Boron carbide nanowires: low temperature synthesis and structural and thermal conductivity characterization

Boron carbide nanowires, a promising class of high temperature thermoelectric nanomaterials, are synthesized by co-pyrolysis of diborane and methane in a low pressure chemical vapor deposition system via the vapor-liquid-solid growth mechanism. Nickel and iron are effective catalytic materials. The synthesis is realized at relatively lower temperatures, with 879 degrees C as the lowest one. Electron microscopy analysis shows that the as-synthesized nanowires have diameters between 15 and 90 nm and lengths up to 10 mu m. The nanowires have single crystalline boron carbide cores and thin amorphous oxide sheaths. Both transverse faults and axial faults with fault planes as {101}(h)-type are observed, which could provide additional measures to tune the nanowire transport properties for better thermoelectric performance. Measurement of individual boron carbide nanowires reveals that the thermal conductivity is diameter-dependent, which indicates that boundary scattering still provides an effective approach to reduce the wire thermal conductivity for enhanced thermoelectric performance.