KrF Excimer Laser Research Articles

准分子激光系统中模拟信号的传输方法

Several analog signal transmission system under harsh electromagnetic interference environment was introduced, and a method of transmission was designed. Firstly, the analog signal was converted into a frequency signal through the detector and sent through the fiber transmitter. Secondly, the fiber signal was received and the frequency of the optical signal was measured within the configurable regularized time and then the analog signal was calculated instead of using the traditional method which converted analog signal to digital signal after frequency-to-voltage conversion. This system not only got the reduced total conversion time and improved response speed, but also can obtain different precision according to system requirements by adjusting converting time. Tested on a 248 nm KrF excimer laser, the system realized high-precision online monitoring of the slow-changing working gas pressure signal compared with traditional method, and then it also measured the fast-responsed energy signal of pulse laser up to 90 Hz well. By calculating the Pearson coefficient, the acquired value of the scheme tends to be consistent with the original signal to meet the application requirements.

Effect of Diamond Grain Orientation on the Local Conductivity of Laser-Induced Graphitized Surface Layer

Graphitized structures are fabricated on a polycrystalline diamond surface using an excimer KrF laser. It is found that the layer grown on the {001} crystallite, has a lower resistance and thickness than that on the {111} surface. A model of the formation of oriented nanocrystalline graphite is proposed to explain the observed effects.

High-Thermoresistant Temporary Bonding Technology for Multichip-to-Wafer 3-D Integration With Via-Last TSVs

In this paper, a high-thermoresistant temporary bonding/debonding system using spin-on glass (SOG) and hydrogenated amorphous silicon layers is proposed for the multichip-to-wafer (MCtW) 3-D integration based on a via-last/backside-via through-silicon via (TSV) approach. The shear strengths of chips bonded to wafers through the SOG layers are evaluated. In addition, the debonding performance of the chips from the wafers is investigated by using the KrF excimer laser irradiation. Finally, a via-last/backside-via MCtW 3-D integration process using the temporary bonding/debonding system is demonstrated to show the high feasibility with the successful interconnect formation of a Cu-TSVs daisy chain (10 $\mu \text{m}$ in diameter and 50 $\mu \text{m}$ in depth) with a SiO2 liner dielectric deposited by O3-tetraethylorthosilicate chemical vapor deposition at 350 °C.

Optimization of silver nanowire formation on laser processed PEN: Surface properties and antibacterial effects

Combination of polymers with their excellent workability and long-term stability with inorganic nanomaterials exhibiting unique physic-chemical properties opens the way for preparation of nanocomposites with wide range of potential applications in electronic, environmental, medical and biomedical industry. Despite of testing of various metal nanostructures in biomedicine, the best results, particularly antibacterial effects, have been achieved with the silver-based ones. Silver nanowire arrays on the surface of polyethylene naphthalate (PEN), first modified by KrF excimer laser irradiation and then silver coated, were prepared. The laser fluence and angle of incidence of laser beam, were changed to achieve required sample surface morphology, which was controlled by AFM, SEM and FIB-SEM techniques. The surface properties of the samples in different phases of their preparation were characterized by XPS and UV–Vis. The influence of the surface morphology of the samples on their antibacterial effect was investigated by drop plate method using Gram-negative bacteria E. coli and Gram-positive S. epidermidis. The release of Ag ions into working medium was controlled by ICP-MS. The surface morphology of polymeric substrate was found to have a great influence on the resulting antibacterial effect of such silver/polymer composites.

Development and Characterization of MgO Coatings on 316L Stainless Steel

The present work deals with the development of MgO coatings on ASTM 316L stainless steel using pulsed laser deposition technique employing KrF excimer laser (λ = 248 nm). Two important process variables, namely oxygen partial pressure and substrate temperature, were varied to get uniform coatings. The process parameters were optimized based on the microstructure and uniformity of the coatings, which had the direct bearing on the performance of the coating. Structural, morphological and microstructural characterizations of the coatings were carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy. While XRD studies confirmed the phase purity and the strain associated with the coating and the substrate, SEM studies revealed the microstructural integrity and morphology of the coatings in addition to establishing the chemistry of coatings. Field testing of the coatings for their sodium compatibility, particularly in aggressive conditions of incineration, confirmed the successful performance of the coatings.

