Laser-induced Oxidation Research Articles

Investigations on color quality improvement through laser-induced surface oxidation for coloration

This study focuses on laser-induced oxidation of TC4 alloy surfaces and achieves precise color control on TC4 surfaces at room temperature using laser post-processing. The current research lacks an in-depth understanding of the mechanism responsible for color changes due to the number of processing cycles. This study aims to improve the quality of coloration through secondary processing and establish a color control mechanism based on accumulated energy density. Statistical analyses revealed notable reductions in ΔE, ΔC∗, and Δh∗, indicating enhanced color uniformity. Surface morphology and reflectance data further confirmed these findings, demonstrating the effectiveness of secondary processing in achieving consistent and uniform coloration.

Mechanisms of gelation induced by laser irradiation for CaO powder dispersed in ethanol – Formation of calcium acetate and its role in gelation

Our recent study of gelation induced by laser ablation of CaO powders dispersed in ethanol proposed that CaO particle size composition would be an important factor affecting gelation because gelation is brought about by mixing a colloid composed of laser-fragmented particles and a raw CaO colloid. The present work was conducted to clarify this point. Results showed that, differing from our assumption, laser-fragmented particles are not necessary for gelation because gelation occurred even when laser-fragmented particles were removed from a laser-irradiated colloid before mixing it with a raw CaO colloid. Moreover, findings revealed that acetic acid generated by laser-induced oxidation of ethanol causes gelation, as confirmed by the fact that gelation also occurred when a proper amount of acetic acid was added to a raw CaO colloid. Results also revealed that nanofibers composed of calcium acetate hydrate play an important role in the gel structure formation. Results demonstrated that the gel structure and composition can be controlled simply by adjusting the amount of acetic acid without laser irradiation, suggesting that the results obtained from this study are useful as a newly developed and simple method of preparing calcium gel with various structures.

Improved lifetime of a pulsed electric field (PEF) system-using laser induced surface oxidation

In this research, we explore the possibility and effectiveness of using laser-induced surface oxidation methods to enhance the durability and effectiveness of PEF (Pulsed Electric Field) systems. Despite advantages over thermal pasteurisation, PEF faces challenges like electrode corrosion and biofouling, hindering its adoption. This research introduces laser-induced oxidation to mitigate metal ion release during PEF, directly targeting electrode alteration. Our examination adopts a comprehensive method, integrating Design of Experiments (DoE) parameter sets for PEF trials, morphological analysis, evaluation of metal ion release via Inductively Coupled Plasma Quadrupole Mass Spectrometry (ICP-QMS), waveform capture utilizing a Data Acquisition (DAQ) system, electrochemical assessment via impedance spectroscopy, and examination of oxide layer composition employing X-ray photoelectron spectroscopy. Pulse waveform characteristics shows the intricate relationship between PEF processing parameters with metal ion release, alongside XPS analysis providing insights into surface chemistry. Optimized results show a three-fold reduction in metal ion release post-PEF, with laser-treated samples outperforming untreated stainless steel due to selective surface chemistry alteration, notably an increased Cr/Fe ratio, reducing harmful elements. This study highlights laser-induced oxidation as a practical solution for enhancing PEF electrode performance and reducing metal ion release, addressing key challenges in PEF technology. It advances sustainable food processing, promising extended PEF system lifespan while maintaining efficiency and product quality.

Femtosecond pulse train-facilitated periodic nanostructuring on TiN films via laser-oxidation

Laser-induced periodic surface structure is a universal phenomenon observed when solid materials are irradiated with pulsed lasers. Typically, these structures are generated using Gaussian pulses. Here, we investigate the formation of periodic nanostructures on titanium nitride thin films using two different laser sources: Gaussian pulses and femtosecond pulse trains generated through a Fabry-Perot cavity. Our findings indicate that the formation of self-organized nanostructures on the thin films can occur through either laser-induced oxidation or laser ablation processes, depending on laser fluence, scanning speed, and pulse duration. Interestingly, when utilizing femtosecond pulse trains, we observe that the range of laser fluence thresholds for oxidative nanostructure formation is significantly wider compared to Gaussian pulses. To comprehend the underlying mechanisms driving these observations, we employ a two-temperature model to calculate the ultrafast dynamics of hot electrons when exposed to laser irradiation. Our results reveal that the initial sub-pulse generates a substantial population of hot electrons, exciting surface plasmons and resulting in the creation of a periodic energy distribution. Before these hot electrons can dissipate, subsequent sub-pulses reach the thin film, re-exciting a large number of hot electrons. Consequently, the periodic energy distribution persists for an extended duration, creating more favorable conditions for the formation of periodic oxidative nanostructures when using pulse trains. These findings contribute to a comprehensive understanding of the mechanisms involved in the formation of periodic nanostructures under femtosecond laser irradiation.

