Femtosecond Pulsed Laser Ablation Research Articles

Elucidating the Role of Electron Transfer in the Photoluminescence of MoS2 Quantum Dots Synthesized by fs-Pulse Ablation.

Herein, MoS2 quantum dots (QDs) with controlled optical, structural, and electronic properties are synthesized using the femtosecond pulsed laser ablation in liquid (fs-PLAL) technique by varying the pulse width, ablation power, and ablation time to harness the potential for next-generation optoelectronics and quantum technology. Furthermore, this work elucidates key aspects of the mechanisms underlying the near-UV and blue emissions the accompanying large Stokes shift, and the consequent change in sample color with laser exposure parameters pertaining to MoS2 QDs. Through spectroscopic analysis, including UV-visible absorption, photoluminescence, and Raman spectroscopy, we successfully unraveled the mechanisms for the change in optoelectronic properties of MoS2 QDs with laser parameters. We realize that the occurrence of a secondary phase, specifically MoO3-x, is responsible for the significant Stokes shift and blue emission observed in this QD system. The primary factor influencing these activities is the electron transfer observed between these two phases, as validated by excitation-dependent photoluminescence and XPS and Raman spectroscopies.

Low energy femtosecond pulsed laser ablation of Nd:YAG laser crystal in high-pressure oxygen and nitrogen background gas

A low-energy femtosecond (fs) pulsed laser was utilized to ablate the Nd:YAG laser crystal target in high-pressure oxygen (O2) and nitrogen (N2) background gases. Only minute amounts of neodymium (Nd), yttrium (Y), and aluminum (Al) were detected in the deposited material due to the thermalization resulting from low laser pulse energy and significant scattering caused by the high background gas pressure. We used a collision-based model and peak-fitting method of the angular distribution of the plume to explain the result. The collision-based model was used to explain and determine the probability distribution of the elements arriving from the target to the substrate. The magnitude of the probability distribution obtained with O2 background gas is higher as compared to N2 background gas owing to the former’s higher collision frequency. The peak-fitting method of the angular distribution of Nd, Y, and Al provided better approximations of the ratio of atoms arriving after ablation as compared to the collision-based model. Further improvements can be carried out to better predict the deposited material ratio.

Unexpected Electronic Features of NiO Quantum Dots Produced by Femtosecond Pulsed Laser Ablation in Water.

This study examines the effect of quantum confinement and surface orientations on the electronic properties of NiO quantum dots. It compares NiO nanocrystals produced via atmospheric-pressure microplasma and femtosecond laser (fs-laser) ablation in water, finding that both methods yield quantum-confined nanocrystals with a defined face-centered cubic lattice. Notably, fs-laser synthesis generates crystalline nanocrystals from both crystalline and amorphous targets. While the electronic properties, i.e., energy of the highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO), of microplasma-synthesized NiO nanocrystals are consistent with the literature, the electronic characteristics of NiO nanocrystals produced by a fs-laser, particularly the high-lying LUMO level, are unusual for NiO quantum dots. Supported by density functional theory calculations, we show that the observed level positions are related to the different polar and nonpolar faces of the nanocrystal surface.

Modelling thermal energy transfer in a femtosecond pulsed laser ablation of metal using a coupled spring-mass oscillator

Femtosecond pulsed laser ablation (fs-PLA) is an interesting yet complicated field of study especially for undergraduate students entering the field. Hence, a bridging concept using classical and mechanical analog will be helpful. In this paper, we modelled the thermal energy transfer between electron and lattice system in a fs-PLA of metal described by two temperature model (TTM) using a coupled spring-mass oscillator. This was achieved by providing correspondence of TTM parameters to the coupled spring-mass oscillator, with temperature as position, electron thermal conductivity as coefficient of friction, electron-phonon coupling factor as spring term, electron/lattice heat capacity as the mass m 1/m 2 respectively, and laser source term as the driving force. The thermophysical properties considered are temperature dependent leading to position dependent parameters of coupled spring-mass oscillator. Results showed that the coupled spring-mass oscillator exhibit many behavior similar to the TTM. Additionally, maximum positions achieved by m 2 behave similarly with maximum lattice temperature after achieving certain threshold value. However, many features of TTM such as spatial dependence and crater formation are not observed in the coupled spring-mass oscillator. Despite its limitation, the coupled spring-mass oscillator model was able to represent many features of the thermal energy transfer of fs-PLA, and could be an easy and useful model in understanding fs-PLA.

