Fabrication, Characterization and Theoretical Modeling of Te-doped Bi Nanowire Systems

In this thesis, I present a novel fabrication technique for synthesizing Te-doped Bi nanowire arrays, which represent a unique class of one-dimensional systems. Due to the small electron effective mass and the highly anisotropic Fermi surface of Bi, Bi nanowires are especially intriguing for the study of one-dimensional systems, as well as novel thermoelectric materials. Te, which acts as an electron donor in Bi, is introduced to synthesize n-type Bi nanowires to optimize the thermoelectric performance. The fabrication of Te-doped Bi nanowires consists of preparing porous anodic alumina, followed by the pressure injection of Te-doped liquid Bi into the porous template. With this technique, nanowires with diameters ranging from 7 nm to 200 nm, and lengths of ~ 50 pim are achieved. The nanowires are highly crystalline, dense and continuous, as determined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies. From XRD studies, we found that our nanowires possess a preferred growth orientation along the wire axis, and this orientation is found to be dependent on the wire diameter. This thesis also presents an improved theoretical model for Bi nanowire systems, which takes into account the circular wire boundary conditions, anisotropic carrier pockets, and non-parabolic dispersion relation for L-point electrons and holes. A powerful numerical method that can be generalized to other problems has been designed to help solve the complicated electronic band structure of Bi nanowires. Theoretical calculations show that Bi nanowires with small diameters (< 10 nm) would have a thermoelectric performance superior to bulk materials. An even more significant enhancement in the thermoelectric performance is expected if the T-point hole pocket can be removed or suppressed. The transport properties of pure and Te-doped Bi nanowires have been studied experimentally over a wide range of temperatures (4-300 K) in this thesis. The temperature dependence of the resistance for Bi nanowires with different diameters shows good agreement with theoretical modeling, and provides strong evidence for