Electrodeposition of nanostructured thermoelectric materials

Dimensionally restricted materials present a wide range of potential applications ranging from thermoelectric power generation to information storage and processing. In particular, nanowires are promising materials for thermoelectric applications because quantum confinement has been shown to increase thermoelectric efficiency. This dissertation describes the fabrication of thick films and nanowires of Bi₂Te₃, CoSb₃, and Bi_1−x Sb_x, all thermoelectric materials of current interest.; Electrochemical deposition into porous anodic alumina templates was used to fabricate nanowires of three different thermoelectric materials. Electrodeposition of material into the pores of the templates ensures that the as-deposited wires are electrically continuous, and provides a wide range of control via anodization potentials, electrolytes, and temperature. Characterization of the nanowire/porous A1203 composite materials was accomplished using X-Ray diffraction (XRD) to determine the phase, degree of crystallinity, and orientation of the nanowires. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in conjunction with energy dispersive spectroscopy (EDS) were used to determine the extent of pore-filling, the morphology of the wires, and the composition of the wires.; High quality Bi₂Te₃ wires with 200 nm and 40 nm average diameters were obtained by direct electrodeposition. A high degree of pore filling was accomplished by minimizing the rate of growth by using 0.03 V vs. Ag/AgCl as the deposition potential, Ag as an electrode material, and ∼50 μm thick templates. Nucleation in 95% of the pores in a 4-cm 2 sample was achieved. The wires are crystalline, dense, and highly textured along the optimal growth direction for thermoelectric properties.; Polycrystalline CoSb₃ films have been electrodeposited from an aqueous solution of CoSO₄, Sb₂O₃, potassium citrate, and citric acid. The conditions used to deposit the films could not be used to make nanowires. A multilayered method involving the deposition of layers of the elements followed by post-annealing was developed in order to fabricate nanowires of crystalline CoSb₃ with three-dimensional periodicity.; The electrodeposition of films, 200 nm and 50 nm wires of Bi_1−x Sb_x has been accomplished. Phase separation occurs under rapid growth conditions for the films, and for the wires even at low Sb compositions. The wires do not fill the pores completely, but are continuous, dense and of uniform diameter.