Femtosecond Laser Ablation Process Research Articles

Experimental and Simulation Research on Femtosecond Laser Induced Controllable Morphology of Monocrystalline SiC.

Silicon carbide (SiC) is utilized in the automotive, semiconductor, and aerospace industries because of its desirable characteristics. Nevertheless, the traditional machining method induces surface microcracks, low geometrical precision, and severe tool wear due to the intrinsic high brittleness and hardness of SiC. Femtosecond laser processing as a high-precision machining method offers a new approach to SiC processing. However, during the process of femtosecond laser ablation, temperature redistribution and changes in geometrical morphology features are caused by alterations in carrier density. Therefore, the current study presented a multi-physics model that took carrier density alterations into account to more accurately predict the geometrical morphology for femtosecond laser ablating SiC. The transient nonlinear evolutions of the optical and physical characteristics of SiC irradiated by femtosecond laser were analyzed and the influence of laser parameters on the ablation morphology was studied. The femtosecond laser ablation experiments were performed, and the ablated surfaces were subsequently analyzed. The experimental results demonstrate that the proposed model can effectively predict the geometrical morphology. The predicted error of the ablation diameter is within the range from 0.15% to 7.44%. The predicted error of the ablation depth is within the range from 1.72% to 6.94%. This work can offer a new way to control the desired geometrical morphology of SiC in the automotive, semiconductor, and aerospace industries.

A 3D tailored monolithic glass chip for stimulating and recording zebrafish neuronal activity with a commercial light sheet microscope

Microfluidic technology is unrivaled in its ability to apply soluble chemical stimuli with high spatiotemporal precision. Analogous, light–sheet microscopy is unmatched in its ability of low phototoxic but fast volumetric in vivo imaging with single cell resolution. Due to their optical translucency during the larval stages, zebrafish (Danio rerio) are an ideal model to combine both techniques; yet, thus far this required light–sheet microscopes, which were in most cases custom–built and adapted to the available softlithographic chip technology. Our aim was to use a commercial light–sheet microscope to illuminate a microfluidic chip from two opposite lateral directions and to record images with the detection objective placed orthogonally above the chip. Deep tissue penetration can be achieved by superimposing beams from opposite directions to form a single light sheet. But a microfluidic chip that allows a) targeted stimulus application in a closed microenvironment, b) interference–free incoupling of excitation light from two directions and c) outcoupling of fluorescence in the perpendicular direction through an optically perfect cover glass was not known until now. Here, we present a monolithic glass chip with the required plane-parallel sidewalls and cover slide closure at the top, constructed by advanced femtosecond laser ablation, thermal bonding and surface smoothing processes. In addition, the 3D shape of a fish fixator unit was tailored to match the body shape of a zebrafish larva to ensure stable positioning during whole–brain recording. With hydrodynamic focusing a targeted partial exposure of the larva’s head to chemical stimuli and fast position switching (in less than 10 s) was possible. With the capabilities of this unique monolithic glass chip and its up–scalable wafer–level fabrication process, the new NeuroExaminer is prone to become an excellent addition to neurobiology laboratories already equipped with high–quality commercial light sheet microscopes.

Evaluation of synthesized MWCNTs-COO@Fe3O4 nanocomposite based on laser-assisted method for highly-efficient clean water

In this study, the surface of MWCNTs was treated with acid by adding a carboxyl group to be ready to load nanostructured materials on their surface in a novel way. The femtosecond laser ablation process was used for decorating magnetic nanoparticles (Fe3O4) on the functionalized carbon nanotubes (MWCNTs-COOH) to form the MWCNTs-COO@Fe3O4 nanocomposite structure to be used for the heavy metal removal of Pb(II). Different techniques have all been used to identify the functionality groups that are present on the MWCNTs. Raman spectroscopy showed the decrease of G band when Fe3O4 nanoparticles embedded MWCNTs-COOH, indicating a greater degree of defect in MWCNTs. VSM showed the magnetic characteristic properties of the composite. XRD showed the reduction of MWCNTs diffraction peaks after embedding with iron oxide, explained the partial full coverage of the MWCNTs surface by the Fe3O4 nanoparticles. FT-IR showed the composite exhibit a peak at 579 cm−1, which is brought on by the Fe–O stretching vibrational modes. Zeta potential showed the surface of the MWCNTs-COO@Fe3O4 had a more positive charge under neutral pH compared with that of MWCNTs. TGA showed the weight loss of MWCNTs-COO@Fe3O4 was greater than that of MWCNTs, confirming the interaction of some Fe3O4 on MWCNTs-COOH. Also, tested pH, contact time, initial Pb (II) concentration, and adsorbent mass were carried to improve Pb (II) ion adsorption on the nanocomposite. The optimal removal effectiveness of Pb (II) on the MWCNTs-COO@Fe3O4 nanocomposite is attained when the experiment is conducted at a pH of 6, with a contact time of 10 min, an initial concentration of 100 mg/L, and under alkaline conditions. Pb (II) ions were adsorbing using a pseudo-second-order equation to reflect their chemical adsorption, with a rate constant of (k2 = 0.00446 g mg−1 min−1). The highest adsorption capacity obtained was 66.85 mg g−1. MWCNTs-COO@Fe3O4 nanocomposite efficiently collected Pb (II) utilizing green and easy to use method to protect public health.

