Nanosecond laser-based high-throughput surface nanostructuring (nHSN)

Abstract

We present a novel nanosecond laser-based high-throughput surface nanostructuring (nHSN) process that can simultaneously create random nanostructures and attain desirable surface chemistry over large-area metal alloy surfaces. nHSN consists of two sequential steps: (1) nanosecond laser texturing (NLT) and (2) chemical immersion treatment (CIT). NLT step in water confinement (wNLT) does not generate topological patterns but preconditions the metal surface chemically and mechanically. Our analysis shows that surface nanostructuring results from a combined effect of chemical etching and attachment of functional groups during the CIT phase of nHSN. A proper silane reagent can be selected for the CIT phase to achieve the desired surface wetting behavior, while laser parameters can also be adjusted during the NLT phase to finely tune the nanostructuring mechanism. nHSN nanostructures with fluorosilane chemistry repel water, while those with cyanosilane chemistry attract water. Extreme wettability including superhydrophobicity and superhydrophilicity is assessed for multiple engineering metal alloys including aluminum, steel and titanium alloys. Compared with existing ultrashort laser-based surface-texturing methods, the nHSN laser scan time represents a significant improvement in processing efficiency and enables a practical throughput for large-area processing of engineering alloys.