Photofragmentation laser-induced fluorescence of ozone using narrowband and broadband KrF excimer lasers

Photofragmentation laser-induced fluorescence (PF-LIF) is used for the high-sensitivity measurement of ozone density; however, its theoretical basis is not well established. In this paper, O3 PF-LIF, using a tunable KrF excimer laser (248–249 nm), was examined using both measurements and calculations to provide a theoretical basis for this measurement method. The KrF laser photolyzed O3 to produce O, which was then measured using LIF with the same laser pulse that had photolyzed the ozone. A calculation including photochemical reactions and a LIF model of O reproduced the measured results well which demonstrated the reliability of the calculation. A recommended laser energy density of 100–400 mJ cm−2 was obtained by considering the depletion of ozone by the laser photolysis and the saturation of the LIF. It was also demonstrated that a broadband KrF excimer laser, which is not line narrowed and therefore not tunable, could also be used for O3 PF-LIF. The signal intensity of the broadband PF-LIF was only reduced to 1/2–1/3 of the narrowband PF-LIF.

Growth of two-dimensional WS2 thin films by pulsed laser deposition technique

Tungsten disulfide (WS2) is a promising material for potential applications in next-generation 2D-electronics. However, for such applications large-area films will be required. Fabrication techniques involving exfoliation give films of high crystal quality but suffer from the problem of extremely small size of the films which makes it very challenging to realize real devices for industrial applications. In this study, we are reporting the growth of large area two-dimensional (2D) films of WS2 using pulsed laser deposition technique. A polycrystalline WS2 target was ablated using a pulsed KrF excimer laser (wavelength: 248 nm; pulse width: 25 ns). The ablated material was deposited over a c-axis aligned single crystal sapphire substrate maintained at 500°C in an ambient vacuum of 10−5 Torr. Thickness of the resulting films was controlled by controlling the number of incident laser pulses. Detailed characterization of the films was carried out using several state-of-the-art techniques including atomic force microscopy, Raman spectroscopy, and ultraviolet–visible spectroscopy. Relationship between the number of monolayers in the WS2 films and the spacing between the A1g(Γ) and E2g1 (Γ) Raman peaks (Δf) was determined. Effect of post annealing on the optical properties of the films was also investigated.

In-situ temperature and thickness control grown 2D-MoS2 via pulsed laser ablation for photovoltaic devices

Two dimensional molybdenum disulphide thin films are fabricated via pulsed laser ablation technique and used as counter electrode for photovoltaic devices. MoS2 thin films are laser ablated using KrF excimer laser, the parameters like temperature and thickness of thin films being controlled under in-situ condition. The effects of parameters on the laser ablated MoS2 thin film exhibit a superior electrocatalytic activity thereby indicating an ability to be employed as a counter electrode in dye-sensitized solar cells. With increase in temperature, there is an improvement in crystallinity which leads to enhancement of active sites in MoS2 resulting into its effectual for use in the photo-conversion devices. Raman and XRD studies clearly confirm the formation of MoS2 and its associated phase structure. The crystalline nature and interlayer spacing of stacked MoS2 structure are observed from HRTEM. The growth and thickness of MoS2 thin films are evaluated from FESEM and AFM. Electrocatalytic behaviour of laser ablated films are carefully investigated and its photovoltaic performances are analyzed. MoS2 films fabricated under room temperature delivers photo-conversion efficiency of 1.48%, while on the increasing temperature and thickness of MoS2 films it delivers four times increase in efficiency up to 5.66% under one sun condition.

