Conformal Electrochemical Nanoimprinting of Silicon: Toward Bio-Inspired Hierarchical Infrared Meta-Optics.

Abstract

Nanostructured anti-reflection metasurfaces for infrared lenses are designed for imaging in harsh environments such as dust (e.g., moon or battlefield), micrometeorites (e.g., Lagrange points), and high-radiation fluctuations (e.g., Mars) with limited lifetimes. These multifunctional optical meta-surfaces (MOMS) simultaneously deliver high thermal stability and anti-fouling behavior due to their monolithic nature (e.g., no mismatch in the coefficient of thermal expansion), hydrophobicity, and low dust adherence. However, the incompatibility of inorganic semiconductor micromachining with non-planar substrates has limited MOMS to polymeric and glass lenses. Here, a new method of conformal electrochemical nanoimprinting is presented to directly micromachine a nature-inspired MOMS onto a silicon lens. Uniquely, stretchablegold-coated patterned porous PVDF stamps are made by lithographically templated thermally induced phase separation (lt-TIPS), which simultaneously embeds it with (i) interconnected porosity for promoting mass transport, (ii) HF-resistance for increasing operational lifetime, and (iii) stretchable electronic nanocoatings (i.e., Au) that can catalyze the electrochemical process. In a demonstration of its hierarchical micromachining capability, a sharklet microscale pattern is successfully transferred to a silicon lens with anti-reflective and hydrophobic properties. This work paves the way for MOMS' extension onto inorganic semiconductors and IR lenses.