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Wetting angle stability of steel surface structures after laser treatment
摘要： In this work, we have used a nanosecond pulsed fiber laser to modify the wettability characteristics of AISI 430 steel. For this, various surface morphologies were created on the samples by laser irradiation with different overlapping and intensity parameters. Immediately upon laser treatment, all the structured samples acquired either hydrophilic or superhydrophilic wetting angles. All the samples were also analyzed with XRD. Then, laser-treated samples were kept in ambient air and/or low-temperature annealing was applied to reach hydrophobic surface properties. Interestingly, these surfaces returned back practically to their initial wetting state by cleaning in an ultrasonic bath. The obtained results are analyzed based on the existing wettability models.
关键词： Nanosecond laser structuring,Hydrophobic and hydrophilic surfaces,Wettability transition,Wetting angle stability
更新于2025-09-19 17:13:59
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Underwater persistent bubble-assisted femtosecond laser ablation for hierarchical micro/nanostructuring
摘要： In this study, we demonstrate a technique termed underwater persistent bubble assisted femtosecond laser ablation in liquids (UPB-fs-LAL) that can greatly expand the boundaries of surface micro/nanostructuring through laser ablation because of its capability to create concentric circular macrostructures with millimeter-scale tails on silicon substrates. Long-tailed macrostructures are composed of layered fan (central angles of 45-141°) hierarchical micro/nanostructures, which are produced by fan-shaped beams refracted at the mobile bubble interface (≥ 50°light tilt, referred to as the vertical incident direction) during UPB-fs-LAL line-by-line scanning. Marangoni flow generated during UPB-fs-LAL induces bubble movements. Fast scanning (e.g., 1 mm/s) allows a long bubble movement (as long as 2 mm), while slow scanning (e.g., 0.1 mm/s) prevents bubble movements. When persistent bubbles grow considerably (e.g., hundreds of microns in diameter) due to incubation effects, they become sticky and can cause both gas-phase and liquid-phase laser ablation in the central and peripheral regions of the persistent bubbles. This generates low/high/ultrahigh spatial frequency laser-induced periodic surface structures (LSFLs/HSFLs/UHSFLs) with periods of 550-900, 100-200, 40-100 nm, which produce complex hierarchical surface structures. A period of 40 nm, less than 1/25th of the laser wavelength (1030 nm), is the finest laser-induced periodic surface structures (LIPSS) ever created on silicon. The NIR-MIR reflectance/transmittance of fan-shaped hierarchical structures obtained by UPB-fs-LAL at a small line interval (5 μm vs 10 μm) is extremely low, due to both their extremely high light trapping capacity and absorbance characteristics, which are results of the structures’ additional layers and much finer HSFLs. In the absence of persistent bubbles, only grooves covered with HSFLs with periods larger than 100 nm are produced, illustrating the unique attenuation abilities of laser properties (e.g. repetition rate, energy, incident angle, etc.) by persistent bubbles with different curvatures. This research represents a straightforward and cost-effective approach to diversifying the achievable micro/nanostructures for a multitude of applications.
关键词： femtosecond laser,persistent bubble,beam refraction,fan-shaped microstructure,surface structuring,hierarchical micro/nanostructures,LIPSS
更新于2025-09-19 17:13:59
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The Effect of Laser Structuring of Carbon Nanotubes on the Proliferation of Chondroblasts and Mesenchymal Stem Cells
摘要： The density of cartilage cells (chondroblasts) proliferating on a silicon substrate coated with vertically oriented arrays of multi-walled carbon nanotubes (MWCNTs) was shown to be higher than on a pure silicon substrate. Electron microscopy showed that the cells in a nutrient medium affected the vertical position of the nanotubes in the array. A method for structuring the MWCNT arrays by 100-ns laser pulse scanning and abrasive water processing on planar substrates was developed. As a result of the structuring of the MWCNTs, the arrays become resistant to bending under the influence of the nutrient medium with mesenchymal stem cells. Structured MWCNT arrays were shown to have no toxic or pathological effect on the viability and morphology of stem cells. Thus, such materials can be suggested for use in cell-adhesive components of biomedical devices.
关键词： carbon nanotubes,laser structuring,mesenchymal stem cells,chondroblasts,cell proliferation
更新于2025-09-19 17:13:59
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Metal Polymer Connections: Laser-Induced Surface Enlargement Increases Joint Strength
摘要： The trend towards hybrid materials consisting of metals and polymers is strongly driven by requirements such as weight reduction and improved functionality. A crucial step towards new hybrid materials is the advancement of joining technology. While metals and polymers are currently often joined using adhesives, this technology has major drawbacks such as long process cycle time, low robustness with regard to changes of the material composition, and are almost impossible to recycle, a point which is becoming increasingly important. A promising joining method is thermal direct joining of metals and thermoplastic polymers due to its fast cycle time, its robustness of the process and the absence of duroplastic adhesives. Direct joining requires surface treatment of the metallic joining partner prior to the thermal joining process to achieve a sufficiently high contact strength. It is known that laser-induced topologies on the metal surface are beneficial with regard to contact strength of the joints. Designing a joint based on laser structured metals requires a fundamental understanding of the interface interactions. The present paper focuses on the influence of surface enlargement on the joint strength. Laser pretreatment was utilized to generate surface structures with specific surface enlargement on the metallic joining partner. The pretreated metallic parts were subsequently joined with a thermoplastic polymer by injection molding. The joint strength was investigated in single lap shear tests. The key finding is that the contact strength increases almost linearly with the surface area within the tested parameter range, while the structure geometry parameters have only a minor influence. This may help as a design guideline for future adhesive-free hybrid material joining technologies.
