Showing papers on "Excimer published in 1990"
TL;DR: In this article, the potential of these new UV sources for industrial UV processing is demonstrated and large-area metal deposition induced by the 172 nm radiation from a silent discharge in xenon is shown.
Abstract: Excimers, known from electron beam experiments and UV lasers, can also fomi in silent discharges, a discharge type used for large-scale ozone production. In this high pressure non-equilibrium discharge a dielectric barrier leads to the formation of localized short-lived microdischarges. Inside the microdischarge filaments energetic electrons can excite rare gas (RG) atoms which, under appropriate conditions, react to form RG/RG dimers or RG/halogen dimers. With the pure RG dimers Ar2*, Kr2*, Xe2*, their chlorides ArCl*, KrCl*, XeCl* and their fluorides ArF*, KrF*, XeF* a number of narrow-band UV sources can be obtained in the wavelength region between 120 nm and 360 nm. The physical parameters of the microdischarges and the reaction kinetics of excimer formation in silent discharges are discussed. The potential of these new UV sources for industrial UV processing is demonstrated. As an example of an application for such incoherent excimer UV sources structured and large-area metal deposition induced by the 172 nm radiation from a silent discharge in xenon is shown. Patterned thin palladium films could be produced by irradiating a palladium acetate coating through a contact mask. In a second step thicker copper layers were deposited on top of the palladium patterns by an elec@oless plating process.
227 citations
107 citations
TL;DR: In this article, both unpolarized and linearly polarized radiation at 248 and 308 nm produce well ordered, micron-scale structures over dimensions greatly exceeding the coherence area of the laser at the surface.
Abstract: Periodic surface structures have been observed on organic polymers when photoablated using low coherence excimer lasers. Both unpolarized and linearly polarized radiation at 248 and 308 nm produce well ordered, micron‐scale structures over dimensions greatly exceeding the coherence area of the laser at the surface. Surface scattered wave effects appear to explain these structures.
96 citations
84 citations
TL;DR: The properties of PIATm were similar to previously studied pyrenylmaleimide-labeled Tm (PMTm) except that S1 binding to actin-Tm increased the excimer fluorescence in contrast to the time-dependent decrease seen for PMTm.
Abstract: Rabbit skeletal tropomyosin (Tm) specifically labeled at cysteine groups with N-(1-pyrenyl)-iodoacetamide (PIA) exhibits excimer fluorescence. The excimer fluorescence was sensitive to the local conformation of Tm, to actin binding, and, in reconstituted thin filaments, to the Tm state change induced by binding of myosin subfragment 1 (S1). The properties of PIATm were similar to previously studied pyrenylmaleimide-labeled Tm (PMTm) [Ishii, Y., & Lehrer, S.S. (1985) Biochemistry 24, 6631] except that S1 binding to actin-Tm increased the excimer fluorescence in contrast to the time-dependent decrease seen for PMTm. The fluorescence properties of PIATm are sensitive to the Tm chain-chain interaction via equilibria among pyrene configurations and nonfluorescent dimer as well as the monomer and excimer-forming configurations. The effect of bound troponin (Tn) on the excimer fluorescence of PIATm in the reconstituted systems was dependent on ionic strength with a slight Ca2+ dependence. S1 titrations in the absence and presence of Tn and Ca2+ indicated that the excimer fluorescence probes the state change of Tm from the weak S1 binding state to the strong S1 binding state which is facilitated by Ca2+ [Hill et al. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 3186]. Binding of MgADP-S1 and MgAMPPNP-S1 produced the same total excimer fluorescence change as for nucleotide-free S1, showing that the strong S1 binding state of Tm-actin is independent of nucleotide.(ABSTRACT TRUNCATED AT 250 WORDS)
78 citations
TL;DR: In this article, a 50 W CO 2 laser (10.6 μm) and a 40 W 2J/20 Hz XeCl excimer laser (308 nm) were used for ablation and surface modification of glass.
