Liquid-Assisted Laser Nanotexturing of Silicon: Onset of Hydrodynamic Processes Regulated by Laser-Induced Periodic Surface Structures


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Upon systematic studies of femtosecond-laser processing of monocrystalline Si in oxidation-preventing methanol, it is shown that the electromagnetic processes dominating at initial steps of the progressive morphology evolution define the onset of the hydrodynamic processes and morphology upon subsequent multi-pulse exposure. Under promoted exposure quasi-regular subwavelength laser-induced periodic surface structures (LIPSSs) are justified to evolve through the template-assisted development of the Rayleigh-Plateau hydrodynamic instability in the molten ridges forming quasi-regular patterns with a supra-wavelength periodicity and preferential alignment along polarization direction of the incident light. Subsequent exposure promotes fusion-assisted morphology rearrangement resulting in a spiky surface with random orientation, yet constant inter-structure distance correlated with initial LIPSS periodicity. Along with the insight onto the physical picture driving the morphology evolution and supra-wavelength nanostructure formation, this experiments also demonstrated that resulting quasi-regular and random spiky morphology can be tailored by the intensity/polarization distribution of incident laser beam allowing on-demand surface nanotexturing with diverse hierarchical surface morphologies exhibiting reduced reflectivity at visible and shortwave-IR wavelengths. Finally, the practical attractiveness of the suggested approach for improving near-IR photoresponse and expanding operation spectral range of vertical p-n junction Si photodetector operating under room temperature and zero-bias conditions via single-step annealing-free nanopatterning is highlighted.