Laser Modification Research Articles

Femtosecond laser modification of the ZnO:Ag sol-gel films within dichroism emergence

Femtosecond laser modification of the ZnO:Ag sol-gel films within dichroism emergence

Mechanism and regulation of thermal damage on picosecond laser modification dicing of SiC wafer

Picosecond laser modification dicing (PLMD), compared with blade dicing, is more suitable for high-efficiency and low-damage processing of high hardness and brittleness SiC materials. However, the potential thermal damage restricts the further promotion of PLMD technology. To solve this problem, in this paper, the thermal damage behavior and mechanism of PLMD are studied by means of experiment and molecular dynamics (MD) simulations. In sidewall, the thermal damage manifests as thermal decomposition and amorphization. The thermal decomposition, which is essentially the graphitization caused by the gasification of Si and enrichment of C, occurs in the atmospheric pressure modified layers. The amorphization, caused by 470.0 GPa high pressure and 1.58 × 1013K/s cooling rate, occurs in the high pressure modified layers. Other forms of thermal damage, including cracking, chipping, and oxidation, are caused by heat accumulation in kerf region. The focal overlap rate is refined through an intensity correction factor, then transformed into the effective pulse number, serving as input for the model. This contributes to model with an average accuracy of 81 %. By adopting a thermal damage regulation strategy, PLMD of SiC wafers without thermal damage is realized.

Laser‐processed lithium niobate wafer for pyroelectric sensor

AbstractDuring the past few decades, pyroelectric sensors have attracted extensive attention due to their prominent features. However, their effectiveness is hindered by low electric output. In this study, the laser processed lithium niobate (LPLN) wafers are fabricated to improve the temperature–voltage response. These processed wafers are utilized to construct pyroelectric sensors as well as human–machine interfaces. The laser induces escape of oxygen and the formation of oxygen vacancies, which enhance the charge transport capability on the surface of lithium niobate (LN). Therefore, the electrodes gather an increased quantity of charges, increasing the pyroelectric voltage on the LPLN wafers to a 1.3 times higher voltage than that of LN wafers. For the human–machine interfaces, tactile information in various modes can be recognized by a sensor array and the temperature warning system operates well. Therefore, the laser modification approach is promising to enhance the performance of pyroelectric devices for applications in human–machine interfaces.image

Enhancing interfacial bond strength between PEEK and inkjet-printed silver film through laser surface modification for additive manufacturing of electronics

Electronic 3D printing is a very promising technology, which is widely used in the manufacturing of conformal antennas, flexible electronics and sensors. Polyether ether ketone (PEEK) is one of the most popular substrate materials for electronic 3D printing due to its superior fatigue resistance, heat tolerance, chemical resistance, and mechanical properties. However, the deficient bond between the PEEK substrate and the conductive ink leads to the peeling and shedding of the conductive pattern. This paper investigated the enhancement of the bond strength between the PEEK substrate and the conductive layer through PEEK surface modification. A 355 nm ns solid-state laser was used to treat the PEEK surface with different values of laser scanning spacing (S) and spot overlap rate (R). The surface microstructure, surface roughness, wettability, and functional groups of the treated substrates have been measured. Then the nanoparticle silver ink was printed and cured on the treated substrate. After that, the bonding strength was measured using a pull-off adhesion tester. Results showed that regular grooves were generated and the content of active oxygen atoms was increased on the PEEK surface through laser modification. The mechanical interlocking between the grooves and silver particles and hydrogen bonds induced by the active oxygen atoms and the hydroxyl groups contribute to the enhancement of bond strength between PEEK and silver film. The bond strength for the laser treated PEEK reached the maximum of 1.9 MPa, which was 413.51% higher than that of the untreated PEEK. The laser modification can effectively enhance the interfacial bond strength for additive manufacturing of reliable electronics.

The ablation behavior and modification mechanism of SiC under different laser energy

The laser modification pretreatment method is an effective way to address the machining difficulties of silicon carbide (SiC), a typical hard-to-machine material. Therefore, the ablation behavior and modification mechanism of SiC under different laser energy were explored in this paper. A new multi-scale model of laser irradiation SiC that couples heat transfer and fluid motion is first established. Then, a series of experiments is carried out to evaluate the model's accuracy, and the interaction between laser and SiC is discussed in detail. The results show that the dominant modification mechanism changes from coulomb explosion to multiphoton absorption, incubation effect, and heat accumulation with the laser energy increase. This leads the surface topography of SiC to transition from nanoparticle formation to disorder to a melting state. In ablative state, micro/nano porous and humps are formed at the edge of ablation groove due to surface tension, generation and rupture of bubbles, respectively. Furthermore, the surface roughness is not proportional to the laser energy due to the plasma shielding effect, and the surface roughness can be reduced by enhancing the flow of the molten material. Amorphous Si–O–C, Si and spherical SiO2 exist in deposition area, leading to SiC elastic modulus decreases from 347 GPa to 103.82 GPa, and the shear strength decreases from 20.9 GPa to 17.25 GPa. The results of this study can provide references for parameters selection and theoretical support for improving the machinability of SiC.