74 citations
TL;DR: In this paper, the nature of the UV-induced decomposition process of thin solid palladium acetate films was investigated on different substrate materials (Al2O3, quartz, polyimide) with a pulsed KrF∗ excimer laser at 248 nm and an incoherent Xe∗2 excimer source peaking at λ = 172 nm.
74 citations
69 citations
59 citations
TL;DR: Substantial saturation effects are noted for resonance Raman (RR) bands of the aromatic residues in cytochrome c (excited at 230 nm) with an H2 Raman-shifted YAG or a frequency-doubled excimer-pumped dye laser.
Abstract: Substantial saturation effects are noted for resonance Raman (RR) bands of the aromatic residues in cytochrome c (excited at 230 nm) with an H2 Raman-shifted YAG or a frequency-doubled excimer-pumped dye laser At a given average power, saturation is much lower for excimer than for YAG excitation because of the longer pulse and higher repetition rate of the excimer laser The signal quality at low average power is significantly higher for the excimer-excited spectra Ultraviolet RR cross-sections have been redetermined for aqueous phenylalanine, tyrosine and tryptophan at a series of wavelengths from 240 to 192 nm The excimer laser was used at 209 nm and longer wavelengths, and in addition deconvolution techniques were applied to better define the individual RR bands These improvements led to quantitative changes in the cross-section values from those reported previously, but the interpretation of the excitation profiles in terms of excited-state properties of the aromatic residues remains unchanged
59 citations
TL;DR: In this paper, the excitation of resonance and excimer radiation in mixtures of mercury and rare gases has been investigated and the emission features of such discharges which are mostly in the UV and VUV range were studied in detail.
Abstract: The excitation of resonance and excimer radiation in mixtures of mercury and the rare gases has been investigated. The gas mixtures were excited in a dielectric barrier discharge. The emission features of such discharges which are mostly in the UV and VUV range were studied in detail. Whereas resonance radiation dominates in mixtures of mercury with He, Ne, and Ar, efficient excimer formation takes place in mixtures of mercury with Kr and Xe. All the emission features of the HgXe excimer which are expected between and around the resonance lines of mercury were found and measured. A theoretical model of HgXe excimer formation is presented. This model takes both the discharge formation and the charged particle kinetics as well as the excimer and excited species formation into account. Experimentally determined Boltzmann temperatures show a decline with mercury density as is predicted by the theory for the average electron temperature. Furthermore it is, e.g., possible to calculate the efficiency of the gene...
TL;DR: Values of pE derived in this way are found to be consistent with pE values derived from the milling crowd analysis of fluorescence yield titration experiments, suggesting that the rotation of the the pyrene moiety is the rate-limiting step for both the lateral mobility of py10 PC and intramolecular excimer formation in dipy10 PC.
Journal Article•
TL;DR: Time-resolved measurements showed that fluorescence occurs on the nanosecond time scale, and an estimate gives the quantum yield for photons emitted in the 260-350-nm range as approximately 1 X 10(-5), which is significant in the evaluation of the safety of surgery with an argon fluoride excimer laser.
Abstract: The epithelium and stroma of bovine and human corneas were exposed to both ablative and subablative levels of 193-nm excimer laser radiation and the spectra of the induced fluorescence recorded. Two broad peaks in the emission spectra were observed, at 310 nm and 460 nm, with a difference in the relative height of these peaks between epithelium and stroma. The lower cut-off for fluorescence (260 nm) was similar for both tissues. Time-resolved measurements showed that fluorescence occurs on the nanosecond time scale, and an estimate gives the quantum yield for photons emitted in the 260-350-nm range as approximately 1 X 10(-5). The significance of these results in the evaluation of the safety of surgery with an argon fluoride excimer laser is discussed.
TL;DR: The Langmuir-Blodgett obtained films show little excimer emission and fluorescence decay analysis showed that pyrene moieties are randomly distributed in two-dimensional films.
Abstract: The Langmuir-Blodgett obtained films show little excimer emission. The fluorescence decay analysis show that pyrene moieties are randomly distributed in two-dimensional films. Interlayer energy migration is observed at high pyrene concentrations
TL;DR: In this paper, the authors measured dilute solutions of model compounds for polymers of 2,6-naphthalene dicarboxylic acid and eight different glycols.
