(527f) Evaporation-Induced Hierarchical Assemblies of Rigid Silicon Nanowires

Periodic arrays of silicon nanowires (SiNWs) over large areas are of great technological importance in developing novel electrical, optical, biosensing, and electromechanical devices. Traditional metal-catalyzed vapor-liquid-solid (VLS) growth of SiNWs requires high-temperature and high-vacuum operations. Additionally, the precise control over the diameter and location of SiNWs, the unwanted doping of gold in SiNWs, and the controlled epitaxial growth of SiNWs on conventional (100) silicon wafers, are challenging. This paper reports a facile and scalable bottom-up technology for fabricating periodic arrays of single-crystalline SiNWs over wafer-sized area. Spin-coated 2-D nonclose-packed silica colloidal crystals are utilized as etching mask to generate ordered polymer posts whose size can be much smaller than the templating silica spheres. Using the resulting polymer posts as deposition mask to create gold nanoholes, highly ordered SiNWs with tunable structural parameters can be easily fabricated by a room-temperature wet-etching technology. As the SiNWs are produced by direct wet-etching in single-crystalline silicon wafer, they are relatively free of volume defects and thus their bending strength approaches the predicted theoretical maximum. Most importantly, the nonclose-packing of the colloidal template and the close-to-ideal mechanical property enable the formation of unusual open-structured hierarchical assemblies of rigid SiNWs during solvent evaporation. These assemblies exhibit excellent broadband antireflective and dewetting properties, promising for developing self-cleaning antireflection coatings for crystalline silicon solar cells.