Tuning the crystallinity of thermoelectricBi2Te3 nanowire arrays grown by pulsed electrodeposition

Abstract

Arrays of thermoelectric bismuth telluride(Bi2Te3)nanowires were grown into porous anodic alumina (PAA) membranes prepared by a two-step anodization.Bi2Te3 nanowire arrays were deposited by galvanostatic, potentiostatic and pulsedelectrodeposition from aqueous solution at room temperature. Depending on theelectrodeposition method and as a consequence of different growth mechanisms,Bi2Te3 nanowires exhibit different types of crystalline microstructure.Bi2Te3 nanowire arrays, especially those grown by pulsed electrodeposition, have a highly orientedcrystalline structure and were grown uniformly as compared to those grown by otherelectrodeposition techniques used. X-ray diffraction (XRD) analyses are indicative of theexistence of a preferred growth orientation. High resolution transmission electronmicroscopy (HRTEM) and selected area electron diffraction (SAED) confirm the formationof a preferred orientation and highly crystalline structure of the grown nanowires. Thenanowires were further analyzed by scanning electron microscopy (SEM). Energydispersive x-ray spectrometry (EDX) indicates that the composition of Bi–Tenanowires can be controlled by the electrodeposition method and the relaxationtime in the pulsed electrodeposition approach. The samples fabricated by pulsedelectrodeposition were electrically characterized within the temperature range240 K≤T≤470 K.Below T≈440 K, the nanowire arrays exhibited a semiconducting behavior. Dependingon the relaxation time in the pulsed electrodeposition, the semiconductorenergy gaps were estimated to be 210–290 meV. At higher temperatures, as aconsequence of the enhanced carrier–phonon scattering, the measured electricalresistances increased slightly. The Seebeck coefficient was measured for everyBi2Te3 sample at room temperature by a very simple method. All samples showed a positive value(12–33 µV K−1), indicating a p-type semiconductor behavior.