TL;DR: In this paper, the fluorescence from disordered phenanthrene adlayers on Al2O3(0001) was examined in ultrahigh vacuum at 20 K using laser-induced fluorescence techniques.
Abstract: The fluorescence from disordered phenanthrene adlayers on Al2O3(0001) was examined in ultrahigh vacuum at 20 K using laser‐induced fluorescence techniques. The fluorescence spectra was consistent with emission from a phenanthrene excimer. The fluorescence lifetime of the phenanthrene excimer was studied versus phenanthrene coverage and versus distance from the Al2O3(0001) surface using xenon spacers. As a function of coverage on Al2O3(0001), the fluorescence lifetime decreased from τ=34±0.5 ns at phenanthrene coverages of Θ≥20 ML to τ=7±0.5 ns at Θ=1 ML. As a function of xenon spacer distance from the Al2O3(0001) surface, the fluorescence lifetime also decreased from τ=34±0.5 ns at distances of d>100 A to τ=7±0.5 ns at d=7 A. Fluorescence measurements versus phenanthrene coverage on xenon, butane, acetonitrile and methanol multilayers revealed that the phenanthrene excimer fluorescence lifetime was constant at τ≊35 ns on the molecular multilayer surfaces. These results indicated that the reduction of the fluorescence lifetime was particular to the Al2O3(0001) surface. The fluorescence lifetimes versus phenanthrene coverage and xenon spacer distance on Al2O3(0001) were equivalent when the phenanthrene coverage was converted to total adlayer thickness. This correspondence suggested that the excited electronic energy in disordered phenanthrene adlayers transfers rapidly to phenanthrene excimers at the phenanthrene–vacuum interface. Subsequently, competition occurs between fluorescence quenching by the Al2O3(0001) surface and phenanthrene excimer fluorescence. In addition, fluorescence lifetime measurements vs phenanthrene coverage on CaF2 thin films displayed similar fluorescence quenching. Fluorescence lifetimes versus phenanthrene coverage on O2 molecular multilayers also revealed fluorescence quenching that was attributed to a charge‐transfer mechanism. The observed fluorescence quenching on Al2O3(0001) indicates that the surface states of this ionic crystal may be accessible for electronic energy transfer even though Al2O3 is a known insulator. A Forster electronic energy transfer mechanism was used to analyze the observed fluorescence lifetimes vs phenanthrene coverage or xenon spacer distance on Al2O3(0001).
TL;DR: In this paper, high periodic stable microstructures appeared on the surface of polyethersulfone (PES) by XeCl excimer laser ablation with a single polarized beam in ambient air.
Abstract: Highly periodic stable microstructures appeared on the surface of polyethersulfone (PES) by XeCl excimer laser ablation with a single polarized beam in ambient air Its formation mechanism was investigated using the time‐resolved light scattering technique with the pulsed light of an XeF excimer laser In addition to the polarization of the ablating beam, thermal processes on the etched surface play a significant role in microstructure formation
TL;DR: A measurement of the ablation rate of bovine corneal stroma over the range of fluences most likely to be useful forCorneal surgery (50-400 mJ/cm2) is presented, showing a more precise measurement than previously published tissue ablated rate data.
Abstract: Excimer lasers operating at 193 nm may become important surgical instruments in ophthalmology because of their ability to ablate tissue with excellent precision and minimal damage to adjacent tissue. However, the precision is limited by the accuracy of the measurement of the amount of tissue ablated per pulse at the fluence used. A measurement of the ablation rate of bovine corneal stroma over the range of fluences most likely to be useful for corneal surgery (50-400 mJ/cm2) is presented. The technique used produced reproducible results, the data from 47 animal eyes being averaged to further increase the precision. For this range of fluences, these results show a more precise measurement than previously published tissue ablation rate data. These results should be useful in accurately predicting the result of corneal surgery using the excimer laser if species differences are not major.
TL;DR: A theoretical model is developed which allows for well-defined lenses to be formed with different dioptric properties using lasers that are known to ablate a variety of materials and this arrangement is used to form lenses with highly smooth surfaces in three polymeric materials.
