Picosecond Pulsed Laser Ablation Research Articles

Breaking the vitrification limitation of monatomic metals.

The question of whether all materials can solidify into the glassy form proposed by Turnbull half a century ago remains unsolved. Some of the simplest systems of monatomic metals have not been vitrified, especially the close-packed face-centred cubic metals. Here we report the vitrification of gold, which is notoriously difficult to be vitrified, and several similar close-packed face-centred cubic and hexagonal metals using a method of picosecond pulsed laser ablation in a liquid medium. The vitrification occurs through the rapid cooling during laser ablation and the inhibition of nucleation by the liquid medium. Using this method, a large number of atomic configurations, including glassy configurations, can be generated simultaneously, from which a stable glass state can be sampled. Simulations demonstrate that the favourable stability of monatomic metals stems from the strong topological frustration of icosahedra-like clusters. Our work breaks the limitation of the glass-forming ability of matter, indicating that vitrification is an intrinsic property of matter and providing a strategy for the preparation and design of metallic glasses from an atomic configuration perspective.

Enhanced heat transfer of laser-fabricated copper nanofluid at ultra-low concentration driven by the nanoparticle surface area

As solar thermal energy systems are an important pillow toward green energy production, the enhancement of their thermophysical properties using nanofluids is a highly relevant topic. However, when nanofluids are designed by the addition of nanoparticles (NPs), their colloidal stability is frequently impaired during high-temperature processing, a phenomenon related to particle size, morphology, and concentration. In this work, we synthesized nanofluids composed of ligand-free colloidal CuNPs dispersed in ethylene glycol by continuous-flow, picosecond-pulsed laser ablation in liquids synthesis, yielding monomodal-CuNPs with mean diameters of 2.5 and 4.8 nm. The nanofluids’ thermal conductivity (knf) was measured using a guarded-hot-plate method in the temperature range from 298 to 318 K. We observed a nanoparticle surface area-dependent enhancement of the knf up to 30 % at ultra-low volume concentration of 20 ppm. This corresponds to 30 times higher concentration-normalized knf in comparison to the state-of-the-art, while the resulting nanofluids retain their rheological properties. The findings are matched with Yu–Choi’s theoretical model calculations, indicating that heat transfer at the nanoparticle-solvent interface is driven by an interfacial layer of solvent molecules. These findings highlight the suitability of laser-fabricated ligand-free CuNPs as additives for heat transfer fluids, maximizing performance in mid-temperature heat transfer applications like solar thermal collectors.

Ultralarge suspended and perforated graphene membranes for cell culture applications.

With its high mechanical strength and its remarkable thermal and electrical properties, suspended graphene has long been expected to find revolutionary applications in optoelectronics or as a membrane in nano-devices. However, the lack of efficient transfer and patterning processes still limits its potential. In this work, we report an optimized anthracene-based transfer process to suspend few layers of graphene (1-, 2- and 4-layers) in the millimeter range (up to 3 mm) with high reproducibility. We have explored the advantages and limitations for patterning of these membranes with micrometer-resolution by focused ion beam (FIB) and picosecond pulsed laser ablation techniques. The FIB approach offers higher patterning resolution but suffers from the low throughput. We demonstrate that cold laser ablation is a fast and flexible method for micro-structuring of suspended graphene. One promising field of application of ultimately thin, microporous graphene membranes is their use as next-generation cell culture supports as alternative to track-etched polymer membranes, which often exhibit poor permeability and limited cell-to-cell communication across the membranes. To this end, we confirmed good adhesion and high viability of placental trophoblast cells cultivated on suspended porous graphene membranes without rupturing of the membranes. Overall, there is high potential for the further development of ultrathin suspended graphene membranes for many future applications, including their use for biobarrier cell culture models to enable predictive transport and toxicity assessment of drugs, environmental pollutants, and nanoparticles.

