Femtosecond Laser Ablation Technique Research Articles

Flexible Mini‐Inductors with Ultra‐High Inductance Density Directly Cut from Soft Magnetic Amorphous Alloys by Femtosecond Laser

AbstractInductors are indispensable parts in power modules of electronic devices. With the rapid development of flexible and wearable electronic devices, developing flexible micro‐inductors with large energy storage has become an urgent task. In this research, a sophisticated femtosecond laser ablation technique is employed to craft circular spiral mini‐inductors via selective etching of soft magnetic amorphous alloy ribbons. Remarkably, while these inductors possess dimensions akin to human fingerprints, they demonstrate an impressively elevated inductance value of ≈1.15 µH at 1 MHz. The inductance density is ≈280–390 nH mm−2, which is ≈10 times larger than conventional circular spiral inductors and is attributed to the high permeability of the amorphous alloys. Furthermore, the inductors showcase commendable flexibility, marked by stellar elasticity and a bending endurance exceeding 2500 cycles, thanks to the amorphous alloys' superior elastic strain limit. When integrated with an LM2576‐3.3BT buck converter, the fabricated inductor achieved a peak power conversion efficiency nearing 70%. These findings underscore the potential of such flexible mini‐inductors in the landscape of flexible electronics.

High-performance amplified spontaneous emission in inorganic CsPbBr3 perovskite thin films grown on engineered quartz substrates.

In this work, periodic rectangular arrays were fabricated on quartz substrates using the femtosecond laser ablation technique, on which inorganic cesium lead bromide thin films were grown using the spin coating method. Enhanced photoluminescence emission was investigated using a homebuilt confocal microscope, and increased light absorption due to the engineered structures was also measured. High-performance amplified spontaneous emission with typical narrow lasing emission peaks excited using a nanosecond laser centered at 266 nm was obtained. This work provides a method to modify the performance of optoelectrical devices, which helps develop light-emitting diodes, photodetectors, solar cells, and lasers.

Super anti-corrosion surface of Al-Li alloy via femtosecond laser ablation treatment in water

Al-Li alloys are widely used in aerospace industry owing to their low density and high specific strength, but they are facing corrosion challenges in marine environment. In this work, femtosecond laser ablation (FLA) technique is employed to modify the surface of Al-Li alloy in order to enhance the corrosion resistance, and the effects of FLA in the air (FLA-Air) and FLA in the water (FLA-Water) are compared. It is found that the FLA-Air treated surfaces are hydrophilic, while the FLA-Water treated surfaces are near superhydrophobic with contact angle of 140–150°. The FLA-Water surface, treated by using the laser power of 240 mW, shows superior passivation ability, and its corrosion current density is three orders of magnitude lower than that of the alloy matrix. The synergistic effect of hair-like porous nanostructure and high oxidation degree of the surface contributes to the superior corrosion resistance of the FLA-Water treated alloy. Our work provides a novel strategy for the effective corrosion protection of light metal surfaces.

High‐Quality CsPbBr3 Perovskite Films with Modal Gain above 10 000 cm−1 at Room Temperature

AbstractHalide perovskite lasers based on CsPbBr3 micro‐ and nanoscale crystals have demonstrated fascinating performance owing to their low‐threshold lasing at room temperature and cost‐effective fabrication. However, chemically synthesized thin films of CsPbBr3 usually have rough polycrystalline morphology along with a large amount of crystal lattice defects and, thus, are mostly utilized for the engineering of light‐emitting devices. This obstacle prevents their usage in many photonic applications. Here, a protocol to deposit large‐grain and smooth CsPbBr3 thin films is developed. Their high quality and large scale allow to demonstrate a maximum optical gain up to 12 900 cm−1 in the spectral range of 530–540 nm, which is a record‐high value among all previously reported halide perovskites and bulk semiconductors (e.g., GaAs, GaN, etc.) at room temperature. Moreover, femtosecond laser ablation technique is employed to create high‐quality microdisc lasers on glass from these films to obtain excellent lasing characteristics. The revealed critical roles of thickness and grain size for the CsPbBr3 films with extremely high optical gain pave the way for development of low‐threshold lasers or ultimately small nanolasers, as well as to apply them for polaritonic logical elements and integrated photonic chips.

High-Quality Patterning of CsPbBr3 Perovskite Films through Lamination-Assisted Femtosecond Laser Ablation toward Light-Emitting Diodes.

