The influence of the conditions of the anodic formation and the thickness of Ag(I) oxide nanofilm on its semiconductor properties

Abstract

The anodic formation of Ag(I) oxide nanofilms on polycrystalline silver and Ag–Au alloys as well as on low-index single crystals of silver in 0.1 М KOH was examined. By the methods of photocurrent i ph and photopotential E ph measurements, the n-type conductivity of Ag2O film was established. Since the film (6–120 nm) is thinner than the space charge region, the dependence of photocurrent and photopotential appears on the film thickness L: i ph ~L and E ph ~L 2. The transition from polycrystalline silver to single crystals as well as the addition of a small amount of gold (X Au ≤ 4 at.%) into the silver lattice decreases the degree of deviation from the stoichiometric composition Ag2O. The parameters of Ag2O film (optical absorption coefficient α, donor defects concentration N D, space charge region W, and Debye’s length of screening L D) depend on the index of a crystal face of silver, volume concentration of gold X Au in the alloy, and film-formation potential E. At Е = 0.52 V, the sequences of variation of these parameters correlate with the reticular density sequence. The growth of the potential disturbs these sequences. The band gap in Ag2O formed on Agpoly, Aghkl, and Ag–Au is 2.32, 2.23, and 2.19 eV. Flat band potential in Ag(I) oxide, formed on Agpoly in 0.5 M KOH is 0.37 V. The appearance of the clear dependence between the state of the oxide/metal interface and the structure-sensitive parameters of semiconductor Ag(I) oxide phase allows considering the anodic formation of Ag2O on Ag as a result of the primary direct electrochemical reaction, not of the precipitation from the near-electrode layer.