Comparative study of GaAs nanostructures synthesized in air and distilled water by picosecond pulsed laser ablation and application in hazardous molecules detection

This work explored the fundamental differences/mechanisms between the GaAs substrates ablated in two different media of air and distilled water (DW). A scan area of 5 × 5 mm2 was ablated by a picosecond laser with a pulse duration of 30 ps, a repetition rate of 10 Hz, a wavelength of 1064 nm, and a pulse energy of 2 mJ. The spacing between raster scan lines was varied (0.05–0.35 mm), keeping the scan speed (0.15 mm/s) constant. The obtained GaAs nanostructures (NSs) were thoroughly analyzed using microscopy techniques. A clear increase in separation between the raster scan lines was observed with an increase in the scan spacing for the GaAs NSs fabricated in air, whereas the same result was not observed in DW. Moreover, structures with debris were formed in air irrespective of the spacing, unlike the formation of uniform quasiperiodic GaAs NSs throughout the sample in the case of DW ablation. To the best of our knowledge, there are no reports on the detailed studies involving DW in the fabrication of quasiperiodic NSs of GaAs. Further, these quasiperiodic GaAs NSs formed in DW were coated with a thin layer of gold using the thermal evaporation method, annealed at 400 °C for 1 h in an ambient atmosphere. As a consequence of annealing, Au NPs were uniformly decorated on the quasiperiodic NSs of GaAs imparting plasmonic nature to the whole structures. Subsequently, the Au NPs decorated GaAs NSs were utilized as surface enhanced Raman scattering substrates for the detection of methylene blue (dye molecule) and Thiram (pesticide molecule) at low concentrations.

Wavelength dependence of picosecond-pulsed laser ablation of hot-dip galvanized steel

Laser ablation of galvanized steel at a wavelength of 343, 515 and 1030 nm was compared for single as well as multiple picosecond laser pulses. The characteristics of ablated craters, such as ablation rate, crater shape and chemical composition, in relation to the processing parameters were studied. Surface morphology of the laser ablated craters were characterized with the help of confocal laser scanning microscopy and scanning electron microscopy. Chemical compositional and crystallographic changes were analyzed by energy-dispersive X-ray spectroscopy and electron backscatter diffraction respectively. Three ablation regimes were identified in the ablation process of galvanized steel. For equal amount of fluence, ablation rates are found to increase with decreasing laser wavelength. Analyzing the crater shape and the cross-sectional chemical composition, three possible applications are identified for three different wavelengths when processing galvanized steel with picosecond pulsed lasers, namely coating removal, surface texturing and micro-drilling.

Multi-functional gallium arsenide nanoparticles and nanostructures fabricated using picosecond laser ablation

GaAs based nanomaterials have attracted significant attention owing to their applications in electronic, photonic, and sensing devices. In the present communication, we report on the simultaneous fabrication of GaAs nanoparticles (NPs) and nanostructures (NSs) in a single experiment achieved using picosecond pulsed laser ablation in liquids along with the demonstration of their versatile multifunctional applications. GaAs substrates are ablated in three different liquids of distilled water (DW), ethanol, and polyvinyl alcohol (PVA). The morphology and compositions of the synthesized NPs and NSs are analysed using various characterization techniques. Optical and nonlinear optical (NLO) studies are carried out for these NPs in the colloidal form which demonstrated the presence of two-photon absorption. Further, the ablated GaAs substrates exhibited quasi-periodic surface structures with wide angle anti-reflection property and hydrophobic nature. These NSs with a thin layer of gold acted as surface-enhanced Raman scattering (SERS) substrates for detecting trace level hazardous materials such as thiram (a pesticide molecule) and malachite green (a dye molecule). Furthermore, these NSs provided superior Raman enhancements with excellent reproducibility and reusability thereby evidencing their versatility. Collectively, this work reveals quite a few possible multifunctional applications of the laser ablation products of GaAs (NPs and NSs).

Towards synthetic L10-FeNi: Detecting the absence of cubic symmetry in Laser-Ablated Fe-Ni nanoparticles

The L10 crystal structure underlines an important class of chemically ordered alloys that exhibits uniaxial magnetocrystalline anisotropy. The near-equiatomic L10-FeNi extracted from meteorites has demonstrated intriguing magnetic properties for permanent magnet applications. However, the synthesis of this chemically ordered non-cubic structure has been a longstanding challenge. Here, we demonstrate the absence of cubic symmetry in near-equiatomic Fe-Ni nanoparticles synthesized by picosecond-pulsed laser ablation in liquids. The non-cubic phase detected in these particles can only be L10-FeNi or hexagonal close-packed (HCP) FeNi, and the absence of cubic symmetry was unequivocal. The orientation relationship between the non-cubic phase and the adjacent cubic phase was characterized by a series of transmission electron microscopy (TEM) techniques, which consistently suggests that the formation of the non-cubic phase involves a martensitic transformation process.