Repetitive Nanosecond Laser-Induced Oxidation and Phase Transformation in NiTi Alloy

NiTi shape memory alloys, known as Nitinol, are highly valuable in medical fields for their unique attributes, including superelasticity, wear resistance, and biocompatibility. Laser treatment provides precise control over surface characteristics, enhancing biocompatibility. This study focuses on the effects of laser irradiation on NiTi alloy surfaces, particularly considering the number of laser scans and their impact on surface features. Even at low laser power, multiple high-frequency scans significantly alter surface roughness and induce phase transformation. After 16 repeated laser irradiations, amorphous Ti oxide transforms into crystalline anatase. Remarkably, anatase can further transform into rutile due to the influence of Ni nearby and TiO, due to insufficient oxygen content. The most notable outcome is the formation of a thick Ti oxide layer, causing unbound Ni to emerge on the surface, resulting in a Ni oxide layer. These findings highlight the importance of precisely adjusting laser parameters to achieve tailored surface properties for medical applications, addressing challenges and enhancing biocompatibility.Graphical abstract

Morphological evolution and biocorrosion response of a hierarchical micro- nano-structured Ti alloy: Physico-chemical characterization and electrochemical studies

In the present study, hierarchically architectured micro/nano-scale surface topography inspired from the leaves of Euphorbia myrsinites was fabricated on Ti-6Al-4V ELI alloy through laser micro-texturing (LT) followed by alkaline hydrothermal treatment (HT). The hybrid (LT + HT) surface revealed distinct multi-scaled morphological features differing from individually treated LT and HT surfaces. Alongside topographical cues, the evolved elemental and phase constitution also influenced the wettability, mechanical and corrosion properties. The (LT + HT) surface exhibited improved hydrophilicity and reduced surface stiffness of ~14.82 GPa (closely mimicking human bone-tissue), attributing to a hydrothermally-induced porous titania-layer extending up to a few microns depth. Corrosion tests in Hank's solution revealed that HT alone couldn't substantially improve the corrosion resistance as compared to polished surface (control). Integrating LT with HT not only altered the surface topography, but also introduced a relatively denser barrier-oxide layer (laser-induced oxidation) that transformed into a stable anatase-rich phase structure upon hydrothermal etching and subsequent annealing. Both LT and (LT + HT) recorded reduced corrosion current densities and suppressed corrosion rates, but (LT + HT) performed substantially better in the anodic polarization regime (till 2 V), with passivation current densities reduced by at least two orders of magnitude. AC impedance studies affirmed the role of an adsorptive nanostructured outer-layer in (LT + HT) towards accelerating the passivation kinetics, while the inner barrier layer imposed higher charge transfer resistance. Also, better biomineralization ability was observed in (LT + HT) after 30 days immersion in Hank's solution, with Ca: P (at. ratio) ~1.4, thereby indicating higher propensity of apatite nucleation.

Femtosecond Laser-Induced Emission of Coherent Terahertz Pulses from Ruthenium Thin Films.