(Invited) Modelling and Experiments to Guide Scale-up of Structured Electrode Manufacturing for Fast-Charging and Long-Life Li-Ion Cells

For widespread adoption of electric vehicles, lithium-ion batteries (LiBs) need to achieve energy densities of around 350 Wh/kg, cost less than $100/Wh, and be able to charge quickly within around 15 minutes. To achieve this aim, the material properties of lithium-ion electrodes need to be optimized across multiple length scales, from particle to cell. Leveraging advanced characterization techniques to acquire representative particle- and electrode-level microstructures, we develop models to simulate the behavior of individual particles and novel electrode architectures that are feasible to synthesize and scale up to manufacture high performance batteries. We then demonstrate manufacturing of the novel electrode architectures at pilot scale roll-to-roll processing using high-speed laser-ablation to tune the electrode architecture. Guided by multi-scale models, we observe substantial improvements in cell performance.For the particle level optimization, the primary objective is to develop a predictive cathode-particle cracking model that captures secondary-particle fracture dynamics, relate damage to observed capacity fade, and provide design criteria for future cathode development. The novel coupled electrochemistry-transport-mechanics model is implemented on realistic three-dimensional LiNixMnyCozO2 (NMC) secondary particles. Realistic secondary particles are generated using statistically representative particle generation software. The generated particle architecture is used in chemo-mechanical models to simulate Li (de)intercalation during cycling. The model considers diffusion-induced stress, mismatch strain, and damage evolution coupled through the spatial and temporal evolution of geometric, transport, and mechanical properties. Contrary to most cathode-cracking models, instead of a cohesive-zone implementation, a continuum-damage model is used. Additionally, the model simulates several realistic secondary particle geometries to study the effect of secondary-particle size and grain size on damage. The model is expected to provide insights into ideal cathode geometries (e.g., grain morphology, orientation, and particle sizes) and optimal cathode-sensitive charge-protocol development.For electrode level optimization, structuring the electrode with channels to provide straight diffusion paths along the electrode thickness is a promising approach with demonstrated improved capacity retention at fast charge. The optimal shape and spatial distribution of these channels, that together form the so-called Secondary Pore Network (SPN), taking into consideration the manufacturing technique limitations, is however still unknown. Battery manufacturing cost is another key limiting factor for the wide adoption of electric vehicles. The electrolyte wetting process is an expensive step as complete infiltration can takes days, thus requiring expensive storage space and time. Structured electrodes have also demonstrated reduced wetting time as channels offer highways indifferently for capillary-driven or concentration gradient-driven transport mechanisms. However, the optimal channel pattern for enhanced wetting is also unknown. In this work, we identify both optimal patterns, for fast charging, and for fast wetting, independently, through use of a genetic algorithm (GA). The final proposed structured electrode is therefore the baseline porous matrix, a Secondary Pore Network (SPN) tailored for fast charging, and a Tertiary Pore Network (TPN) tailored for fast wetting, with less than 10% of active material removed in total.High-speed laser-ablation is applied to manufacturing this electrode architecture. Laser ablation is a scalable technique for decreasing the effective tortuosity of electrodes by selectively removing material with high precision. Applied to thick electrode coatings, this work focuses on understanding the impact of laser ablation on electrode material properties at the beginning of life and synergistic impacts of ablated channels on cell performance throughout their cycle life. Post laser ablation, local changes in chemistry, crystallography, and morphology of the laser-impacted electrode regions are investigated. It is shown that femtosecond pulsed laser ablation can achieve high-rate material removal with minor material damage locally at the interface of the impacted zones. The capacity achieved during a 6C (10 min) constant-current constant-voltage charge to 4.2 V improved from 1 mAh cm−2 for the non-ablated electrodes to almost 2 mAh cm−2 for the ablated electrodes. This benefit is attributed to a synergistic effect of enhanced wetting and decreased electrode tortuosity. The benefit was maintained for over 120 cycles, and upon disassembly decreased Li-plating on the graphite anode was observed.From the particle to the electrode level, we demonstrate that there remains ample opportunity for optimizing the material properties of conventional electrode chemistries for faster charging and longer-life performance. Our combined use of advanced characterization, modelling, and data-guided manufacturing shows that a multi-scale and multi-modal approach can be applied to build electrodes from the particle up and achieve enhanced electrochemical performance at the cell level through advanced and scalable manufacturing techniques. Figure 1

