Orthogonally superimposed laser-induced periodic surface structures (LIPSS) upon nanosecond laser pulse irradiation of SiO2/Si layered systems

Abstract

In this study we examined the formation of laser-induced periodic surface structures (LIPSS) on silicon (Si) in dependence on the thickness of silicon-dioxide (SiO2) on top. LIPSS were generated in air by linearly polarized ≈8 nanosecond laser pulses with a fluence per pulse of 2.41Jcm−2 at a repetition rate of 100kHz. For SiO2 layers <80nm, LIPSS oriented perpendicular to the laser polarization were obtained, but for SiO2 layers >120nm parallel oriented LIPSS were observed. In both cases the periodicity was about 80–90% of the applied laser wavelength (λ0=532nm). By variation of the SiO2 layer thickness in the range between 80nm–120nm, the dominating orientation changes. Even orthogonally superimposed LIPSS with a periodicity of only 60% of the laser wavelength were found. We show that the transition of the orientation direction of LIPSS is related to the penetration depth of surface plasmon polariton (SPP) fields into the oxide layer.