Transmission enhancement via metasurfaces with tunable waveband performance by dewetting and seeded masking

Abstract

This study demonstrates the fabrication of tunable masking layer consisting of gold islands on fused silica substrates. The goal is to produce anti-reflective structured surfaces (ARSS) that correlate to the repeatable and scalable masking step. The transmission enhancement waveband of fused silica is controlled by variations in gold masking islands created through repetitive dewetting process. Gold layer is formed by physical vapor deposition and thermal annealing. Varying deposition thickness and annealing temperature, size and periodicity of gold islands is controlled. With each iterative step of deposition and annealing, relative periodicity established by the initial island formation, or "seed", is maintained while increasing fill factor in subsequent iterations. Optical transmission spectra were analyzed of the masking layer and formation of metasurface by plasma etching. Results showed that larger deposition thicknesses required higher annealing temperatures to generate circular islands. The seed layer sets the mask periodicity, then the mask fill factor can be increased to allow for deeper etching of ARSS features, for broadband performance. For example, initial deposition thickness of 10 nm and repeated iterative steps of deposition and annealing, the fill factor increased (28%, 39%, 47%, 49%), while the island periodicity was maintained at average 91 ± 6 nm for all iterative steps. Etching these masked samples resulted in broadband transmission enhancement, over 94% of theoretical maximum. A comprehensive database of masking layer fabrication, resultant surface feature dimensions, and ARSS transmission enhancement capabilities was generated. This scalable masking approach can broaden high laser damage threshold applications utilizing tunable performance ARSS.