Exotic femtosecond nonlinear optical properties of laser ablated MoS2 quantum dots

Molybdenum disulfide (MoS2) quantum dots (QDs) of sizes 2.05–4.40 nm were synthesized using the femtosecond pulse laser ablation in liquid (PLAL) method. The optical and ultrafast nonlinear optical (NLO) properties of MoS2 QDs were comprehensively studied using photoluminescence and femtosecond Z-scan method. We synthesized these QDs in ethanol (Et) and DI water (DW) with varying ablation times of 20 min and 10 min; the sample names are Et20 and Et10, DW20, and DW10, respectively. The nonlinear absorption (NLA) coefficients [three-photon absorption (3PA)], nonlinear refractive index, etc., of these QDs, were studied using the fs Z-scan method. Interestingly, Et20 possessed saturable absorption (SA) followed by reverse saturable absorption (RSA) due to the free carrier absorption (FCA) with FCA cross-section values of – (0.61–0.89) × 10−18 cm2. While for Et10, DW20, and DW10, we found 3PA, a rare finding for MoS2 QDs. The estimated values of the second hyperpolarizability of these samples were found to be ∼10−30 esu. Due to the strong NLA phenomena, these samples have the optical limiting (OL) onset values in the range of ∼ (5.11–8.43) mJ/cm2, proving the optical limiting application potential of these QDs. The obtained optical, NLO parameters, and Kane energy values of laser-ablated MoS2 QDs suggest that these can be suitable material systems for optoelectronic, NLO switching, logic gates, and other photonic applications.

Surface texturing, residual stresses and edge treatment of hardmetal tools by means of femtosecond pulsed laser

Laser induced periodic surface structures (LIPSS) have been produced at the surface of a WC-Co turning insert by femtosecond pulsed laser ablation. Wavelengths of approx. 500 nm have been obtained with a 1030 nm incident radiation and with a spot size of 30 μm. No thermal damage is induced by following this procedure, although a slight surface stress relaxation is detected as fluence increases. The higher material removal needed for chamfering operations requires accumulated fluences over 1 kJ/cm2. At lower energy densities, material removal is not completed. If fluence is increased by reducing the laser spot size, material removal is also inefficient since signicant amount of debris is accumulated on the irradiated areas. Best chamfering strategy involves the combination of relatively large spot sizes and fluences. Form factors (Κappa) of the chamfered cutting edges range from 4 to 10 although the laser is oriented at 45° of the rake face. Lower Κ values can be obtained by adjusting the laser focus along the machining process.

Nanocomposite Fe3O4-MWCNTs based on femtosecond pulsed laser ablation for catalytic degradation

Magnetite nanoparticle/multi-walled carbon nanotube composites (Fe3O4/MWCNTs) were prepared using femtosecond pulsed laser ablation of iron target immersed in functionalized MWCNTs by facile one-pot synthesis of pulsed laser ablation in liquid environmental for catalytic degradation of 4-ntrophenol from aqueous solution. The easily obtained magnetic nanocomposites were systematically characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). According to XRD, magnetite is the magnetic phase that has formed. A network of MWCNTs is seen in the FESEM image, together with nano‑iron oxides. Raman spectroscopy revealed that the reduction of the sp2 bond domains due to the strong contacts between iron oxide and MWCNT increased the D/G ratio, which may lead to structural distortions in the nanotubes. From FT-IR, the presence of new peaks in the finger print region related to Fe-O-Fe in Fe3O4, indicates that Fe3O4 has been successfully loaded onto the surface of MWCNTs. In addition, the prepared magnetic nanocomposite showed outstanding catalytic reduction activity for 4-NP when compared to MWCNTs and Fe3O4. The results demonstrated that the prepared nanocomposite could be a promising nanocatalyst for the catalytic reduction of 4-NP. The straightforward, speedy, and dependable Fe3O4/MWCNTs-based approach was found to be a possibly relevant technology for the targeted removal of pollutants and the treatment of wastewater.

