Thin SiNWS grown by using Ti as catalyst. (a) SEM image of thin SiNWs with high flow rate of gas (H2, 3,000 sccm∙min−1). HRTEM images of thin SiNWs. It shows that all the thin SiNWs are single crystal and the growth direction is  (b-d). That is the diameter becomes smaller with the flow rate of hydrogen. (b) 1,000 sccm∙min−1, (c) 2,000 sccm∙min−1, and (d) 3,000 sccm∙min−1.