Experimental investigation and optimization of modification during coaxial waterjet-assisted femtosecond laser drilling

Waterjet-assisted laser drilling technology facilitates the fabrication of high-quality micro-holes by utilizing the collaborative benefits of waterjets and lasers. In this study, the coaxial waterjet-assisted laser drilling (CWALD) technique was employed to improve the properties of micro-holes during femtosecond laser drilling. Based on computational fluid dynamics (CFD) simulations, the stability of the waterjet was initially verified by optimizing the structure of the watercourse and nozzle shape in the CWALD device. Furthermore, a comparative experiment between laser direct drilling (LDD) and CWALD revealed that while CWALD can produce well-rounded micro-holes with a high aspect ratio, it exhibits lower efficiency and results in a larger heat-affected zone (HAZ). To address these drawbacks associated with CWALD, a two-step coaxial waterjet-assisted composite laser drilling (TS-CWALD) method was proposed. TS-CWALD involves applying CWALD for secondary modification of micro-hole shape following LDD with punching. This modification process is pivotal for enhancing drilling accuracy but requires consideration of multiple parameters. For this purpose, regression models were established for the inlet diameter, outlet diameter, and taper; response surface methodology was then employed to optimize these parameters. Subsequently, interactive effects analysis was conducted on different responses based on laser pulse energy, frequency, modification speed, and number of modification cycles. The adequacy of the developed models was subsequently verified using analysis of variance methods. Finally, the successful fabrication of a film hole with an inlet diameter of 205 μm and an outlet diameter of 200 μm, featuring a taper of only 0.2°, was achieved ultimately through meticulous parameter optimization. Furthermore, the micro-hole retained a minimal HAZ. The optimized parameters encompassed a pulse energy of 20.6 μJ, frequency of 127 kHz, modification speed of 3 mm/s, and shape modification carried out over 335 cycles.

Ultra-corrosion-resistant aluminum alloys achieved by femtosecond laser complete remediation of microarc oxidation defects

Microarc oxidation (MAO) is a widely employed technology for the corrosion protection of metal surfaces due to the formation of thick-layer ceramic substances. However, its practical effectiveness is strictly limited by the inevitable concomitant generation of numerous microscale pores/cracks on the oxidation surface to directly expose the substrate materials. As concerning this problem, we here introduced a novel method of the femtosecond laser irradiation to completely eliminate the above MAO defects on aluminum alloys, which consequently modulates the passivation layer into the dense and the superhydrophobic. Meanwhile, with the deep insights into the phase composition variations of the oxide layer, we can find that the laser treatments enable the development of both γ-Al2O3 and α-Al2O3 nanocrystallines with embedment in the amorphous substances to significantly improve the chemical stability of materials. Such laser modifications eventually result in the ultra-corrosion-resistant surface of aluminum alloys, with the measured corrosion current density of 1.46 × 10-13 A/cm2 as well as the impedance value over 112 GΩ∙cm2, about two orders of magnitude enhancement in the anticorrosion compared to the initial MAO sample.

Modifying single-crystal silicon and trimming silicon microring devices by femtosecond laser irradiation

Single-crystal silicon (c-Si) is a vital component of photonic devices and has obvious advantages. Moreover, femtosecond-pulsed laser interactions with matter have been widely applied in micro/nanoscale processing. In this paper, we report the modification mechanisms of c-Si induced by a femtosecond laser (350 fs, 520 nm) at different pulse fluences, along with the mechanism of this technique to trim the phase error of c-Si-based devices. In this study, several distinct types of final micro/nanostructures, such as amorphization and ablation, were analyzed. The near-surface morphology was characterized using optical microscopy, scanning electron microscopy, and atomic force microscopy. The main physical modification processes were further analyzed using a two-temperature model. By employing Raman spectroscopy, we demonstrated that a higher laser fluence significantly contributes to the formation of more amorphous silicon components. The thickness of the amorphous layer was almost uniform (approximately 30 nm) at different induced fluences, as determined using transmission electron microscopy. From the ellipsometry measurements, we demonstrated that the refractive index increases for amorphization while the ablation decreases. In addition, we investigated the ability of the femtosecond laser to modify the effective index of c-Si microring waveguides by either amorphization or ablation. Both blue and red shifts of resonance spectra were achieved in the microring devices, resulting in double-direction trimming. Our results provide further insight into the femtosecond laser modification mechanism of c-Si and may be a practical method for dealing with the fabrication errors of c-Si-based photonic devices.

