The effect of vacuum-ultraviolet laser wavelengths on the surface treatment of polyolefinic polymers

The laser-induced modification of the surface morphology of poly(propylene) fibers and films was investigated. It is known that strongly absorbing fibers such as poly(ethylene terephthalate) and polyamide obtain characteristic surface morphologies after treatment with 193 or 248 nm laser irradiation. Polyolefinic material cannot be modified directly (i.e., without doping) by irradiation with these wavelengths. Therefore experiments were carried out using a 157 nm F₂-laser. After irradiation in a vacuum chamber at fluences in excess of 50 mJ/cm² poly(propylene) also reveals the well-known surface morphology. Compared with aromatic polymers a rather high number of pulses is needed to generate the effect. © 1993 John Wiley & Sons, Inc.     

LASER-LIGHT INDUCED CHROMOSOME ABERRATIONS IN CHINESE HAMSTER CELLS

Wild-type Chinese hamster cells CHO Kl and their radiosensitive mutant xrs5 were irradiated at 308 nm, using light pulses of a XeCl excimer laser with total energy fluences of 0.1 kj/m² to 4.08 kj/m². Chromosome-type and chromatid-type chromosome aberrations have been observed at pulse irradiances of 2.5 × 10⁷ W/m² and 1.7 × 10⁸ W/m², indicating that in mammalian cells DNA double-strand breaks occur already in this irradiance range. The results obtained with laser irradiation are compared with X-ray irradiation.     

Intranasal irradiation with the xenon chloride ultraviolet B laser improves allergic rhinitis

We earlier reported that the 308 nm xenon chloride (XeCl) ultraviolet B (UVB) laser is highly effective for the treatment of inflammatory skin diseases. Since UVB irradiation has been shown to exert both local and systemic immunosuppression, we investigated the clinical efficacy of UVB irradiation in allergic rhinitis. In an open study, groups of patients with severe allergic rhinitis received intranasal irradiation with a 308 nm XeCl UVB excimer laser for two weeks. In the low-dose group (n=10), treatment was given twice weekly, starting with 0.25x the individual minimal erythema dose (MED), whereas patients in the medium-dose group (n=8) were treated four times weekly, starting with 0.4x MED. In each group, the dosage was gradually increased. Evaluation was based on the symptom scores. The effect of the XeCl laser on the skin prick test reaction was also studied. In the low-dose group, seven patients completed the study, and there was no improvement in the nasal symptoms. In the medium-dose group, the XeCl UVB irradiation significantly inhibited the rhinorrhoea, the sneezing, the nasal obstruction and the total nasal score (p<0.05). The XeCl UVB excimer laser also inhibited the allergen-induced skin prick test in a dose-dependent manner. These results suggest that the XeCl UVB excimer laser might serve as a new therapeutic tool in the treatment of allergic rhinitis.     

Ion Beam Modification of Polymethyl methacrylate (PMMA) Polymer Matrix Filled with Organometallic Complex

A Nickel Dimethylglyoxime (Ni‐DMG) compound was dispersed in polymethyl methacrylate (PMMA) films at different concentrations. PMMA was synthesized by a solution polymerization technique. These films were irradiated with 120 MeV Ni¹⁰⁺ ions at the fluences of 1×10¹¹ and 1×10¹² ions/cm². The radiation induced changes in dielectric properties and average surface roughness were investigated by using an LCR meter in the frequency range 50 Hz to 10 MHz and atomic force microscopy (AFM), respectively. The electrical properties of irradiated films are found to increase with the fluence and also with the concentration of Ni‐DMG. From the analysis of frequency, f, dependence of dielectric constant, ?, it has been found that the dielectric response in both pristine and irradiated samples obey the Universal law given by ? α f ^n?1. The dielectric constant/loss is observed to change significantly due to the irradiation. This suggests that ion beam irradiation promotes (i) the metal to polymer bonding (ii) convert the polymeric structure in to hydrogen depleted carbon network due to the emission of hydrogen gas and/or other volatile gases. Atomic force microscopy (AFM) shows that the average surface roughness and surface morphology of irradiated films are observed to change.     