A comparative study of femtosecond pulsed laser ablation of meloxicam in distilled water and in air

The increasing prevalence of water insoluble or poorly soluble drugs calls for the development of new formulation methods. Common approaches include the reduction of particle size and degree of crystallinity. Pulsed laser ablation is a clean technique for producing sub-micrometre sized drug particles and has the potential to induce amorphization. We studied the effect of femtosecond pulsed laser ablation (ELI ALPS THz pump laser system: λc = 781 nm, τ = 135 fs) on meloxicam in distilled water and in air. The ablated particles were characterized chemically, morphologically and in terms of crystallinity. We demonstrated that femtosecond laser ablation can induce partial amorphization of the particles in addition to a reduction in particle size. In the case of femtosecond pulsed laser ablation in air, the formation of pure meloxicam spheres showed that this technique can produce amorphous meloxicam without the use of excipients, which is a unique result. We also aimed to describe the ablation processes in both investigated media.

Nanostructured Thermoelectric PbTe Thin Films with Ag Addition Deposited by Femtosecond Pulsed Laser Ablation

Pulsed laser deposition operated by an ultra-short laser beam was used to grow in a vacuum and at room temperature natively nanostructured thin films of lead telluride (PbTe) for thermoelectric applications. Different percentages of silver (Ag), from 0.5 to 20% of nominal concentration, were added to PbTe deposited on polished technical alumina substrates using a multi-target system. The surface morphology and chemical composition were analyzed by Scanning Electron Microscope and X-ray Photoelectron Spectroscopy, whereas the structural characteristics were investigated by X-ray Diffraction. Electrical resistivity as a function of the sample temperature was measured by the four-point probe method by highlighting a typical semiconducting behavior, apart from the sample with the maximum Ag concentration acting as a degenerate semiconductor, whereas the Seebeck coefficient measurements indicate n-type doping for all the samples. The power factor values (up to 14.9 µW cm−1 K−2 at 540 K for the nominal 10% Ag concentration sample) are competitive for low-power applications on flexible substrates, also presuming the achievement of a large reduction in the thermal conductivity thanks to the native nanostructuring.

Preparation and Evaluation of 64Cu-Radiolabled Dual-Ligand Multifunctional Gold Nanoparticles for Tumor Theragnosis.

Gold nanoparticles (AuNPs) are cutting-edge platforms for combined diagnostic and therapeutic approaches due to their exquisite physicochemical and optical properties. Using the AuNPs physically produced by femtosecond pulsed laser ablation of bulk Au in deionized water, with a capping agent-free surface, the conjugation of functional ligands onto the AuNPs can be tunable between 0% and 100% coverage. By taking advantage of this property, AuNPs functionalized by two different types of active targeting ligands with predetermined ratios were fabricated. The quantitatively controllable conjugation to construct a mixed monolayer of multiple biological molecules at a certain ratio onto the surface of AuNPs was achieved and a chelator-free 64Cu-labeling method was developed. We report here the manufacture, radiosynthesis and bioevaluation of three different types of dual-ligand AuNPs functionalized with two distinct ligands selected from glucose, arginine-glycine-aspartate (RGD) peptide, and methotrexate (MTX) for tumor theragnosis. The preclinical evaluation demonstrated that tumor uptakes and retention of two components AuNP conjugates were higher than that of single-component AuNP conjugates. Notably, the glucose/MT- modified dual-ligand AuNP conjugates showed significant improvement in tumor uptake and retention. The novel nanoconjugates prepared in this study make it possible to integrate several modalities with a single AuNP for multimodality imaging and therapy, combining the power of chemo-, thermal- and radiation therapies together.