Picosecond pulsed underwater laser ablation of silicon and stainless steel: Comparing crater analysis methods and analysing dependence of crater characteristics on water layer thickness

Liquid layer thickness dependence of 515 nm, 7 picosecond pulsed laser ablation of stainless steel 304 and silicon is analyzed. Ablated crater volume and diameter are compared to ablated craters in ambient air by means of a novel, objective numerical procedure. While silicon ablation under a water layer is found to be more efficient in terms of removed material volume per pulse than ablation in ambient air, an opposite trend is found for stainless steel 304. For both materials, the ablation efficiently drops when the liquid layer thickness is decreased to 1 milimeter. A probable reason for the ablation efficiency drop is persistent bubble formation.

Silicon Nanoparticles Formed via Pulsed Laser Ablation of Porous Silicon in Liquids

Picosecond pulsed laser ablation of meso- and microporous silicon layers in water and ethanol leads to the formation of nanosilicon suspensions with particle diameters below 100 nm. It is established that the use of porous silicon targets allows the laser ablation threshold to be reduced and the nanoparticle concentration increased as compared to the ablation of crystalline silicon.

Fabrication of silicon carbide nanoparticles using picosecond pulsed laser ablation in acetone with characterizations from TEM and XRD

We fabricated SiC nanoparticles (NPs) using a laser ablation method in acetone with a picosecond pulsed laser and characterized the resulting sizes, shapes, and crystal structures using transmission electron microscopy (TEM) and X-ray diffraction (XRD). We revealed two formation processes for the SiC NPs. The main process was the formation of spherical NPs with diameters primarily less than 10 nm. The crystal structure was 3C-SiC, which did not depend on a target polytype. Therefore, it is concluded that these NPs are grown from atomic molecules that disassociate from targets in the ablation process. As a result of a Rietbelt analysis of the XRD patterns, we clearly found that almost all NPs were single crystals. In addition, a stacking fault in the crystal was observed in the TEM image, which affects the XRD pattern. The other process was the formation of NPs with diameters from 30 to 80 nm with crystal structures that were the same as the targets. This indicates that these NPs were generated as fragments of the target. Our findings are useful for applications of SiC NPs to selectively control their size, shape, and crystal structure using laser ablation.

Innovative Sub-5-$\mu$ m Microvias by Picosecond UV Laser for Post-Moore Packaging Interconnects

This article presents for the first time microvias scaled down to sub-5 μm in diameter fabricated using picosecond UV laser ablation in a nonphotoimageable dielectric film. The motivation of this article is to address post-Moore and More-than-Moore packaging interconnect needs. Microvias play a critical role in package interconnections in IO density and the IC bump pitch for 2.5-D interposers and fan-out packages. UV laser ablation has been the key technology for fabricating small microvias in high density interconnect (HDI) packaging for more than two decades. The state-of-the-art microvia fabricated by UV laser ablation is still at 20 μm in diameter and 50 μm in pitch. This article explores the feasibility of fabricating microvias of 5 μm or less in diameter with a commercially available picosecond UV laser system. The experimental results show that microvias of 5 μm or less in diameter in a 5-μm-thick Ajinomoto buildup dielectric film (ABF) are achieved. This article also addresses the fundamentals of picosecond pulsed laser ablation on polymer dielectric materials and processes optimization to generate sub-5-μm microvias. The via pitch of 8-12 μm is demonstrated. UV laser ablation also addresses the issue of limited availability of photosensitive dielectric materials for photolithography-based microvia fabrication.

