Correlation between surface chemistry, gasochromism and field emission properties of tungsten oxide nanowire thin films when exposed to atomic oxygen

Abstract

Excellent field emission is observed from vertically aligned W₂₀O₅₈ nanowires that are prepared by thermal evaporation. The effects of atomic oxygen (AO) exposure on its surface chemistry, gasochromism, and field emission properties have been investigated. Morphology and structural characterization indicates little change was observed in the nanowire after a high dose of AO exposure. It is worth noting that a stable and high emission current could be retained, with a little increase of turn-on electric field (defined at 10 μA cm⁻²). Work function measurement indicates that the Fermi level has a distinctive decrease of ∼0.29 eV after AO exposure. The W valence state shows a clear transition from +5 to +6, corresponding to AO exposure induced color bleaching process. The origin of the work function increase is ascribed to the strengthened surface dipole, which is the main reason that accounts for the observed field emission characteristics.