Abstract: A theoretical model is developed which allows for well-defined lenses to be formed with different dioptric properties using lasers that are known to ablate a variety of materials. With the theoretical development as a guide an experimental arrangement is defined for the ArF excimer laser and this arrangement is used to form lenses with highly smooth surfaces in three polymeric materials (polymethyl methacrylate, polycarbonate, and polyvinyl chloride) to test the validity of the theory. As part of the procedure to obtain these lenses, ablation curves (etch depth per pulse vs log of the laser fluence) were measured for each of these polymers and these curves are also reported. The experiments were extended to the rabbit cornea in which the corneal button was reshaped as part of keratomileusis surgery. This preliminary experiment resulted in a clear cornea with a smooth corneal surface and a measured change of 3 diopters in the treated eye.
TL;DR: In this article, the authors investigated the excimer formation process of poly(3,6-di-ter-butyl-9-vinyl carbazole) and its dimeric model compounds, meso- and rac-2,4-bis(3.6, di-tert, butyl 9-carbazolyl)pentanes (meso-and rac-BCzPe), and found that they exhibit a unique excimer formed by the syndiotactic diads.
Abstract: Poly(3,6-di-ter-butyl-9-vinylcarbazole) (PBVCz) and its dimeric model compounds, meso- and rac-2,4-bis(3,6-di-tert-butyl-9-carbazolyl)pentanes (meso- and rac-BCzPe), are investigated. PBVCz and rac-BCzPe show broad excimer emission at wavelengths slightly shifted from the excited monomer band. Since sandwich excimer formation is hindered by the bulky groups, this polymer exhibits a unique excimer formed by the syndiotactic diads. To investigate the excimer formation process, 1 H NMR analysis and calculation of conformational energies were carried out for rac-BCzPe
TL;DR: In this paper, the Hg(63P1)-photosensitized decomposition of SiH4 and NH3 using the 254-nm radiation of a low-pressure Hg discharge lamp was measured using laser-induced fluorescence (LIF).
Abstract: Silicon nitride thin films are obtained from the Hg(63P1) ‐photosensitized decomposition of SiH4 and NH3 using the 254‐nm radiation of a low‐pressure Hg discharge lamp. Several diagnostics are associated to characterize the physicochemical mechanisms and measure the densities of reactive species or reaction products. The photon flux is obtained by radiometry, the Hg density is determined by absorption of the 254‐nm radiation, and the SiH4 gas depletion is measured by mass spectrometry. The luminescence at 340 nm of HgNH3 excimers is used as a probe of the metastable Hg(63P0) density and the NH2 radical is detected by laser‐induced fluorescence (LIF) using the 597.8‐nm line to excite NH2(A2A1) Σ(0,9,0) vibronic states.The interpretation of LIF results in terms of NH2 density takes into account collisional transfer and quenching of NH2(A2A1) revealed by nonexponential time decay of the fluorescence. In addition, the silicon nitride film deposition rate is monitored and the N/Si stoichiometry is determined...
TL;DR: In this article, it was shown that conjugated poly(pyridine-2,5-diyl) and poly(2,2′-bipyridine5,5′-diamidyl) give rise to fluorescence in formic acid solutions, in the solid state (film), and in an adduct with poly(vinyl alcohol); the fluorescence was interpreted by assuming excimer formation.
Abstract: π-Conjugated poly(pyridine-2,5-diyl) and poly(2,2′-bipyridine-5,5′-diyl) give rise to fluorescence in formic acid solutions, in the solid state (film), and in an adduct with poly(vinyl alcohol); the fluorescence in the solid state, in the adduct with poly(vinyl alcohol), and in the formic acid solution with relatively high concentration of the polymer is interpreted by assuming excimer formation.
TL;DR: Examining the relative safety and thrombogenicity of pulsed excimer and thermal laser angioplasty systems in normal coronary artery segments found that the former resulted in fewer complications and, as a consequence, lessThrombosis and platelet accumulation than did the latter.
