Oxidation states of molybdenum in oxide films formed in sulphuric acid and sodium hydroxide

• Published in: Thin solid films 2012-07, Vol.520 (19), p.6318-6327
• Main Authors: Okonkwo, I.A., Doff, J., Baron-Wiecheć, A., Jones, G., Koroleva, E.V., Skeldon, P., Thompson, G.E.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electrolytes; Exact sciences and technology; Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids); Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Molybdenum; Nuclear reaction analysis; Other nonelectronic physical properties; Oxidation state; Oxide coatings; Oxides; Physical properties of thin films, nonelectronic; Physics; Rutherford backscattering spectroscopy; Sodium hydroxide; Spectra; Structure and morphology; thickness; Sulphuric acid; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Thin films; Valence; X-ray photoelectron spectroscopy
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2012.05.031

X-ray photoelectron spectroscopy is used to investigate the oxidation states of molybdenum in thin films formed potentiostatically, over a range of potentials, in either 1moldm−3 H2SO4 or 10moldm−3 NaOH at 20°C. Mo 3d spectra suggested that MoO2 and Mo(OH)2 were the main components of the films, with smaller amounts of MoO3 and possibly Mo2O5. O 1s spectra indicated the presence of oxygen as oxide and hydroxide species and as bound water. Ion beam analysis revealed the formation of thin films at all potentials, with significant losses of oxidized molybdenum to the electrolyte. ► Oxides are formed on molybdenum in sulphuric acid and sodium hydroxide solutions. ► Molybdenum IV and VI are identified by XPS, with MoO2 species dominating. ► Thicknesses of films are determined by ion beam analysis for a range of potentials. ► Films form at low efficiency due to loss of molybdenum species to electrolyte.