ArF Excimer Laser Research Articles

Wettability measurements of agarose thin films patterned by 193 nm ArF excimer laser

Wettability measurements of agarose thin films patterned by 193 nm ArF excimer laser

Numerical investigation of discharge evolution and breakdown characteristics of ArF excimer lasers

The corona bar induced pre–ionization is a crucial preliminary process in the operation of ArF excimer lasers, directly impacting the uniformity and stability of output laser. The ultraviolet corona pre–ionization, as the mainstream method, is tightly coupled with the main discharge process, which complicates analysis. Here, we establish a numerical model of a single pulse discharge incorporating an external circuit to analyze the pre–ionization process and its influence on the breakdown characteristics. (1) By adopting detailed input parameters of photoionization model, we observe uniform and dispersed plasma propagation from the corona bar to the main gap. (2) An artificial boundary condition is proposed to investigate the phenomenological effect of high–energy electrons emission, emphasizing the influence of surface discharge along the cathode. (3) The propagation and breakdown characteristics of the two pre–ionization setup methods, photoionization and background electron density, are compared numerically. This study enhances the understanding of the pre–ionization process in ArF excimer lasers and provides theoretical insights for their optimization and design.

Cathode failure behavior of ArF excimer laser glow discharge

Abstract In this paper, the failure behavior of the glow discharge cathode of the ArF excimer laser was investigated. The morphology and composition of the cathode were characterized by scanning electron microscopy, energy spectrometer and high resolution laser confocal microscope. The results show that Ar ions sputtering occurs in the cathode discharge area, resulting in sputtering pit, molten morphology and resolidified particles. Due to the thermal effect induced by sputtering, Zn element evaporates violently, which intensifies the cathode erosion. Argon ion sputtering experiments proved the influence of random sputtering on the generation of sputtering pits. The main failure form of the non-discharge region is the corrosion of F2 molecule, which is dominated by Cu and Zn fluoride, and the fluorination layer is not dense.

Photochemical formation of hollow silicone microcapsule arrays on periodic microswelling structures of silicone rubber using 193 nm ArF excimer laser for microencapsulation of electrolytes

Microencapsulation for developing energy storage devices has been widely reported recently. In heat storage, many studies have been conducted to microencapsulate phase change materials with various shell materials. In contrast, there are still few studies on microencapsulation in power storage. In this paper, we found a new method to form hollow silicone microcapsule arrays for microencapsulation of electrolytes and suggested a new micropower storage application. Single layer of silica microspheres was formed on silicone rubber, then an ArF excimer laser irradiated the surface. Main chains of Si–O–Si bonds of silicone rubber underneath the microspheres could be photodissociated to lower the molecular weight, resulting in the formation of periodic microswelling structure of silicone rubber. Concurrently, a spherical microcapsule was also photochemically formed on each the microswelling structure. We systematically investigated the optimal conditions for chemical pre-etching to tune the gaps between microspheres to form spherical microcapsules and for chemical post-etching to completely remove the enclosed microspheres to form hollow microcapsules. The microcapsules formed consisted of silicone and were porous. Moreover, micro/nanoholes on the side/top of each microcapsule to encapsulate various electrolytes were successfully formed. The present results are expected to be applied as a micropower storage device that functions underwater.

Superhydrophobic silicone microcup array on periodic microswelling structure of silicone rubber formed by 193 nm ArF excimer laser-induced photodissociation

Many reports have been made on the study of imparting high functionality to materials surface by micro/nanofabrication of three-dimensional structures. In various three-dimensional structural geometries, the nanocups enable high-sensitivity analysis by combining with localized plasmon resonance. On the other hand, the formation of microcups and their applications have not been found much. In this paper, we found a new formation method of the silicone microcups and suggested its application. Single layer of silica glass microspheres was formed on silicone rubber, then a 193 nm ArF excimer laser irradiated the surface. Main chains of SiOSi bonds of the silicone rubber underneath the microspheres could be photodissociated to lower the molecular weight, resulting in the photochemical formation of periodic microswelling structure of silicone rubber. Concurrently, a hemispherical microcup was also formed on each the microswelling structure. The optimal laser irradiation conditions for their formation as well as the chemical etching time of microspheres were examined. It was also confirmed that the microcups are consisted of silicone. Moreover, the microcups exhibit superhydrophobicity. The results make it possible to confine the microcups in an air gap underwater, and it is expected to be applied as a micropower storage device that functions in seawater.

