Kinetics and Initial Stages of Bismuth Telluride Electrodeposition

The kinetics and initial stages of Bi2Te3 electrodeposition on gold from an aqueous electrolyte composed of bismuth and telluryl ions and nitric acid were investigated using voltammetry and chronopotentiometry. For tellurium alone, it is found that the reduction of tellurium ions to tellurium occurs with four exchanging electrons at -0.05 V vs Ag/AgCl (3 M KC1). At -0.6 V, tellurium reduces to H2Te under kinetic control and the following simultaneous diffusion-controlled reaction occurs with one exchange electron per tellurium atom: HTeO2 + + H2Te + H+ + 2e- - > 2Te + 2H2O. Bismuth telluride deposition starts at more positive potential than bismuth and tellurium deposit individually. It is suggested that the electrodeposition of Bi2Te3 proceeds via a Stransky-Krastanov mechanism. From the Bard correctionjto the Sand equation, the diffusion coefficients of bismuth and telluryl ions were determined to be 1.90 x 10~5 and 1.39 x 10(-6) cm2/s, respectively, in the investigated solutions. Due to the low diffusivity and solubility of telluryl ions, the limiting current density for Bi2Te3 deposition in the investigated solution is low; it is only 2 mA/cm2. Above the limiting current density, a sniooth deposit cannot be obtained without agitation. A smooth deposit can be achieved when the depletion of anions is eliminated.