Formation of ceramic coating on VAL10 aluminum alloy surface via laser modification in polysilicate solution

This article presents the results of an experimental study on the physical and mechanical properties of the surface layer of the VAL10 aluminum alloy after pulsed laser treatment, conducted in a bath with an aqueous solution of polysilicates (PS) at various concentrations. Ceramic coatings were produced on specimens measuring 10×10×3 mm. The laser processing of aluminum alloy specimens was carried out using an Nd:YAG laser. The study demonstrates that the quality of the resulting surface and its properties can vary depending on the laser exposure parameters, the concentration of the polysilicate solution, and the overall processing technique. The scattering of radiation by the PS solution layer leads to a significant reduction in surface roughness. In specimens processed in ambient air, the crater sizes on the surface exceeded 400 μm, while for specimens processed in a PS solution, they did not exceed 100 μm. A comparative analysis of the impact of solution concentration on elemental composition was performed. The study also included an investigation of friction characteristics and the measurement of microhardness of the modified surface. The research revealed that surface hardening processes occur as a result of the treatment, associated with the filling of recesses with high-strength oxides. This enabled the creation of a mixture containing silicon carbide and aluminum oxide in the surface layer of the specimens. Furthermore, wear tests of the modified surface were conducted using a “ball–specimen” tribological coupling. Specimens subjected to laser irradiation in a PS solution demonstrated increased wear resistance (a 40 % reduction in wear) and a 30 % decrease in the friction coefficient. Additionally, an increase in microhardness was observed.

Transitions of nitrogen optical centers induced by femtosecond laser pulses in treated natural diamond

Diamond is a unique optical material with ultra-hard lattice, which properties can be altered by optically active doping defects combined with carbon interstitials and vacancies. Direct laser writing by focused ultrashort laser pulses enables local modification of color centers in diamonds with excellent three-dimensional positioning accuracy, providing unique capabilities for quantum technologies, magnetometry, laser generation and photoluminescence (PL) micromarking. To shed light on currently unknown underlying atomistic transformations, we exposed electron-irradiated and annealed natural IaAB1-type diamond with an initially high content of various nitrogen-vacancy centers (NV, H3, N3 and H4) to millions of 0.2-ps, 525-nm laser pulses focused inside the sample. The modified areas were characterized by Fourier-transform infrared (FT-IR) and ultraviolet–visible transmission spectroscopy and confocal Raman/PL microspectroscopy with excitation wavelengths of 405 nm and 532 nm. We report on a local decrease in originally strong PL yield of NV, H3 and H4 centers with a monotonic dependence on both pulse energy and exposure time, as well as a rise of H1b and H1c lines in the FT-IR spectra accompanied by a drop in the concentration of H1a center. The results indicate that laser-induced processes make possible both creation and destruction of NV, H3 and H4 centers influenced by their initial concentration and the parameters of laser modification, which can be useful for adjusting of laser writing regimes for PL micromark inscription and other local modification of diamond for photonics applications.

Modification of Polysulfide Surfaces with Low‐Power Lasers

AbstractThe modification of polymer surfaces using laser light is important for many applications in the nano‐, bio‐ and chemical sciences. Such capabilities have supported advances in biomedical devices, electronics, information storage, microfluidics, and other applications. In most cases, these modifications require high power lasers that are expensive and require specialized equipment and facilities to minimize risk of hazardous radiation. Additionally, polymer systems that can be easily modified by lasers are often complex and costly to prepare. In this report, these challenges are addressed with the discovery of low‐cost sulfur copolymers that can be rapidly modified with lasers emitting low‐power infrared and visible light. The featured copolymers are made from elemental sulfur and either cyclopentadiene or dicyclopentadiene. Using a suite of lasers with discreet wavelengths (532, 638 and 786 nm) and powers, a variety of surface modifications could be made on the polymers such as controlled swelling or etching via ablation. The facile synthesis and laser modification of these polymer systems were exploited in applications such as direct laser lithography and erasable information storage.