Photoinitiated grafting polymerization of acrylic acid onto the surface of polyethylene under pulsed laser radiation

Photoinduced grafting polymerization on the surface of PE films induced by nanosecond pulsed laser radiation is studied. The grafting is performed from the liquid phase composed of acrylic acid and a photoinitiator (benzophenone) dissolved in it. Pulsed laser radiation with a wavelength of 355 nm, a pulse duration of 11 ns, and a repetition rate of 10 Hz is used. Formation of the surface-graft polymer is followed by IR-ATR spectroscopy and contact-angle measurements. It is found that the time of laser treatment sufficient for the efficient modification of the PE surface with the grafted poly(acrylic acid) is in the range from 0.5 to 1.0 s at a laser-pulse energy density of 200–500 mJ/cm². At energy densities beyond this range, the efficiency of the reaction decreases rapidly. The results on laser grafting are compared with the results of grafting during UV irradiation with a lamp at a wavelength of 365 nm.     

Indirect Photo-Induced Phosphorylation Via a C-Ester Caged Troika Acid

Abstract

Use of a photoremovable “caging” group allows the generation of reactive molecules under mild conditions. Photo-induced phosphorylations typically have involved attachment of the photosensitive group at phosphorus.[1] We now have investigated indirect photolytic activation of an unmodified phosphonic acid group using broad band UV (Hg lamp), 308 nm XeCl excimer laser or 355 nm YAC laser irradiation of the o-nitrobenzyl C-ester of “troika acid” [(E)-1²]. In alcohols or neutral buffer, irradiation of (E)-2 gave phosphorylation of the solvent plus phosphorocyanidate, the expected 2-isomer product.²All thrce UV sources gave -1:2 E:Z product distribution in MeOH. In the (E)-1 methyl C-ester, the oxime functionality absorbed strongly near 205 nm (E_max 5200), weakly at 308 nm and negligibly above 355 nm, and no photoisomerization was seen using the 355 nm source. Thus, oxime isomerization in (E)-2 at least using 355 nm irradiation. requires the o-nitrobenzyl group, and possibly involves an energy- or charge-wansfer effect. Phosphorylation of EtOH/t-BuOH mixtures by photolysis of (E)-2 showed little alkyl selectivity. consistent with photoinduced formation of an intermediate. plausibly (E)-1, which undergoes spontaneous dissociative fragmentation via a monomeric metaphosphate-like species.     

Comparison of Single Pulse and Double Simultaneous Pulse Laser Induced Breakdown Spectroscopy

A simple and cost-effective variant of laser induced breakdown spectroscopy is presented that involves a double simultaneous pulse configuration employing a single laser source. Its performance is compared with conventional single pulse configuration. Double simultaneous pulses were accomplished by splitting a Nd:YAG laser (1064 nm, 6 ns, 360 mJ) beam into two components that were focused on the sample surface to produce two concurrent breakdowns. Experiment was repeated for single pulse and double simultaneous pulses under different ambient pressures. The performance was evaluated on the basis of self-absorption, signal-to-noise ratio (SNR), and relative standard deviation (RSD) of the Mg II doublet (280.2704 nm, 279.553 nm). Optically thin emission lines of better profiles with higher signal-to-noise ratio resulted from double simultaneous pulses. The lowest relative standard deviations obtained by single pulse and double simultaneous pulse configurations were 18.89% and 12.01%, respectively. In fact, double simultaneous pulses have performed better than single pulse in all respects within the studied regime.     

Dielectric properties and surface morphology of swift heavy ion beam irradiated polycarbonate films

Swift heavy ion beam irradiation induces modification in the dielectric properties and surface morphologies of polycarbonate (PC) films. The PC films were irradiated by 55 MeV energy of C⁵⁺ beam at various ions fluences ranging from 1 × 10¹¹ to 1 × 10¹³ ions cm^?2. The dielectric properties (i.e., dielectric constant, dielectric loss, and AC conductivity) and surface morphologies of pristine and SHI beam irradiated PC films were investigated by dielectric measurements, atomic force microscopy (AFM), and optical microscopy. The dielectric measurements show that the dielectric constant, dielectric loss, and AC conductivity increase with ion fluences and temperature, however, the dielectric constant and AC conductivity decrease while dielectric loss increases with frequency. AFM shows the increase in average roughness values with ion fluences. The change of color in PC films has been observed from colorless to yellowish and then dark brown with increases of ion fluence by using optical microscopy.     