Metal halide perovskites have exhibited promising potential for practical applications such as image sensors and displays benefiting from their outstanding optoelectronic properties. However, owing to the instability of the perovskite materials, producing patterned perovskite films with adequately high quality and high precision for such practical applications poses a challenge for existing patterning methods. Herein, the lamination-assisted femtosecond laser ablation (LA-FsLA) technique was successfully applied to fabricate patterned CsPbBr3 films with sufficiently high quality and high precision. A sandwich-laminated structure (glass/CsPbBr3/glass) was introduced to avoid the impact of debris on the patterned perovskite film. As a result, arbitrarily patterned perovskite films with high quality, submicron precision, and well-defined edges were successfully prepared. Moreover, the light-emitting diodes (LEDs) based on the patterned perovskite films also exhibit good emission characteristics. This work provides a promising strategy for the fabrication of patterned perovskite films with adequately high quality and high precision toward perovskite-based optoelectronic devices.

Laser ablation enhancing the electrochemical sensing performance of copper foam toward glucose

In this work, a copper foam with surface oxidation and micro-nano structure was fabricated via a femtosecond laser ablation technique. The change in surface microscopic morphology and electronic structure was investigated by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Based on its rough surface, unique electronic state and oxygen defects, the laser-treated copper foam exhibited excellent electrochemical sensing performance for glucose. The sensitivity and detection limit was determined to be 27.4517 mA cm −2 mM −1 and 1.5 μM, respectively. Furthermore, the good selectivity of the present laser-treated copper foam was also demonstrated by the anti-interference experiment.

Femtosecond laser nano-structuring for surface plasmon resonance-based detection of uranium

Surface plasmon resonance (SPR) is a proven technique in sensorics. Wide application of the method is still limited by a necessity of a complex optical equipment using special dispersion elements like a prism or diffraction grating (DG). We have implemented a novel and inexpensive way for fabrication of the DG on a silicon substrate using femtosecond laser ablation (highly regular laser-induced periodic surface structures - HR-LIPSS) technique. The potential of the method has been illustrated for the case of detection of uranium in water. For this purpose, fabricated gratings were coated with thermally evaporated nanofilms of gold and then used as substrates for deposition of nanoparticles of bioinspired polymer polydopamine (PDA) highly selective to uranium under neutral pH. Synergistic combination of the advanced nanofabrication and SPR sensing techniques with advanced PDA ligand allowed preparation of sensing elements with a sub-microgram sensitivity to uranium (∼1.0 × 10−7g/cm2). Even though the results reported here are just a proof of concept, we believe the approach can be expanded to selective detection of various types of analytes (heavy metals, biomolecules, viruses etc.) under different environments (water, air, aerosols) in the future.

Ultraviolet second harmonic generation from Mie-resonant lithium niobate nanospheres

Abstract Lithium niobate (LN), as a nonlinear material with a large nonlinear susceptibility, has been widely employed in second harmonic generation (SHG) up to ultraviolet (UV) frequency range due to its broad low-absorption window. In nanophotonics, it is possible to harness the Mie resonances associated with the single dielectric particles to boost the nonlinear light–matter interactions. Here, we fabricate single Mie-resonant LN nanospheres on a SiO2 substrate via the femtosecond (fs) laser ablation technique. By exploiting the magnetic dipole (MD) Mie resonance, UV SHG from the LN nanosphere is significantly enhanced with a measured conversion efficiency of 4.45 × 10−8 under the excitation of an fs laser at 750 nm. The single LN nanospheres achieved in this work could serve as Mie resonators for building nonlinear nanophotonic devices such as frequency converters and quantum light sources, etc.

Fabrication of S-shaped micron-sized constrictions on FeC (steel) surface using femtosecond laser ablation with beam shaping

In this paper, we demonstrate the fabrication of S-shaped micron-sized constrictions on steel (Fe3CII) surface using the femtosecond laser ablation technique. The femtosecond laser used has a wavelength of 775 nm, a power range of 0–1000 mW, a pulse duration of 130 fs, and a pulse repetition rate of 1–2 kHz. The ultra-low-pulse duration of 130 fs enables ablation of material surfaces without excessive thermal heating of the material around the zone of ablation. This becomes useful when ablating materials that are thermally sensitive such as superconducting thin films. This practice run of ablating S-shaped micron-sized constrictions on steel surfaces shown in this paper will enable one to use the same technique in ablating micron- and nano-sized structures on superconducting thin films without thermally altering the superconductive film. In this paper, S-shaped micron-sized constrictions on steel were fabricated with a constriction width of 37.1 and 47.3 μm whose images were created using an optical microscope (OM) and S-shaped micron-sized constrictions with a constriction width of 30.8 and 35.2 μm whose images were created using an atomic force microscope (AFM). The reduction in the constriction widths was achieved by reducing the laser ablation width or laser ablation spot size and then bringing the laser ablation spots closer together in G-code program. The reduction of the laser ablation width is achieved by reducing the laser fluence applied closer to the ablation threshold of steel and by using laser beam shaping techniques such as beam collimation and beam focusing.