Modification of Polysulfide Surfaces with Low-Power Lasers.

The modification of polymer surfaces using laser light is important for many applications in the nano-, bio- and chemical sciences. Such capabilities have supported advances in biomedical devices, electronics, information storage, microfluidics, and other applications. In most cases, these modifications require high power lasers that are expensive and require specialized equipment and facilities to minimize risk of hazardous radiation. Additionally, polymer systems that can be easily modified by lasers are often complex and costly to prepare. In this report, these challenges are addressed with the discovery of low-cost sulfur copolymers that can be rapidly modified with lasers emitting low-power infrared and visible light. The featured copolymers are made from elemental sulfur and either cyclopentadiene or dicyclopentadiene. Using a suite of lasers with discreet wavelengths (532, 638 and 786 nm) and powers, a variety of surface modifications could be made on the polymers such as controlled swelling or etching via ablation. The facile synthesis and laser modification of these polymer systems were exploited in applications such as direct laser lithography and erasable information storage.

Comparison of Zirconia Implant Surface Modifications for Optimal Osseointegration.

Zirconia ceramic implants are commercially available from a rapidly growing number of manufacturers. Macroscopic and microscopic surface design and characteristics are considered to be key determining factors in the success of the osseointegration process. It is, therefore, crucial to assess which surface modification promotes the most favorable biological response. The purpose of this study was to conduct a comparison of modern surface modifications that are featured in the most common commercially available zirconia ceramic implant systems. A review of the currently available literature on zirconia implant surface topography and the associated bio-physical factors was conducted, with a focus on the osseointegration of zirconia surfaces. After a review of the selected articles for this study, commercially available zirconia implant surfaces were all modified using subtractive protocols. Commercially available ceramic implant surfaces were modified or enhanced using sandblasting, acid etching, laser etching, or combinations of the aforementioned. From our literature review, laser-modified surfaces emerged as the ones with the highest surface roughness and bone-implant contact (BIC). It was also found that surface roughness could be controlled to achieve optimal roughness by modifying the laser output power during manufacturing. Furthermore, laser surface modification induced a very low amount of preload microcracks in the zirconia. Osteopontin (OPN), an early-late osteogenic differentiation marker, was significantly upregulated in laser-treated surfaces. Moreover, surface wettability was highest in laser-treated surfaces, indicating favorable hydrophilicity and thus promoting early bone forming, cell adhesion, and subsequent maturation. Sandblasting followed by laser modification and sandblasting followed by acid etching and post-milling heat treatment (SE-H) surfaces featured comparable results, with favorable biological responses around zirconia implants.

Droplet collision with hydrophobic and superhydrophobic surfaces: Experimental studies and numerical modeling

The characteristics of the collision of water droplets with textured hydrophobic and superhydrophobic surfaces obtained using two techniques were studied experimentally. The surface processing techniques are based on laser modification of the surface layer and changes in its chemical composition. Weber numbers in the experiments were varied in the range of 10–200. Regimes of water droplet-surface collision, the critical conditions for the transition between regimes, as well as integral characteristics of the formed liquid fragments were identified. The main characteristics of the process under study, such as the droplet spreading diameter, the height of its rebound from the surface, the number of secondary fragments during its break up were obtained experimentally. A model with a two-dimensional axisymmetric formulation was used to predict the characteristics of water droplet-textured surface collision based on the phase field method. The results of experimental studies and numerical modeling are in satisfactory agreement (differences of no more than 3–5 %). The conditions, when it is necessary to consider the values of static and dynamic contact angles during the modeling process, were determined.

Direct observation and quantification of nanosecond laser induced amorphization inside silicon

The nature of structural changes of nanosecond laser modification inside silicon is investigated. Raman spectroscopy and transmission electron microscopy measurements of cross sections of the modified channels reveal highly localized crystal deformation. Raman spectroscopy measurements prove the existence of amorphous silicon inside nanosecond laser induced modifications, and the percentage of amorphous silicon is calculated based on the Raman spectrum. For the first time, the high-resolution transmission electron microscopy images directly show the appearance of amorphous silicon inside nanosecond laser induced modifications, which corroborates the indirect measurements from Raman spectroscopy. The laser modified channel consists of a small amount of amorphous silicon embedded in a disturbed crystal structure accompanied by strain. This finding may explain the origin of the positive refractive index change associated with the written channels that may serve as optical waveguides.

