Electrochemical atom-by-atom growth of highly uniform thin sheets of thermoelectric bismuth telluride via the route of ECALE

Abstract

Thermoelectric films of Bi 2Te 3 with highly uniform thin sheets structure were grown on Au substrate via the route of electrochemical atomic layer epitaxy (ECALE) in this work. Electrochemical aspects of Te and Bi on Au, Te on Bi-covered Au, and Bi on Te-covered Au were characterized by means of cyclic voltammetry and coulometry. A steady ECALE deposition for Bi 2Te 3 compound could be attained after positively adjusting the underpotential deposition (UPD) potentials of Bi and Te on Au in steps over the initial 40 cycles, and the potentials could be kept constant for the following deposition. A 400-cycle deposit, which was grown with the steady deposition potentials, was proved to be a single phase Bi 2Te 3 compound by X-ray diffraction (XRD) analysis. The 2:3 stoichiometric ratio of the deposit was further verified by energy dispersive X-ray (EDX) quantitative analysis. The band gap of the Bi 2Te 3 film was determined as 0.33 eV by Fourier transform infrared spectroscopy (FTIR) and blueshifted in comparison with that of the bulk Bi 2Te 3 single crystal. The field emission scanning electron microscope (FE-SEM) observation shows the deposit consisted of numberless interlaced thin sheets, which grown perpendicularly with the substrate. The formation mechanism of the morphology is investigated and it should be related to the property of the substrate and the lattice structure of Bi 2Te 3 compound. It is believed that the interlaced thin sheets structure may be profitable for the improvement of the thermoelectric properties.