Controlled Deposition of Silicon Nanowires on Chemically Patterned Substrate by Capillary Force Using a Blade-Coating Method

Abstract

We demonstrate a new method for depositing silicon nanowires (NWs) on selected areas of large-scale substrates with a high deposition yield. The method is based on blade-coating, which takes advantage of capillary force. First, water is blade-coated onto the chemically patterned substrate surface on which hydrophilic areas are surrounded by a hydrophobic self-assembled monolayer, selectively depositing water onto those areas. Second, before the water evaporates, a silicon NW dispersion is blade-coated onto the same surface, and in this step, the dispersion comes into contact with the water. An NW dispersion consists of water-insoluble solvent and NWs that have been chemically modified such that they tend to be adsorbed at the water/solvent interface due to capillary force or to minimize the free energy. Thus, in the second step, NWs position themselves on the hydrophilic areas after the water and dispersion solvent have evaporated. Using this method, NWs were selectively deposited on 2 × 15 μm2 hydrophilic areas on a substrate with an area of 20 cm2 with a probability over 0.9. We investigated the mechanism of NW deposition on the hydrophilic areas by the free energy calculation with the interfacial tension between NW and water, between NW and the solvent of the NW dispersion, and between water and the solvent. The energy calculation showed that the NWs are stabilized in the state where roughly half of the NWs sink into the water on the hydrophilic areas in the blade-coating process.