Electrodeposition of Cobalt Selenide Thin Films Using Combined Voltammetry and Electrochemical Quartz Crystal Microgravimetry

Abstract

Electrodeposition and composition of CoSe thin films have been studied using electrochemical quartz crystal microgravimetry and stripping voltammetry. CoSe thin films were synthesized using 0.1 M KNO3 solution containing SeO2 and Co(NO3)2 at room temperature. During the electrodeposition, selenium was electrodeposited first, followed by the induced under potential deposition of cobalt to result in CoSe films. Photocurrent transients proved that as synthesized Se and CoSe are p-type semiconductors and their band gaps have been determined with reflectance spectrometry. Deposition mechanism and effect of electrolyte composition on the film composition were studied in detail using electrolyte containing different ratio. Composition of CoSe thins films has been determined by combining EQCM and stripping voltammetry. First, free selenium in the electrodeposited film was reduced to soluble Se2- at –0.8 V in 0.1 M Na2SO4 solution and frequency change was used to determine the content of free selenium. The film was again subjected to –1.5 V in the same blank electrolyte to reduce CoSe to Co+Se2- and accompanied frequency change was used to determine selenium in CoSe based on the 1:1 stoichiometry. Finally, the content of free cobalt in the electrodeposited film was determined from the frequency change during the oxidation of Co to Co2+ and difference between total cobalt and cobalt in CoSe thin film. Compositional analysis indicated that film composition is sensitive to electrodeposition potential as well as composition of electrolyte.