Wet chemistry applications for low dimensional bismuth-based solid

This dissertation investigates the relationship between nanoporous microstructures and transport properties. A liquid-phase metalorganic deposition (IMOD) method has been implemented to synthesize Bi films with nano-size pores. Typical nanoporous Bi film preparation involves a spin-coat of a solution of Bi 2-ethylhexanoate with glycerol into 2-methyl-1-propanol solvent on Si substrates followed by a pyrolysis under pure H2.;MOD was also used in Bi-based films and patterns. Bi2Te 3 films were prepared by mixing Bi and Te 2-methoxyethoxides in 2-methoxyethanol. Composite films of Bi2Te3-Bi and Bi2Se 3-Bi were obtained by mixing in Bi2Te3 and Bi 2Se3 platelet powders during MOD spin-coating. Patterns of Bi and Bi2Te3 were accomplished by using MOD solutions and soft lithography methods.;Nanoporous Bi films with porosity of 11--50% (thickness from 20 to 570 nm) were prepared. The nanoporous Bi films exhibited some preferred orientation, with the (003) aligned parallel to the substrate. A H2 plasma treatment was applied to the Bi film to reduce the residual carbon impurities coming from MOD precursors. The nanoporous structure of the Bi films consists of inter-connected nanoporous channels between polygonal Bi crystallites (∼36 nm).;Phonon scattering was influenced more by nanopore size than by the number of pores. Calculations suggested that the phonon mean free path of nanoporous Bi films was limited to 7A and was nearly independent of temperature (100 to 300K). The thermal conductivity of nanoporous, Bi films at 300K was dramatically reduced, to 0.1 W/mK, from the 2.5 W/mK value for dense films. In contrast, the electrical conductivity of nanoporous Bi films was slightly reduced, to 800 S/cm, only a factor of 2 less than that of a dense film at 300K. The Seebeck coefficient of nanoporous; Bi films with porosity of 11--23% at 300K varied from -25 to -45 muV/K. In general, both electrical and thermal conductivities were reduced as the porosity increased, while the Seebeck coefficient tended to be slightly more negative. The results suggested that nanopores in Bi films selectively scattered phonons more than electrons. The sigma/kappa ratio of nanoporous; Bi films increased by a factor of 14 as compared to dense films. The resulting ZT values were increased by as much as a factor of 10 (e.g. for 23% porosity, ZT ∼ 0.4 at 300K) as compared to dense films.