Background gas effect on the generation of nanopatterns on a pure silicon wafer with multiple femtosecond near field laser ablation

Significant laser energy was transferred from the near field scanning optical microscope tip to a silicon wafer producing nanopatterns on the sample surface. The patterns changed from nanoprotrusions to nanocraters when the background gas was changed from air to argon. Two physical mechanisms were attributed to this dramatic change, namely, oxidation and laser ablation. When air was present, oxidation dominated over ablation in the formation of the nanoprotrusions obtained after multiple laser pulses. When oxygen was absent, e.g., pure argon was the background gas, laser ablation was dominant, and nanocraters resulted after multiple laser pulses.