Laser Modification Research Articles

Improving polishing efficiency of RB-SiC through femtosecond laser pretreatment

It is a great technical challenge to precisely and efficiently polish RB-SiC substrates due to their two-phase structure and extreme hardness, especially for large-optics fabrication. Here, a simple laser pretreatment process is demonstrated for improving the polishing efficiency using femtosecond laser to modify the RB-SiC surface pre-coated with silicon powder. Material characterization and finite-element analyses reveal that the pre-coated surface is oxidized under femtosecond laser irradiation. As oxidation gradually penetrates deeper into the interface, the modified layer forms a bonding with the RB-SiC substrate. By optimizing laser scanning parameters to adjust the oxidation depth, a high-quality modified layer with stronger adhesion strength can be obtained. The approach is capable of delivering a modified layer that is easier to polish and tightly bonded to the RB-SiC substrate with an adhesion strength of 55.46 N. Thanks to the femtosecond laser modification, the surface roughness of the pretreated RB-SiC can be reduced to Sq 4.5 nm in just a few hours of polishing, which increases polishing efficiency over 3 times compared with direct abrasive polishing. Low requirements for substrate surface profile and simple operation make this laser pretreatment approach possible to be applied to more complex RB-SiC surfaces and significantly improve polishing efficiency.

Integration of cross-scale milli/microlenses by ion beam etching and femtosecond laser modification.

Integrated cross-scale milli/microlenses offer irreplaceable functions in modern integrated optics with the advantage of reducing the size of the optical system to millimeters or microns. However, the technologies for fabricating millimeter-scale lenses and microlenses are always incompatible, which makes the successful fabrication of cross-scale milli/microlenses with a controlled morphology challenging. Here, ion beam etching is proposed as a means to fabricate smooth millimeter-scale lenses on various hard materials. In addition, by combining femtosecond laser modification and ion beam etching, an integrated cross-scale concave milli/microlens (27,000 microlenses on a lens with a diameter of 2.5 mm) is demonstrated on fused silica, and can be used as the template for a compound eye. The results provide a new, to the best of our knowledge, route for the flexible fabrication of cross-scale optical components for modern integrated optical systems.

Fabrication of wear-resistant and superhydrophobic aluminum alloy surface by laser-chemical hybrid methods

To achieve rapid, efficient, and low-cost preparation of large-scale stable aluminum alloy superhydrophobic surfaces, a new preparation method is proposed. The outer surface of the array micro-protrusions was coated with a layer of armor, which was the molten spatter produced during picosecond laser processing. The molten sputters and micro-protrusions combined to form micro–nano composite multi-layer structures. Through these special array micro–nano composite multi-layer structures and chemical modification, the wear-resistant and superhydrophobic properties of aluminum alloy surfaces were realized. According to test results, the array micro–nano composite structures prepared by picosecond laser and chemical modification had a water drop contact angle of 154.6° and a water drop rolling angle of 2°, exhibiting excellent superhydrophobic and anti-adhesion properties. Its self-cleaning, corrosion resistance and friction and wear behavior were systematically analyzed. The analysis results showed that the rolling droplets on the prepared surface could easily take away contaminants. The corrosion voltage and corrosion current density of the prepared superhydrophobic surface are significantly lower than that of the raw surface. In addition, a water drop contact angle of the aluminum alloy sample maintained at 145.1° after five wear tests, indicating the prepared surface after wear testing still had hydrophobic performance. The innovative method proposed in this study provides a simple and effective method for preparing large-scale wear-resistant superhydrophobic surface of aluminum alloy.

Some Initial Results on Modification of aC:H Films by Pulsed Laser Irradiation

It has recently been shown both theoretically and experimentally that a significant modification of the aC:H films is possible using UV irradiation even with a very low irradiation fluence. Some initial results on the modification of aC:H films with thickness of about 40 nm with UV laser irradiation are presented here. The fourth harmonic (λ = 266 nm) of a Nd:YAG laser system (the fundamental wavelength λ = 1064 nm) was used in our experiments. The modified areas of the aC:H films were characterized by optical microscopy, Raman spectroscopy as well as by atomic force microscopy (AFM). A significant modification of aC:H films under certain conditions (laser irradiation fluence and modification modes) to multi-layer graphene accompanied by ablation of a part of the film was established. It was also found that similar aC:H films deposited on 330 nm SiO2/Si substrates did not undergo significant modification under these conditions.

