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.

中文翻译：

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硅的液体辅助激光纳米纹理：由激光诱导周期性表面结构调节的流体动力学过程的开始

对防氧化甲醇中的单晶硅进行飞秒激光处理的系统研究表明，在渐进形态演化的初始步骤中占主导地位的电磁过程决定了后续多脉冲曝光时流体动力学过程和形态的开始。在促进曝光下，准规则亚波长激光诱导周期性表面结构（LIPSS）被证明是通过模板辅助发展熔脊中的瑞利-高原流体动力学不稳定性而演化的，形成具有超波长周期性和优先性的准规则图案沿入射光的偏振方向排列。随后的曝光促进融合辅助的形态重排，从而形成具有随机方向的尖峰表面，但结构间距离与初始 LIPSS 周期性相关。除了对驱动形态演化和超波长纳米结构形成的物理图像的洞察之外，该实验还证明，可以通过入射激光束的强度/偏振分布来定制所产生的准规则和随机尖峰形态，从而允许按需表面具有不同层次表面形态的纳米纹理，在可见光和短波红外波长下表现出较低的反射率。最后，强调了所提出的通过单步无退火纳米图案化在室温和零偏置条件下工作的垂直pn结硅光电探测器的近红外光响应和扩大工作光谱范围的实际吸引力。