Anisotropic Wettability Induced by Femtosecond Laser Ablation

Laser ablation has been utilized for locally and selectively modifying the surface wettability of materials in situ and enabling on‐demand microfabrication. The anisotropic wettability has been observed on chemical and/or topographical patterns, such as an array of laser‐inscribed strips with spacings, created on surfaces during the fabrication process. Herein, the effectiveness of the femtosecond laser ablation is evaluated in selectively modifying surface wettability. The areas processed by laser ablation exhibit anisotropic wetting behavior, even after the laser strips are overlapped. The laser‐induced anisotropic surface wettability is present in space governed by laser scanning speed, scan/strip overlap, laser fluence, scan repetition, and bidirectional scanning angle. Moreover, the femtosecond laser ablation process is optimized to enhance the conventional laser inscription, leading to a modified and consistent methodology to achieve cost‐effective fabrication.

Femtosecond Laser Ablation-Induced Magnetic Phase Transformations in FeRh Thin Films

In this study, we present a novel investigation into the magnetic and morphological properties of equiatomic B2-ordered FeRh thin films irradiated with single high-intensity ultrashort laser pulses. The goal is to elucidate the effect of femtosecond laser ablation on the magnetic properties of FeRh. We employed Scanning Magneto-Optical Kerr Effect (S-MOKE) microscopy to examine the magnetic phase after laser processing, providing high spatial resolution and sensitivity. Our results for the first time demonstrated the appearance of a magneto-optical signal from the bottom of ablation craters, suggesting a transition from antiferromagnetic to ferromagnetic behavior. Fluence-resolved measurements clearly demonstrate that the ablation threshold coincides with the threshold of the antiferromagnet-to-ferromagnet phase transition. The existence of such a magnetic phase transition was independently confirmed by temperature-dependent S-MOKE measurements using a CW laser as a localized heat source. Whereas the initial FeRh film displayed a reversible antiferromagnet-ferromagnet phase transition, the laser-ablated structures exhibited irreversible changes in their magnetic properties. This comprehensive analysis revealed the strong correlation between the femtosecond laser ablation process and the magnetic phase transformation in FeRh thin films.

One-step fabrication of robust liquid-repellent mesh induced by femtosecond laser

Super liquid-repellent surfaces are deemed as an ideal candidate for self-cleaning and liquid separation. However, these surfaces still confront challenges in the aspect of inadequate mechanical durability, environmentally harmful reagents and complex fabrication procedures. Herein, a one-step femtosecond laser ablation process on various porous mesh with PDMS-assisted coverage was conducted. Then, the uniform and hierarchical micro-groove structures were formed on the cylindrical wires during the successive laser pyrolysis, accompanying by the hydrophobic silica deposited inside the micro-groove structures. The whole processing has no chemical solvents and complicated modification, which is of great significance for time-saving and eco-friendly preparation of mesh with super-hydrophobicity. Significantly, the super-hydrophobic mesh can bear 2000 abrasion cycle tests, 400 ℃ heat treatment and violent outdoor robustness tests, verifying its strong mechanical durability and thermal stability. The mechanisms involved in liquid-repellence and abrasion-resistance have been elucidated systematically. Furthermore, self-cleaning and on-demand oil water separation could be accomplished via tailoring the wettability of the mesh according to the oxygen plasma treatment and re-heating. The unique advantages of the as-prepared porous mesh provide feasibilities for wettability-oriented application such as protective surface with self-cleaning ability, multitasking immiscible liquid separation.

Pulse-to-pulse detection of terahertz radiation emitted from the femtosecond laser ablation process.

