Generation of Supra-Wavelength Grooves in Femtosecond Laser Surface Structuring of Silicon

Abstract

Extensive research work has been carried out on the generation and application of laser-induced periodic surface structures (LIPSS). LIPSS with a sub-wavelength period generated by femtosecond laser irradiation, generally indicated as ripples, have been extensively investigated. Instead, the other ordered surface structures characterized by a supra-wavelength period, indicated as grooves, have been much less studied. Grooves typically form at larger irradiance levels or for higher number of laser pulses. Here, we report a comprehensive overview of recent investigations on the supra-wavelength grooves formed on crystalline silicon irradiated by femtosecond laser pulses. The authors’ recent experimental work is mainly addressed giving an explicit picture of the grooves generation process, namely illustrating the influence of the various experimental parameters, including, e.g., polarization, wavelength, fluence and repetition rate of the laser beam as well as number of laser pulses hitting the surface of the material. The effect of irradiation of a static or moving target and of the environmental conditions (e.g., vacuum or air ambient) will also be discussed. Finally, possible mechanisms envisaged to explain grooves formation and still open issues are briefly discussed.

Ten Open Questions about Laser-Induced Periodic Surface Structures

“…Briefly, the basic classification involves LIPSS with low-spatial frequency (LSFL) and high-spatial frequency (HSFL), where the period Λ of LSFL is of the order of the utilized laser wavelength (Λ ~λ) and for HSFL much smaller structures with Λ << λ are achievable. Besides LSFL and HSFL also supra-wavelength sized "grooves" and "spikes" are reported in the pertinent literature of self-organized laser-generated surface structures [12,13]. A review of experimental work over the last decades leads to the conclusion that LSFL can be produced on all types of material including metals, semiconductors, dielectrics (glasses, ceramics, polymers) and also composite materials, thin films, or 2D nanomaterials [14][15][16][17][18][19][20].…”

Fundamentals of Scanning Surface Structuring by Ultrashort Laser Pulses: From Electron Diffusion to Final Morphology

“…[ 69 ] This could be the reason for the high fluence threshold for grooves usually reported in previous studies for low repetition rates. [ 40,41 ]…”

“…[ 17,19–21,23 ] However, the regularity of the grooves and their dependence on the laser wavelength imply a direct connection to the LSFL. [ 41,45 ] In general, the LSFL period decreases and their depth increases as the pulse number increases. [ 47–49 ] This affects SPP excitation, surface‐wave propagation, and near‐surface light scattering, [ 17,20,22,49,50 ] indicating a change in the IED as machining progresses, which may lead to a new secondary modulation (see Figure 1).…”

Zebrafish: A Promising Real-Time Model System for Nanotechnology-Mediated Neurospecific Drug Delivery

“…Zebrafish is extensively used as a model system to evaluate nanoparticle toxicity and biocompatibility [ 111 – 113 ], and it holds great potential as a model for studying neurotoxicity and high throughput screening of nanoparticles [ 114 – 117 ]. No model other than the zebrafish is so aptly suited for such analyses.…”