Analysis of glass by UV laser ablation inductively coupled plasma atomic emission spectrometry. Part 2. Analytical figures of merit

Two lasers working in the UV part of the spectrum have been used for the direct analysis of glass samples by laser ablation ICP-AES. An XeCl excimer laser (308 nm) and a Nd:YAG laser operating at the third harmonic (355 nm) and the fourth harmonic (266 nm) have been selected. The energy was 70 mJ and 5 mJ for the excimer laser and the Nd:YAG laser, respectively, with a 10 Hz repetition rate. Figures of merit such as repeatability, reproducibility, accuracy and limits of detection have been studied. Si was used as an internal standard to improve the repeatability, the reproducibility and the accuracy. Use of internal standardardization led to an RSD of less than 1% for most elements and to a linear calibration graph irrespective of the colour of the glass samples. Limits of detection in the solid were of the same magnitude as those obtained using sample dissolution and pneumatic nebulization. Results confirmed that the XeCl laser provided the best results of detection whereas the Nd:YAG laser, particularly at 266 nm, was less sensitive to glass colour.     

Influence of polymer molecular weight on the chemical modifications induced by UV laser ablation

This paper investigates the influence of polymer molecular weight (M(W)) on the chemical modifications of poly(methyl methacrylate), PMMA, and polystyrene, PS, films doped with iodonaphthalene (NapI) and iodophenanthrene (PhenI), following irradiation at 248 nm (KrF excimer laser, 20 ns fwhm and hybrid excimer-dye laser, 500 fs fwhm) and at 308 nm (XeCl excimer laser, 30 ns fwhm). The changes of intensity and position of the polymer Raman bands upon irradiation provide information on cleavage of the polymer bonds. Degradation of PMMA, which is a weak absorbing system at 248 nm, occurs to a higher extent in the case of a larger M(W), giving rise to the creation of unsaturation centers and to degradation products. For highly absorbing PS, no degradation is observed upon irradiation with a KrF laser. Consistently irradiating doped PS at 308 nm, where the absorption is low, induces degradation of the polymer. Results provide direct support for the bulk photothermal model, according to which ejection requires a critical number of broken bonds. In the case of irradiation of doped PMMA with pulses of 248 nm and 500 fs, neither degradation nor dependence with polymer M(W) are observed, indicating that mechanisms involved in the femtosecond laser ablation differ from those operating in the case of nanosecond laser ablation. Participation of multiphoton/avalanche processes is proposed.     

Combined laser and magnetic field treatment of YFeO<Subscript>3</Subscript>—containing films grown by spray-pyrolysis

Thin films (50–1200 nm) of YFeO₃ were deposited on fused silica substrates by spray-pyrolysis using ethylene glycol solution of Y-Fe(III) citric complexes. The films were post deposition annealed at 750°C in static air for 2 h. Films obtained in this way were afterwards irradiated by a burst mode operated Nd-YAG laser (pulse energy 650 mJ, pulse duration 700 μs, energy density 110 mJ/cm²). The laser’s onset was synchronized with that of a magnetic field pulse of nearly square shape (magnetic induction 0.5 T, pulse duration 900 μs). The samples were placed normally to the direction of the magnetic field. The treatment does not affect the phase composition of the film but significantly increases the crystallite sizes of the phases presenting in the sample. The saturation magnetization of the films decreases as a result of the laser and magnetic field treatment and the coercive force increases by 50%.     

