Schematic diagram of fabrication process of SiGe NRs. (a) TEM image of 1-μm-thick Si0.8Ge0.2 epilayer with the SiGe buffer layer grown on Si wafer. (b) PS nanospheres in diluted colloidal form were drop-placed onto the freshly prepared hydrophilic SiGe substrate. (c) The sizes of the PS spheres were reduced by RIE treatment. (d) A 20-nm-thick Au film was deposited by e-beam evaporation. (e) SiGe NRs were formed by Au-assisted wet chemical etching. (f) Finally, Au film is removed by an Au etchant.