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Liquid vortexes and flows induced by femtosecond laser ablation in liquid governing formation of circular and crisscross LIPSS
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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. -
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References
[1] Phillips KC, Gandhi HH, Mazur E, Sundaram SK. Ultrafast laser processing of materials: a review. Adv Opt Photonics 7, 684–712 (2015). doi: 10.1364/AOP.7.000684 [2] Li L, Hong MH, Schmidt M, Zhong ML, Malshe A et al. Laser nano-manufacturing–state of the art and challenges. CIRP Ann 60, 735–755 (2011). doi: 10.1016/j.cirp.2011.05.005 [3] Zhang DS, Gökce B, Barcikowski S. Laser synthesis and processing of colloids: fundamentals and applications. Chem Rev 117, 3990–4103 (2017). doi: 10.1021/acs.chemrev.6b00468 [4] Sugioka K, Cheng Y. Ultrafast lasers—reliable tools for advanced materials processing. Light Sci Appl 3, e149 (2014). doi: 10.1038/lsa.2014.30 [5] Zhou R, Zhang Z, Hong MH. The art of laser ablation in aeroengine: the crown jewel of modern industry. J Appl Phys 127, 080902 (2020). doi: 10.1063/1.5134813 [6] Grigoropoulos CP. Laser synthesis and functionalization of nanostructures. Int J Extrem Manuf 1, 012002 (2019). doi: 10.1088/2631-7990/ab0eca [7] Palneedi H, Park JH, Maurya D, Peddigari M, Hwang GT et al. Laser irradiation of metal oxide films and nanostructures: applications and advances. Adv Mater 30, 1705148 (2018). doi: 10.1002/adma.201705148 [8] Chen L, Cao KQ, Li YL, Liu JK, Zhang SA et al. Large-area straight, regular periodic surface structures produced on fused silica by the interference of two femtosecond laser beams through cylindrical lens. Opto-Electron Adv 4, 200036 (2021). [9] Zhang D, Liu R, Li Z. Irregular LIPSS produced on metals by single linearly polarized femtosecond laser. Int J Extrem Manuf 4, 015102 (2022). [10] Zhang D, Ranjan B, Tanaka T, Sugioka K. Carbonized Hybrid Micro/Nanostructured Metasurfaces Produced by Femtosecond Laser Ablation in Organic Solvents for Biomimetic Antireflective Surfaces. ACS Appl Nano Mater 3, 1855–1871 (2020). [11] Vorobyev AY, Guo CL. Direct femtosecond laser surface nano/microstructuring and its applications. Laser Photon Rev 7, 385–407 (2013). doi: 10.1002/lpor.201200017 [12] Malinauskas M, Žukauskas A, Hasegawa S, Hayasaki Y, Mizeikis V et al. Ultrafast laser processing of materials: from science to industry. Light Sci Appl 5, e16133 (2016). doi: 10.1038/lsa.2016.133 [13] Liu R, Zhang DS, Li Z G. Femtosecond laser induced simultaneous functional nanomaterial synthesis, in situ deposition and hierarchical LIPSS nanostructuring for tunable antireflectance and iridescence applications. J Mater Sci Technol 89, 179–185 (2021). doi: 10.1016/j.jmst.2021.02.024 [14] Livakas N, Skoulas E, Stratakis E. Omnidirectional iridescence via cylindrically-polarized femtosecond laser processing. Opto-Electron Adv 3, 190035 (2020). doi: 10.29026/oea.2020.190035 [15] Zhang CY, Zhou W, Geng D, Bai C, Li WD et al. Laser direct writing and characterizations of flexible piezoresistive sensors with microstructures. Opto-Electron Adv 4, 200061 (2021). [16] Stratakis E, Bonse J, Heitz J, Siegel J, Tsibidis GD et al. Laser engineering of biomimetic surfaces. Mater Sci Eng R Rep 141, 100562 (2020). doi: 10.1016/j.mser.2020.100562 [17] Shukla P, Waugh DG, Lawrence J, Vilar R. Laser surface structuring of ceramics, metals and polymers for biomedical applications: a review. Vilar R, ed. Laser Surface Modification of Biomaterials. 