes of surface chemical states and electronic structures during bombardment were monitored by in situ XPS. The morphological evolution with different Ar + bombardment time was observed by ex situ scanning electron microscopy (SEM). At the start of Ar + bombardment partial W 6+ in WO 3 was reduced to W 5+ immediately, subsequently to W 4+ and then to W x + (intermediate chemical state between W 4+ and W 0 ), finally to W 0 . Multiple oxidation states of tungsten coexisted until finally only W 0 left. SEM images showed that the nanowires were broken and then fused together to be divided into clusters with a certain orientation after long-time high-energy ion beam bombardment. The mechanism of the ion-induced reduction during bombardment and the reason of the orientated cone arrays formation were discussed respectively.