Analysis of glass by UV laser ablation inductively coupled plasma atomic emission spectrometry. Part 1. Effects of the laser parameters on the amount of ablated material and the temporal behaviour of the signal for different types of laser

Two lasers working in the UV part of the spectrum have been used for the analysis of glass samples. An XeCl excimer laser (308 nm) and a Nd:YAG laser operating at the third harmonic (355 nm) and the fourth harmonic (266 nm) have been selected. The energy was 100 mJ and 5 mJ for the excimer laser and the Nd:YAG laser, respectively. Because of different spot sizes, the fluence was of the same magnitude for both lasers. Crater characterization indicated that the laser ablation efficiency was similar for the two lasers when normalized to the same energy. However, the XeCl was found to be more efficient when the results were normalized to irradiance unit. The amount of probed material and ablated material was measured, leading to an efficiency higher than 80%. The influence of the glass colour and the laser wavelength was evaluated. The XeCl laser provided the largest amount of material but was sensitive to the glass colour. This laser was mainly suitable for bulk analysis. In contrast, the Nd:YAG, particularly at 266 nm, was insensitive to the glass colour and was appropriate for localized analysis. Inductively coupled plasma atomic emission spectrometry was used for atomization and excitation of the ablated material. A good agreement was found between the temporal behaviour of the amount of ablated material and the analyte signal.     

Structure induced by irradiation of femtosecond laser pulse in dyed polymeric materials

We investigated the structures induced by an irradiation of a near‐infrared (NIR) femtosecond laser pulse in dye‐doped polymeric materials {poly(methyl methacrylate) (PMMA), thermoplastic epoxy resin (Epoxy), and a block copolymer of methyl methacrylate and ethyl acrylate‐butyl acrylate [p(MMA/EA‐BA) block copolymer]}. Dyes used were classified into two types—type 1 with absorption at 400 nm and type 2 with no absorption at 400 nm. The 400‐nm wavelength corresponds to the two‐photon absorption region by the irradiated NIR laser pulse at 800 nm. Type 1 dye‐doped PMMA and p(MMA/EA‐BA) block copolymer showed a peculiar dye additive effect for the structures induced by the line irradiation of a NIR femtosecond laser pulse. On the contrary, dye‐doped Epoxy did not exhibit a dye additive effect. The different results among PMMA, p(MMA/EA‐BA) block copolymer, and Epoxy matrix polymers are supposed to be related to the difference of electron‐acceptor properties. The mechanism of this type 1 dye‐additive‐effect phenomenon for PMMA and p(MMA/EA‐BA) block copolymer is discussed on the basis of two‐photon absorption of type 1 dye at 400 nm by the irradiation of a femtosecond laser pulse with 800 nm wavelength and the dissipation of the absorbed energy to the polymer matrix among various transition processes. Dyes with a low‐fluorescence quantum yield favored the formation of thicker grating structures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2800–2806, 2002     

Plasma chemistry in laser ablation processes

Based on the results of quantitative spectroscopic diagnostics (LIF in combination with time resolved emission spectroscopy) chemical dynamics in laser-produced plasmas of metallic (Ti, Al,), and graphite samples have been examined. The Nd-YAG (1064 nm, 10 ns, 100 mJ) and excimer XeCl (308 nm, 10 ns, 10 mJ) lasers were employed for ablation. The main attention was focused on the elucidation of a role of oxide and dimer formation in controlling spatio-temporal distributions of different species in the ablation plume. The results of the spatial and temporal analysis of a laser-produced plasma in air indicates the existence of diatomic oxides in the ablation plume both in the ground and excited states, which are formed from reactions between ablated metal atoms and oxygen. The efficiency of the oxidation reaction depends on the intensity and spot diameter of the ablation laser beam. The maximal concentration of TiO molecules are estimated to be of 1×10¹⁴ cm⁻³ at the time of 10 μs after the start of the ablation pulse. A comparison of spatial–temporal distributions of Ti atoms and excited TiO molecules allow us to find a correlation in their change, which proves that electronically excited Ti oxides are most probably formed from oxidation of atoms in the ground and low lying metastable states. The spectroscopic characterization of pulsed laser ablation carbon plasma has also been performed. The time–space distributions as well as the high vibrational temperature of C₂ molecules indicate that the dominant mechanism for production of C₂ is the atomic carbon recombination.     

