ZT of 12-Å-diameter Si NW's (red) and bulk Si (black). The dashed (red) line is the ZT of the same Si NW calculated with bulk lattice thermal conductivity. The inset shows the cross-section atomic configuration of the NW. The NW axis direction is . The lattice contributions of thermal conductivity of bulk Si and the NW, 254 and 2.8 W/Km, respectively, were derived from MD calculations. (Color online).