Evolution of local surface roughness in 193 nm ArF excimer laser ablation of ground Yb:YAG crystal

The surface quality of YAG crystals plays a decisive role in the output performance of the device. In this investigation, it was found that the surface quality of Yb:YAG crystal was improved by 193 nm ArF excimer laser ablation. The influence of laser energy density and pulse numbers on the surface roughness of Yb:YAG crystal was obtained. The possible laser ablation mechanism of YAG crystal was analyzed by thermal conduction and photodissociation theory. Surface profile analyses reveal that photochemical ablation was the dominant mechanism of material removal.

Pulsed laser annealed rare earth doped TiO2 thin films for luminescence and sensing applications

Many research activities target functional luminescent materials based on metal oxides activated with trivalent rare earth ions. Specific applications necessitate optimization of material preparation, annealing and excitation-detection techniques. Hereby we utilized pulsed laser deposition to obtain thin (150 nm) TiO2 films containing 1at% of samarium (Sm) or neodymium (Nd) impurity ions. The effect of pulsed laser annealing (ArF excimer laser, wavelength 193 nm, pulse duration 20 ns) on their structural and luminescent properties was investigated. It was found that, compared to conventional thermal annealing at 700 °C, proper laser annealing (fluence 50 mJ/cm2, 5–15 shots) induced much better crystallization (nearly phase-pure anatase) along with respective improvement of host-sensitized trivalent rare earth fluorescence. The outcome significantly depends on the applied fluence and number of laser shots. Effects of under- and overannealing were witnessed (poor or mixed phase crystallization, weak luminescence and melting/dewetting of the film). A strong luminescence from optimally annealed samples was detected under excitation of 365 nm light emitting diode, which is favorable for potential applications of such thin films. As an example, trace oxygen sensing is demonstrated with the laser annealed TiO2:Sm film.

STDGL3, a Reference Material for Analysis of Sulfide Minerals by Laser Ablation ICP‐MS: An Assessment of Matrix Effects and the Impact of Laser Wavelengths and Pulse Widths

A new reference material, STDGL3, for the calibration of in situ analyses of sulfide minerals by LA‐ICP‐MS has been developed and characterised. It represents a lithium‐borate‐based glass containing a mixture of Zn‐ and Fe‐sulfide concentrates doped with several chalcophile elements as well as Zr, Gd, Hf and Ta required for assessing common interferences on Ag, Au and Pt. STDGL3 has a wider range of elements and a better homogeneity compared with existing reference materials for LA‐ICP‐MS analysis of sulfides. Compositional variations for most elements are below 3% RSD, below 5% RSD for Ag, Au and Pt, and below 7% RSD for Se, when performing spot analyses with a 50 μm beam size. Its preparation recipe is reproducible allowing for multiple batches to be made. Use of STDGL3 significantly improves accuracy of sulfide mineral analysis by LA‐ICP‐MS when compared with use of other available reference materials. Performance of STDGL3 was evaluated using several different laser systems. No significant change was observed between 193 nm ArF excimer lasers with 5 and 20 ns pulse widths, but use of 213 and 248 nm lasers displays more systematic differences, especially when analysing galena. Correction coefficients are needed for some elements (Zn and Cd in particular) when analysing sulfide minerals using STDGL3 as a calibration reference material.