281–299 (Elsevier, 2016). [18] Zhang DS, Ranjan B, Tanaka T, Sugioka K. Underwater persistent bubble-assisted femtosecond laser ablation for hierarchical micro/nanostructuring. Int J Extrem Manuf 2, 015001 (2020). doi: 10.1088/2631-7990/ab729f [19] Zhao LL, Liu Z, Chen D, Liu F, Yang Z et al. Laser synthesis and microfabrication of micro/nanostructured materials toward energy conversion and storage. Nano-Micro Lett 13, 49 (2021). doi: 10.1007/s40820-020-00577-0 [20] Wu ZP, Yin K, Wu JR, Zhu Z, Duan JA et al. Recent advances in femtosecond laser-structured Janus membranes with asymmetric surface wettability. Nanoscale 13, 2209–2226 (2021). doi: 10.1039/D0NR06639G [21] Wang XD, Yu HB, Li PW, Zhang YZ, Wen YD et al. Femtosecond laser-based processing methods and their applications in optical device manufacturing: a review. Opt Laser Technol 135, 106687 (2021). doi: 10.1016/j.optlastec.2020.106687 [22] Han JD, Zhang F, van Meerbeek B, Vleugels J, Braem A et al. Laser surface texturing of zirconia-based ceramics for dental applications: a review. Mater Sci Eng C 123, 112034 (2021). doi: 10.1016/j.msec.2021.112034 [23] Zhang B, Wang L, Chen F. Recent advances in femtosecond laser processing of LiNbO3 crystals for photonic applications. Laser Photon Rev 14, 1900407 (2020). doi: 10.1002/lpor.201900407 [24] Zhang YY, Jiao YL, Li CZ, Chen C, Li JW et al. Bioinspired micro/nanostructured surfaces prepared by femtosecond laser direct writing for multi-functional applications. Int J Extrem Manuf 2, 032002 (2020). doi: 10.1088/2631-7990/ab95f6 [25] Jia YC, Wang SX, Chen F. Femtosecond laser direct writing of flexibly configured waveguide geometries in optical crystals: fabrica-tion and application. Opto-Electron Adv 3, 190042 (2020). [26] Wan ZF, Chen X, Gu M. Laser scribed graphene for supercapacitors. Opto-Electron Adv 4, 200079 (2021). [27] Wang HT, Hao CL, Lin H, Wang YT, Lan T et al. Generation of super-resolved optical needle and multifocal array using graphene oxide metalenses. Opto-Electron Adv 4, 200031 (2021). [28] Maksimovic J, Ng SH, Katkus T, Cowie BCC, Juodkazis S. External field-controlled ablation: magnetic field. Nanomaterials 9, 1662 (2019). doi: 10.3390/nano9121662 [29] Maksimovic J, Ng SH, Katkus T, Le NHA, Chon JWM et al. Ablation in externally applied electric and magnetic fields. Nanomaterials 10, 182 (2020). doi: 10.3390/nano10020182 [30] Zhang DS, Wu LC, Ueki M, Ito Y, Sugioka K. Femtosecond laser shockwave peening ablation in liquids for hierarchical micro/nanostructuring of brittle silicon and its biological application. Int J Extrem Manuf 2, 045001 (2020). doi: 10.1088/2631-7990/abb5f3 [31] Dittrich S, Barcikowski S, Gökce B. Plasma and nanoparticle shielding during pulsed laser ablation in liquids cause ablation efficiency decrease. Opto-Electron Adv 4, 200072 (2021). [32] Bonse J, Höhm S, Kirner SV, Rosenfeld A, Krüger J. Laser-induced periodic surface structures—a scientific evergreen. IEEE J Sel Top Quantum Electron 23, 9000615 (2017). [33] Buividas R, Mikutis M, Juodkazis S. Surface and bulk structuring of materials by ripples with long and short laser pulses: recent advances. Prog Quantum Electron 38, 119–156 (2014). doi: 10.1016/j.pquantelec.2014.03.002 [34] Birnbaum M. Semiconductor surface damage produced by ruby lasers. J Appl Phys 36, 3688–3689 (1965). doi: 10.1063/1.1703071 [35] Tan DZ, Sharafudeen KN, Yue YZ, Qiu JR. Femtosecond laser induced phenomena in transparent solid materials: fundamentals and applications. Prog Mater Sci 76, 154–228 (2016). doi: 10.1016/j.pmatsci.2015.09.002 [36] Cerkauskaite