Laser micro-structuring of silicon in dry and wet environments

The impact effect of a vapor recoil pressure on single-shot threshold-like laser micro-structuring of Si via the Kelvin-Helmholtz-type instability has been revealed during transient and postmortem studies of explosive boiling of predeposited micron-size water droplets on a Si wafer surface. The micro-structuring mechanism assumes local excitation of surface capillary waves in a molten surface layer of the material underneath each water droplet by near-GPa recoil pressure of explosively boiling water and the following steam bubble oscillations. Water droplets and produced structural features (micron-size craters, bumps or others) have exhibited high symmetries in their surface arrangements. Similar structures were also observed on dry clean Si surfaces irradiated by single fs-laser pulses resulted from the same "impact" excitation of surface capillary waves in the Coulomb explosion regime.