Doping of Laser‐Induced Graphene and Its Applications

AbstractLaser‐induced graphene (LIG) has attracted extensive attention owing to its facile preparation of graphene and direct engraving patterns for devices. Various applications are demonstrated such as sensors, supercapacitors, electrocatalysis, batteries, antimicrobial, oil and water separation, solar cells, and heaters. In recent years, doping has been employed as a significant strategy to modulate the properties of LIG and thereby improve the performance of LIG devices. Due to the patternable manufacture, controllable morphologies, and the synergistic effect of doped atoms and graphene, the doped LIG devices exhibit a high sensitivity of sensing, pseudocapacitance performance, and biological antibacterial. This paper reviews the latest novel research progress of heteroatom and nanoparticles doped LIG in synthesis, properties, and applications. The fabrications of LIG and typical doping approaches are presented. Special attention is paid to two doping processes of LIG: the one‐step laser irradiation method and the two‐step laser modification consisting of deposition, drop‐casting, and duplicated laser pyrolysis. Doped LIG applications with improved performance are mainly highlighted. Taking advantage of doped LIG's properties and device performances will provide excellent opportunities for developing artificial intelligence, data storage, energy, health, and environmental applications.

High-temperature oxidation and TGO growth behaviors of laser-modified YAG/YSZ double-ceramic-layer TBC

Yttrium—aluminum garnet/yttria-stabilized zirconia (YAG/YSZ) double-ceramic-layer thermal barrier coating (TBC) with NiCoCrAlY bond coating was deposited by atmospheric plasma spraying (APS) on Inconel 738 alloy substrate, and laser modification was carried out on the surface of YAG ceramic coating to improve the high- temperature oxidation resistance of TBC. Then, isothermal oxidation tests were designed to study the high-temperature oxidation and thermally grown oxide (TGO) growth behaviors of the as-sprayed (AS) and the laser modified (LM) YAG/YSZ TBC. Results show that TGO thickness and structure of both AS-TBC and LM-TBC exhibit the similar evolution trend, TGO thickness increases with the increasing of isothermal oxidation time, and TGO structure develops from single Al2O3 layer to the double-layer structure of upper mixed oxides and lower Al2O3. Because of the crucial inhibition effect of the laser modification on oxygen permeation, the appearance time of mixed oxides in LM-TBC is postponed, and the total TGO thickness of LM-TBC is reduced at the middle and final oxidation stages. The Al2O3 layer thickness proportion of total TGO in LM-TBC is always greater than or equal to that in AS-TBC at the same isothermal oxidation time. Compared with the AS-TBC, the parabolic oxidation rate of LM-TBC is decreased by 18.42%. Therefore, YAG/YSZ LM-TBC presents better oxidation resistance and lower TGO growth rate than AS-TBC.

Scanning with Laser Beam over the TiO2 Nanotubes Covered with Thin Chromium Layers towards the Activation of the Material under the Visible Light.

This work presents pulsed UV laser treatment (355 nm, 2 Hz) of TiO2 nanotubes decorated with chromium oxides. The modification was performed in a system equipped with a beam homogenizer, and during the irradiation, the samples were mounted onto the moving motorized table. In such a system, both precisely selected areas and any large area of the sample can be modified. Photoelectrochemical tests revealed photoresponse of laser-treated samples up to 1.37- and 18-fold under the illumination with ultraviolet-visible and visible light, respectively, in comparison to bare titania. Optimal beam energy fluence regarding sample photoresponse has been established. Scanning electron microscopy images, X-ray diffraction patterns, along with Raman and X-ray photoelectron spectra, suggest that the enhanced photoresponse results from changes solely induced in the layer of chromium oxides. It is believed that the results of the present work will contribute to a wider interest in laser modification of semiconductors exhibiting improved photoelectrochemical activity.

Volume plasma grating by noncollinear interaction of femtosecond filament arrays.

