Arrays of thermoelectric bismuth telluride (Bi(2)Te(3)) nanowires were grown into porous anodic alumina (PAA) membranes prepared by a two-step anodization. Bi(2)Te(3) nanowire arrays were deposited by galvanostatic, potentiostatic and pulsed electrodeposition from aqueous solution at room temperature. Depending on the electrodeposition method and as a consequence of different growth mechanisms, Bi(2)Te(3) nanowires exhibit different types of crystalline microstructure. Bi(2)Te(3) nanowire arrays, especially those grown by pulsed electrodeposition, have a highly oriented crystalline structure and were grown uniformly as compared to those grown by other electrodeposition techniques used. X-ray diffraction (XRD) analyses are indicative of the existence of a preferred growth orientation. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) confirm the formation of a preferred orientation and highly crystalline structure of the grown nanowires. The nanowires were further analyzed by scanning electron microscopy (SEM). Energy dispersive x-ray spectrometry (EDX) indicates that the composition of Bi-Te nanowires can be controlled by the electrodeposition method and the relaxation time in the pulsed electrodeposition approach. The samples fabricated by pulsed electrodeposition were electrically characterized within the temperature range 240 K≤T≤470 K. Below T≈440 K, the nanowire arrays exhibited a semiconducting behavior. Depending on the relaxation time in the pulsed electrodeposition, the semiconductor energy gaps were estimated to be 210-290 meV. At higher temperatures, as a consequence of the enhanced carrier-phonon scattering, the measured electrical resistances increased slightly. The Seebeck coefficient was measured for every Bi(2)Te(3) 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.

We have performed four-probe electrical transport measurements on solitary highly crystalline wires of semimetallic bismuth with aspect ratios up to 60 at room and at cryogenic temperatures. By proper choice of the substrate material and the film deposition parameters, lithographic wires with lateral dimensions of down to one single grain, $\sim 250$ nm, were fabricated. The electrical resistance of each wire was measured against its thickness through successive reactive ion etching of the self-same wire. Quantum size effects revealed themselves as regular oscillations in the electrical resistance. Some evidence for the semimetal-to-semiconductor phase transition has been detected. The measured data are discussed within the framework of the existing theoretical models.Comment: 5 pages, 6 figures, and the LaTeX sourc

We study theoretically the quantum size effects in a one-dimensional semimetal by a Boltzmann transport equation. We derive analytic expressions for the electrical conductivity, Hall coefficient, magnetoresistance, and the thermoelectric power in a nanowire. The transport coefficients of semimetal oscillate as the size of the sample shrinks. Below a certain size the semimetal evolves into a semiconductor. The semimetal-semiconductor transition is discussed quantitatively. The results should make a theoretical ground for better understanding of transport phenomena in lowdimensional semimetals. They can also provide useful information while studying low-dimensional semiconductors in general.

Abstract. By employing a semiclassical Boltzmann transport equation and using an energy and size dependent relaxation time (τ ) approximation (RTA), we evaluate the thermoelectric figure-of-merit ZT of a quantum wire with rectangular cross-section. The inferred ZT shows abrupt enhancement in comparison to its counterparts in bulk systems. Still, the estimated ZT for the representative Bi 2 Te 3 nanowires and its dependence on wire parameters deviate considerably from those predicted by the existing RTA models with a constant τ . In addition, we address contribution of the higher energy subbands to the transport phenomena, the effect of chemical potential tuning on ZT , and correlation of ZT with quantum size effects (QSEs). Particularly, we show that within each subband, ZT has an optimum value which depends on wire dimensions and chemical potential. The obtained results are of general validity for a wide class of systems and may prove useful in the ongoing development of the modern thermoelectric applications.