Evaluating the efficacy of Nd:YAG fourth harmonic (266 nm) in comparison with ArF excimer (193 nm) in laser corneal reshaping: ex vivo pilot study

PurposeLaser corneal reshaping is a common eye surgery utilized to overcome many vision disorders. Different UV laser wavelengths can be effective in the treatment. However, the ArF excimer laser (193 nm) is the most commonly used due to its high absorption in the cornea. In the current study, we investigate the efficacy of applying a solid-state laser (Nd:YAG fourth harmonic at 266 nm) for the corneal reshaping procedure. MethodsThe utilized laser is generated using an optical setup based on a BBO nonlinear crystal which converts the Q-switched laser (532 nm) to its fourth harmonic (266 nm). Different pulse energies were applied with the same number of the shoots on ex vivo rabbit corneas, and the histological effect is studied. Moreover, the possible thermal damage on the treated corneal tissues was inspected via electron microscope. Additionally, the DNA damage on the corneal cells due to the application of the proposed laser was examined and compared with the existing technology (ArF Excimer laser at 193 nm) using the comet assay. ResultsThe histological examination revealed an appropriate ablation result with the minimum thermal effect at 1.5 mJ and 2.0 mJ. The overall results show that applying 50-shoots of the 1.5-mJ pulse energy using the proposed 266-nm solid-state laser produces the optimum ablation effect with the minimum thermal damage, and almost the same DNA damage occurred using the commercial 193-nm ArF excimer laser. ConclusionSolid-state laser at 266 nm could be a good alternative to the common 193-nm excimer laser for corneal reshaping procedures.

Excimer Laser Surface Patterning for Photoluminescence Enhancement of Silicon Nanocrystals

A method for enhancing the photoluminescence of silicon nanocrystals in a silicon oxide matrix by fabrication of periodic surface structures through laser irradiation is demonstrated. ArF excimer lasers are used to produce periodic line structures by material ablation. Photoluminescence, Raman, and transmission electron microscope measurements consistently show the formation of crystalline silicon after high-temperature annealing. A 2.6-fold enhancement of photoluminescence signal is measured for a periodic line structure with 600 nm period. The influence of a surface structure on the photoluminescence from the silicon oxide layer is discussed in terms of a simple model describing the main effect.

A novel approach to pulsed laser deposition of platinum catalyst on carbon particles for use in polymer electrolyte membrane fuel cells.

The research undertaken aimed to develop an efficient Pt-based catalyst for polymer electrolyte membrane fuel cells (PEMFCs) by using a cost-effective and efficient physical method to deposit platinum nanoparticles (PtNPs) on carbon supports directly from the platinum target. The method developed avoids the chemical functionalization of the carbon substrate and the chemical synthesis of PtNPs during catalyst fabrication. Platinum was deposited on carbon particles at room temperature using a pulsed laser deposition (PLD) system equipped with an ArF excimer laser (λ = 193 nm). The uniform deposition of PtNPs on carbon supports was achieved thanks to a specially designed electromechanical system that mixed the carbon support particles during platinum deposition. In the studies, Vulcan XC-72R carbon black powder, a popular material used as support in the anodes and cathodes of PEMFCs, and a porous carbon material with a high degree of graphitization were used as carbon supports. The best electrochemical measurement results were obtained for Pt deposited on Vulcan XC-72R. The peak power density measured for this material in a membrane electrode assembly (MEA) of a PEMFC (fed with H2/Air) was 0.41 W/cm2, which is a good result compared to 0.57 W/cm2 obtained for commercial 20% Pt Vulcan XC-72R. This result was achieved with three times less Pt catalyst on the carbon support compared to the commercial catalyst, which means that a higher catalyst utilization factor was achieved.

Study of Toner Penetration in Papers by Laser Induced Plasma Spectroscopy and Optical Profilometry

Four major toners are used in the printing industry, cyan, magenta, yellow and black (Key) for making color images on paper. Paper brands suitable for printing have thin mineral/latex coatings, and toners are applied on top of the coating in the printing process. Chemical compositions from toner to toner, as well as from coating to coating, vary according to the needs of the end user. Interactions between the toner and the coating define the final color formation of the images in printing. Hence, it is important to study characteristics and dynamics of toners on coated papers. In this paper, we have used laser-induced plasma spectroscopy (LIBS) to provide information on elemental distributions of the toner and the coating layers on three coated papers and the base paper at a sub-micrometer resolution. Ablation crater depth profiles in the three different material layers were converted into metric scale by combining elemental information from the LIBS measurements and optical profilometry. Ablation efficiencies for a toner of 150 nm/pulse, for a coating of approximately 350 nm/pulse and for a base paper of approximately 1 μm at a fluence of 0.6 J/cm2 of an ArF excimer laser were determined. Using these results, the average layer thicknesses of the toner and the coating layers were evaluated. The detailed analysis of the elemental profiles of the two cyan toners studied revealed strong accumulation of silicon and titanium compounds of the toner on the toner–air interface but also on the toner–coating interface, but to a much smaller extent. The observation reveals the significance of toner component diffusion due to substrate–machine interaction in the printing process. Such diffusion processes must have an important role in final color formation of the images in printing. The method developed provides a unique and accurate means to study toner diffusion processes in coated papers under printing conditions.