TL;DR: In this paper, the segmental motions of the polymer matrix involved in the glass transition phenomenon were investigated, and it was shown that at a fixed frequency of the probe motion, the fractional free volume as well as the free volume per atomic group vary from one polymer to another.
TL;DR: In this paper, the fluorescence and excitation spectra of pyrene at high concentrations were studied along the sol to xerogel stages of the sol-gel silica formed by the acidic hydrolysis of tetraethyl orthosilicate.
Abstract: The fluorescence and excitation spectra of pyrene at high concentrations were studied along the sol to xerogel stages of the sol–gel silica formed by the acidic hydrolysis of tetraethyl orthosilicate. The monomer and excimer fluorescence of pyrene were observed in the reaction system. Their relative intensities revealed that complex changes occurred that depended on the reaction time and the excitation wavelengths. The environmental polarity of the probe molecules also changed as shown by the fluorescence vibronic structure. The excitation spectrum of the excimer fluorescence in some stages was red shifted in comparison with that of the monomer fluorescence, indicating the existence of bimolecular ground-state pyrene associations. The mechanism by which pyrene molecules are trapped in the silica network is discussed on the basis of the results.
TL;DR: The temperature-dependent CD studies further indicated retention of thermodynamic stability of the crystallins after chemical modifications and a difference in the micro-environments around the labeled -SH residues around the lens proteins.
TL;DR: In this paper, the van der Waals spectra of fluorene with durene, 1,2,4,5-tetrafluorobenzene, and 1, 2, 4, 5-tetrachlorobenzenesene have been studied in supersonic jets.
Abstract: The fluorescence excitation and dispersed fluorescence spectra of the van der Waals complexes of fluorene with durene, 1,2,4,5-tetrafluorobenzene, and 1,2,4,5-tetrachlorobenzene have been studied in supersonic jets. In each system, the excitation spectra reveal long progressions in low-frequency models which can be assigned to the intermolecular vibrations between the constituent molecules.
TL;DR: In this paper, the performance of singlecrystal silicon in PF5 atmosphere by means of an ArF (193 nm) excimer laser has been investigated as a function of laser fluence, number of pulses, and PF5 gas pressure.
Abstract: Doping of single‐crystal silicon in PF5 atmosphere by means of an ArF (193 nm) excimer laser has been investigated as a function of laser fluence, number of pulses, and PF5 gas pressure. We find that phosphorus atoms are only produced by pyrolysis of the PF5 molecules but not by photolysis. The doping experiments were performed in PF5 ambients or using an adsorbed PF5 layer. The results indicate that the incorporation process is external rate limited for doping in PF5 ambients and mainly diffusion limited when using the adsorbed layer. Moreover, the evolution of the incorporated dose with the PF5 pressure shows that at low pressures (<0.5 Torr), the phosphorus atoms are supplied by a chemisorbed PF5 layer formed at the silicon surface, whereas at high pressures the main dopant source appears to be a layer of loosely bound PF5 molecules which has been physisorbed at the surface. It is also found that the surface quality is affected neither by the successive irradiation or by the heavy doping.
TL;DR: In this article, the conformationally sensitive excited charge transfer state of the 7-diethylamino-4-methylcoumarin (C1) laser dye in moderately polar to polar solvents was investigated.
Abstract: Picosecond time-resolved pump-probe excited state absorption measurements (with a 400–700 nm window) were used to investigate the conformationally sensitive excited charge transfer state of the 7-diethylamino-4-methylcoumarin (C1) laser dye in moderately polar to polar solvents. Time-dependent spectral changes due to amplified (probe beam) emission (AE) were observed in the short wavelength region of our window, together with excited state absorption (ESA) at longer wavelengths. These time-dependent changes are consistent with a single excited state species. Since the transient ESA spectrum of C1 is similar to that of the “rigid” C102 aminocoumarin in aqueous solution and to that of C1 in less polar solvents, the transient is assigned to an excited internal charge transfer (ICT) state rather than to a twisted internal charge transfer (TICT) state of C1. These results do not appear to support previous evidence for the formation of a TICT—solvent exciplex in moderately polar to polar solvents.