Threshold Dependence of Deep- and Near-subwavelength Ripples Formation on Natural MoS₂ Induced by Femtosecond Laser

摘要

Deep sub-wavelength ripples (DSRs) and near sub-wavelength ripples (NSRs) with uniform periods of ~160?nm and ~660?nm generated at the MoS₂-vacuum interface is reported for the first time by the processing of femtosecond laser (800?nm, 120?fs, 1?kHz) in this paper. The DSRs and NSRs formation fluence thresholds are experimentally determined as 160?mJ/cm2 and 192?mJ/cm2, respectively. In addition, the ripple period is insensitive to the pulse number. Moreover, Raman analyses show that the MoS₂ lattice in the irradiated area does not exhibit oxidation at room environment and the crystalline representation is well preserved in NSRs region. We attribute our result to the joint interactions of the spallation and sublimation of layered MoS₂ together with the laser induced surface plasmon polaritons and propose an explanation to the threshold dependence of the ripple period. Our study provides some insights for ultrafast laser-matter interactions and indicates a simple effective method for future nano-fabrication of MoS₂.