The so-called dry laser cleaning governed by humidity at the nanometer scale

Illumination with single nanosecond pulses leads to the detachment of silica particles with 250 nm radii from silicon surfaces. We identify two laser-energy dependent cleaning regimes by time-of-flight particle-scattering diagnostics. For the higher energies, the ejection of particles is produced by nanoscale ablation due to the laser field enhancement at the particle-surface interface. The damage-free regime at lower energy is shown to be governed by the residual water molecules, which are inevitably trapped on the materials. We discuss the great importance that the humidity plays on the cleaning force and on the adhesion in the experiments. (C) 2008 American Institute of Physics.