Laser surface patterning with curved periodic nanostructures using cavitation bubbles

The quest for surface functionalization has driven the development of methods to create nanometer-scale features on surfaces. Conventional laser methods for surface patterning are limited in terms of resolution and pattern control. Here we demonstrate a method that takes advantage of the stable diffraction of light that occurs when a laser beam scans a solid surface immersed in a liquid. The cavitation bubbles formed during irradiation serve as spherical diffraction objects. They are precisely manipulated with thermo-optical tweezers that take advantage of thermocapillary forces generated by the temperature gradient in the surrounding liquid near the irradiation point. In contrast to much of the literature, where laser-induced bubbles are often considered an undesirable side effect, we demonstrate the utility of cavitation bubbles as an advantage for laser patterning in liquid environments. The high viscosity of the liquid, leading to laminar flow conditions, provides sufficient stability of cavitation bubble dynamics for the generation of regular arc-shaped concentric microgroove channels with a depth of several hundred nanometers and a radius of curvature in the micrometer range.