Thermoelectric properties of individual Bi$_{1-x}$Sb$_{x}$Te$_{3-y}$ nanowires

The low-dimensional materials exhibit innovative behaviors different from the bulk materials. The tuning of phonon-electron interactions could enhance the energy conversion efficiency of the one-dimensional thermoelectric materials. In order to study the intrinsic thermoelectric properties of an individual nanowire without external interferences, a measurement platform for such a purpose was successfully designed. A single crystalline Bi$_{1.75}$Sb$_{0.25}$Te$_{2.02}$ nanowire having thickness 250 nm was grown from a Bi$_{1.5}$Sb$_{0.5}$Te$_{3}$ film via thermal annealing method. The growth direction along [110] and composition of Bi$_{1.75}$Sb$_{0.25}$Te$_{2.02}$ for this nanowire were confirmed by TEM results. The self-heating 3$\omega $ technique was employed to characterize the thermal conductivity of this nanowire. The thermal conductivity increases from 0.5 W/m-K at 10 K to 1.4 W/m-K at 300 K. It is observed that the phonon drag at 20 K is about 6 times lower than that of Bi$_{0.5}$Sb$_{1.5}$Te$_{3}$ bulk. This enormous thermal conductivity reduction is mainly attributed to the enhanced phonon-boundary scattering of nanosized geometric effects. In the meantime the electrical resistivity and Seebeck coefficient were also measured by the heaters and electrodes built in the platform.