We demonstrate emission of electromagnetic pulses with frequencies in the terahertz (THz) range from ruthenium thin films through a second-order nonlinear optical process. Ruthenium deposited on different substrates showed different THz emission properties. We provide evidence that for Ru on glass above a certain power threshold, laser-induced oxidation occurs, resulting in an increased slope of the linear dependence of the THz electric field amplitude on pump power. The THz electric field is mainly polarized parallel to the sample surface, pointing in the same direction everywhere. In contrast to Ru on glass, the electric field amplitude of the THz pulses emitted by Ru on sapphire and on CaF2 shows a simple single linear dependence on pump power, and it is polarized orthogonal to the sample surface. In this case, thermal oxidation in an oven enhances the emission and introduces an additional polarization component along the sample surface. This component also points in the same direction everywhere on the surface, similar to the as-deposited Ru on glass. Although the precise THz generation mechanism remains an open question, our results show a strong correlation between the emission strength and the degree of oxidation. Furthermore, the results highlight the importance of the interfaces, i.e., both the choice of the substrate and the chemical composition of the top surface in THz emission experiments. Knowledge of the state of the sample surface is therefore crucial for the interpretation of THz emission experiments from (nonmagnetic) metal surfaces.

Study on the effect of laser-induced oxidation on color change and hydrophilicity of 2D codes

The effect of laser-induced oxidation on color change and surface wettability of anti-oil and super-hydrophobic two-dimensional code (2D Code) is demonstrated, where the color change and wettability are very important to the reading quality and durability of 2D Code. The poor oleophobicity and hydrophobicity, which render laser direct part marking of 2D Code inadequate for application in oil pollution, corrosion environment, are greatly improved with combination method of accurate laser-induced oxidation and surface modification. To obtain the control mechanism for the color change and wettability of 2D Code, the influence of laser processing parameters on the oxidation and microstructure change of the modules laser-marked on titanium alloy were studied, and then the influence of oxidation, microstructure and surface modification processing parameters on the hydrophilicity of 2D Code were analyzed. From the experimental results, with the laser energy density increasing, the oxidation degree increases and the modules show platinum grey, violet blue, graphite black, light ivory, jet black and other color states, with its hydrophilicity of the modules laser processed becoming stronger first and weaker later. The modules also present various microstructures with different laser processing parameters, such as pits, cracks, wormlike protrusions, which also have an important effect on the color change and wettability of modules. By laser parameters optimizing, it is found that when laser power is 10 W, Q frequency 45 KHZ, scanning speed 200 mm/s and hatching spacing 0.03 mm, the 2D code with high contrast and hydrophilic oleophylic property was obtained, where the static water contact angle could be a minimum to about 6.0° and the static oil contact angle could be a minimum to 8.1°. After the surface modification processing, where a coating consisting of heptadecafluorotrichlorosilane and n-heptanea with specific ratio is sprayed by special process on the surface, the 2D code show anti-oil and super-hydrophobic property, within the static water contact angle being a maximum to about 178.7° and the static oil contact angle being a maximum to 132.8°. In addition, it is found that the stronger hydrophilicity of modules laser processed before coating spraying, the stronger hydrophobicity of 2D code after coating spraying shall show.

Impact of film thickness in laser-induced periodic structures on amorphous Si films

We report self-organized periodic nanostructures on amorphous silicon thin films by femtosecond laser-induced oxidation. The dependence of structural periodicity on the thickness of silicon films and the substrate materials is investigated. The results reveal that when silicon film is 200 nm, the period of self-organized nanostructures is close to the laser wavelength and is insensitive to the substrates. In contrast, when the silicon film is 50 nm, the period of nanostructures is much shorter than the laser wavelength, and is dependent on the substrates. Furthermore, we demonstrate that, for the thick silicon films, quasi-cylindrical waves dominate the formation of periodic nanostructures, while for the thin silicon films, the formation originates from slab waveguide modes. Finite-difference time-domain method-based numerical simulations support the experimental discoveries.Graphical abstract

Oxidation mechanism of high-volume fraction SiCp/Al composite under laser irradiation and subsequent machining

