XeCl Excimer Laser Irradiation Research Articles

Stimulated Thermal Scattering Induced by Two-Photon Absorption and Experimental Observation of the Genuine Stimulated Brillouin Scattering in the Near-Ultraviolet Region

Part of the experimental measurements of the frequency shift and the phase-conjugation (PC) fidelity gained from previous studies of stimulated scattering (SS) of nanosecond ( ) near-ultraviolet (UV) ( ) laser pulses in liquids (hexane, heptane, and others) are found to disagree with the theory of SS, which takes into account only the linear (single-photon) light absorption. To resolve the inconsistency, SS of XeCl excimer laser radiation ( ) with the duration of in liquid hexane is investigated experimentally. A theoretical analysis of the results obtained revealed three new nonlinear optical phenomena induced by the heating due to two-photon absorption: stimulated thermal scattering (two-photon STS-2), phase mismatch for stimulated Brillouin scattering (SBS), and phase self-modulation. Experimental SS spectrum contains two new lines - a previously unknown two-photon STS-2 line and a genuine SBS line newly discovered in the near-UV region

Stimulated thermal scattering induced by two-photon absorption and experimental observation of genuine stimulated brillouin scattering in the near-ultraviolet region

Some of the experimental measurements of the frequency shift and phase-conjugation fidelity gained from previous studies of stimulated scattering (SS) of nanosecond (5 ÷ 10 ns) near-ultraviolet (uv) (λ = 193 ÷ 351 nm) laser pulses in liquids (hexane, heptane, and others) are found to disagree with the theory of SS, which takes into account only the linear (single-photon) light absorption. To resolve the inconsistency, SS of XeCl excimer laser radiation (λ = 308 nm) with the duration of 8 ns in liquid hexane is investigated experimentally. A theoretical analysis of the results obtained revealed three nonlinear optical phenomena induced by the heating due to two-photon absorption: stimulated thermal scattering (two-photon STS-2), phase mismatch for stimulated Brillouin scattering (SBS), and phase self-modulation. The experimental SS spectrum contains two additional lines - a two-photon STS-2 line and a genuine SBS line in the near-uv region.

P‐182L: Late‐News Poster: Improvements in the Device Performance of Amorphous Indium Gallium Zinc Oxide Thin Film Transistors by XeCl Excimer Laser Irradiation

AbstractThe effect of XeCl excimer laser irradiation on amorphous indium gallium zinc oxide (a‐IGZO) thin films was investigated. The resistivity of the a‐IGZO thin films dramatically decreased upon their exposure to the XeCl excimer laser compared to that of the as‐deposited thin film from 104 to 10−3 Ωcm. The source/drain regions were selectively laser irradiated in the a‐IGZO channel layer using metal mask for reducing a contact resistance. Our TFT had a field‐effect mobility of 21.79 cm2/Vs, an on/off ratio of 6.0 × 107, a threshold voltage of −0.15 V, and a subthreshold swing of 0.26 V/decade.

Quantitative dopant profiling of laser annealed focused ion beam-prepared silicon p-n junctions with nanometer-scale resolution

Silicon p-n junction specimens have been prepared by focused ion beam milling for examination using off-axis electron holography. By using 28nS pulsed XeCl excimer laser irradiation we have reduced the total electrically “inactive” thickness in these specimens from 142to5nm. A platinum layer has been sputtered onto the specimen surfaces to remove the build up of charge from the region of interest during examination. Subsequently, a value of the built in potential has been determined directly from a phase image which is consistent with theory.

Photochemical reduction of flavone with NaBH 4 in batch and micro-channel reactors using excimer lasers

Photochemical reduction of a stable enone, flavone ( 1), was accomplished by excimer laser photolysis using NaBH 4 in ethanol, which formed flavanone ( 2) as a primary product in contrast to the formation of dimers that predominate in conventional photolysis. Flavanone ( 2) underwent successive thermal reduction with NaBH 4 leading to flavanol ( 3) and photolysis to ethyl salicylate ( 4), in which the formation of 4 was completely suppressed when a single laser shot was used for the photolysis. The photolysis was conducted using quartz batch reactors having different optical paths and a quartz micro-channel reactor, in combination with KrF and XeCl excimer laser irradiation. This showed a considerable acceleration of the reaction with the micro-channel reactor, and the selectivity of the photoproducts 2, 3, and 4 depended on the optical path of the reactors, the laser wavelengths, the concentration of NaBH 4, and the laser repetition rate. An optimal irradiation condition - application of sufficient time interval between the XeCl laser pulses, a low concentration of 1, and high concentration of NaBH 4 - showed a considerable increase in the selectivity of 3 by eliminating the formation of 2 and 4.