关键词： hybrid joining,laser material processing,metal polymer connection,micro structuring,metal polymer joints,lightweight,adhesion,in-mold assembly
更新于2025-09-16 10:30:52
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Investigations of Transient Plasma Generated by Laser Ablation of Hydroxyapatite during the Pulsed Laser Deposition Process
摘要： The optimization of the pulsed laser deposition process was attempted here for the generation of hydroxyapatite thin films. The deposition process was monitored with an ICCD (Intensified Coupled Charged Device) fast gated camera and a high-resolution spectrometer. The global dynamics of the laser produced plasma showed a self-structuring into three components with different composition and kinetics. The optical emission spectroscopy revealed the formation of a stoichiometric plasma and proved that the segregation in the kinetic energy of the plasma structure is also reflected by the individual energies of the ejected particles. Atomic Force Microscopy was also implemented to investigate the properties and the quality of the deposited film. The presence of micrometric clusters was seen at a high laser fluence deposition with in-situ ICCD imaging. We developed a fractal model based on Schr?dinger type functionalities. The model can cover the distribution of the excited states in the laser produced plasma. Moreover, we proved that SL(2R) invariance can facilitate plasma substructures synchronization through a self-modulation in amplitude.
关键词： hydroxyapatite thin film,pulsed laser deposition,plasma diagnostic,plasma structuring,SL(2R) invariance
更新于2025-09-16 10:30:52
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Laser Dissimilar Joining of Al7075T6 with Glass-Fiber-Reinforced Polyamide Composite
摘要： Dissimilar joining between metal and composite sheets is usually carried out by mechanical or adhesive joining. Laser dissimilar joining between metal and composite sheets could be an alternative to these methods, as it is a cost-effective and versatile joining technique. Previously, textured metallic and composite parts have been held together and heated with a laser beam while pressure is applied to allow the melted polymer to flow into the cavities of the metal part. The main issue of this process relates to reaching the same joint strength repetitively with appropriate process parameters. In this work, both initial texturing and laser joining parameters are studied for Al 7075-T6 and glass-fiber-reinforced PA6 composite. A groove-based geometry was studied in terms of depth-to-width aspect ratio to find an optimal surface using a nanosecond fiber laser for texturing. Laser joining parameters were also studied with different combinations of surface temperature, heating strategy, pressure, and laser feed rate. The results are relatively good for grooves with aspect ratios from 0.94 to 4.15, with the widths of the grooves being the most critical factor. In terms of joining parameters, surface reference temperature was found to be the most influential parameter. Underheating does not allow correct material flow in textured cavities, while overheating also causes high dispersion in the resulting shear strength. When optimal parameters are applied using correct textures, shear strength values over 26 kN are reached, with a contact area of 35 × 45 mm2.
关键词： metal polymer joint,groove aspect ratio,laser structuring,laser direct joining,shear strength
更新于2025-09-16 10:30:52
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Lorenz Type Behaviors in the Dynamics of Laser Produced Plasma
摘要： An innovative theoretical model is developed on the backbone of a classical Lorenz system. A mathematical representation of a differential Lorenz system is transposed into a fractal space and reduced to an integral form. In such a conjecture, the Lorenz variables will operate simultaneously on two manifolds, generating two transformation groups, one corresponding to the space coordinates transformation and another one to the scale resolution transformation. Since these groups are isomorphs various types isometries become functional. The Lorenz system was further adapted to describe the dynamics of ejected particles as a result of laser matter interaction in a fractal paradigm. The simulations were focused on the dynamics of charged particles, and showcase the presence of current oscillations, a heterogenous velocity distribution and multi-structuring at different interaction scales. The theoretical predictions were compared with the experimental data acquired with noninvasive diagnostic techniques. The experimental data confirm the multi-structure scenario and the oscillatory behavior predicted by the mathematical model.