Cu-Au core-shell nanostructures induced by ArF excimer laser irradiation

In this paper, Cu-Au nanospherical structures were formed on glass surfaces by nanosecond UV laser irradiation. ArF laser pulses (193 nm wavelength, 15 ns time duration) were used for the experiments. Cu-Au bimetallic thin-film sample surfaces are structured under ArF excimer laser irradiation during the ablation process. Laser irradiation experiments were carried out using different laser fluences, the number of pulses, and focusing optics. Morphology of the irradiated surfaces and images of the nanostructures were obtained by the scanning electron microscopy method. Also, the optical and plasmonic behaviors of the nanostructures were collected by UV-Vis spectroscopy. Elemental composition and its spatial distribution were obtained using energy-dispersive x-ray spectroscopy (EDS) and mapping. EDS mapping shows that bimetallic nanospheres have a core-shell structure. Our results show that different laser irradiation parameters change the nanostructures’ composition, size, distribution, morphology, and optical properties. Cu-Au nanospherical structures can be used for nano-biosensing, catalysis, and enhanced spectroscopy applications.

Analysis of preionization effect of excimer laser

Excimer laser plays an important role in the national economic production because of its short wavelength, high repetition frequency and large energy. In the output characteristics of excimer lasers, high beam quality and high energy stability are the characters of high-end excimer light source, and whether the excimer laser system can sufficiently develop the preionization process is the key to output laser pulses with high beam quality and stable energy. This paper is mainly to study the preionization process of ArF excimer laser, and establish one-dimensional simulation calculation model and two-dimensional simulation calculation model. Based on the fluid calculation method of Comsol Multiphysics software, the numerical simulation analysis and calculation are carried out, with the study focusing on the ionization wave propagation process in the preionization process and the relationship between preionization and main discharge. The results show that the spatial structure of corona rod and main electrode should be considered comprehensively when an excimer laser system is designed. Appropriate preionization structure and voltage can make the main discharge triggered during the maintenance of free electrons, which can effectively reduce the discharge voltage, avoid streamer and arc discharge, and improve the output beam quality and system energy stability.

The Synthesis of the High Resolution i Line Novolak Resist

Semiconductors have continued to grow smaller alongside the development of shorter wavelength exposure sources and the development of photoresists optimized for such exposure wavelengths. For the g-line (436 nm) and i-line (365 nm) exposure wavelengths, novolak resists made of novolak resin have been used for patterning at pattern sizes of 0.5 μm-1 μm. For the exposure wavelength of 248 nm (KrF excimer laser), polyhydroxystyrene (PHS) has been used for patterning at pattern sizes of 0.2 μm-0.35 μm. For the exposure wavelength of 193 nm (ArF excimer laser), acrylic-based resin has been used for patterning at pattern sizes of 30 nm-0.2 μm. With the most advanced current lithography technologies, patterning at pattern sizes finer than 20 nm can be performed using exposure wavelengths of 13.5 nm (EUV). Apparently, then, lithography using novolak resists made of novolak resins is an outdated technology. However, it continues to be employed in LCD processes that involve TFT technology, where the development of higher definition LCDs continues to drive miniaturization. We studied the novolak resist, from synthesis to formulation and to evaluation of its resolution, to reexamine which factors are key to achieving high resolution in novolak resists.