Stimulated thermal scattering induced by two-photon absorption and experimental observation of genuine stimulated Brillouin scattering in the near-ultraviolet region

Some of the experimental measurements of the frequency shift and phase conjugation fidelity gained from previous studies of stimulated scattering (SS) of nanosecond $(5\ensuremath{-}10\text{ }\text{ns})$ near-ultraviolet (uv) $(\ensuremath{\lambda}=193\ensuremath{-}351\text{ }\text{nm})$ laser pulses in liquids (hexane, heptane, and others) are found to disagree with the theory of SS, which takes into account only linear (single-photon) light absorption. To resolve the inconsistency, SS of XeCl excimer laser radiation $(\ensuremath{\lambda}=308\text{ }\text{nm})$ with the duration of 8 ns in liquid hexane is investigated experimentally. A theoretical analysis of the results obtained revealed three nonlinear optical phenomena induced by the heating due to two-photon absorption: stimulated thermal scattering (two-photon STS-2), phase mismatch for stimulated Brillouin scattering (SBS), and phase self-modulation. The experimental SS spectrum contains two additional lines---a two-photon STS-2 line and a genuine SBS line in the near-uv region.

Heating Layer of Diamond-Like Carbon Films Used for Crystallization of Silicon Films

Rapid thermal crystallization of silicon films with a heating layer of diamond-like carbon (DLC) films is reported. DLC films 200 nm thick have an optical absorbance higher that 0.7 for wavelengths shorter than 1000 nm. They are also heat resistant to about 5000 K. A crystalline volume ratio of 0.85 is achieved for silicon films through heat diffusion from DLC heated by 30-ns-pulsed XeCl excimer laser irradiation at 200 mJ/cm2 for 100 nm DLC/5 nm SiO2/25 nm Si/quartz, while it is only 0.4 for 25 nm Si/quartz because of high reflection loss. Crystallization of silicon films is also achieved by 1064 nm YAG laser heating of the 200 nm DLC layer overlying the silicon films.

Stimulated thermal scattering induced by two-photon absorption and experimental observation of stimulated Brillouin scattering in the UV region

An analysis of the results of previous studies of stimulated scattering of UV pulses in liquids has shown that they disagree with the theory of stimulated scattering. To resolve the inconsistency, stimulated scattering of XeCl excimer laser radiation (λ = 308 nm) with pulse duration τ ≈ 8 ns in liquid hexane is investigated experimentally. A theoretical analysis of the results obtained revealed a new nonlinear optical phenomenon: stimulated thermal scattering induced by the heating due to two-photon absorption, called two-photon stimulated thermal scattering (two-photon STS-2). The stimulated backscatter spectrum contains a previously unknown line corresponding to two-photon STS-2 and a newly discovered SBS line in the UV region. The line is observed in experiment on liquid hexane and is characterized by the frequency shift ΩB = 0.33 cm−1 relative to the pump wavelength λ = 308 nm, in complete agreement with the theory of stimulated Brillouin scattering (SBS). The spectral line called the SBS line in previous studies has a frequency shift much smaller than that predicted by the SBS theory and must be interpreted as an unshifted two-photon STS-2 line. When two-photon STS-2 is used to obtain a phase-conjugate wave, the phase-conjugation fidelity is lower than that achieved by using SBS because of thermal self-action and slow decay of the thermal grating.

Fabrication of self-organized conical microstructures by excimer laser irradiation of cyanoacrylate-carbon nanotube composites

Self-organized conical microstructures are fabricated by 308 nm XeCl excimer laser irradiation of cyanoacrylate-carbon nanotube composites in air. The morphology of the surface on the composite films is studied, varying the total number and fluence of the applied laser pulses. A simple mechanism of the fabrication based on the evaporation of cyanoacrylate and the burning of carbon nanotubes is proposed. The conical peak structures of cyanoacrylate-carbon nanotube composite films show good field-emission properties. Similar structures are also observed on carbon nanotube arrays.

Low-Resistance Ti∕Al∕Ni∕Au Ohmic Contact of GaN Employing Silicon Diffusion by XeCl Excimer Laser Irradiation

Low-Resistance Ti∕Al∕Ni∕Au Ohmic Contact of GaN Employing Silicon Diffusion by XeCl Excimer Laser Irradiation

Study on crystallization of amorphous silicon using CeO 2 seed layer patterned on the plastic substrate

Many researchers are working these days on crystallization of amorphous silicon (a-Si) for application in thin film transistor-liquid crystal display (TFT-LCD) on the plastic substrate. In this paper, we have presented our work on crystallization of amorphous silicon film using XeCl excimer laser annealing on the polyethersulfone (PES) substrate. We have also reported here the consequences of our attempt to pattern CeO 2 seed layer as dot and line between Si film and the PES substrate. Previous researchers in this field have shown that laser of high-energy density is required to crystallize a-Si films without using seed layer. But, we have successfully obtained the crystallization condition using laser of low-energy density using a seed layer of CeO 2. This paper reports the achievement in details. Also, we have drawn a comparison of a-Si crystallization between the case with and without seed layer. Generally, a-Si films are deposited at low temperature on plastic substrates. In our experiment, CeO 2 film was grown by RF sputtering using plasma ON/OFF method at the room temperature. Amorphous silicon was deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) at the room temperature. Then, active layer was crystallized by XeCl excimer laser irradiation. We determined the crystallinity through Fourier transformation Raman spectroscopy (FT-Raman spectroscopy).