Robust Hierarchical Porous PTFE Film Fabricated via Femtosecond Laser for Self-Cleaning Passive Cooling.

Passive cooling materials that spontaneously cool an object are promising choices for mitigating the global energy crisis. However, these cooling effects are usually weakened or lost when dust contaminates the surface structure, greatly restricting their applications. In this work, a robust hierarchical porous polytetrafluoroethylene (PTFE) film with coral-like micro/nanostructures is generated by a facile and efficient femtosecond laser ablation technique. Owing to its unique micro/nanostructures, the as-prepared surface exhibits an outstanding self-cleaning function for various liquids with ultralow adhesion. This self-cleaning characteristic enhances the durability of its passive cooling effect. It is demonstrated that the titanium (Ti) sheet covered with laser-ablated PTFE film can realize a maximum temperature decrease of 4 and 10 °C compared to the Ti sheet covered with pristine PTFE film and uncovered, respectively. This study reveals that femtosecond laser micromachining is a facile and feasible avenue to produce robust self-cleaning passive cooling devices.

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.

Effect of microstructure on fracture behavior of freestanding plasma sprayed 7 wt.% Y2O3 stabilized ZrO2

Air plasma sprayed (APS) 7 wt.% yttria-stabilized zirconia (7YSZ) coatings have a multitude of microstructural defects, at various length scales, such as pores, intra-splat and inter-splat micro-cracks, which cumulatively affect the mechanical properties and fracture behavior of the material. This microstructure is also susceptible to changes including sintering during high temperature operation. The kinetics of “healing” of these microstructural defects are widely different, such that the smallest defects heal at significantly lower temperatures and in shorter periods. Here, the effect of thermal exposure-induced change in the microstructure on the fracture behavior, in terms of crack path and apparent fracture energy, of free-standing APS 7YSZ has been examined using miniaturized cantilever samples. Femto-second laser ablation technique was used to fabricate a sharp notch in the sample. Apparent fracture toughness in Mode I increased with the bending modulus of the material, revealing a monotonic effect of the density, which directly affects the modulus of the coating, on the overall fracture resistance of the coating. The relative density, crack tortuosity and the average apparent fracture energy of the as-deposited coating were 0.82, 2.1 and 62 ± 15 J/m2, respectively, which evolved to 0.94, 1.2 and 170 ± 30 J/m2, respectively, after a heat treatment at 1300 °C for 100 h. The detailed microstructural characterization and fractography revealed that the healing of inter-splat and intra-splat cracks led to the transition from fracture along the splat interface to quasi-cleavage fracture through the splats, thereby increasing the fracture resistance of these coatings toward monolithic fully-dense 7YSZ. The work readily reveals the relative importance of defects at various length scales on the overall energy absorbed during fracture of the coating.

Dark-current reduction accompanied photocurrent enhancement in p-type MnO quantum-dot decorated n-type 2D-MoS2-based photodetector

A highly crystalline single- or few-layered 2D-MoS2 induces a high dark current, due to which an extremely small photocurrent generated by a few photons can be veiled or distorted. In this report, we show that suppression in the dark current with the enhancement in the photocurrent of a 2D-based photodetector, which is a prerequisite for photoresponse enhancement, can be achieved by constructing an ideal p-n junction based on functionalizing n-type 2D-MoS2 with p-type quantum dots (QDs). Highly crystalline solution-processed manganese oxide QDs (MnO QDs) are synthesized via the pulsed femtosecond laser ablation technique in ethanol. The ablated MnO QDs are spray-coated on an exfoliated 2D-MoS2 substrate with interdigitated Au electrodes through N2-assisted spraying. In the resulting MnO QD-decorated 2D-MoS2 photodetector with a heterojunction, dark current is reduced and is accompanied by photocurrent enhancement, thereby markedly improving the photoresponsivity and detectivity of MoS2-based devices. To elucidate the underlying mechanisms contributing to this enhancement, power- and wavelength-dependent photoresponses, along with material characterizations based on spectroscopic, chemical, morphological measurements, and analyses, are discussed.

