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Fabrication of silicon nanowire arrays by near-field laser ablation and metal-assisted chemical etching
We present an elegant route for the fabrication of ordered arrays of vertically-aligned silicon nanowires with tunable geometry at controlled locations on a silicon wafer. A monolayer of transparent microspheres convectively assembled onto a gold-coated silicon wafer acts as a microlens array. Irradiation with a single nanosecond laser pulse removes the gold beneath each focusing microsphere, leaving behind a hexagonal pattern of holes in the gold layer. Owing to the near-field effects, the diameter of the holes can be at least five times smaller than the laser wavelength. The patterned gold layer is used as catalyst in a metal-assisted chemical etching to produce an array of vertically-aligned silicon nanowires. This approach combines the advantages of direct laser writing with the benefits of parallel laser processing, yielding nanowire arrays with controlled geometry at predefined locations on the silicon surface. The fabricated VA-SiNW arrays can effectively transfect human cells with a plasmid encoding for green fluorescent protein.
Dense arrays of uniform submicron pores in silicon and their applications
We report a versatile particle-based route to dense arrays of parallel submicron pores with high aspect ratio in silicon, and explore the application of these arrays in sensors, optics, and polymer micropatterning. Polystyrene (PS) spheres are convectively assembled on gold-coated silicon wafers and sputter-etched, resulting in well-defined gold disc arrays with excellent long-range order. The gold discs act as catalysts in Metal-Assisted Chemical Etching (MACE), yielding uniform pores with straight walls, flat bottoms and high aspect ratio. The resulting pore arrays can be used as robust antireflective surfaces, in biosensing applications, and as templates for polymer replica molding.