Reliable Poly-Si TFT Employing XeCl Excimer Laser Irradiation on Gate Oxide

A new polycrystalline silicon thin film transistor (poly-Si TFTs) employing XeCl excimer Laser Irradiation on the Gate Oxide (LIGO), which exhibits long term stability under electrical stress, is proposed and fabricated. The proposed method causes a rapid high temperature at poly-Si/SiO2 after gate insulator deposition. Laser irradiation on the gate oxide improved the properties of the oxide so that the transfer characteristics and electrical reliability of the proposed TFTs can be improved.

Oxygen plasma and high pressure H 2 O vapor heat treatments used to fabricate polycrystalline silicon thin film transistors

Oxygen plasma and high pressure H2O vapor heat treatment were applied to fabrication of n-channel polycrystalline silicon thin film transistors (poly-Si TFTs). 13.56 MHz-oxygen-plasma treatment at 250 °C, 100 W for 5 min effectively reduced defect states of 25-nm-thick silicon films crystallized by 30 ns-pulsed XeCl excimer laser irradiation. 1.3×106-Pa-H2O vapor heat treatment at 260 °C for 3 h was carried out in order to improve electrical properties of SiOx gate insulators and SiOx/Si interfaces. A carrier mobility of 470 cm2/V s and a low threshold voltage of 1.8 V were achieved for TFTs fabricated with crystallization at 285 mJ/cm2.

Electrochemical micromachining of titanium using laser oxide film lithography: excimer laser irradiation of anodic oxide

In electrochemical micromachining using oxide film laser lithography (OFLL), the pattern is formed by laser irradiation of an anodic oxide film. On the irradiated areas of the film the underlying metal is then selectively dissolved in an appropriate electrolyte, the non-irradiated oxide acting as a mask. The physical interactions of 308 nm XeCl excimer laser radiation with anodically formed oxide films on titanium were studied using single pulse irradiation at varying fluence and two different pulse durations. The irradiated surfaces were characterized by secondary electron microscopy (SEM), Auger electron spectroscopy (AES) profiling and X-ray-induced photoelectron spectroscopy (XPS), additionally, their electrochemical dissolution behaviour in an electropolishing electrolyte was evaluated. Numerical simulation was applied to the estimation of the temperature profiles at the surface of the irradiated samples. Results suggest that depending on irradiation conditions different mechanisms may be responsible for the loss of the protective properties of the oxide film. The creation of a Ti(O) solid solution resulting from diffusion of oxygen from the film into the underlying molten metal was shown to be effective at high fluences. The loss of protective properties observed at lower fluences was tentatively attributed to the creation of ionic defects in the oxide by a photolytic process.

High-resolution investigations of C2 andCN optical emissions in laser-induced plasmas during graphiteablation

Graphite ablation in low-pressure nitrogen atmosphere has beencarried out by XeCl excimer laser radiation at the fluenceof 12 J cm-2. The induced-plasma plume has beeninvestigated by time- and space-resolved emission spectroscopy.The recorded spectra are dominated by diatomic molecule bands:the C2 Deslandres-D'Azambuja and Swan systems and the CNviolet system. From experimental measurements, it turns out that the continuum, the atomic emissions and the C2Deslandres-D'Azambuja bands are predominant in the plasma coreregion (d⩽1 mm) at short times, whereas the molecularbands of the Swan and violet systems are very intense in theouter plasma regions. The different temporal and spatial histories of emissions of the different chemical species in theplasma plume could be attributed to the peculiar processesoccurring during plasma expansion.

Ablation of cobalt with pulsed UV laser radiation

The ablation of cobalt with 20 ns pulses of 308 nm XeCl excimer laser radiation is investigated. The dependence of the ablation rate on laser fluence, spot area, and pulse number is determined. The experimental results are compared with a numerical calculation based on an improved thermal model. The model, which considers proper vapor attenuation, is shown to be in good agreement with experiment.

