Spray-Coating Route for Highly Aligned and Large-Scale Arrays of Silicon Nanowires

Technological implementation of nanowires (NWs), such as silicon (Si) NWs, requires these components to be organized with controlled orientation and density on various substrates. Here, we report on a simple and efficient route for the deposition of highly ordered and aligned Si NW arrays on a wide range of receiver substrates, including silicon, glass, metals and flexible plastics with controlled density. The deposition approach is based on spray-coating of Si NW suspension under controlled conditions of the nozzle flow rate, droplet size of the sprayed Si NW suspension, spray angle and the temperature of the receiver substrate. Presumably, the dynamics of droplet elongation and spreading on the substrate relies on the combined action of viscous shear forces and capillary forces. Provided that the size of the deposited droplet is comparable to the length of the Si NWs, the shear-driven elongation of the deposited droplets results in the alignment of the confined Si NWs prior to their immobilization on the substrate due to solvent evaporation. The quality and reproducibility of the spray-coated Si NW arrays is illustrated by the production of highly uniform Si NW field effect transistors. The availability of the spray-coating technique in the current microelectronics technology would assure immediate implementation in the production lines, with minimal changes in the fabrication design and/or auxiliary tools used for this purpose.