A, Drevinskas R, Solodar A, Abdulhalim I, Kazansky PG. Form-birefringence in ITO thin films engineered by ultrafast laser nanostructuring. ACS Photonics 4, 2944–2951 (2017). doi: 10.1021/acsphotonics.7b01082 [37] Lam B, Zhang JH, Guo CL. Generation of continuously rotating polarization by combining cross-polarizations and its application in surface structuring. Opt Lett 42, 2870–2873 (2017). doi: 10.1364/OL.42.002870 [38] Han WN, Jiang L, Li XW, Liu PJ, Xu L et al. Continuous modulations of femtosecond laser-induced periodic surface structures and scanned line-widths on silicon by polarization changes. Opt Express 21, 15505–15513 (2013). doi: 10.1364/OE.21.015505 [39] Reinhardt H, Kim HC, Pietzonka C, Kruempelmann J, Harbrecht B et al. Self-organization of multifunctional surfaces – the fingerprints of light on a complex system. Adv Mater 25, 3313–3318 (2013). doi: 10.1002/adma.201205031 [40] Dusser B, Sagan Z, Soder H, Faure N, Colombier JP et al. Controlled nanostructrures formation by ultra fast laser pulses for color marking. Opt Express 18, 2913–2924 (2010). doi: 10.1364/OE.18.002913 [41] Varlamova O, Costache F, Reif J, Bestehorn M. Self-organized pattern formation upon femtosecond laser ablation by circularly polarized light. Appl Surf Sci 252, 4702–4706 (2006). doi: 10.1016/j.apsusc.2005.08.120 [42] Han W, Liu F, Yuan Y, Li X, Wang Q et al. Femtosecond laser induced concentric semi-circular periodic surface structures on silicon based on the quasi-plasmonic annular nanostructure. Nanotechnology 29, 305301 (2018). doi: 10.1088/1361-6528/aac282 [43] Romashevskiy SA, Ashitkov SI, Agranat MB. Circular ripple patterns on silicon induced by bubble-diffracted femtosecond laser pulses in liquid. Opt Lett 45, 1005–1008 (2020). doi: 10.1364/OL.385672 [44] Ouyang J, Perrie W, Allegre OJ, Heil T, Jin Y et al. Tailored optical vector fields for ultrashort-pulse laser induced complex surface plasmon structuring. Opt Express 23, 12562–12572 (2015). doi: 10.1364/OE.23.012562 [45] Cheng HC, Li P, Liu S, Chen P, Han L et al. Vortex-controlled morphology conversion of microstructures on silicon induced by femtosecond vector vortex beams. Appl Phys Lett 111, 141901 (2017). doi: 10.1063/1.4994926 [46] Nivas JJ, He ST, Song ZM, Rubano A, Vecchione A et al. Femtosecond laser surface structuring of silicon with Gaussian and optical vortex beams. Appl Surf Sci 418, 565–571 (2017). doi: 10.1016/j.apsusc.2016.10.162 [47] Tsibidis GD, Skoulas E, Stratakis E. Ripple formation on nickel irradiated with radially polarized femtosecond beams. Opt Lett 40, 5172–5175 (2015). doi: 10.1364/OL.40.005172 [48] Zhang DS, Sugioka K. Hierarchical microstructures with high spatial frequency laser induced periodic surface structures possessing different orientations created by femtosecond laser ablation of silicon in liquids. Opto-Electron Adv 2, 190002 (2019). [49] Tsibidis GD, Fotakis C, Stratakis E. From ripples to spikes: a hydrodynamical mechanism to interpret femtosecond laser-induced self-assembled structures. Phys Rev B 92, 041405 (2015). doi: 10.1103/PhysRevB.92.041405 [50] Zhang DS, Chen F, Yang Q, Yong JL, Bian H et al. A simple way to achieve pattern-dependent tunable adhesion in superhydrophobic surfaces by a femtosecond laser. ACS Appl Mater Interfaces 4, 4905–4912 (2012). doi: 10.1021/am3012388 [51] Zhang DS, Ranjan B, Tanaka T, Sugioka K. Multiscale hierarchical micro/nanostructures created by femtosecond laser ablation in liquids for polarization-dependent broadband antireflection. Nanomaterials 10, 1573 (2020). doi: 10.3390/nano10081573 [52] Nguyen TTP, Tanabe-Yamagishi R, Ito Y. Impact of liquid layer thickness on the dynamics of nano- to sub-microsecond phenomena of nanosecond pulsed laser ablation in liquid. Appl Surf Sci 470, 250–258 (2019). doi: 10.1016/j.apsusc.2018.10.160 [53] Letzel A, Santoro M, Frohleiks J, Ziefuß AR, Reich S et al. How the re-irradiation of a single ablation spot affects cavitation bubble dynamics and nanoparticles properties in laser ablation in liquids. Appl Surf Sci 473, 828–837 (2018). [54] Zhang DS, Gökce B, Sommer S, Streubel R, Barcikowski S. Debris-free rear-side picosecond laser ablation of thin germanium wafers in water with ethanol. Appl Surf Sci 367, 222–230 (2016). doi: 10.1016/j.apsusc.2016.01.071 [55] Florian C, Déziel JL, Kirner SV, Siegel J, Bonse J. The role of the laser-induced oxide layer in the formation of laser-induced periodic surface structures. Nanomaterials 10, 147 (2020). doi: 10.3390/nano10010147 [56] Long JY, Eliceiri MH, Ouyang YX, Zhang YK, Xie XZ et al. Effects of immersion depth on the dynamics of cavitation bubbles generated during ns laser ablation of submerged targets. Opt Lasers Eng 137, 106334 (2021). doi: 10.1016/j.optlaseng.2020.106334 [57] Zeng XZ, Mao XL, Mao SS, Wen SB, Greif R et al. Laser-induced shockwave propagation from ablation in a cavity. Appl Phys Lett 88, 061502 (2006). doi: 10.1063/1.2172738 [58] Shen MY, Crouch CH, Carey JE, Younkin R, Mazur E et al. Formation of regular arrays of silicon microspikes by femtosecond laser irradiation through a mask. Appl Phys Lett 82, 1715–1717 (2003). doi: 10.1063/1.1561162 [59] Shih CY, Streubel R, Heberle J, Letzel A, Shugaev MV et al. Two mechanisms of nanoparticle generation in picosecond laser ablation in liquids: the origin of the bimodal size distribution. Nanoscale 10, 6900–6910 (2018). doi: 10.1039/C7NR08614H [60] Sedao X, Shugaev MV, Wu CP, Douillard T, Esnouf C et al. Growth twinning and generation of high-frequency surface nanostructures in ultrafast laser-induced transient melting and resolidification. ACS Nano 10, 6995–7007 (2016). doi: 10.1021/acsnano.6b02970 [61] Xu YZ, Zhu HR, Zheng J. Effect of Knudsen number on microscale similar flow characteristics. J Aerosp Power 28, 1752–1758 (2013). [62] Tanabe R, Nguyen TTP, Sugiura T, Ito Y. Bubble dynamics in metal nanoparticle formation by laser ablation in liquid studied through high-speed laser stroboscopic videography. Appl Surf Sci 351, 327–331 (2015). doi: 10.1016/j.apsusc.2015.05.030 [63] Nakagawa A, Kumabe T, Ogawa Y, Hirano T, Kawaguchi T et al. Pulsed laser-induced liquid jet: evolution from shock/bubble interaction to neurosurgical application. Shock Waves 27, 1–14 (2017). doi: 10.1007/s00193-016-0696-2 [64] Gad-el-Hak M. The fluid mechanics of microdevices—the freeman scholar lecture. J Fluids Eng 121, 5–33 (1999). doi: 10.1115/1.2822013 [65] Nguyen TTP, Tanabe R, Ito Y. Laser-induced shock process in under-liquid regime studied by time-resolved photoelasticity imaging technique. Appl Phys Lett 102, 124103 (2013). doi: 10.1063/1.4798532 [66] Babenko VA, Bunkin NF, Sychev AA. Role of gas nanobubbles in nonlinear hyper-Raman scattering of light in water. J Opt Soc Am B 37, 2805–2814 (2020). doi: 10.1364/JOSAB.398496 [67] Namura K, Imafuku S, Kumar S, Nakajima K, Sakakura M et al. Direction control of quasi-stokeslet induced by thermoplasmonic heating of a water vapor microbubble. Sci Rep 9, 4770 (2019). doi: 10.1038/s41598-019-41255-5 [68] Derrien TJY, Koter R, Krüger J, Höhm S, Rosenfeld A et al. Plasmonic formation mechanism of periodic 100-nm-structures upon femtosecond laser irradiation of silicon in water. J Appl Phys 116, 074902 (2014). doi: 10.1063/1.4887808 [69] Stratakis E, Zorba V, Barberoglou M, Fotakis C, Shafeev GA. Laser writing of nanostructures on bulk Al via its ablation in liquids. Nanotechnology 20, 105303 (2009). doi: 10.1088/0957-4484/20/10/105303 [70] Bonse J. Quo vadis LIPSS?