Inscription and investigation of the spectral characteristics of chirped fiber Bragg gratings

The results of investigations of the spectral characteristics of chirped fiber Bragg gratings induced in an optical fiber using a Talbot interferometer and a KrF excimer laser system of the master oscillator–power amplifier type with enhanced coherence are presented. Dependences of the full width of the reflection spectrum at half maximum and the reflectivity of chirped fiber Bragg gratings on their length are obtained and analyzed. Through the inscription of seven superimposed chirped fiber Bragg gratings, a diffraction structure with a spectral width of 32 nm was obtained. In addition, a chirped fiber Bragg grating whose spectral response shape is almost rectangular is presented.

Fabrication of self-assembled spherical Gold Particles by pulsed UV Laser Treatment

We report on the fabrication of spherical Au spheres by pulsed laser treatment using a KrF excimer laser (248 nm, 25 ns) under ambient conditions as a fast and high throughput fabrication technique. The presented experiments were realized using initial Au layers of 100 nm thickness deposited on optically transparent and low cost Borofloat glass or single-crystalline SrTiO3 substrates, respectively. High (111)-orientation and smoothness (RMS ≈ 1 nm) are the properties of the deposited Au layers before laser treatment. After laser treatment, spheres with size distribution ranging from hundreds of nanometers up to several micrometers were produced. Single-particle scattering spectra with distinct plasmonic resonance peaks are presented to reveal the critical role of optimal irradiation parameters in the process of laser induced particle self-assembly. The variation of irradiation parameters like fluence and number of laser pulses influences the melting, dewetting and solidification process of the Au layers and thus the formation of extremely well shaped spherical particles. The gold layers on Borofloat glass and SrTiO3 are found to show a slightly different behavior under laser treatment. We also discuss the effect of substrates.

Investigation on stable superhydrophobic polycarbonate based compound induced by KrF excimer laser irradiation

This study demonstrates a reliable method for the manufacturing of Polycarbonate based compound (PCBC) superhydrophobic surface by KrF excimer laser irradiation. The water contact angle (CA) of PCBC samples surface was increased from 75° to 170°, and the CAH of most samples was between 2° and 6°. The CA of samples remained at about 158° for 2 months. The abrasion resistance test showed that the CA reached about 115° for 1% mass losses. Optical contact angle meter, XRD, LCM, SEM, EDS, FTIR and XPS were used to analyze surface properties of PC samples. It was indicated that the increase in surface roughness caused by PC surface precipitation of small organometallic complexes particles was the main factor to the preparation of superhydrophobic surface. It showed that the hydrophilicity of PCBC surface could be converted into superhydrophobicity quickly and effectively by laser irradiation.

Inscription and visualization of tilted fiber Bragg gratings

In this work the inscription and investigation of tilted fiber Bragg gratings induced in a single-mode isotropic optical fiber with increased photorefractivity are demonstrated. Using the Talbot interferometer and the KrF excimer laser system, tilted fiber Bragg gratings with different angles were fabricated, the spectra of the formed diffraction structures were analyzed, and their photographic images were taken with a confocal laser scanning fluorescence microscope in transmitted light. The calculated dependence of the tilt angle of tilted fiber Bragg gratings fabricated in the Talbot interferometer on the angle between the interference fringes created in the interferometer and the cross section of the optical fiber is experimentally verified.

Phase-shifted fiber Bragg gratings fabrication method

In this paper, we showed a technique for the formation of phase-shifted fiber Bragg gratings. The analysis of the efficiency of the obtained structures was carried out with the help of an optical spectrum analyzer with the subsequent calculation of the full width at half maximum of a bandpass in reflection spectrum. Fiber Bragg gratings inscription was performed on the Talbot interferometer, the KrF excimer laser system was used as a UV radiation source, and a phase shift was introduced by the electrical discharge of an arc fusion splicer. The experimental dependence between the length of the obtained structure and the full width at half maximum of a bandpass in reflection spectrum of a phase-shifted grating was presented, the value of the last parameter varies in the range from 24 pm to 96 pm.