Stable propagation of multifilament arrays in transparent bulk media with adjustable separation distances between adjacent child filaments has always been desired for advanced manufacturing. Here, we report on the generation of an ionization-induced volume plasma grating (VPG) by the interaction of two batches of noncollinearly propagating arrays of multiple filaments (AMF). The VPG can externally arrange the propagation of the pulses along regular plasma waveguides via spatial reconstruction of electrical fields, which is compared with the self-formation of randomly distributed multiple filamentation originated from noises. The separation distances of filaments in VPG are controllable by readily changing the crossing angle of the excitation beams. In addition, an innovative method to efficiently fabricate multidimensional grating structures in transparent bulk media through laser modification using VPG was demonstrated.

Precise preparation of quartz pendulous reed by using picosecond laser modification assisted wet etching

The Quartz pendulous reed is the core part of the quartz flexible accelerometer. The current quartz pendulous reed forming technology has shortcomings, such as poor processing quality and high production cost. In this paper, picosecond laser modification assisted wet etching technology is proposed to prepare quartz pendulous reed. The modification mechanism of fused silica induced by picosecond laser was investigated. Different from the network structure changes caused by femtosecond laser, mechanical damage is the main form of picosecond laser modification. The mapping among etching time, etching temperature and HF solution concentration were studied by using the control variable method. The proposed picosecond laser assisted wet etching technology has the advantages of high dimensional accuracy, good edge quality, low residual stress, and high efficiency.

Thermally sprayed coatings resistant to environmental degradation: Columnar-like coatings through laser ablation and surface melting approach

The limited lifespan of protective coatings attracted interest in studying the failure phenomena and investigating various coating deposition techniques. In this study, a new laser modification technique is proposed and examined on air plasma sprayed thermal barrier coatings. Thermal barrier coatings must have a minimal mechanical response to temperature variations, i.e. thermal expansion-induced stresses while having low thermal conductivity and excellent resistance to environmental agents. This paper reports a novel post-treatment approach allowing independent control of the elastic modulus in the coating and on its surface by creating a hollow internal anatomy covered by a dense protective layer. The hollow internal microstructure aims to recreate a columnar-like structure in air plasma sprayed coatings inspired by the electron-beam physical vapour deposited coatings, known for their excellent strain tolerance properties. To protect the coating from chemical and mechanical degradation and to cut the generated oxygen short path, the top surface of the coating is subsequently melted with a continuous-wave laser, creating a dense erosion and corrosion-resistant surface. The modification approach was applied to the state-of-the-art air plasma sprayed 8 wt% Yttria Stabilized Zirconia topcoats and comprehensively benchmarked against the same air plasma sprayed, non-modified, coating in terms of thermal shock, erosion resistance and response to molten silicon sand penetration, and showed significant improvements in erosion and CMAS tests, and 11 % improvement of thermal fatigue.

Influence of Laser Modification of Nitride Ceramics Surface Layer on the Milling Cutters Reliability During the Finishing of Hardened Steel Workpieces

Influence of Laser Modification of Nitride Ceramics Surface Layer on the Milling Cutters Reliability During the Finishing of Hardened Steel Workpieces

Effect of Au Nanoparticle Agglomeration on SERS Signal Amplification.

An analyzed substance's signal intensity and detection sensitivity in surface-enhanced Raman spectroscopy (SERS) significantly depend on the size and agglomeration degree of nanoparticles (NPs) forming the enhancing structure. Structures were manufactured by aerosol dry printing (ADP), where NPs' agglomeration depends on printing conditions and additional particle modification techniques. The influence of agglomeration degree on SERS signal enhancement was studied in three types of printed structures using the methylene blue model molecule as an analyte. We demonstrated that the ratio between individual NPs and agglomerates in a studied structure strongly affects SERS signal amplification, and structures formed mainly from non-agglomerated NPs enhance the signal better. In this sense, aerosol NPs modified by pulsed laser radiation provide better results than thermally modified NPs, since in laser modification a larger number of individual NPs is observed due to the absence of secondary agglomeration effects in the gas stream. However, increasing gas flow may minimize the secondary agglomeration, since the time allotted for the agglomeration processes is reduced. In this paper, we show how different NPs' agglomeration tendencies influence SERS enhancement to demonstrate the process of using ADP to form inexpensive and highly efficient SERS substrates with huge application potential.