—recent and future trends on laser-induced periodic surface structures. Nanomaterials 10, 1950 (2020). doi: 10.3390/nano10101950 [71] Bonse J, Gräf S. Maxwell meets marangoni—a review of theories on laser-induced periodic surface structures. Laser Photonics Rev 14, 2000215 (2020). doi: 10.1002/lpor.202000215 [72] Ji LF, Lv XZ, Wu Y, Lin ZY, Jiang YJ. Hydrophobic light-trapping structures fabricated on silicon surfaces by picosecond laser texturing and chemical etching. J Photonics Energy 5, 053094 (2015). doi: 10.1117/1.JPE.5.053094 [73] Zhang CY, Yao JW, Liu HY, Dai QF, Wu LJ et al. Colorizing silicon surface with regular nanohole arrays induced by femtosecond laser pulses. Opt Lett 37, 1106–1108 (2012). doi: 10.1364/OL.37.001106 [74] Liu HG, Lin WX, Lin ZY, Ji LF, Hong MH. Self-organized periodic microholes array formation on aluminum surface via femtosecond laser ablation induced incubation effect. Adv Funct Mater 29, 1903576 (2019). doi: 10.1002/adfm.201903576 [75] Yuan DQ, Wu QR, Xu JT, Zhou M, Yang HF. Periodic nanohole array structure induced on a silicon surface by direct writing with a femtosecond laser. J Opt Technol 82, 353–356 (2015). doi: 10.1364/JOT.82.000353 [76] Perry AE, Chong MS, Lim TT. The vortex-shedding process behind two-dimensional bluff bodies. J Fluid Mech 116, 77–90 (1982). doi: 10.1017/S0022112082000378 [77] Akram M, Bashir S, Rafique MS, Hayat A, Mahmood K et al. Morphological and spectroscopic characterization of laser-ablated tungsten at various laser irradiances. Appl Phys A 119, 859–870 (2015). doi: 10.1007/s00339-015-9052-0 [78] Gu DD, Guo M, Zhang HM, Sun YX, Wang R et al. Effects of laser scanning strategies on selective laser melting of pure tungsten. Int J Extrem Manuf 2, 025001 (2020). doi: 10.1088/2631-7990/ab7b00 [79] Tuerke F, Pastur LR, Sciamarella D, Lusseyran F, Artana G. Experimental study of double-cavity flow. Exp Fluids 58, 76 (2017). doi: 10.1007/s00348-017-2360-8 [80] Liu Y, Cui J, Jiang YX, Li WZ. A numerical study on heat transfer performance of microchannels with different surface microstructures. Appl Therm Eng 31, 921–931 (2011). doi: 10.1016/j.applthermaleng.2010.11.015 [81] Wang W, Zhang YN, Li BX, Han HZ, Gao XY. Influence of geometrical parameters on turbulent flow and heat transfer characteristics in outward helically corrugated tubes. Energy Convers Manag 136, 294–306 (2017). doi: 10.1016/j.enconman.2017.01.029 [82] Nivas JJ, He ST, Rubano A, Vecchione A, Paparo D et al. Direct femtosecond laser surface structuring with optical vortex beams generated by a q-plate. Sci Rep 5, 17929 (2015). doi: 10.1038/srep17929 [83] Lou K, Qian SX, Wang XL, Li YN, Gu B et al. Two-dimensional microstructures induced by femtosecond vector light fields on silicon. Opt Express 20, 120–127 (2012). doi: 10.1364/OE.20.000120 [84] Han WN, Li DF, Liu FR, Yuan YP, Li XW. Controllable formation of si nanostructures based on quasi-plasmonic planar nanostructures formed by annular-shaped femtosecond laser pulse. IEEE Photonics J 11, 2400208 (2019). [85] Ben-Yakar A, Byer RL, Harkin A, Ashmore J, Stone HA et al. Morphology of femtosecond-laser-ablated borosilicate glass surfaces. Appl Phys Lett 83, 3030–3032 (2003). doi: 10.1063/1.1619560 [86] Ben-Yakar A, Harkin A, Ashmore J, Byer RL, Stone HA. Thermal and fluid processes of a thin melt zone during femtosecond laser ablation of glass: the formation of rims by single laser pulses. J Phys D Appl Phys 40, 1447–1459 (2007). doi: 10.1088/0022-3727/40/5/021 -
