화학공학소재연구정보센터
Applied Surface Science, Vol.372, 52-56, 2016
Femtosecond laser-induced subwavelength ripples formed by asymmetrical grating splitting
The formation process and mechanism of subwavelength ripples were studied upon irradiation of ZnO by a femtosecond laser (800 nm, 50 fs, 1 kHz). An abnormally asymmetrical grating-splitting phenomenon was discovered. At relatively high laser fluences (F=0.51-0.63 J/cm(2)), near-wavelength ripples were split asymmetrically to create subwavelength laser-induced periodic surface structures (LIPSS) with dual gaps (similar to 230 nm and similar to 430 nm) on the primary grooves. At relatively low laser fluences (F=0.4-0.45 J/cm(2)), near-wavelength ripples were split symmetrically, leading to the formation of uniform subwavelength structures with a period of similar to 340 nm. The splitting phenomena are related to the varying laser beam dose induced by the overlapping during line scanning. The two grating-splitting types further imply that the dominated mechanism for LIPSS formation may be changed under different processing conditions. 2016 Elsevier B.V. All rights reserved.