Ribbon-shaped SiNWs using Fe catalyst. (a) SEM image of ribbon-shaped SiNWs with 200 nm width at the bottom and at the top (H2 - 1,000 sccm∙min−1). (b) 5 μm width at the bottom and top (H2 - 2,000 sccm∙min−1). (c) 20 μm width at the bottom and top (H2 - 3,000 sccm∙min−1). (d) HR-TEM image of SiNW, showing single crystal with <100 > growth direction along  zone axis. (e) DES spectra of the SiNW and Fe catalyst. The data show that the body of the nanowire is Si and the metal alloy is Fe and Si component. (f) Low-magnification TEM image show that narrow bottom and wide top must lead the growth of the shape. (g) AFM image of SiNW. The thickness is about 20 nm.