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Figure 1.
(a–b) SEM images showing the side and top views of the cracked structures obtained by fs-LAL of Si at a laser power of 700 mW, a scan interval of 15 μm, and a scan speed of 1 mm/s. (c) Structure of a macropore. (d) Enlarged CLIPSS morphology in (c). (e, f) Twin CLIPSS in a macropore. (g, h) SEM images of the grooves obtained by 50mW-fs-LAL. High contrast applied to (g) is to see macropores in the valleys of grooves more clearly. (i/k, j/l) Enlarged images of green and blue rectangles in (g) and (h), respectively. The direction of laser polarization is shown in (b, l). (i, j, k) and (l) Irregular and normal LIPSS, respectively. (m) Velocity vector of a fluid vortex formed in a hole structure upon the impact of high-speed superimposed horizontal and vertical flows of fluids.
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Figure 2.
(a) Side view and (b) top view of the static pressure distribution of the simulated liquid vortex. (c) SEM image of the tungsten groove created by fs-LAL of W in water at a laser power of 600 mW, a scan interval of 5 μm, and a scan speed of 1 mm/s, which indicates that liquid vortexes induce a series of horizontal cracks. (d, e) and (f) SEM images showing the morphologies of the side walls of grooves generated by fs-LAL of Si in water at fixed conditions of a laser power of 700 mW and a scan interval of 15 μm with two different scan speeds of 0.5 and 1 mm/s, respectively. SEM images were taken from the side view with a 30° tilt.
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Figure 3.
(a) Fluidic velocity vector in four consecutive macropores upon the impact of high speed liquids from both horizontal and vertical directions, which indicates the formation of liquid vortexes on the side walls of the groove, near the openings of the macropores. (b–c) SEM images of CLIPSS formed on the openings of the macropores which are produced by fs-LAL of Si in water under the conditions of a laser power of 700 mW, a scan interval of 15 μm, and a scan speed of 1 mm/s. (c) Enlarged morphology of the white rectangle region in (b).
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Figure 4.
(a) SEM images of CLIPSS formed on the openings of macropores which are produced by fs-LAL of Si in water under the conditions of a laser power of 700 mW, a scan interval of 5 μm, and a scan speed of 1 mm/s. (b) Enlarged morphology of the green rectangle in (a) which indicates the convergence of LIPSS oriented in two different directions. (c) Fluidic velocity vector of the flows while encountering a mountain-like structure like (b), which vary their directions at different heights of the structure. Simulation conditions: an enlarged mountain-like structure with height and radius of 6 and 10 μm, respectively. A small trench with a depth of 2 μm is located beneath the mountain-like structure. The simulation model is a little enlarged compared with the structure shown in (b), which is aimed to ensure different directional flows on different parts of the structures to be seen more clearly. The starting flow is horizontal from top right to bottom left at a speed speed of 5 km/s.
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Figure FIG. 1301..
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