Conventional mechanical machining of a composite material comprising an aluminum matrix reinforced with a high volume fraction of SiC particles (hereinafter referred to as an SiCp/Al composite) faces problems such as rapid tool wear, high specific cutting force, and poor surface integrity. Instead, a promising method for solving these problems is laser-induced oxidation-assisted milling (LOAM): under laser irradiation, the local workpiece material reacts with oxygen, thus forming loose and porous oxides that are easily removed. In the present work, the oxidation mechanism of SiCp/Al irradiated by a nanosecond pulsed laser is studied to better understand the laser-induced oxidation behavior and control the characteristics of the oxides, with laser irradiation experiments performed on a 65% SiCp/Al composite with various laser parameters and auxiliary gases (oxygen, nitrogen, and argon). With increasing laser pulse energy density, both the ablated groove depth and the width of the heat-affected zone increase. When oxygen is used as the auxiliary gas, an oxide layer composed of SiO2 and Al2O3 forms, and CO2 is produced and escapes from the material, thereby forming pores in the oxides. However, when nitrogen or argon is used as the auxiliary gas, a recast layer is produced that is relatively difficult to remove. Under laser irradiation, the sputtered material reacts with oxygen to form oxides on both sides of the ablated groove, and as the laser scanning path advances, the produced oxides accumulate to form an oxide layer. LOAM and conventional milling are compared using the same milling parameters, and LOAM is found to be better for reduced milling force and tool wear and improved machined surface quality.

Effect of laser-induced texture on lubrication retention and tribological properties of 40Cr alloy surfaces

Continuous and proper oil lubrication between the friction pair can reduce wear and increase the service life of mechanical components. The synergistic effects of oil wettability and spreadability on lubrication durability and tribological properties were investigated. The results indicate that the capillary action of textured structures can promote the oil spreadability and reduce the relaxation time of the contact angle, and the final contact angle will be affected by the laser-induced oxidation and hydroxylation. However, the excessive absorption behavior of textures limits the oil wettability and spreadability. In addition, capillary action and hydroxylation formed a textured surface with excellent oil spreadability and a relatively high contact angle. This is a critical factor in maintaining surface lubrication and improving tribological properties.

Study on surface thermal oxidation of silicon carbide irradiated by pulsed laser using reactive molecular dynamics.

Pulsed lasers are a powerful tool for fabricating silicon carbide (SiC) that has a hard and brittle nature, but oxidation is usually unavoidable. This study presents an exploration of the oxidation mechanism of 4H-SiC in oxygen and water under different temperatures via reactive force field molecular dynamics. Single pulse irradiation experiments were conducted to study the oxygen content of the laser-affected zone through energy dispersive x-ray spectrometry. The results show that laser-induced thermal oxidation is a complex dynamic process with the interactions among H, C, O, and Si atoms. The oxidation zone includes an oxide layer, a graphite layer, and a C-rich layer. With an increase in oxygen concentration, the amorphous oxide layer changes from silicon oxide to silicon dioxide. In addition, the formation of carbon clusters at the interface between SiOx and C-rich layers promotes the desorption of the oxide layer. The mechanism revealed in this study provides theoretical guidance for high-quality processing of 4H-SiC at atomic and close-to-atomic scales.

Static Hydrophobic Cuprous Oxide Surface Fabricated via One-Step Laser-Induced Oxidation of a Copper Substrate.

In this study, we developed a one-step method for fabricating hydrophobic surfaces on copper (Cu) substrates. Cuprous oxide (Cu2O) with low free energy was successfully formed after low-fluence laser direct irradiation. The formation of Cu2O enhanced the hydrophobicity of the Cu substrate surface, and the contact angle linearly increased with the proportion of Cu2O. The Cu2O fabricated by low-fluence laser treatment showed the same crystal plane orientation as the pristine Cu substrate, implying an epitaxial growth of Cu2O on a Cu substrate.

Enhancing the machinability of Cf/SiC composite with the assistance of laser-induced oxidation during milling