Laser processing of indium tin oxide thin film to enhance electrical conductivity and flexibility

This work reports a method that uses a KrF excimer laser to enhance the electrical and mechanical properties of amorphous indium tin oxide (ITO) thin films on flexible substrates. Irradiation with nanosecond laser pulses induces thermal crystallization of ITO, and thereby increases the electrical conductivity and flexibility of film deposited on polyethylene terephthalate substrates. The shallow optical (~45 nm) and thermal penetration (~100 nm) of the laser beam confines the thermal effect to within the ITO layer without damaging the substrate. The laser treatment changed the crystallinity of ITO film from amorphous to poly-crystalline; as a result, its electrical-conductivity increased by 20–25%. Moreover, the treatment decreased the critical bending radius to avoid loss of electrical property from 8 mm to 5 mm. The adhesion strength and transparency of the ITO film were not affected significantly by the laser treatment. This work suggests that laser treatment can be an effective tool to enhance the crystallinity, of sputtered ITO thin film, and its electrical and mechanical properties on flexible substrate.

A detailed study on melting dynamics influenced by the pulse laser-induced transient heating

This paper presents a detailed study on the melting dynamics induced by the pulse laser heat transfer process. A numerical model has been developed in an open-source based computational fluid dynamics (CFD) platform, known as OpenFOAM. Upon development, its predictions have been compared with the experimental results of nanosecond pulse laser annealing of silicon with a pulse duration of 30 ns and wavelength (λ) of 308 nm, in which an excellent agreement with the experimental results for both of the melt depth and the melting duration has been observed. In the second part of this study, the numerical model has been implemented to explain the pulse laser-induced melting dynamics of silicon wafers irradiated with KrF excimer laser, which is similar to the cases used for processing of industry compatible photovoltaic solar cells. Since the results explain how thermal process, induced by the transient energy, controls the propagation of melting dynamics, this contribution can be used as a guide for designing new laser systems as well as optimisation of a chosen application.

Long-Period Gratings in Highly Germanium-Doped, Single-Mode Optical Fibers for Sensing Applications

Long-period fiber gratings (LPGs) are well known for their sensitivity to external influences, which make them interesting for a large number of sensing applications. For these applications, fibers with a high numerical aperture (i.e., fibers with highly germanium (Ge)-doped fused silica fiber cores) are more attractive since they are intrinsically photosensitive, as well as less sensitive to bend- and microbend-induced light attenuations. In this work, we introduce a novel method to inscribe LPGs into highly Ge-doped, single-mode fibers. By tapering the optical fiber, and thus, tailoring the effective indices of the core and cladding modes, for the first time, an LPG was inscribed into such fibers using the amplitude mask technique and a KrF excimer laser. Based on this novel method, sensitive LPG-based fiber optic sensors only a few millimeters in length can be incorporated in bend-insensitive fibers for use in various monitoring applications. Moreover, by applying the described inscription method, the LPG spectrum can be influenced and tailored according to the specific demands of a particular application.

Lithography-Free Fabrication of Crystalline Silicon Nanowires Using Amorphous Silicon Substrate for Wide-Angle Energy Absorption Applications

We report a one-step fabrication technique of silicon nanowires using KrF excimer laser. Nanowires (NWs) are fabricated by redistributing the silicon mass within the sample without etching any of t...

Poly(N-isopropylacrylamide) grafting solution parameters for controlling temperature responsiveness in PET membranes fabricated using 248 nm KrF excimer laser

A fast, simple, and efficient method to fabricate thermo-responsive membranes using 248 nm KrF excimer laser has been reported. For that process, monomer and crosslinker concentration effects on hydrogel network formation were studied during 248 nm pulsed laser polymerization (PLP) of poly(N-isopropylacrylamide) (PNIPAM) on laser ablated polyethylene terephthalate (PET) membranes. Water permeability of over 6 orders could be easily achieved, at room temperature, by appropriately tuning the hydrogel network parameters. The network growth could be controlled by reducing the monomer and crosslinker concentrations in the grafting solution. Caffeine diffusion studies established that controlled amounts of a model drug could be transported across the membranes. Crosslinker concentration had a more pronounced effect on the temperature responsivity of the grafted network across the lower critical solution temperature (LCST) of PNIPAM. A transition from positive to reverse temperature responsiveness was also observed for highly crosslinked grafted networks. Quantitative ATR-FTIR studies were performed to evaluate the relative amount of PNIPAM grafted in the membranes which was correlated to chain growth in pulsed laser polymerization.

