On the Insignificant Role of the Oxidation Process on Ultrafast High-Spatial-Frequency LIPSS Formation on Tungsten.

Priya Dominic,Florence Garrelie,Stéphanie Reynaud,Florent Bourquard,Arnaud Weck,Jean-Philippe Colombier

doi:10.3390/nano11051069

Abstract

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-frequency LIPSS (HSFL) during ultrafast laser-induced nano-structuring. This paper reports the effect of the laser texturing environment on the resulting surface oxides and its consequence for HSFLs formation. Nanoripples are produced on tungsten samples using a Ti:sapphire femtosecond laser under atmospheres with varying oxygen contents. Specifically, ambient, 10 mbar pressure of air, nitrogen and argon, and 10−7 mbar vacuum pressure are used. In addition, removal of any native oxide layer is achieved using plasma sputtering prior to laser irradiation. The resulting HSFLs have a sub-100 nm periodicity and sub 20 nm amplitude. The experiments reveal the negligible role of oxygen during the HSFL formation and clarifies the significant role of ambient pressure in the resulting HSFLs period.

Highlights

2e.5,e.6) of the high-spatial-frequency LIPSS (HSFL) formed in vacuum conditions agrees with the sub 20 nm amplitude obtained by AFM
Femtosecond-laser-induced HSFLs with sub 100 nm period and sub 20 nm amplitude were achieved on tungsten with a given fluence (Fp = 0.35 J/cm2 ) and number of laser pulses (N = 25) under different processing atmospheres, namely ambient, air (10 mbar), nitrogen (10 mbar), argon (10 mbar), and vacuum (10−7 mbar) with and without sputtering
This points toward neither ambient oxygen nor the native oxide layer playing a significant role in the formation of HSFLs

Summary

Introduction

Ultrafast laser machining on material surfaces including metals [1,2], semiconductors [3,4,5], and polymers [6,7] to generate laser-induced periodic surface structures (LIPSS)has a broad spectrum of applications in biomedical surface engineering [8,9,10], tribology [11,12,13,14], color marking [15,16], memory devices fabrication [17,18,19], etc. W surfaces were irradiated in different atmospheres including ambient, 10 mbar pressure of air, nitrogen (Air Products, Paris, France), argon (Air Products, Paris, France), and under high vacuum (10−7 mbar.).

Results

Conclusion