Scheme of the fabrication of Si/Ge NWs. (a) The starting MQW consists of alternating 1-nm-thick Ge layers and 54-nm-thick Si layers, grown by MBE. This unit is repeated 62 times. (b) Deposition of an Au thin layer (2 nm) by EBE. (c) Formation of Si/Ge NWs by dipping the sample in an aqueous solution of HF and H2O2. (d) Removal of Au particles by using an aqueous solution of KI + I2. Steps (b,c,d) are performed at room temperature.