Effect of hybrid modification by ceramic layer formation in MAO process and laser remelting on the structure of titanium bio-alloy Ti13Nb13Zr

To improve the biological properties of titanium alloy Ti13Nb13Zr, hybrid modifications involving micro-arc oxidation (MAO) and Nd: YAG laser remelting were carried out in two combinations. The first consisted of laser modification before the production of the ceramic layer by the micro-arc oxidation process, and the second combination involved Nd: YAG laser modification after the MAO process. The creation of developed surface morphologies on titanium alloys used in implant manufacturing is currently a widely discussed trend. The modifications used by the authors offer the possibility of obtaining a porous, wettable surface with altered nanohardness.To investigate the structural properties of the obtained hybrid Nd: YAG-MAO and MAO-laser Nd: YAG modifications, the structure roughness tests were performed with a suitable apparatus and atomic force microscope (AFM) and available software. The surface wettability was evaluated and the surface of the modified Ti13Nb13Zr alloy was subjected to evaluation using a scanning electron microscope (SEM), and an optical microscope. Using available software, chemical composition analysis, porosity analysis, and, adhesion analysis were performed.Based on the tests carried out, the possibility of carrying out hybrid modification in various combinations was demonstrated. The presence of Na+ and Ca2+ ions was demonstrated for samples in the combination of laser modification and MAO modification, which is important for biomedical reasons. Each modification allowed changing of the nanohardness, wettability, and roughness in the direction expected, required from biomedical materials. This paper presents an innovative approach to the use of two modifications one using the effect of heat on the matrix and the other focused on the formation of a ceramic coating. Currently, hybrid modifications are desirable in that they allow them to interact positively with each other.

Space-resolved light emitting and lasing behaviors of crystalline perovskites upon femtosecond laser ablation

Femtosecond laser processing of lead halide perovskites has recently sparked wide popularity for creating various micro/nanostructures and instigating interesting properties. However, it is still lacking detailed insights into correlating the laser induced morphology and defect chemistry of perovskite materials to their light emitting properties. Here, the space-resolved photoluminescence and lasing behaviors are investigated for both the single crystal (SC) and polycrystalline (PC) perovskites upon femtosecond laser ablation. In the case of SC sample, three different regions based on the laser ablation, recast deposition, and modification respectively exhibits distinguished carrier recombination mechanisms due to their variable defect chemistries and morphologies identified, which helps to realize the amplified spontaneous emission with the recrystallized micro/nanostructures. On the other hand, the laser modified region on the PC sample reveals the significant enhancement of random lasing performance (the lasing threshold was reduced by ∼7 times and the slope efficiency increased by ∼1.5 times), which is attributed to the femtosecond laser induced non-radiative defect passivation and the average crystalline grain size reduction by more than 1.5 times. This study unveils the physical and chemical modification effects of the femtosecond laser irradiation on perovskite materials, and thus is an optimal strategy to fabricate desired perovskite light-emitting microstructures by ultrafast laser processing.

Effect of femtosecond laser modification on magnetorheological finishing of magnesium aluminate spinel

Effect of femtosecond laser modification on magnetorheological finishing of magnesium aluminate spinel

Structural and Functional Picosecond Laser Modification of the Nimonic 263 Superalloy in Different Environmental Conditions and Optimization of the Irradiation Process.

In this experimental study, picosecond laser treatment was performed on a nickel-based superalloy Nimonic 263, aiming to investigate the surface effects induced by irradiation in different atmospheric conditions and, concerning changes in surface composition, regarding the possibility for improvement of its functionality. Besides the varying laser parameters, such as a number of pulses and pulse energy, environmental conditions are also varied. All surface modifications were carried out in standard laboratory conditions and a nitrogen- and argon-rich atmosphere. The resulting topography effects depend on the specific laser treatment and could be categorized as increased roughness, crater formation, and formation of the laser-induced periodic surface structures (LIPSS). Changes in the chemical surface composition are distinguished as the potential formation of the protective oxides/nitrides on the sample surface. Numerous characterization techniques analyse the resulting effects on the topography and surface parameters. The multi-response parametric optimization of the picosecond laser process was performed using an advanced statistical method based on Taguchi's robust parameter design. Finally, the optimal parameter conditions for Nimonic 263 modification are suggested.

