• PDF / 923,306 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 73 Downloads / 261 Views

DOWNLOAD

REPORT

---

0886-F03-13.1

Growth and Characterization of 1D Bi2Te3 Nanowires M. Craps, N. Gothard, R. Rao, J. He, J. Hudson, Terry M. Tritt and A. M. Rao Dept of Physics and Astronomy, Clemson University, Clemson, SC, USA ABSTRACT Bulk bismuth telluride (Bi2Te3) is one of the best known thermoelectric materials with a figure of merit ZT ~1 at room temperature. Theoretical studies have suggested that lowdimensional materials may exhibit ZT values that exceed 1. In this study, we used the pulsed laser vaporization (PLV) method to prepare Bi2Te3 nanowires on silicon and quartz substrates by ablating Bi2Te3 targets in an inert atmosphere. Nano-sized gold or iron catalyst particles were used to seed the growth of the Bi2Te3 nanowires. Results from electron microscopy and Raman spectroscopy are discussed. INTRODUCTION It is well known that Bi2Te3 is one of the best known thermoelectric materials with a figure of merit ZT ~1. Theoretical studies have suggested that as the dimensions in bulk Bi2Te3 is reduced an improved ZT should results from the enhanced electron density of states near energy band in low dimensioned Bi2Te3 structures. For example, Venkatasubramanian et al. have reported a room temperature ZT value of 2.5 in 2D Bi2Te3/Sb2Te3 superlattices [1]. The possibility of a further increase in ZT in 1D Bi2Te3 has also been explored and reported in the literature [2-4]. The PLV [2], electro-deposition template [3] and the cyclic deposition [4] methods have been used to prepare Bi2Te3 nanowires. However, no further improvement in ZT has been reported in recent years which may due to the challenges associated with ZT measurements in individual nanowires. Nanocomposites that involve the incorporation of nanowires in its corresponding bulk are gaining much interest since enhanced thermoelectric properties are expected to result from interfacial reflection and scattering of phonons in the nanocomposites. This manuscript focuses on the synthesis of Bi2Te3 nanowires using the PLV method which has been very successful in the synthesis of highly crystalline 1D structures of several semiconducting materials via the vapor-liquid-solid growth (VLS) process in which nano-sized catalyst particles seed and template the growth [5,6]. In particular, this study finds that high quality crystalline Bi2Te3 nanowires can be obtained using iron catalyst particles. EXPERIMENTAL DETAILS In the PLV method a laser beam is reflected off a rastering mirror and focused onto a rotating target placed inside a quartz tube reactor (Fig. 1). The laser ablates the target (ablating time ranging between 30 minutes to 2 hours) and the resulting vapor is carried downstream by flowing Ar (~150 sccm) and H2 (~15 sccm) gases. The reactor is maintained at 200 torr and bare silicon (or quartz) substrates are placed in the hot zone between the target and the water-cooled cold finger. Since Bi2Te3 melts at ~585 ºC and the metal which serve as the catalysts melt above 1000 ºC (Au and Fe melts at ~1064 and 1538 ºC, respectively), the temperatures of the target and substrates