Determining the dynamics of electrons and ions emitted from a target material during laser ablation is crucial for desirable control of laser processing. However, these dynamics are still challenging to understand because of a lack of ubiquitous spectroscopic tools to observe tangled-up dynamics appearing at ultrafast timescales. Here by harnessing highly sensitive single-shot terahertz time-domain spectroscopy using an echelon mirror, we investigate pulse-to-pulse temporal profile of terahertz radiation generated from the material surface. We clearly found that the carrier-envelope phase and the electric field amplitude of the terahertz waveform systematically vary between the pre- and post-ablation depending on the laser fluence and irradiated pulse numbers. Our results provide a stepping-stone towards perception of Coulomb explosion occurring throughout the laser ablation process, which is indispensable for future laser processing applications.

Exploring Femtosecond Laser Ablation by Snapshot Ultrafast Imaging and Molecular Dynamics Simulation

Femtosecond laser ablation (FLA) has been playing a prominent role in precision fabrication of material because of its circumvention of thermal effect and extremely high spatial resolution. Molecular dynamics modeling, as a powerful tool to study the mechanism of femtosecond laser ablation, still lacks the connection between its simulation results and experimental observations at present. Here we combine a single-shot chirped spectral mapping ultrafast photography (CSMUP) technique in experiment and a three-dimensional two-temperature model-based molecular dynamics (3D TTM-MD) method in theory to jointly investigate the FLA process of bulky gold. Our experimental and simulated results show quite high consistency in time-resolved morphologic dynamics. According to the highly accurate simulations, the FLA process of gold at the high laser fluence is dominated by the phase explosion, which shows drastic vaporized cluster eruption and pressure dynamics, while the FLA process at the low laser fluence mainly results from the photomechanical spallation, which shows moderate temperature and pressure dynamics. This study reveals the ultrafast dynamics of gold with different ablation schemes, which has a guiding significance for the applications of FLA on various kinds of materials.

Nanoscale-Precision Removal of Copper in Integrated Circuits Based on a Hybrid Process of Plasma Oxidation and Femtosecond Laser Ablation.

Copper (Cu) is the main interconnect conductor for integrated circuits (IC), and its processing quality is very important to device performance. Herein, a hybrid process of plasma oxidation and femtosecond laser (fs-laser) ablation was proposed for the nanoscale precision removal of Cu in integrated circuits. In this hybrid process, the surface layer of Cu was oxidized to the copper oxide by plasma oxidation, and then the fs-laser with a laser fluence lower than the Cu ablation threshold was used to remove the copper oxide without damaging the underlying Cu. Theoretically, the surface temperature evolutions of Cu and copper oxide under the femtosecond laser were studied by the two-temperature model, and it was revealed that the ablation threshold of copper oxide is much lower than that of Cu. The experimental results showed that the ablation threshold of copper oxide is lower than that of Cu, which is consistent with the theoretical analysis. Using the hybrid process, a surface roughness of 3 nm and a removal accuracy of 4 nm were obtained in the process of Cu film processing, which were better than those obtained by fs-laser ablation. This demonstrated that the hybrid process has good application potential in the field of copper micromachining.

Formation of waveguides in crystalline organic N-benzyl-2-methyl-4-nitroaniline thin films using femtosecond laser ablation process

This paper reports the feasibility of femtosecond laser etching of microstructures directly onto crystalline N-benzyl-2-methyl-4-nitroaniline (BNA) films grown on glass to realize single crystal BNA waveguides. The threshold fluence has been estimated and fluence range of 318.5–1274 mJ/cm2 at 800 nm is used for ablation. Holes with diameter ranging from 13 to 26 μm and waveguide patterns with width of 100 μm are demonstrated. Grooves with laser transit gap <20 μm is used to form smaller waveguides. Input faces of the waveguides have been simultaneously irradiated with red laser of 630 nm. The optical image of transmission confirms the wave-guiding. This study shows the feasibility of laser-etching waveguides on crystalline BNA films.

