On the Insignificant Role of the Oxidation Process on Ultrafast High-Spatial-Frequency LIPSS Formation on Tungsten
Résumé
The presence of surface oxides on the formation of laser-induced periodic surface structures(LIPSS) is regularly advocated to favor or even trigger the formation of high-spatial-frequencyLIPSS (HSFL) during ultrafast laser-induced nano-structuring. This paper reports the effect ofthe laser texturing environment on the resulting surface oxides and its consequence for HSFLsformation. Nanoripples are produced on tungsten samples using a Ti:sapphire femtosecond laserunder atmospheres with varying oxygen contents. Specifically, ambient, 10 mbar pressure of air,nitrogen and argon, and 10−7mbar vacuum pressure are used. In addition, removal of any nativeoxide layer is achieved using plasma sputtering prior to laser irradiation. The resulting HSFLs havea sub-100 nm periodicity and sub 20 nm amplitude. The experiments reveal the negligible roleof oxygen during the HSFL formation and clarifies the significant role of ambient pressure in theresulting HSFLs period.
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