Electrochemical quartz crystal microbalance study of the electrodeposition mechanism of molybdenum oxide thin films from peroxo-polymolybdate solution

The electrodeposition of molybdenum oxide thin films from aqueous peroxo-polymolydate solution was studied using chronocoulometry and electrochemical quartz crystal microbalance (EQCM) techniques. Analysis of EQCM as well as spectroelectrochemical data have allowed us to identify at least four distinct regimes for film growth. EQCM was used to estimate apparent equivalent molecular weights and corresponding reaction mechanisms were established for films grown at different deposition potentials. We propose a new electrodeposition mechanism that involves the graded reduction of several solution components, primarily comprising molybdic acid and peroxo-polymolybdates, to form amorphous hydrates of non-stoichiometric, mixed-valent molybdenum oxides. Careful regulation of the deposition parameters allows for fine-tuning of molybdenum oxide composition to produce films with varied water content and valency