Picosecond pulsed laser ablation of dielectric rods: Angle-dependent ablation process model for laser micromachining

The ablation of fused silica and sapphire is investigated from the perspective of laser micromachining. In this study, dielectric rods are machined using a 12 ps pulsed laser at 1064 nm wavelength. The machining of the rods is a calibration method to determine process parameters for an analytical ablation model. More specifically, the ablation threshold fluence and effective penetration depth are determined under process-relevant conditions due to the removal of macroscopic volumes, which leads to a higher accordance. The introduced ablation model predicts macroscopic ablation volumes and ablation efficiencies of dielectric materials as a function of the angle of incidence. Originally, the ablation process model was developed for metals under the normal incidence, but this work extends its applicability to dielectrics. In contrast to metals, the optical penetration depth should be independent of the angle of incidence. Altogether, the presented model is universally applicable and can be seen as a first step toward computer-aided 3D-manufacturing using ultrashort pulsed lasers. The ability to predict ablation volumes and machine heat-sensitive tool materials with high accuracy and precision is demonstrated by the fabrication of end mills made of fused silica and sapphire with a diameter of 1 mm. This shows that picosecond lasers are well suited for the fabrication of such microcutting tools. In particular, the ability of ultrashort pulses to ablate materials independent of their hardness and without any wear makes this technology highly promising for the tooling industry.

Picosecond Pulsed Laser Ablation of Liquid Covered Stainless Steel: Ef-fect of Liquid Layer Thickness on Ablation Efficiency

Under liquid laser ablation is a material removal technique in which a focused laser beam passes through a liquid layer on top of the surface of a sample to be processed. When compared to laser ablation without a liquid layer, material (re)deposition around ablated regions, as well as the size of the Heat Affected Zone (HAZ) is decreased. In addition, the ablation efficiency of the process, in terms of the amount of material removed per pulse, can be optimized by careful variation of the height of the liquid layer: a liquid layer height variation as small as a few tens of millimeters already has a measurable effect on the amount of ablated material. In studies reported in existing literature, the required liquid layer height is typically realized by pouring a pre-defined amount of liquid on top of the sample surface. Surface tension, however, causes the air-liquid interface at the boundaries of the domain to deviate from the planar interface away from the boundaries, which affects the accuracy with which the liquid layer height can be determined. To the best of our knowledge, these accuracy issues have not been studied in previous research. Therefore, an experimental set-up is proposed which circumvents the issues of a curved free surface. Next, a 7 picosecond pulsed laser source (M2≤1.3) at a wavelength of 515nm was employed to study the efficiency of laser ablation of stainless steel for a range of liquid layer heights. Our findings provide a more detailed quantification of crater depth as a function of liquid layer height than is available through existing literature.

Physics of picosecond pulse laser ablation

This study investigates the physical processes involved in picosecond pulse (20-28 ps FWHM) laser ablation of Al 6061, 316L stainless steel, and undoped crystalline Si (〈100〉) over a range of laser wavelength (355 nm and 1064 nm) and fluence (0.1-40 J/cm2). Experimental measurements of material ablation rate show enhanced removal at the 355 nm wavelength, primarily due to laser-plasma interaction (LPI) within the ablative plume that approaches an order of magnitude increase over the measured removal at 1064 nm. A transition in the ablation rate at 355 nm is identified around ∼10 J/cm2 above which the removal efficiency increases by a factor of two to three. Multi-physics radiation hydrodynamic simulations, considering LPI effects and utilizing a novel mixed-phase equation of state model, show that the transition in ablation efficiency is due to the onset of melt ejection through cavitation, where laser-driven shock heating sets the depth of melt penetration and the ensuing release wave from the ablation surface drives cavitation through the imposition of tensile strain within the melt. High-speed pump-probe imaging of the ejecta and ejecta collection studies, as well as scanning electron microscopy of the ablation craters, support the proposed cavitation mechanism in the higher fluence range. The ablation process is critically influenced by LPI effects and the thermophysical properties of the material.

Quantifying the uncertainty of picosecond pulsed laser ablation in sapphire

One of the most prevalent materials used in sensor technologies is silicon which suffers degradation in operating regimes that exceed 1000 °C unless the sensor is actively cooled. Substitution of silicon with sapphire in pressure sensors offers unique capabilities due to its high melting point and chemical inertness; however, these same properties present manufacturing challenges for micromachining sensor components. To overcome the manufacturing challenges, research has focused on picosecond laser machining. A series of picosecond pulsed laser experiments have been conducted and compared to both one-dimensional and three-dimensional modeling of the ablation process. Bayesian uncertainty analysis is used to quantify the parametric uncertainty and error propagation from continuum scale constitutive approximations that can be directly compared with laser ablation experiments. The one dimensional model calibration is found to provide accurate estimations of picosecond laser ablation of sapphire and it enables extrapolation to predict three dimensional ablation.

