 0  10  20  1  2  3  4  5  6  7 (cm −1 ) (a) [110] [111] [100]  0  10  20  30  1  2  3  4  5  6  7 (cm −1 ) (b)  0  10  20  30  40  1  2  3  4  5  6  7 (cm −1 ) length/width (c) FIG. 3: (Color online) The frequency of three lowest-energy phonon modes in SiNW with different size. (a). bending mode, (b). twisting mode, (c). longitudial mode. 11