Controlled etching of silica nanospheres monolayer for template application: A systematic study

Monolayers of silica nanospheres (SNs), via self- or guided-assembly has been extensively used for template fabrication in thin films, employed in the areas of plasmonics, photonic crystals, and solar cells. We report on a versatile, rapid, and controllable process to obtain non-close-packed structure by restructuring the SNs geometry at two-particle level. A geometrical model has been proposed to quantify parameters that control the final morphology of the monolayer. SNs of different sizes (viz. 140 nm, 170 nm, and 220 nm) were self-assembled as a close-packed monolayer on a silicon substrate using a three-step spin coating method and then sintered at 950 °C before being exposed to an etchant. We investigate the dependence of particle radius, neck (formed due to sintering) parameters and distance between the SNs, on etching time and etchant concentration. The intermediate and final morphology of the restructured monolayer is used as a template to grow silicon nanowires using metal-assisted chemical etching. We provide quantitative estimates of the parameters pertaining to the restructuring of the monolayer of SNs, which can be used as tunable templates for the growth of nanowires. The optimized process can be scaled-up for industrial application because of its faster and controllable rate of production.