Enhancement of electrical conductivity during the femtosecond laser trimming process for OLED repair

In OLED panel repair process, femtosecond laser ablation has been adopted for last 10 years. Because femtosecond laser process can be performed with negligible thermal effect, it is suitable for modifying the organic materials whose lifetime is negatively affected by heat. Because of it, femtosecond laser ablation process has been applied to repair process of OLED panel such as elimination of internal debris, disconnection of over connected electrodes, and etc. However, it has been limitedly applied to certain types of defects. In order to increase a production yield, various types of defects should be treated. Thus, additive repair process needs to be developed. In last few decades, various research groups have been developing electrode printing techniques. But it is very hard to print an electrode with width of 1 µm scale so far. Therefore, we suggest new repair technique that combines additive and subtractive methods. It is the technique that conductive material is printed with width of few micrometers scale followed by femtosecond laser trimming with width of 1 µm scale. During an electrode printing followed by femtosecond laser trimming (EPFLT) process, we could enhance electrical conductivity of printed electrode. After EPFLT process, the average electrical conductivity of electrodes increases from 1.51ⅹ107 S/m to 2.31ⅹ107 S/m. Here, we carefully claim that the heat accumulation during a femtosecond laser trimming causes an annealing of printed electrode and the electrical conductivity is enhanced.

Femtosecond Pulse Ablation Assisted Mg-ZnO Nanoparticles for UV-Only Emission.

The need for improved UV emitting luminescent materials underscored by applications in optical communications, sterilization and medical technologies is often addressed by wide bandgap semiconducting oxides. Among these, the Mg-doped ZnO system is of particular interest as it offers the opportunity to tune the UV emission by engineering its bandgap via doping control. However, both the doped system and its pristine congener, ZnO, suffer from being highly prone to parasitic defect level emissions, compromising their efficiency as light emitters in the ultraviolet region. Here, employing the process of femtosecond pulsed laser ablation in a liquid (fs-PLAL), we demonstrate the systematic control of enhanced UV-only emission in Mg-doped ZnO nanoparticles using both photoluminescence and cathodoluminescence spectroscopies. The ratio of luminescence intensities corresponding to near band edge emission to defect level emission was found to be six-times higher in Mg-doped ZnO nanoparticles as compared to pristine ZnO. Insights from UV-visible absorption and Raman analysis also reaffirm this defect suppression. This work provides a simple and effective single-step methodology to achieve UV-emission and mitigation of defect emissions in the Mg-doped ZnO system. This is a significant step forward in its deployment for UV emitting optoelectronic devices.

B/N co-doped graphene oxide gel with extremely-high mobility and ION/IOFF for large-area field effect transistors

Thin films of large-area graphene and graphene-based materials are highly desired for electrical applications. However, the current state-of-art synthesis methods produce large-area graphene films with multiple grain boundaries (GBs) that highly hinder their charge carrier mobilities and Ion/Ioff ratios. Here, we demonstrate a femtosecond laser ablation process to produce B and N co-doped graphene oxide (GO) gels with controllable total doping percentage (between 0.8 at%-2.3 at%) and effectively reduced GBs concentration. The charge carrier mobilities and Ion/Ioff ratios of the produced large-area gel (∼100 × 2400 μm2) field effect transistors (FETs) revealed extremely-high values of up to 9000 ± 3000 cm2/V and 9.7E+5, respectively, comparable to the state-of-art values of a single monolayer graphene nanoflake. The increased total doping percentage also proved to improve the chemical reactivity of the gels. This femtosecond laser ablation approach could prove effective for large-area FETs with controllable mobility, Ion/Ioff ratio, and chemical reactivity.

A model of femtosecond laser ablation of metal based on dual-phase-lag model

Femtosecond laser ablation possesses a variety of applications due to its better control, high power density, smaller heat-affected zone, minimal collateral material damage, lower ablation thresholds, and excellent mechanical properties. The non-Fourier effect in heat conduction becomes significant when the heating time becomes extremely small. In order to analyze the femtosecond laser ablation process, a hyperbolic heat conduction model is established based on the dual-phase-lag model. Taken into account in the model are the effect of heat source, laser heating of the target, the evaporation and phase explosion of the target material, the formation and expansion of the plasma plume, and interaction of the plasma plume with the incoming laser. Temperature-dependent optical and thermophysical properties are also considered in the model due to the fact that the properties of the target will change over a wide range in the femtosecond laser ablation process. The effects of the plasma shielding, the ratio of the two delay times, and laser fluence are discussed and the effectiveness of the model is verified by comparing the simulation results with the experimental results. The results show that the plasma shielding has a great influence on the femtosecond laser ablation process, especially when the laser fluence is high. The ratio between the two delay times (the ratio &lt;i&gt;B&lt;/i&gt;) has a great influence on the temperature characteristic and ablation characteristic in the femtosecond laser ablation process. The augment of the ratio &lt;i&gt;B&lt;/i&gt; will increase the degree of thermal diffusion, which will lower down the surface temperature and accelerate the ablation rate after the ablation has begun. The ablation mechanism of femtosecond laser ablation is dominated by phase explosion. The heat affected zone of femtosecond laser ablation is small, and the heat affected zone is less affected by laser fluence. The comparison between the simulation results and the experimental results in the literature shows that the model based on the dual-phase-lag model can effectively simulate the femtosecond laser ablation process.