Laser Modification of Aluminum Bronze

Laser Modification of Aluminum Bronze

Dual biomimetic surfaces with anisotropic wettability for multi-scale droplets manipulation

Droplets manipulation on functional biomimetic surfaces have been highly anticipated for their wide range of applications. However, preparing a metal platform for manipulating multi-scale droplets without external energy input remains a challenge. Herein, dual biomimetic surfaces (DBSs) were fabricated by twice laser and thiol modification. The unique interfacial behavior of the droplets can be realized under the synergistic effect of the special “millimeter-micrometer-nanometer” multi-hierarchical composite structure and chemical composition. The as-prepared DBSs can achieve multi-scale droplets manipulation, directional self-cleaning in various media, and efficient directional fog collection. Further, the mechanism of specific interface behavior is analyzed in depth. Nanoparticles endow DBSs with more capture points and condensation cores and micrometer mastoids realized the transmission and aggregation of microscopic droplets through the action of Laplace force. Based on resistance, energy barriers and three-phase contact line, influence of millimeter grooves on anisotropic wettability and directional transportation of the droplets is analyzed. Besides, the multi-hierarchical structure also endows DBSs with good droplets manipulation ability and stability. This work not only provides an advanced biomimetic platform, but also provides an important reference for metal-based lab-on-a-chip for multi-scale droplets manipulation.

Microstructure Formations Resulting from Nanosecond and Picosecond Laser Irradiation of a Ti-Based Alloy under Controlled Atmospheric Conditions and Optimization of the Irradiation Process.

This paper presents a study and comparison of surface effects induced by picosecond and nanosecond laser modification of a Ti6Al4V alloy surface under different ambient conditions: air and argon- and nitrogen-rich atmospheres. Detailed surface characterization was performed for all experimental conditions. Damage threshold fluences for picosecond and nanosecond laser irradiation in all three ambient conditions were determined. The observed surface features were a resolidified pool of molten material, craters, hydrodynamic effects and parallel periodic surface structures. Laser-induced periodic surface structures are formed by multi-mode-beam nanosecond laser action and picosecond laser action. Crown-like structures at crater rims are specific features for picosecond Nd:YAG laser action in argon-rich ambient conditions. Elemental analysis of the surfaces indicated nitride compound formation only in the nitrogen-rich ambient conditions. The constituents of the formed plasma were also investigated. Exploring the impact of process control parameters on output responses has been undertaken within the context of laser modification under different environmental conditions. Parametric optimization of the nanosecond laser modification was carried out by implementing an advanced method based on Taguchi's parametric design and multivariate statistical techniques, and optimal settings are proposed for each atmosphere.

Investigating the Effect of Nanosecond Laser Surface Texturing on Microstructure and Mechanical Properties of AISI 301LN

This study explores pulsed Nd:YLF laser surface modification (LSM) effects on AISI 301LN stainless steel. Laser-treated surfaces underwent SEM characterization, revealing patterns and irregularities. Higher heat input surfaces showed significant microstructural changes, while lower heat input surfaces experienced less alteration. Increased laser spot overlap led to larger exposed areas and higher heat input, influencing groove width, depth, and surface roughness. Three-dimensional reconstructions illustrated the correlation between laser parameters and surface characteristics. XRD (X-ray diffraction analysis) and EBSD (Electron backscatter diffraction) analyses revealed a transformation from austenite to martensite, with an increase in the α’-martensite phase, particularly in patterns with high laser power, attributed to rapid cooling during laser modification. Grain size analysis indicated a 42% reduction post-treatment, enhancing the surface fraction of fine grains. Hardness measurements demonstrated an overall increase in laser-treated samples, linked to fine-grained microstructure formation, induced residual stresses, and the α’-martensitic phase.

Investigations on electrochemical corrosion behavior of 7075 aluminum alloy with femtosecond laser modification

The effects of the surface integrity of 7075 aluminum alloy by femtosecond laser modification (FLM) were investigated, and subsequently the electrochemical corrosion behavior of the samples in 3.5 % NaCl solution. It was found that hydrophobic textures, amorphous oxidative layers, and deformed layers were formed sequentially from the outside to the inside of the treated samples. These help to reduce the solid-liquid contact area on the surface, improve the polarization resistance, reduce the corrosion current, impede the diffusion of chloride in the interior, and thus enhance the corrosion resistance of the aluminum alloy. Additionally, it was determined that the contribution of hydrophobic textures and amorphous oxidative layers to the enhancement of corrosion resistance was dominant.