Carbon fiber-reinforced silicon carbide matrix (Cf/SiC) composites have been widely used in aerospace for its superior properties. However, due to high hardness, heterogeneity, and anisotropy, many problems such as machining damage, low process efficiency, and rapid tool wear are encountered in machining Cf/SiC composite. In this study, laser-induced oxidation-assisted milling (LOAM), as novel hybrid machining process, was proposed to enhance machinability of Cf/SiC composites. Pulsed laser was used to induce reaction between Cf/SiC composites and oxygen. Easily removable loose and porous oxides were produced, which were simultaneously removed with milling tool, leading to improved material removal rate and tool life. Oxidation mechanisms and influences of laser parameters on oxidation behavior of Cf/SiC composite were studied. Conventional milling (CONV) without the assistance of laser was also performed on Cf/SiC composite for comparative analysis. Milling force, tool wear, and surface quality were studied in detail. Under laser irradiation, Cf/SiC composite was modified into metamorphic-layer that consisted of oxide layer and transition layer. Material irradiated with laser got melted, vaporized, and then reacted with oxygen, producing oxide. Oxide layer was formed due to the accumulation of oxide. Increasing laser energy density boosted oxidation reaction and increased the thickness of oxide layer. In contrast, increase in laser scanning speed decreased thickness of oxide layer. Results show that cutting force was extremely low and no tool wear occurred during milling oxide layer, indicating significant enhancement in machinability. Abrasive wear mainly occurred on flank face when milling transition layer. Surface damages, for instance fiber fracture and matrix fragmentation, were significantly contained by LOAM. Surface roughness Sa obtained via LOAM was 9.5 μm, which was lower than that obtained by CONV (35 μm). This study indicates that LOAM can achieve high-efficiency processing, low-defect surface, and prolonged tool life when machining Cf/SiC composite.

On the oxidation of VS2 2D platelets using tip-enhanced Raman spectroscopy

2D materials are enabling disruptive advancements in electronic and photonic devices yielding to the development of sensing and wearable materials and in the field of energy production and storage as key components of photovoltaic technology and batteries. Nevertheless, little attention has been paid to TMDs and oxides that contain vanadium, as it is the case of vanadium disulfide (VS2) and vanadium dioxide (VO2). In this study we review the synthesis and characterization using Raman spectroscopy of VS2 and its oxidized states. Laser-induced oxidation occurring during the Raman experiments in ambient conditions is described and plateau values of laser power levels to induce oxidation are provided. Furthermore, tip-enhanced Raman spectroscopy (TERS) spectra and maps are conducted to reveal at the single flake level the onset of oxidation mechanisms at the surface of the 2D platelets.

Heating influence on hierarchical structures fabricated by direct laser interference patterning

The combination of direct laser interference patterning (DLIP) with laser-induced periodic surface structures (LIPSS) enables the fabrication of functional surfaces reported for a wide spectrum of materials. The process throughput is usually increased by applying higher average laser powers. However, this causes heat accumulation impacting the roughness and shape of produced surface patterns. Consequently, the effect of substrate temperature on the topography of fabricated features requires detailed investigations. In this study, steel surfaces were structured with line-like patterns by ps-DLIP at 532 nm. To investigate the influence of substrate temperature on the resulting topography, a heating plate was used to adjust the temperature. Heating to 250 ^{circ }C led to a significant reduction of the produced structure depths, from 2.33 to 1.06 µm. The reduction is associated with the appearance of a different LIPSS type, depending on the grain orientation of the substrates and laser-induced superficial oxidation. This study revealed a strong effect of substrate temperature, which is also to be expected when heat accumulation effects arise from processing surfaces at high average laser power.

Channel Scaling Dependent Photoresponse of Copper-Based Flexible Photodetectors Fabricated Using Laser-Induced Oxidation.

Copper (Cu) oxide compounds (CuxO), which include cupric (CuO) and cuprous (Cu2O) oxide, have been recognized as a promising p-channel material with useful photovoltaic properties and superior thermal conductivity. Typically, deposition methods or thermal oxidation can be used to obtain CuxO. However, these processes are difficult to apply to flexible substrates because plastics have a comparatively low glass transition temperature. Also, additional patterning steps are needed to fabricate applications. In this work, we fabricated a metal-semiconductor-metal photodetector using laser-induced oxidation of thin Cu films under ambient conditions. Raman spectroscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and atomic force microscopy were used to study the composition and morphology of our devices. Moreover, the photoresponse of this device is reported herein. We performed an in-depth analysis of the relationship between the channel size and number of carriers using scanning photocurrent microscopy. The carrier transport behaviors were identified; the photocurrent decreased as the length and width of the channel increased. Furthermore, we verified the suitability of the device as a flexible photodetector using a variety of bending tests. Our in-depth analysis of this Cu-based flexible photodetector could play an important role in understanding the mechanisms of other flexible photovoltaic applications.