Instantaneous trace detection of nitro-explosives and mixtures with nanotextured silicon decorated with Ag–Au alloy nanoparticles using the SERS technique

The development of recyclable surface enhanced Raman scattering (SERS) based sensors has been in huge demand for trace level explosives detection. A simple, hybrid Silicon (Si) nanotextured target-based SERS platform is fabricated through patterning micro square arrays (MSA) on Si using femtosecond (fs) laser ablation technique at different fluences. Using the hybrid target Si MSA substrate loaded/decorated with Ag–Au alloy NPs (obtained using femtosecond ablation in liquids) we demonstrate the trace level detection of organic nitro-explosives [picric acid (PA), 2,4-dinitrotoluene (DNT), and 1, 3, 5-trinitroperhydro-1, 3, 5-triazine (RDX)] and their mixtures. The microstructures/nanostructures of MSA fabricated at an input fluence of 9.55 J/cm2, and decorated with Ag–Au alloy NPs, exhibited exceptional SERS enhancement factors (EFs) up to ∼1010 for MB, ∼106 for PA, and ∼104 for RDX with the detection limits obtained being ∼5 pM, ∼36 nM, and ∼400 nM for MB, PA and RDX respectively. Furthermore, we demonstrate these SERS substrates possess good reproducibility (RSD values < 15%) and a superior performance compared to a commercial Ag substrate (SERSitive, Poland). Three binary mixtures, i.e. MB-PA, MB-DNT, PA-DNT at different concentrations, were also investigated using the same SERS substrate to test the efficacy. Further, the SERS spectra of dyes, explosives, and complex mixtures were utilized for discrimination/classification using principal component analysis.

Photothermal tuning and stabilization of a photonic crystal nanofiber cavity.

We report the photothermal properties of a photonic crystal nanofiber (PhCN) cavity, which is fabricated using a femtosecond laser ablation technique, under ultra-high vacuum conditions. The results show that by launching a non-resonant guided light, the stopband of the PhCN, along with the cavity modes, can be tuned at a rate of 250GHz (∼0.5 nm)/mW. Moreover, due to the thermal self-locking effect of a resonant light, a cavity mode with a finesse of 25 can be tuned over a few free spectral ranges using only a few μW of guided light. As an enabling step, we demonstrate a dual-mode locking scheme to thermally stabilize a cavity mode to the atomic line for single atom-based cavity quantum electrodynamics experiments.

Surface Processing: An Elegant Way to Enhance the Femtosecond Laser Ablation Rate and Ablation Efficiency on Human Teeth.

The employability of the non-invasive femtosecond laser ablation technique for dental treatment has been severely limited by its low ablation rate despite the advantage of minimal tissue damage. The study explores a means ofimproving the femtosecond laser ablation rate and efficiency by physiochemical surface modification. Surface modification of dental hard tissues hasbeen carried out by food graded orthophosphoric acid and Carie care gel pretreatment. The laser ablation characteristics were studied by using a Ti:Sapphire laser (10 kHz, 10 mm/s, 100 fs, 800 nm) to ascertain the influence of pretreatment. Surface morphology and chemical composition were obtained by using an optical profiler, SEM and EDAX. The ablation threshold fluence decreased by almost one-third whereas the ablation rate and ablation efficiency nearly tripled upon pretreatment. The microstructural and compositional analysis clearly reveals that surface modification and demineralization reduce the threshold fluence and increase the ablation rate by effective utilization of the laser beam energy. The pretreatment effect is more pronounced in orthophosphoric acid as compared with Carie care gel. Physiochemical surface modification can be an efficient method to improve the laser ablation rate and ablation efficiency. Compositional analysis can be an elegant tool for pre-surgery determination of laser ablation characteristics. Pretreatment surface modification can be an effective way to overcome the limitation of the femtosecond laser for tooth preparation in the clinical setting by strongly enhancing the ablation rate. An enhanced ablation rate along with de nova prediction of ablation characteristics will enable the clinician to perform dental surgery in real time with minimal tissue damage. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Femtosecond Laser Ablation Synthesis of Nanoparticles and Nano-Hybrides in Ethanol Medium

Abstract The nanoparticle production has a significant importance because of its unique optical properties in molecular biology and medicine. Plasmonic metallic nanoparticles are widely used in cancer monitoring studies as contrast agents on the account of their surface plasmon resonance (SPR) effect. Beside, silicon (Si) semiconductor nanoparticles can provide several beneficial properties that they are used commonly intensifying the detecting signals. Nanoalloys/Nanohybides/Nanocomposites are more functional materials than a single material structure and having many restrictions. At that point, the application of Pulsed Laser Ablation (PLA) technique has many advantages if applied in the liquid. Since no any chemical technique is applied, this procedure promises a clean synthesis process; it is a simple and economical technique in the production process. It provides some possibilities to generate particles in the desired size, shape and density, and these properties of nanoparticles produced can be controlled by controlling the laser parameters. In this work, we have focused on the production of nanoparticles to rid off chemical processes using femtosecond laser ablation technique, and this technique presents a process to reach the fast and reliable results for production of nanoshells, nanocomposites and all nanoforms of particles. We have produced Si@Au nanohybrids in ethanol medium using femtosecond laser ablation depending on laser pulse energy. Absorption spectra were recorded day by day to determine the optical characteristics of produced nanoparticles within these time durations, Transmission Electron Microscopy (TEM) images were obtained for monitoring and determining the size/structure of nanoparticles, energy dispersive spectroscopy (EDS) for material compositions were produced, these results obtained are presented in the scope of this paper

