Colorful multifunctional surfaces produced by femtosecond laser pulses

Femtosecond laser ablation of materials can alter their optical, chemical, electrical, and mechanical properties. It has been previously shown that ablated metals can be simultaneously black and superhydrophobic. In this work, we demonstrate a variety of colored superhydrophobic metals. By raster scanning the surface of copper and overlapping a portion of the irradiated area, we create two distinct and geometrically separated nanostructured regions, one forming color, the other inducing superhydrophobicity. Colors forming along the trough of the raster-scanned lines are formed by nanoparticle-induced plasmonic absorption and result in a range of colors from purple to red, depending on the raster scanning speed of the laser. The edges of the raster-scannedarea, having been doubly irradiated, form large hierarchical micro/nanostructures which induce superhydrophobicity. Contact angle measurements, spectral examination, and nanoparticle analysis enable us to fully characterize and understand these structures and how they result in dual functionality colored superhydrophobic surfaces.