Electrical Properties of Solid Phase Crystallized Silicon Films

ABSTRACTIn this study, the carrier mobility and density for solid phase crystallized (SPC) silicon films fabricated at 600 °C for 48 hours are analyzed by free carrier optical absorption. The carrier mobility is 40 cm2/Vs for SPC films doped with 6×1019-cm−3-phosphorus atoms. This analysis suggests the SPC films have fine crystalline grains closed to single crystalline silicon. In addition, initial carrier density was 3×1019 cm−3, which increased to 6×1019 cm−3by XeCl excimer laser irradiation of 500mJ/cm2. The inactivated regions in SPC films are reduced by laser irradiation. However, the electrical conductivity after laser irradiation for SPC films doped with 6×1018-cm−3-phosphorus atoms decreased from 3.3 to 0.018 S/cm as laser energy density increased to 500mJ/cm2. On the other hand, the electrical conductivity increased from 14.7 to 31.3 S/cm with similar increase of laser energy density after H2O vapor heat treatment at 260°C for 3 hours with 1.3 MPa. Furthermore, the characteristics of n-channel TFTs fabricated with initial SPC films as well as SPC films which was irradiated by laser at 425mJ/cm2 are also researched. The threshold voltage is decreased from 3.8 to 2.0 V by laser irradiation. Threshold voltages of both cases are decreased from 3.8 to 2.4 V for no-laser irradiation and from 2.0 to 0.8 V for laser irradiation, after H2O vapor heat treatment at 310°C for 1 hour with 9.0MPa. Based on the above trial, the defect reduction method combining laser irradiation and H2O vapor heat treatment has proved to be very effective for SPC films and SPC TFTs.

Structure and in-depth concentrations in excimer laser irradiated Pb–Co codeposited films

Pb 100− x Co x, x=0, 9, 25, 32 and 36 at.% films composed of mutually immiscible metals were codeposited by two electron beam sources in UHV system at the SiO 2/Si substrate temperature of 40°C. The samples were processed by XeCl excimer laser irradiation at the fluences F≤0.2 J/cm 2 and number of pulses n=1, 10, 100 and 1000. The samples were analyzed by X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), EDAX/SEM and by resistometry. In the films fcc Pb was found. Neither fcc nor hcp Co were detected. From RBS analyses it follows that in Pb–Co films Co segregates at the surface, even in the as-deposited state. This distribution of concentration remains almost unchanged after laser irradiation. The porosity of Pb–Co films was considerably suppressed by laser irradiation in the melting regime.

Substance removal on teeth with and without calculus using 308 nm XeCl excimer laser radiation. An in vitro investigation.

It was the aim of this in vitro study to determine the potential effects of 308 nm XeCl excimer laser radiation on root surfaces when used for removing calcified deposits. The source of laser radiation was a XeCl-excimer laser (MAX 10, Fa. Medolas, Germany) emitting ultraviolet radiation at a wavelength of 308 nm with a pulse duration of 60 ns. Subjects of irradiation were 60 extracted teeth which were divided into 2 groups of 30 samples each with (group 1) and without calculus (group 2). Specimens were irradiated with 800 laser pulses at 5 different energy-densities per pulse of 1.0 J/cm2, 2.0 J/cm2, 3.0 J/cm2, 4.0 J/cm2 and 5.0 J/cm2. For each parameter 6 samples (n=6) were exposed to 308 nm excimer-laser radiation. The ablation of hard tissue on the treated root surfaces was measured 3-dimensionally with a laser scanning device (100,000 surface points per sample; accuracy: 5 microm) and evaluated with a special image analyzing software (volume, mean, median, standard deviation). In addition, a scanning electron microscopic (SEM) evaluation of the irradiated root surfaces was performed. Statistical analysis was done using ANOVA with the Scheffé-test. The lowest amount of ablation on teeth without calculus was induced with 14.01 (+/-5.86) microm using laser radiation at an energy density of 2.0 J/cm2. Maximum tissue removal in this sample group was obtained with 56.67 (+/-21.05) microm with laser treatment at an energy density of 5.0 J/cm2. While no ablation of dental cementum was detectable after irradiating root surfaces without calculus at 1.0 J/cm2, a strong removal of calculus with a mean value of 31.91 (+/-4.2) microm was observed under these conditions. The results seem to indicate that a selective removal of subgingival calculus creating a homogenous shape of the root surface with 308 nm excimer laser radiation is possible. Furthermore, no signs of the formation of a smear layer nor the induction of thermal side-effects were observed.

Formation of granular-like structure of Ag/Co multilayers by excimer laser irradiation

The electron beam deposited Ag/Co multilayers (MLs) showing the giant magnetoresistance (GMR) were thermally processed by XeCl excimer laser irradiation at the fluences between 0.1 and 0.25 J/cm 2 with 1–200 pulses. An increase of the GMR ratio from 7.5 to 15% at 4.2 K was observed for ML with Ag layers composed of randomly oriented Ag grains at lower laser fluences when the ML was not yet melted. The magnetization M(T) curves of the irradiated samples indicate the presence of granular like component, while the anisotropy of GMR due to layering persists. For Ag/Co ML with coherent structure the effect of irradiation on GMR was minor.