Liquid vortexes and flows induced by femtosecond laser ablation in liquid governing formation of circular and crisscross LIPSS

Abstract

Orientations of laser induced periodic surface structures (LIPSS) are usually considered to be governed by the laser polarization state. In this work, we unveil that fluid dynamics induced by femtosecond (fs) laser ablation in liquid (fs-LAL) can easily break this polarization restriction to produce irregular circular-LIPSS (CLIPPS) and crisscross-LIPSS (CCLIPSS). Fs laser ablation of silicon in water shows formation of diverse LIPSS depending on ablation conditions. At a high power of 700 mW (repetition rate of 100 kHz, pulse duration of 457 fs and wavelength of 1045 nm), single/twin CLIPSS are produced at the bottom of macropores of several microns in diameter due to the formation of strong liquid vortexes and occurrence of the vortex shedding effect. Theoretical simulations validate our speculation about the formation of liquid vortex with an ultrahigh static pressure, which can induce the microstructure trenches and cracks at the sidewalls for fs-LAL of Si and tungsten (W) in water, respectively. At a low power of 50 mW, weak liquid vortexes are produced, which only give birth to curved LIPSS in the valleys of grooves. Consequently, it is deduced that liquid vortex plays a crucial role in the formation of macropores. Mountain-like microstructures induce complex fluid dynamics which can cause the formation of CCLIPSS on them. It is believed that liquid vortexes and fluid dynamics presented in this work open up new possibilities to diversify the morphologies of LIPSS formed by fs-LAL.

Hierarchical WO3–x Ultrabroadband Absorbers and Photothermal Converters Grown from Femtosecond Laser-Induced Periodic Surface Structures

“…Analysis of the subsurface structure of fs-5W-W (Figure 1j) shows that fs-LA can induce deformation and cracks in the subsurface of ablated W metal plates because of the generation of high-pressure shockwaves 29 and plasticity of W metal. 36,41 To identify the compositions of annealed samples, Raman measurement was performed with results shown in Figure 2a−c. Five Raman peaks at 134, 272, 326, 715, and 805 cm −1 are identifiable, being attributable to the formation of α-WO 3 .…”

“…At a lase power of 5 W, only a small amount of NPs deposit on the LIPSS (Figure d,e), while many NPs deposit on the LIPSS using 15W laser power (Figure f,g). Analysis of the subsurface structure of fs-5W-W (Figure j) shows that fs-LA can induce deformation and cracks in the subsurface of ablated W metal plates because of the generation of high-pressure shockwaves and plasticity of W metal. , …”

“…They have been proven to be good precursors to grow metal oxides upon thermal oxidation annealing, hydrothermal treatment, and electrochemical anodization . Among all achievable structures by laser structuring, ,,− laser-induced periodic surface structure (LIPSS) is the unique structure from femtosecond laser structuring, which can be easily produced on metals, polymers, semiconductors, and dielectrics. ,− The absorbance of LIPSS structures, normally indirectly measured by surface reflectance, has been investigated for a long time. However, endowment of LIPSS on metals is merely capable of increasing absorbance in the ultraviolet (UV: 200–400 nm) and visible (vis: 300–750 nm) bands but incapable of increasing the absorbance in the near-infrared (NIR, wavelength: 800–2500 nm) band .…”

Fabrication of anti-icing/de-icing surfaces by femtosecond laser

“…During the laser treatment process, femtosecond laser direct writing occurs on materials surfaces by moving the translation stage ( Figures 1B,C ). In the process of femtosecond laser treatment, high temperature and high pressure will be formed on the laser focus area ( Zhang et al, 2017 ; Zhang and Sugioka, 2019 ; Zhang et al, 2020 ; Liu et al, 2022 ; Zhang D. S et al, 2022 ). Therefore, various bio-inspired structures have been fabricated for superhydrophobic anti-icing surfaces and photothermal de-icing surfaces.…”

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

“…Monocrystalline Si (c‐Si), a critically important semiconductor widely applied in variety of optoelectronic and nanophotonic devices, [ 18,19 ] was widely studied in the context of LIPSSs formation revealing the ability to produce on its surface both high spatial frequency LIPSSs [ 20–30 ] as well as quasi‐regular supra‐wavelength patterns. [ 31–38 ] The latter type of the structures was generally explained by hydrodynamic processes, [ 39 ] yet their ordering along polarization direction and evident correlation between the characteristic periodicity and laser wavelength were established [ 34 ] reflecting the lack of complete understanding of the underlying physical processes driven morphology self‐organization.…”