Maskless 3D Ablation of Precise Microhole Structures in Plastics Using Femtosecond Laser Pulses.

Femtosecond laser ablation is a robust tool for the fabrication of microhole structures. This technique has several advantages compared to other microfabrication strategies for reliably preparing microhole structures of high quality and low cost. However, few studies have explored the use of femtosecond laser ablation in plastic materials because of the lack of controllability over the fabrication process in plastics. In particular, the depth profile of microhole structures prepared by conventional laser ablation techniques in plastics cannot be precisely and reproducibly controlled. In this paper, a novel three-dimensional femtosecond laser ablation technique was developed for the rapid fabrication of precise microhole structures in multiple plastics in air. Using a three-step fabrication scheme, microholes demonstrated extremely clean and sharp geometric features. This new technique also enables the precise creation of arbitrary-shaped microwell structures in plastic substrates through a rapid single-step ablation process, without the need for any masks. As a proof of concept for practical applications, precise microhole structures prepared by this novel femtosecond laser ablation technique were exploited for robust resistive-pulse sensing of microparticles.

Femtosecond laser microstructured Alumina toughened Zirconia: A new strategy to improve osteogenic differentiation of hMSCs

The use of topographic patterns has been a continuously growing area of research for tissue engineering and it is widely accepted that the surface topography of biomaterials can influence and modulate the initial biological response. Ultrafast lasers are extremely powerful tools to machine and pattern the surface of a wide range of biomaterials, however, only few work has been performed on ceramics with the intent of biomedical applications, and the biological characterization of these structured materials is scarce.In this work, relevance is given to the biological performance of such materials. A femtosecond laser ablation technique was used to modify Alumina toughened Zirconia (ATZ) surface topography, developing surfaces structured at the micro and nanoscale levels (μATZ), in a controlled and reproducible manner. Materials characterization was performed before and after laser treatment, and both materials were compared in terms of osteogenic response of human bone marrow derived mesenchymal stem cells cultured under basal conditions, expecting that the micro/nanofeatures will improve the biological response of cells. Cells metabolic activity and proliferation increased with the culture time and surface microtopography modulated cells alignment and guided proliferation. The modified surface, displayed significantly higher expression of osteogenic transcription factors and genes and, additionally, the formation of a mineralized extracellular matrix, when compared to the control surface, i.e. unmodified ATZ.

2,4-dinitrotoluene detected using portable Raman spectrometer and femtosecond laser fabricated Au–Ag nanoparticles and nanostructures

We report results from our studies on the fabrication of bimetallic nanoparticles (NPs) and nanostructures (NSs) using femtosecond (∼50 fs) laser ablation technique. The NPs and NSs were achieved by immersing bulk targets with different Au–Ag compositions in acetone followed by ablation. We demonstrate their application towards detection of an explosive molecule of 2, 4-Dinitrotoluene, DNT (25 μM) using a portable Raman spectrometer (785 nm). A tuneable surface plasmon peak observed in the UV-Visible absorption spectra with varying Au proportions confirmed the formation of bimetallic NPs. The size, shape and crystallographic phases were investigated by transmission electron microscope (TEM) and selected area diffraction pattern (SAED). The surface morphology of fabricated NSs was characterized using field emission scanning electron microscope (FESEM). Both NPs and NSs were employed as Surface Enhanced Raman Scattering (SERS) substrates for sensing Methylene Blue (MB) and DNT. From the results obtained in this investigation we concluded that Au70Ag30 NPs/NSs exhibited superior SERS performance compared to pure Ag, Au and other compositions. A detection limit of ∼10−9 M for MB and ∼10−6 M for DNT was achieved with corresponding enhancement factors of ∼107 and ∼104. Furthermore, we have also observed a ‘factor of 3’ increase in the SERS intensity by simply drop casting Ag NPs on the gaps of Au70Ag30 NSs. This clearly demonstrates that individual NPs, NSs and NPs on NSs (hybrid SERS targets) can be achieved in a single experiment and in combination provide efficient means of detecting trace quantities of explosive molecules.