Modification of Polyhydroxyalkanoates Polymer Films Surface of Various Compositions by Laser Processing.

The results of surface modification of solvent casting films made from polyhydroxyalkanoates (PHAs) of various compositions are presented: homopolymer poly-3-hydroxybutyrate P(3HB) and copolymers comprising various combinations of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 4-hydroxybutyrate(4HB), and 3-hydroxyhexanoate (3HHx) monomers treated with a CO2 laser in continuous and quasi-pulsed radiation modes. The effects of PHAs film surface modification, depending on the composition and ratio of monomers according to the results of the study of SEM and AFM, contact angles of wetting with water, adhesion and growth of fibroblasts have been revealed for the laser radiation regime used. Under continuous irradiation with vector lines, melted regions in the form of grooves are formed on the surface of the films, in which most of the samples have increased values of the contact angle and a decrease in roughness. The quasi-pulse mode by the raster method causes the formation of holes without pronounced melted zones, the total area of which is lower by 20% compared to the area of melted grooves. The number of viable fibroblasts NIH 3T3 on the films after the quasi-pulse mode is 1.5-2.0 times higher compared to the continuous mode, and depends to a greater extent on the laser treatment mode than on the PHAs' composition. The use of various modes of laser modification on the surface of PHAs with different compositions makes it possible to influence the morphology and properties of polymer films in a targeted manner. The results that have been obtained contribute to solving the critical issue of functional biodegradable polymeric materials.

Femtosecond laser surface modification of 4H-SiC improves machinability

The high brittleness and hardness are harmful to the machinability of silicon carbide (SiC). To improve machinability, femtosecond laser (fs laser) surface modification was conducted. The results of scratching test for modification surface showed the fluctuation of tangential force and coefficient of friction (COF) and the decrease of energy of acoustic emission peak. COF under various axial loads tends to be 0.2. The scratching profile has a conformal shape and deeper depth. Experiments elucidate that machinability is improved by fs laser surface modification due to surface decomposition and laser-induced periodic surface structures. Although fs laser processing was treated as cold processing to some extent, the heat-related phenomena were non-negligible in SiC processing. To reveal the dynamic multi-scale mechanism during fs laser modification, the multi-physics finite element model and the molecular dynamics simulations coupled with a two-temperature model were applied. Multi-scale simulation results revealed that the recoil flow has a high speed of >1.2 m/s and the peak temperature exceeds 8000 K, causing the spatter and heat affect zone. The high electronic temperature gradient is generated during irradiating, causing the subsurface void generation. Consequently, fs laser surface modification can improve machinability, but the heat effect and subsurface void should be cautioned.

Direct Laser Irradiation and Modification of 2D Te for Development of Volatile Memristor.

Laser irradiation, as a kind of post-fabrication method for two-dimensional (2D) materials, is a promising way to tune the properties of materials and the performance of corresponding nano-devices. As the memristor has been regarded as an excellent candidate for in-memory devices in next-generation computing system, the application of laser irradiation in developing excellent memristor based on 2D materials should be explored deeply. Here, tellurene (Te) flakes are exposed to a 532 nm laser in the air atmosphere to investigate the evolutions of the surface morphology and atom structures under different irradiation parameters. Laser is capable of thinning the flakes, inducing amorphous structures, oxides and defects, and forming nanostructures by controlling the irradiation power and time. Furthermore, the laser-induced oxides and defects promote the migration of metal ions in Te, resulting in the formation of the conductive filaments, which provides the switching behavers of volatile memristor, opening a route to the development of next-generation nano-devices.

Laser gas-powder surfacing with beam scanning

The proposals and possibilities of technological laser heads for additive technologies and surfacing are considered. The advantages of laser beam processing using a scanning system for gas-powder laser surfacing, its capabilities and modifications are shown. Experiments are carried out to study the effect of the scanning frequency of the laser beam and the scanning trajectory on the geometric characteristics of the deposited layers. The experiments are carried out using carbon dioxide and fiber laser. A multifunctional scanning unit which makes it possible to significantly increase the efficiency of the gas powder laser surfacing process and a powder dosing device designed specifically for additive laser technology are proposed. Their advantages and the possibility of using them as part of laser processing complexes are considered.