Three-Dimensional Bi₂Te₃ Networks of Interconnected Nanowires: Synthesis and Optimization.

Alejandra Ruiz-Clavijo,Olga Caballero-Calero,Marisol Martín-González

doi:10.3390/nano8050345

Alejandra Ruiz-Clavijo, Olga Caballero-Calero + Show 1 more

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https://doi.org/10.3390/nano8050345

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Abstract

Self-standing Bi2Te3 networks of interconnected nanowires were fabricated in three-dimensional porous anodic alumina templates (3D–AAO) with a porous structure spreading in all three spatial dimensions. Pulsed electrodeposition parameters were optimized to grow highly oriented Bi2Te3 interconnected nanowires with stoichiometric composition inside those 3D–AAO templates. The nanowire networks were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and Raman spectroscopy. The results are compared to those obtained in films and 1D nanowires grown under similar conditions. The crystalline structure and composition of the 3D Bi–Te nanowire network are finely tuned by controlling the applied voltage and the relaxation time off at zero current density during the deposition. With this fabrication method, and controlling the electrodeposition parameters, stoichiometric Bi2Te3 networks of interconnected nanowires have been obtained, with a preferential orientation along [1 1 0], which makes them optimal candidates for out-of-plane thermoelectric applications. Moreover, the templates in which they are grown can be dissolved and the network of interconnected nanowires is self-standing without affecting its composition and orientation properties.

Highlights

Thermoelectric devices have raised the interest of the scientific community due to their capability to convert thermal energy directly into electrical energy and vice versa, as in power generators and coolers
If we compare the cyclic voltammetry (CV) obtained with the one obtained when a gold layer over a silicon substrate is used as working electrode, and with that recorded when a 1D-Anodic Aluminum Oxide (AAO) membrane is used as the working electrode; we can see from Figure 1 an evolution of the reduction peak towards more negative potentials when we go from films to nanowire network (3D–AAO/gold) to nanowires (1D-AAO/gold substrates)
When a 3D–AAO is used as working electrode, the reduction peak appears at an applied voltage of around −60 mV, an intermediate value between that obtained for gold over the silicon substrate and 1D-AAO

Summary

Introduction

Thermoelectric devices have raised the interest of the scientific community due to their capability to convert thermal energy directly into electrical energy and vice versa, as in power generators and coolers. The applications of thermoelectric based devices are still limited as consequence of their low efficiency. The performance of a thermoelectric device is proportional to its figure of merit, ZT, which is a dimensionless quantity defined as ZT = σ·S2·T/κ, where T, S, σ, and κ are the absolute temperature, Seebeck coefficient, electrical conductivity, and thermal conductivity, respectively. The ideal thermoelectric material should have a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity; these requirements are not met, though [1]. There has been reported a reduction of the thermal conductivity, κ, of electrodeposited Bi2Te3 nanowires when decreasing their diameter from 200 to 20 nm [2], as a consequence of the increase of the acoustic phonon scattering at the interfaces due to a higher surface to volume ratio

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