Nanosecond laser-induced controllable oxidation of TiB2–TiC ceramic composites for subsequent micro milling

Laser-induced controllable oxidation coupled with micro-milling (LOMM) provides a feasible way to machine difficult-to-machine materials such as TiB 2 –TiC ceramic composites. The oxidation mechanism of the material under laser irradiation represents the fundamental issue of LOMM. In this paper, laser-induced controllable oxidation of spark plasma sintered TiB 2 –TiC ceramic composites as the workpiece material was studied. A three-dimensional finite element model was established based on ABAQUS/CAE 6.14 software to simulate the effect of laser parameters on temperature field distribution and was verified by experiments. The influence of laser processing parameters and assisted gas atmospheres on the oxidation behavior of TiB 2 –TiC ceramic composites was investigated. Results revealed that the irradiated temperature which had a significant impact on oxidation behavior, increased with an increment of the laser fluence and decreased with an increment of scanning speed with other laser parameters fixed. In addition, based on experimental analysis, the thickness of the oxide-layer increased with an increase of laser fluence and reduced with increasing laser scanning speed. At a laser fluence of 10.78J/cm 2 and scanning speed of 1 mm/s as well as in an oxygen-rich atmosphere, a loose and porous oxide-layer was produced on the irradiated surface. Cross-section thicknesses of the oxide-layer and sub-layer reached 63 μm and 22 μm, respectively. Moreover, the thickness of the oxide-layer was 22 μm in air surroundings and hardly be found in argon and nitrogen atmospheres under identical laser parameters, which indicated that oxygen content had a significant influence on the oxidation reaction of the material. The products of the oxide-layer were mainly composed of rutile- and anatase-TiO 2 . Furthermore, the hardness of the sub-layer was 9.6 ± 0.7 GPa at a laser fluence of 10.78J/cm 2 and scanning speed of 1 mm/s, which was far lower than that of the substrate with a hardness of 20 ± 0.7 GPa. This study provides a theoretical basis for subsequent micro-milling.

Spatial Period of Laser-Induced Surface Nanoripples on PET Determines Escherichia coli Repellence.

Bacterial adhesion and biofilm formation on surfaces are associated with persistent microbial contamination, biofouling, and the emergence of resistance, thus, calling for new strategies to impede bacterial surface colonization. Using ns-UV laser treatment (wavelength 248 nm and a pulse duration of 20 ns), laser-induced periodic surface structures (LIPSS) featuring different sub-micrometric periods ranging from ~210 to ~610 nm were processed on commercial poly(ethylene terephthalate) (PET) foils. Bacterial adhesion tests revealed that these nanorippled surfaces exhibit a repellence for E. coli that decisively depends on the spatial periods of the LIPSS with the strongest reduction (~91%) in cell adhesion observed for LIPSS periods of 214 nm. Although chemical and structural analyses indicated a moderate laser-induced surface oxidation, a significant influence on the bacterial adhesion was ruled out. Scanning electron microscopy and additional biofilm studies using a pili-deficient E. coli TG1 strain revealed the role of extracellular appendages in the bacterial repellence observed here.

High capacity color code prepared on titanium alloy using femtosecond laser

This study reported on the high capacity color code obtained by femtosecond laser-induced surface oxidation on titanium alloy. The color code with quaternary numbers was designed. Various colors were obtained by changing the pulse energy and scanning speed. Moreover, the XPS survey spectra showed the surface chemical composition of different colored areas was TiO2. Experimental reflectance data and simulations showed that the increase of oxide layer thickness led to peak shift and color change. Taking into account the effect of color code unit size on coloring, the processing areas with an area of 1 × 1 mm2 and 6 × 6 mm2 were prepared. Since the color difference showed that the colors obtained under different unit sizes were different, the effect of size should be considered in the actual processing. By changing the scanning speed, different color areas with obvious contrast could be obtained to meet the conditions of color code realization. Therefore, this research further realized the encryption of information on the basis of increasing the information capacity of the marking.