Enhanced magnetoresistance in pulsed laser deposited stable chromium oxide thin films

Granular thin films of primarily rutile type tetragonal chromium dioxide (t-CrO2), along with a minor phase of hexagonal Cr2O3 were deposited on rutile type TiO2 layers by KrF excimer laser based pulsed laser deposition (PLD) technique using Cr2O3 targets. The TiO2 under-layer was also deposited by PLD process on oxidized Si substrates followed by annealing at 1100 °C for 10–15 min under O2 ambient. The lattice-matched interfacial TiO2 layer stabilizes the metastable Cr (IV) phase of CrO2, otherwise it readily converts into its stable phase of Cr (III) oxide, Cr2O3, under ambient conditions. Studies with X-ray diffraction (XRD) and Raman spectroscopy confirmed the stable t-CrO2 phase in the films. The microstructure in the films was studied with field emission scanning electron microscope (FESEM) and magnetic force microscope (MFM). As revealed by electrical analysis, the ferromagnetic (FM) t-CrO2 grains in conjunction with the antiferromagnetic (AFM) Cr2O3 phase in the tailored thin films effectively support an electrical transport process based on inter-granular spin-dependent tunneling (SDT) mechanism, giving rise to significantly high magnetoresistance (MR). A typical sample exhibits a markedly improved MR-value, viz., −30% at an applied field (H) of 438 kA/m at 278 K, than reported values in CrO2 thin films. Such a large MR value in the Coulomb blockade regime arises primarily not only because of the considerably suppressed spin flipping but also as a result of the highly effective SDT mechanism through an interlinked FM-AFM structure of chromium oxides in this specially engineered microstructure of the thin films. Such type of stable half-metallic thin films with low-H switching behavior is attractive for pertinent use in spintronics and magnetic sensing based applications.

Laser-synthesized nanocrystalline, ferroelectric, bioactive BaTiO3/Pt/FS for bone implants.

The goal of our study is to design BaTiO3 ferroelectric layers that will cover metal implants and provide improved osseointegration. We synthesized ferroelectric BaTiO3 layers on Pt/fused silica substrates, and we studied their physical and bio-properties. BaTiO3 and Pt layers were prepared using KrF excimer laser ablation at substrate temperature Ts in the range from 200°C to 750°C in vacuum or under oxygen pressure of 10 Pa, 15 Pa, and 20 Pa. The BaTiO3/Pt and Pt layers adhered well to the substrates. BaTiO3 films of crystallite size 60-140 nm were fabricated. Ferroelectric loops were measured and ferroelectricity was also confirmed using Raman scattering measurements. Results of atomic force microscopy topology and the X-ray diffraction structure of the BaTiO3/Pt/fused silica multilayers are presented. The adhesion, viability, growth, and osteogenic differentiation of human osteoblast-like Saos-2 cells were also studied. On days 1, 3, and 7 after seeding, the lowest cell numbers were found on non-ferroelectric BaTiO3, while the values on ferroelectric BaTiO3, on non-annealed and annealed Pt interlayers, and on the control tissue culture polystyrene dishes and microscopic glass slides were similar, and were usually significantly higher than on non-ferroelectric BaTiO3. A similar trend was observed for the intensity of the fluorescence of alkaline phosphatase, a medium-term marker of osteogenic differentiation, and of osteocalcin, a late marker of osteogenic differentiation. At the same time, the cell viability, tested on day 1 after seeding, was very high on all tested samples, reaching 93-99%. Ferroelectric BaTiO3 films deposited on metallic bone implants through a Pt interlayer can therefore markedly improve the osseointegration of these implants in comparison with non-ferroelectric BaTiO3 films.