Nadine Geyer, Zhipeng Huang, Peter Werner
Combining colloidal lithography, plasma- and metal-assisted chemical etching nanowire arrays with a controllable diameter, length and density can be obtained. For patterning the substrate surface, hexagonally closed packed monolayers of monodisperse polystyrene particles (Figure 1a) are transferred into a hexagonal non-closed packed particle arrays. These arrays are used as a mask for metal deposition e.g. Ag by thermal evaporation (Figure 1b). After the removal of the spheres by lift-off the metal layers serve as a catalyst for the wet-etching of silicon in a HF/H2O2 solution (Figure 1c). Using this method, arrays of Si nanowires with diameters ranging from 5 Ám down to 50 nm and with an aspect ratio up to 10 can be obtained.
Fig. 1: Main steps of the formation process of Si nanowires via metal-assisted etching schematically and the corresponding FESEM images to each step: a) Deposition of a monolayer of polystyrene spheres on a silicon substrate by colloidal lithography, b) Modification of the spheres diameter by oxygen plasma etching and afterwards Ag evaporation on this modified mask and removal of the polystyrene mask, c) Metal-assisted etching with HF/ H2O2 and removal of the Ag layer.
Fig. 2: Si nanopillars fabricated by metal-assisted wet chemical etching. Extended arrays of well-ordered, vertically aligned Si nanowires with controllable diameters can be obtained: Si nanowires with diameters of 1.8 Ám (left) and 480 nm (right).