Electrical Utilizations of Air Gap Region Formed on Superhydrophobic Silicone Rubber in NaCl Aqueous Solution

A uniform air gap was successfully formed on a superhydrophobic silicone rubber in water or NaCl aqueous solution. The main chain of Si–O bonds of a silicone rubber was photodissociated by a 193 nm ArF excimer laser to lower the molecular weight only in the laser-irradiated microareas; due to the volume expansion, the microswelling structure was periodically fabricated on a silicone rubber, showing the superhydrophobic property. A pair of metal needles were inserted in the air gap formed on the superhydrophobic silicone rubber in a NaCl aqueous solution; an electrical insulation between two metal needles in the air gap was demonstrated. Additionally, a droplet of NaCl aqueous solution was confined in the air gap, after which the pair of metal needles contacted with the droplet through the air gap. As a result, an electrolysis of the droplet of NaCl aqueous solution occurred to produce hydrogen gas on the cathode in the air gap. Moreover, when Al and Cu wires were provided across the air gap and NaCl aqueous solution on the superhydrophobic silicone rubber, approximately 0.8–0.9 V of electric voltage was successfully generated between the two wires in the air gap based on the difference in electrochemical potential as an energy harvesting device in the sea.

Formation of silicone thin films by ArF excimer laser induced photo‐desorption

AbstractLow molecular weight silicones were ejected from silicone rubber target irradiated by a 193 nm ArF excimer laser through the photo‐desorption. The ejected silicones were successfully deposited on a fused silica glass substrate in air. An approximately 0.3 mm of the target‐substrate distance was required for the deposition. The deposited silicones became a thin film, showing an interference color when the ArF excimer laser was irradiated for a long time. Chemical bonding state of the formed thin films was analyzed by the Fourier transform infrared spectroscopy. The thin films were slightly different from the original silicone rubber structure, still it was composed of Si‐O‐Si bonds and Si‐CH3 bonds. Also, OH bonds were clearly produced in the silicone thin films. As a result, contact angle of water on the silicone thin films was measured to be approximately 20 degrees, indicating a hydrophilic property.

UV laser generated micro structured black surface on commercial TiO2-containing glass

ArF excimer laser (193 nm, 20 ns) irradiation of commercially available TiO2-containing glasses in ambient air leads to a darkening of the surface and a bumpy surface micro structure. This process goes along with a phase separation between silicon-rich and titanium-rich phase near the glass surface. The black appearance can be attributed to the light scattering of the micro structured surface and absorption due to partial reduction of the titanium oxide. The process can be applied for marking the glass surface with high contrast.

Morphological and ablation characteristics of brass and fused silica after interaction with ArF excimer laser

This study investigates the interaction of the 193 nm ArF excimer laser with brass and fused silica in the ambient air. The study compares the differences in surface morphology and ablation rate of craters produced in brass and fused silica at different values of fluence and number of laser pulses using optical and scanning electron microscopy. The ablation rate was found to be slightly lower in fused silica than in brass. The ablation rate increased from 180 to 370 nm/pulse in brass and from 120 to 240 nm/pulse in fused silica when increasing the fluence from 6.8 to 15.2 J/cm2. In contrast to fused silica, melting and ejection of molten material were dominant in the ablation of brass. Various shapes and sizes of particles were observed in the debris deposited around the craters created in brass and fused silica. Resolidified particles with sizes greater than 1 µm were observed at and around the crater edges in brass due to the deposition of the ejected liquid droplets. In fused silica, large cauliflower-like particles were observed around the craters. Nano-size particles were also formed in brass and fused silica at low fluence but with a density smaller than that of the large particles formed at high fluence. The threshold fluence calculated from the relationship between ablation rate and fluence was found to be 0.78 and 3.03 J/cm2 in brass and fused silica, respectively.

Fast fabrication of diffractive patterns on glass by excimer laser ablation

ArF excimer laser ablation is used for the periodic patterning of glass surfaces. Projection of phase gratings provides the parallel generation of high resolution line patterns with structure periods in the µm-range. A fast and efficient process is possible, if laser pulse repetition and work piece motion are synchronized, so that multiple pulses can be applied to each work piece position, while continuously moving the work piece. A writing speed of 0.1 cm2/s is demonstrated and the scalability to 1 cm2/s is presented. Sub-micron periods are obtained by using Schwarzschild objectives. The process is applied for high contrast diffractive marking of glass.