Radiation effects of vacuum ultraviolet lasers in amorphous Si3N4 films
Kazuo NakamaeKou KurosawaMasato OhmukaiMasahito KattoMasahiro OkudaWataru SasakiShigenori NozawaTatsushi Igarashi
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Abstract The carbon thin film as a target for laser‐driven heavy ion acceleration has been developed using the carbonization of polyimide induced by the irradiation of a XeCl excimer laser. The relationship between the depth of the crater produced by the laser irradiation and the laser fluence were measured in order to clear the carbonization mechanisms of polyimide. The melting threshold of polyimide was estimated to 0.058 J/cm 2 . It is found that the carbonization is induced by the irradiation with the laser fluence around or under the threshold.
Carbon fibers
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Saturation (graph theory)
Atmospheric temperature range
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The ablation characteristics of the photoresist SU-8 under 248 KrF excimer pulsed laser radiation have been studied. The variation of SU-8 etch rate with fluence has been investigated in the range 0.05 J/cm2 to 3.01 J/cm2. Threshold fluence for ablation of SU-8 is measured to be about 0.05 J/cm2. The etch rate of SU-8 is found to be higher than that of polyimide under identical conditions. The curves for etch rate dependence on fluence are in agreement with those reported in the literature for polyimides and also obey a theoretical model. We have investigated the effect of different prebake temperatures on the ablation characteristics which are found to be similar for all temperatures. The effect of increasing the number of laser shots has been examined at different fluences to understand the etch rate variation near the 'end of film' stage of ablation. The results of our analyses of these samples using SEM, profilometery and optical microscopy reveal - very smooth morphology of the etched surfaces without significant debris, no noticeable damage to underlying silicon, gradual build up of a carbonaceous film outside and around the etch pits. We find SU-8 very suitable for rapid excimer ablation lithography which has been demonstrated by patterning a gear structure in an SU-8 resist layer with aspect ration of 4.5.
Photoresist
Laser Ablation
Excimer
Etch pit density
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The effect of variation of excimer laser fluences on the surface structuring of titanium (Ti) targets has been investigated. The KrF excimer laser (λ = 248 nm, t = 20 ns, repetition rate 20 Hz) has been employed for this purpose. The targets were irradiated for various laser fluences ranging from 0.86 J cm−2 to 1.27 J cm−2 under vacuum condition. Various diagnostic techniques like scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD) have been utilized to investigate the surface topography and structural changes of laser ablated targets. SEM analysis reveals the formation of laser-induced periodic surface structures (LIPSS) at the central ablated region. The periodicity of LIPSS increases from 5 μm to 88 μm with the increase of fluence from 0.86 J cm−2 to 1.27 J cm−2. The formation of grains is observed at the peripheral ablated region for all laser fluences. Reduction in grain size from 7.7 μm to 3.8 μm is observed with increasing fluence from minimum to maximum value. AFM analysis exhibits the growth of several numbers of bumps and protrusions on irradiated targets. The height of bumps is reduced from 100 nm to 40 nm with increasing fluence. XRD analysis shows that no new phases were formed under vacuum condition for all fluence values. However, an alteration in the peak intensity, crystallinity, and d-spacing for various diffraction planes of Ti has been observed after irradiation.
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The carbon thin film as a target for laser-driven heavy ion acceleration has been developed using the carbonization of polyimide induced by the irradiation of a XeCl excimer laser. The relationship between the depth of the crater produced by the laser irradiation and the laser fluence were measured in order to clear the carbonization mechanisms of polyimide. The melting threshold of polyimide was estimated to 0.058 J/cm2. It is found that the carbonization is induced by the irradiation with the laser fluence around or under the threshold.
Carbon fibers
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The electric conductivity changes markedly when titania is irradited by a proper-fluence excimer laser, it changes from insulator to semiconductor at room temperature, and its color changes too. Several titania samples before and after irradiation are studied with XRD, XPS and microscopic analyses. It is observed that the changes takes place when proper-fluence excimer laser pulse irradites the surface of titania and the temperature of the surface rises quickly. A thin layer of the irradited area melts quickly and soon resolidifies. This leads oxygen in titania to vacate partly, so the stoichiometry of the sample deviates from the normal value. The laser fluence threshold is estimated by the equation of heat transfer and the result agrees approximately with the experiment.
Stoichiometry
Excimer
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ABSTRACT PURPOSE: To evaluate excimer laser fluence after experimentally induced changes in room temperature and relative air humidity. METHODS: Excimer laser fluence was analyzed with a specific power meter under three different grathents of room temperature and relative air humidity as well as the reproducibility of myopic correction of -3.00 diopters in a polymethylmethacrylate plate test. RESULTS: Under the simulated environmental conditions, no significant difference in laser energy fluence and reproduction of myopic correction was observed. CONCLUSIONS: In a setting with controlled temperature and relative air humidity, subtle changes in environmental factors do not appear to influence laser fluence and efficacy. [J Refract Surg. 2007;23:307-309.]
Excimer
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Abstract CO 2 and excimer laser (193, 248, 350 nm) treatments were performed on poly(etheretherketone) (PEEK). High fluence excimer laser irradiation induced efficient etching, mainly due to thermal effects. The irradiation with CO 2 lasers and high fluence excimer lasers introduced limited changes in surface chemistry and morphology. Low fluence excimer laser irradiation, particularly at 193 nm and 248 nm, favored the occurence of photochemical phenomena. Surface chemical modifications leading to oxygen depletion and preferential elimination of the ketonic bridge were assessed. At the same time surface morphological alterations were found, diffraction effects led to cone‐like structures while the redeposition of heavy oligomers caused the formation of debris on the surface.
Excimer
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The neutral and charged species emitted by pulsed-laser irradiation of polytetrafluoroethylene (PTFE) at 248 nm in vacuum have been examined. In particular, the species and properties of the emission products produced at typical fluence regimes used in the pulsed-laser deposition of PTFE thin films have been characterized. The relative intensities of the major products as well as their dependence on laser fluence are presented, and a simple model is used to fit the observed fluence dependence. Evidence that the major neutral component, the monomer (C2F4), is formed from a thermally activated unzipping reaction is presented. The ionic species are derived from the neutral decomposition products, apparently ionized by electron collisions in the weak plasma generated at the target surface.
Polytetrafluoroethylene
Excimer
Pulsed Laser Deposition
Deposition
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