Controlling the spatial distribution of functional groups on 2D materials on a micrometer scale and below represents a fascinating opportunity to achieve anisotropic (opto)electronic properties of these materials. Periodic patterns of covalent functionalization can lead to periodic potentials in the monolayer; however, creating such superstructures is very challenging. Here, we describe an original approach to the periodic functionalization of graphene induced by substrate patterning using a pulsed laser. Laser-induced periodic surface structures (LIPSS) are produced on silicon wafers with thermally-grown oxide layers. The irradiation conditions for the formation of LIPSS confined at the SiO₂/Si interface have been unravelled. LIPSS imprint their periodicity to the reactivity of the monolayer graphene placed on the substrate via modulation of its local doping level. This method is clean, straightforward and scalable with high spatial resolution.

Using different laser irradiation patterns to modify the silicon surface, it has been demonstrated that, at rather small overlapping between irradiation spots, highly regular laser-induced periodic surface structures (LIPSS) can be produced already starting from the second laser pulse, provided that polarization direction coincides with the scanning direction. If the laser irradiation spot is shifted from the previous one perpendicular to light polarization, LIPSS are not formed even after many pulses. This coherence effect is explained by a three-wave interference, involving surface electromagnetic waves (SEWs) generated within the irradiated spot, SEWs scattered from the crater edge formed by the previous laser pulse, and the incoming laser pulse, that provides conditions for amplification of the periodic light-absorption pattern. To study possible consequences of SEW scattering from the laser-modified regions, where the refractive index can change due to material melting, amorphization, and the residual stress formed by previous laser pulses, hydrodynamic modelling and simulations have been performed within the melting regime. The simulations show that stress and vertical displacement could be amplified upon laser scanning. Both mechanisms, three-wave interference and stress accumulation, could enable an additional degree of controlling surface structuring.

Pulsed laser ablation is one of the most efficient and clean methods for high-precision processing and modification of polymers and biomaterials. Polymer ablation has been extensively investigated with ultraviolet lasers while little attention has been given to the infrared (IR) region, which becomes particularly interesting with the recent advances in ultrashort laser technologies. Here, we report the results of a comparative study on 1030-nm ultrashort laser structuring of Kapton polyimide, a polymer important in a variety of applications, with direct comparison of 247-fs and 7-ps laser pulses. The laser-induced damage thresholds for both pulse durations have been determined and the femtosecond laser threshold has been found to be considerably lower than that for picosecond pulses (by a factor of ~ 3.5). Both femtosecond and picosecond laser–produced craters have been thoroughly investigated as a function of pulse energy and focusing conditions. It has been demonstrated that femtosecond laser pulses enable accurate polyimide structuring while picosecond irradiation regimes result in a number of undesired effects such as re-deposition of the ablation debris, surface swelling, and the formation of high rims around the ablation craters. The mechanisms of polyimide ablation with femtosecond and picosecond IR laser pulses are discussed.