A Rapid Fabrication of Novel Dual Band Terahertz Metamaterial by Femtosecond Laser Ablation

In this paper, we present a novel dual-band, polarization insensitive terahertz metamaterial design, numerical simulation, and its fabrication using femtosecond laser ablation process. The proposed design uses periodic patterned copper metallic structure on the polyimide thin film and provides dual resonant characteristics at 0.25 THz and 0.42 THz, respectively. The structure was simulated numerically using CST Microwave studio software and obtained the bandstop characteristics of – 22 dB at both the resonances. The obtained 10-dB bandwidth in numerical simulation at the first and second resonance was 11.7 GHz and 14 GHz, respectively. The normalized transmission, electric field, and the surface current distributions were analyzed for understanding the mechanism of dual-band resonance. In addition, the effect of geometrical parameters on the resonances has been discussed. The simulated structure was fabricated using 800 nm wavelength 100 fs Ti: Sapphire laser and the laser parameters were optimized for the ablation process. The characterization of the fabricated structure has been done using terahertz time-domain spectroscopy (THz-TDS) technique. The measurement results show that the fabricated structure has obtained polarization insensitive and angular stable transmission response.

Cutting thin glass by femtosecond laser ablation

The femtosecond laser ablation process for cutting thin aluminoborosilicate glass sheets of thickness 100 μm was investigated with emphasis on effective cutting speed (Veff) and mechanical strength of diced samples. The process parameters including the laser fluence (F), overlap ratio (r) of the laser beam and polarization direction were varied at a fixed pulse repetition rate f = 1 kHz to find the optimal process condition that maximizes Veff and edge strength. A three-point bending test was performed to evaluate the front-side and back-side bending (edge) strength of the laser-cut samples. Veff was proportional to F unless r exceeded a critical value, at which excessive energy began to be delivered at the same spot. The front-side edge strength was bigger than the back-side strength because of the back-side damages such as chipping. Good edge strength, as high as ∼280 MPa (front-side) and ∼230 MPa (back-side), was obtained at F = 19 J/m2, r = 0.99, with laser polarization vertical to the cutting path.

Formation of x-ray Newton’s rings from nano-scale spallation shells of metals in laser ablation

The initial stages of the femtosecond (fs) laser ablation process of gold, platinum, and tungsten were observed by single-shot soft x-ray imaging technique. The formation and evolution of soft x-ray Newton’s rings (NRs) were found for the first time. The soft x-ray NRs are caused by the interference between the bulk ablated surface and nanometer-scale thin spallation layer; they originate from the metal surface at pump energy fluence of around 1 J/cm2 and work as a flying soft x-ray beam splitter.

The High-Speed Photography Research of Femtosecond Laser Ablation Process

Using the research of high-speed photography method to carry out the dynamic characteristics of the femtosecond laser ablation process, at the same time, explore a kind of high spatial resolution, response rate and the sensitivity of the new technology means and methods, the thorough analysis and research for dynamics of femtosecond laser ablation of crystal material characteristic has been carried on, we have gotten the characteristics of crystal material.

펨토초 레이저 절삭 공정을 이용한 생분해성 나노섬유 표면 미세 패터닝 공정

펨토초 레이저 절삭 공정을 이용한 생분해성 나노섬유 표면 미세 패터닝 공정

Structural properties of silicon nanoparticles obtained via femtosecond laser ablation in gases at different pressures

In this paper, we report on the effect of buffer gas on silicon nanoparticle formation in femtosecond laser ablation process. For the first time the nonmonotonic dependence of the silicon nanoparticle sizes on the gas pressure is obtained. Distributions of the particles on the size received by means of atomic-force microscopy indicate reducing the Si nanoparticle diameter with pressure increase from 50 to 700 mbar for helium and nitrogen atmospheres, with the minimal nanoparticle size up to 5 nm reaching in helium. At further increase in pressure there is a growth of the nanoparticles size and distribution becomes wider. Using argon as a buffer gas results in larger nanoparticle sizes than in helium and more complicated dependence of the size distribution on the argon pressure. The electron diffraction and Raman scattering in the formed silicon nanoparticles evidence their crystallinity.