关键词： plasma structuring,fractal analysis,laser produced plasmas,ionic oscillations,Lorenz system
更新于2025-09-16 10:30:52
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Experimental investigation on a new hybrid laser process for surface structuring by vapor pressure on Ti6Al4V
摘要： Besides conventional structuring processes such as turning, milling or photo-chemical etching, laser processes are increasingly being used for surface structuring of metals. These laser processes differ fundamentally in that structuring is carried out either by material removal or by material redistribution. In this study, a new hybrid process of material ablation by means of pulsed laser radiation and material redistribution based on a remelting process by means of cw laser radiation is experimentally investigated. Besides an introduction to this new hybrid process, we give a detailed description of the equipment and methods used as well as surface structures produced on Ti6Al4V. A melt pool was generated on a prepared Ti6Al4V surface using cw laser radiation with a laser beam diameter of 520 μm, laser power of 220 W, and a scanning velocity of 100 mm/s. In order to create surface structures, simultaneously, superimposed pulsed laser radiation with a laser beam diameter of 65 μm, pulse duration of 60 ns, a maximum pulse energy of 0.35 mJ, and a pulse frequency of 50 kHz was used to evaporate small amounts of molten material from the melt pool. This localized evaporation of molten material is assumed to create vapor pressure that deforms the melt pool surface and therefore leads to surface structures. Our results indicate that by pulsed laser radiation capillary surface waves with a wavelength of the doubled laser beam diameter are excited on the melt pool surface. This forced excitation of capillary surface waves result in surface structures that are analyzed after solidification by means of white light interferometry. Based on this analysis we derived an oscillation frequency of ν = 2.27 (± 0.16) kHz for the excited capillary surface wave as well as an effective kinematic viscosity of μ = 0.1328 cm2 s-1 for the damping of this surface oscillation during solidification. In terms of structural features, we achieved surface structures with heights of up to 100 μm. Furthermore, structure height controllably scales in dependence on pulse energy and number of laser pulses as long as no ejection of molten material takes place. Finally, a comparison of the redistributed material volume per time shows that we achieved a volume redistribution rate of 28.37 mm3/min, which is significantly bigger than has been achieved with other laser texturing techniques so far and demonstrates the high potential of this new hybrid technique not only for surface structuring purposes.
关键词： surface structuring,melt pool,material redistribution,capillary surface wave,Ti6Al4V,remelting
更新于2025-09-16 10:30:52
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Multiple structure formation and molecule dynamics in transient plasmas generated by laser ablation of graphite
摘要： Transient plasmas generated by ns - laser ablation of graphite in air have been investigated by complementary optical diagnosis techniques to study complex multiple structures generated in carbon laser produced plasmas (C-LPP) during the expansion phase. The overall emission was investigated by ICCD fast camera imaging and revealed the structuring of C-LPP into four distinct structures with di?erent evolutions. The dynamic of the C-LPP was analyzed on various expansion directions in order to understand the formation of the main CN dominant structure and of lateral “?aps” with dominant C2 emission. The kinetic and thermal energies of the resulted atoms, ions and molecules were investigated by means of space-and time-resolved optical emission spectroscopy and using the Boltzmann plot and Stark broadening approaches. The e?ect of the background gas pressure on the formation of molecular carbon structures is discussed and an optimum range of working pressure which maximizes the generation of C2 is found. Based on the acquired data a scenario for the complex carbon structures generation in C-PLL as function of the background gas is proposed.
关键词： Complex carbon structures,ns-laser produced plasma,molecule dynamics,Graphite,Multiple plasma structuring,ICCD fast camera imaging
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Stitchless Support-Free Fabrication of Free-Form Micromechanical Structures using Femtosecond Laser 3D Lithography
摘要： Femtosecond laser based 3D nanolithography is gaining popularity in huge variety of fields. However, further improvements are needed to push it from laboratory level use into a wide spread adaptation. These include increasing fabrication throughput without sacrificing quality of a final product and making the most challenging, free-movable 3D structures easy to print. In this work we present several advances needed to achieve these goals. First, linear stage and galvo-scanners synchronization is employed to produce stitch-free mm-sized structures with features down to micrometers. Furthermore, resolution bridge method is used to determine feature sizes acquired by varying objective numerical apertures (NA) from 0.8 NA to 1.4 NA. This way voxel size can be tuned in the range from 330 nm to 1.7 μm in transverse and 1.9 μm to 7.9 μm in longitudinal directions. At 1 cm/s translation velocity it results in voxel volumes from 0.017 μm3 to 3.759 μm3 with structuring rates at 2426 μm3/s and 104767 μm3/s respectively. This two orders of magnitude tunability is exploited to fabricate various functional structures. For instance, deformable microcantilevers and microsprings capable of sustaining multiple deformation cycles were created using 0.8 NA objective chosen for faster printing with acceptable resolution. Performance and longevity of these elements were characterized in both qualitative and quantitative manner. Furthermore, the hard gel form of the SZ2080 photopolymer used in this work allowed to perform support-free structuring of free-movable micromechanical components employing high-resolution structuring achievable with 1.4 NA objective. Possibility to forgo usage of supports needed with liquid resins eliminates the need to remove supports after printing making the whole process simpler. To demonstrate the potency of this approach movable mm-sized micromechanical spider and squid were fabricated, showing possibility to print true 3D hinge-like microstructures (feature size down to micrometers). Such structures have huge potential in the fields of sensors and microrobotics as mechanically induced deformation of movement can be employed as either means to detect outside force or provide a basis for self-propelling functional structures.
关键词： micromechanical structures,free-movable 3D structures,support-free structuring,Femtosecond laser,3D nanolithography
更新于2025-09-12 10:27:22