Synthesis and characterization of selenium nanoparticles obtained by femtosecond pulsed laser ablation in liquid media

Synthesis and characterization of selenium nanoparticles obtained by femtosecond pulsed laser ablation in liquid media

Fabrication of 4H–SiC nanoparticles using femtosecond pulsed laser ablation in deionized water

In this paper, the silicon carbide (SiC) nanoparticle colloidal solution is obtained by using the femtosecond (fs) laser ablation in deionized water. The spherical nanoparticles are uniform in size with an average diameter of 2.84 nm analyzed by transmission electron microscope (TEM). X-ray diffraction patterns (XRD) show that the crystal structure of the nanoparticles is still 4H–SiC. Absorption spectrum shows strong absorption of SiC colloidal solution in ultraviolet region. The optical nonlinearity of SiC nanoparticles colloidal solution is investigated by the Z scan experiment, it is found that the SiC nanoparticles have reverse saturation absorption characteristics. The nonlinear absorption coefficient β is measured to be about 3 × 10−13 m/W.

Femtosecond pulsed laser ablation for paint removal at oblique illumination: Effect of the incidence angle

This research studies how the angle of incidence affects the ablation process when a pulsed femtosecond laser with a wavelength of 1040 nm and a high repetition rate is applied to spray paints used for graffiti. Flat test samples were painted using four different spray paints (red, blue, black and silver). All paints had an organic base but different physicochemical properties. For each paint, the ablation process was characterized using confocal microscopy, determining the threshold fluence and the penetration depth of the laser radiation at normal incidence. For different sample tilt angles in the range of 0°–60°, the effect of oblique incidence was analysed in terms of its effect on the ablation rate and the geometric properties (depth and width) of the ablation grooves on each paint. The results show a clear decrease in the ablation rate as the angle of incidence moves away from normal incidence. Moreover, it can also be observed that for a given angle, groove depth is the property most affected by beam tilt. These results represent a necessary step in addressing both cleaning and other laser ablation processes on non-flat surfaces in a controlled and reproducible manner.

Laser ablation for structuring Li-ion electrodes for fast charging and its impact on material properties, rate capability, Li plating, and wetting

Laser ablation is a scalable technique for decreasing the effective tortuosity of electrodes by selectively removing material with high precision. Applied to ≈ 110μm thick electrode coatings, this work focuses on understanding the impact of laser ablation on electrode material properties at the beginning of life and synergistic impacts of ablated channels on cell performance throughout their cycle life. Post laser ablation, local changes in chemistry, crystallography, and morphology of the laser-impacted electrode regions are investigated. It is shown that femtosecond pulsed laser ablation can achieve high-rate material removal with minor material damage locally at the interface of the impacted zones. The capacity achieved during a 6C (10 min) constant-current constant-voltage charge to 4.2 V improved from 1 mAh cm−2 for the non-ablated electrodes to almost 2 mAh cm−2 for the ablated electrodes. This benefit is attributed to a synergistic effect of enhanced wetting and decreased electrode tortuosity. The benefit was maintained for over 120 cycles, and upon disassembly decreased Li-plating on the graphite anode was observed. Finally, multi-physics modeling in conjunction with wetting analyses showed that laser ablating either one of the electrodes led to substantial improvements in wetting and rate capability, indicating that substantial performance benefits can be achieved by ablating only the graphite anode as apposed to both electrodes.

Effects of fs pulsed laser ablation on synthetic zeolite targets

With the aim to perform nanozeolite re-crystallization by laser treatment, the effects of Femtosecond Pulsed Laser Ablation (fs PLA) on three different targets of zeolite with LTA typology (zeolite A) were investigated. One sample of zeolite A was formed by modified standard IZA protocol (LTA). The other two were synthesised with the addition of red mud (RMFe-LTA) or nanomagnetite (NMFe-LTA) during the hydrothermal process. All the ablated targets were analysed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The results indicate that differences in chemical composition of the targets, together with the local temperature gradient determined by femtosecond laser-matter interaction occurring under high to middle-low pressures, have a significant influence on mineral and morphology changes of starting raw minerals as well as on evolution of reduction reactions. This is due to fast heating and cooling down processes inducing in turn different re-solidification characteristics mainly on RMFe-LTA and NMFe-LTA targets.

