Electrodeposition and stripping analysis of bismuth selenide thin films using combined electrochemical quartz crystal microgravimetry and stripping voltammetry

Combined stripping voltammetry and electrochemical quartz crystal microgravimetry were employed for the compositional analysis of electrodeposited bismuth selenide (Bi–Se) thin films. Electrodeposited films contain free Bi and free Se in addition to the targeted Bi₂Se₃ compound and the amount of these “impurity” phases depends on the electrodeposition variables. Thus the free Se content was determined using the reduction peak of Se to Se²⁻ obtained during the cathodic scan of films in 0.1 M Na₂SO₄ blank electrolyte. The Se content obtained during the cathodic stripping of Bi₂Se₃ to Bi + Se²⁻ was used for the determination of Bi₂Se₃ content using the assumption of 2:3 compound stoichiometry. Finally, the total Bi content was obtained from the anodic scan and the free Bi content was calculated from the difference between total Bi and the Bi present in Bi₂Se₃. The compositional assays thus obtained from the combined use of stripping voltammetry and EQCM are presented as a function of electrodeposition potential and electrolyte composition. The Bi₂Se₃ content decreased as the deposition potential was decreased (made more negative) and was highest when the electrolyte contained the same molar ratio of Bi³⁺ and Se⁴⁺ species. Unlike the Bi₂Te₃ previously studied by us, electrodeposition of Bi₂Se₃ was not efficient at potentials more negative than −0.5 V because of Se stripping and hydrogen evolution.