Picosecond-pulsed laser ablation of zinc: crater morphology and comparison of methods to determine ablation threshold

Ablation of bulk polycrystalline zinc in air is performed with single and multiple picosecond laser pulses at a wavelength of 1030 nm. The relationships between the characteristics of the ablated craters and the processing parameters are analyzed. Morphological changes of the ablated craters are characterized by means of scanning electron microscopy and confocal laser scanning microscopy. Chemical compositions of both the treated and untreated surfaces are quantified with X-ray photoelectron spectroscopy. A comparative analysis on the determination of the ablation threshold using three methods, based on ablated diameter, depth and volume is presented along with associated incubation coefficients. The single pulse ablation threshold value is found to equal 0.21 J/cm2. Using the calculated incubation coefficients, it is found that both the fluence threshold and energy penetration depth show lesser degree of incubation for multiple laser pulses.

SERS sensing of perampanel with nanostructured arrays of gold particles produced by pulsed laser ablation in water

AbstractNoble metal nanoparticles (NPs) are among the most extensively studied colloidal systems, due to their surface plasmon resonances (SPR) of interest for biological sensing. We report here the synthesis of Au nanoparticles as water‐based colloids by nanosecond (τ = 5 ns) and picosecond (τ = 6 ps) pulsed laser ablation at the fixed fluence of 1.5 J/cm2 (λ = 532 nm) and different irradiation times (20 minutes, ns irradiations; 5 minutes, ps irradiations). Both ns and ps ablation lead to the synthesis of highly stable and chemically pure NPs. ps pulses allow synthesizing in remarkably short times (few minutes) smaller NPs with a narrower size distribution than using ns pulses. The surface‐enhanced Raman scattering (SERS) activity of Au NPs produced by ps ablation was tested, obtaining the first SERS spectrum of the new generation antiepileptic drug perampanel, whose clinical interest is relevant.

Zinc oxide nanocolloids prepared by picosecond pulsed laser ablation in water at different temperatures

Zinc oxide with wide direct band gap and high exciton binding energy is one of the most promising materials for ultraviolet (UV) light-emitting devices. It further exhibits good performance in the degradation of non-biodegradable pollutants under UV irradiation. In this work, zinc oxide (ZnO) and zinc oxide/gold (ZnO/Au) nanocolloids are prepared by picosecond pulsed laser ablation (ps-PLA), using a Zn and Au metallic targets in water media at room temperature (RT) and 80°C. ZnO and Au nanoparticles (NPs) with size in the 10–50 nm range are obtained at RT, while ZnO nanorods (NRs) are formed when water is maintained at 80°C during the ps-PLA process. Au NPs, added to ZnO colloids after the ablation process, decorate ZnO NRs. The crystalline phase of all ZnO nanocolloids is wurtzite. Methylene blue dye is used to investigate the photo-catalytic activity of all the synthesised nanocolloids, under UV light irradiation.

Study on picosecond pulse laser ablation of Cr12MoV cold work mold steel

Cr12MoV has wide applications in the molds and dies industry. However, it is also a hard-to-machining material due to its high mechanical strength and hardness. Area ablation of Cr12MoV cold-work mold steel was carried out using a picosecond (ps) pulse Nd:YVO4 laser. The effects of laser fluence and wavelength on the ablation rate and machining quality were investigated with wavelengths of 1064nm, 532nm and 355nm. The experimental results indicate a logarithmic increase of the ablation rate to a maximum value of ~41nm/pulse with the increase of laser fluence using the wavelengths of 1064nm and 355nm. For the wavelength of 532nm, an ablation rate of ~33nm/pulse is achieved at low laser fluence of 8.28J/cm2, then increases logarithmically into about 54nm/pulse at 25.10J/cm2, and then decreases steeply into almost zero as the laser fluence increases above 25.10J/cm2. For the three laser wavelengths, different pore sizes were observed in the laser ablation region. The surface roughness increases exponentially with the increase of the laser fluence. The influence mechanisms of laser fluence and wavelength on the laser ablation rate and machining quality were systematically analyzed and discussed in this paper.

ピコ秒レーザーアブレーションによる金型鋼の加工特性

ピコ秒レーザーアブレーションによる金型鋼の加工特性