Tungsten disulfide nanoparticles produced by femtosecond laser ablation in water for nanophotonic applications

We demonstrate nearly spherical nanoparticles of tungsten disulfide (WS2) produced by femtosecond pulsed laser ablation of bulk target in deionized water. Structural and optical analysis reveals that produced nanospheres preserve the crystalline structure, high refractive index and support strong excitons and Mie resonances in the spectral range 400-700 nm, resulting in enhanced photothermal response probed by Raman spectroscopy.

Rhenium/rhenium oxide nanoparticles production using femtosecond pulsed laser ablation in liquid.

In this study, rhenium/rhenium oxide nanoparticles (Re / ReO3 NPs) have been produced for the first time in ultrapure water by using Femtosecond Pulsed Laser Ablation in Liquid (fsPLAL) method. X-Ray Diffraction (XRD) measurements and results obtained for NPs show the existence of well-crystallized peaks and preferred phases. Re NPs have hexagonal structure while ReO3 NPs have the perovskite-like cubic crystal structures. The Re / ReO3 ratio is also determined to be 53 / 47 with ~ 20 nm crystallite size, while pure ReO3 crystallite sizes were measured to be ~ 25 nm. The TEM results have shown that the produced particles have a spherical shape, and particle sizes changes between ~ 20 nm and ~ 60 nm. The crystallite size is similar due to XRD results. Obtained nanoparticles exhibit promising applications for photonic devices with broad bandgap values which have measured to be 4.71 eV for Re / ReO3 NPs mixture and 4.36 eV for pure ReO3 NPs.

Notch effect on the linear elastic fracture mechanics values of a polysulfone thermoplastic polymer

Users of the most popular procedures for determining the linear elastic fracture mechanics parameters on polymers have noted that the repeatability and reproducibility of the results depend strongly on the quality of the notches generated. In an attempt to provide a better understanding, polysulfone specimens were pre-cracked using classical razor blade methods (tapping and sliding), and also by the femtosecond pulsed laser ablation technique. These specimens were analyzed, and the critical stress intensity factor was determined. The ablated specimens showed very good notch quality, the sharpest crack tip radii, displayed neither mechanical nor thermal damage in front of the crack tip, and were very consistent, providing both a lesser scatter and a statistically significant lower critical stress intensity factor than the razor blade pre-cracked specimens. Finally, some consideration and advice for suitable generation of notches are also given.

Mechanical modeling of metal thin films on elastomers for femtosecond laser patterned interconnects

In this work, we present the mechanical analysis of thin Au/Ti film deposited on elastomer substrate, e.g. Polydimethylsiloxane (PDMS) comparing to samples on Kapton®. After deposition, the metal was patterned by ultrashort (270 femtosecond) pulse laser ablation. Minimizing the thermal damage to the substrate, reducing Heat Affected Zone (HAZ) compared to previously demonstrated laser patterning with longer pulses. One of the major issues in the metallization of thick elastomers is the formation of wrinkles followed by brittle cracks in the metallic thin film during the process, deteriorating the metal lines performance and reliability. Such cracking has not been observed on polyimide. The crack formation was investigated using stress analysis of the metallic-elastomeric system, assuming that cracking appears when the stress in the metal film is exceeding a critical value. A general mechanical model and analysis of a multilayer and multi-material laminated system is presented and applied to the specific case of Au/Ti on PDMS. Using this model, the root cause for the stress development in the metallic film has been investigated.A series of samples had been prepared using various elastomer substrates made of Sylgard 184, Dow Corning PDMS. A series of samples was prepared using different monomer/cross-linker ratios in the range of 1:2 to 1:19 monomer to cross-linker weight percentage ratio. Using the thin film stress analysis, the inner stress between and inside the different layers was calculated. Based on the calculations, we could estimate the specific stress in the metallic film. Using this value, we could choose the right specific materials that would not surpass their critical failure stress. This hypothesis was tested and verified by the failure analysis conducted by optical microscope and scanning electrons microscopy (SEM) secondary electrons (SE) images. We report here on a good correlation between the mechanical analysis predictions and the various samples integrity. Therefore, using that model, we could define a “safe zone”, i.e. for what elastic modulus and Coefficient of Thermal Expansion (CTE) there are no “mud-crack” defects.