Confinement effects, surface effects, and transport in Bi and Bi_1-x Sb _x semiconducting and semimetallic nanowires

Hicks and Dresselhaus predicted that quantum well and nanowire thermoelectric materials could show a meaningful enhancement of the heat-to-electricity conversion efficiency compared to their bulk counterparts. The unique transport properties of bismuth, specifically the low effective mass, high mobility, and large Bohr radius of its charge carriers, enabled the study of size-quantization effects in Bi nanowires following those theoretical predictions. In this review, the band structure of Bi and Bi_1-x Sb _x alloys is discussed as a function of their composition, temperature, and size-quantization effects. Further, the theoretical basis of the thermoelectric performance enhancement in Bi nanowires is reviewed and compared to experimental data. Single-wire conductivity and Hall data are reviewed. Finally, several synthesis routes for Bi_1-x Sb _x nanowire samples are discussed, including liquid pressure impregnation, vapor impregnation, electrochemical deposition and wet chemistry impregnation in a template.