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The self-organization of micrometer/sub-micrometer spheres into a monolayer with a hexagonal close-packed structure is the basis of the so-called nanosphere lithography (NSL). Typical materials used for the spheres are silica and polystyrene, which are commercially available with narrow size distributions. The deposition of a single layer of the spheres on a substrate can be used as a lithography shadow mask and template to nanostructure the substrate surface. This talk will focus on two different applications of polystyrene spheres used either as a mask or a template to synthesize arrays of 1D silicon nanowires (NWs) or 3D hollow urchin-like ZnO.
The first application is based on the combination of two techniques developed in the last years: the nanosphere lithography and the metal-assisted wet etching of bulk silicon enabling to prepare silicon NWs with controllable diameter, length and density. Polystyrene spheres of various diameters and gold as the catalyst in the metal-assisted etching were used. Progress made in the development of the application, by downsizing the diameter of the spheres (100 nm) and optimizing the thickness of the gold layer and composition of the etching solution will be shown. Extended arrays of 60 nm diameter silicon NWs on large size silicon wafers were obtained. Application in solar cells will be discussed.
The second application is new and is related to the electrochemical growth of thin film of ZnO with complex hierarchical structures, using the polystyrene nanospheres as sacrificial templates1. The patterning of the conductive glass substrate surface was performed with polystyrene spheres of a few micron diameters which first were rendered electrically conductive before growing electrochemically ZnO NWs on their surface. Elimination of the spheres in an organic solvent reveals the formation of well-ordered ZnO hollow-urchins composed of single-crystal NWs. Physical properties of the urchin-like ZnO will be shown. This new nanostructure exhibits a dramatic increased Light diffusion which makes it very promising for semiconductor sensitized solar cells