A representative SEM image of Ge NWs in a vertical view after a growth time of 40 min (a) and 60 min (b).(c) SEM image of (b) in the top view, showing that most Ge NWs were vertically grown against a Si (111) wafer with a thick Ge buffer layer. (d) and (e) show low- and high-magnified TEM images of (b). The Ge NWs became tapered due to the CVD growth on the sidewall. The diffusion of Au from the tip at the top of the wire is shown in the EDX results of (f) and (g), extracted from the red rectangle region in (e).