Excimer Laser Crystallization of SnO2:Sb Sol-Gel Films

Instead of classical or rapid thermal annealing, KrF excimer laser irradiation has been successfully applied to crystallize dried SnO₂:Sb films elaborated by a sol-gel process. The penetration of the crystallization front below the film surface, as imaged by transmission electron microscopy, is controlled by the laser fluence and the number of pulses and can thus be confined in the film itself without affecting sensitive substrates. All films laser irradiated at fluences higher than 40 mJ/cm² become conductive. At constant laser fluence, the electrical sheet resistance goes through a minimum with increasing number of pulses. The consequence of film's densification and morphology on electrical properties is discussed.     

Swift heavy ion induced modification in dielectric and microhardness properties of polymer composites

Polymer composites with different concentrations of organometallics (ferric oxalate) dispersed PMMA were prepared. PMMA was synthesized by solution polymerization technique. These films were irradiated with 120 MeV Ni¹⁰⁺ ions in the fluence range 10¹¹-5 × 10¹² ions/cm². The radiation induced modifications in dielectric properties, microhardness, structural changes and surface morphology of polymer composite films have been investigated at different concentrations of filler and ion-fluences. It was observed that electrical conductivity and hardness of the films increase with the concentration of the filler and also with the fluence. The dielectric constant (?) obeys the Universal law given by ?αfⁿ⁻¹. The dielectric constant/loss is observed to change significantly due to irradiation. This suggests that ion beam irradiation promotes the metal to polymer bonding and convert polymeric structure into hydrogen depleted carbon network. This makes the composites more conductive and harder. Surface morphology of the films has been studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The average surface roughness is observed to increase after irradiation as revealed by AFM studies. The SEM images show the blisters type of phenomenon on the surface due to ion beam irradiation.     

Surface nitridation by multipulse excimer laser irradiation

A review is presented of the results obtained on the formation of nitride surface layers on semiconductor (Si) and metal (Ti) samples by multipulse (up to 2500) XeCl excimer laser (λ=308 nm) irradiation in N₂ and NH₃ atmosphere through a collaboration of Italian, Czechoslovak and Romanian laboratories. Different diagnostic techniques (optical and electron microscopy, Rutherford backscattering spectroscopy, nuclear reaction analysis, Auger and x-ray photoelectron spectroscopy) were used to positively identify the formed compounds. Silicon nitride formation was obtained only when laser irradiation was performed in ammonia atmosphere. In contrast, when titanium samples were irradiated the nitridation process resulted very efficient in both atmospheres. The characteristics of laser synthesized nitride layers are illustrated and discussed as a function of the kind of irradiated materials, the number of subsequent laser pulses and the nature of the ambient gas.     

A two-color laser photolysis method for determining reaction rates of short-lived intermediates by product analysis: application to the o-quinodimethane problem

A time-delayed, two-color pulse laser photolysis technique was used for a kinetic study of short-lived transient species through product analysis, the determination of the rate constant of the cycloaddition of o-quinodimethane (1) and maleic anhydride (2) in room-temperature solutions. o-Quinodimethane (1) was generated from 1,2-bis[(phenylseleno)methyl]benzene (3) by the irradiation of a pulse of a KrF excimer laser (248 nm) in the presence of excess 2, and a successive pulse of a XeCl excimer laser (308 nm) was irradiated to the reaction mixture after varied delay times from 0 to 0.1 s for the decomposition of the remaining 1 to quench the cycloaddition reaction. The rate constant of the cycloaddition of 1 and 2 was 2.1 x 10(5) M(-1) s(-1), which was obtained by the analysis of the delay-time dependence of the product yields.     

A Study on Liquid Hybrid Material for Waveguides—Synthesis and Property of PSQ‐Ls for Waveguides

Silicate‐based inorganic‐organic hybrid polymer systems have many unique properties including thermal stability and photo‐stability, chemical resistance with the combination of tunable optical properties. Two kinds of new UV‐patternable hybrid materials PSQ‐Ls were synthesized by a sol‐gel process at room temperature, which can be used for low cost fabrication of optical waveguides. Thick films (up to 8.31 µm) can be coated by a single spin‐coating process without any cracking and the average surface roughness (Ra), detected by atomic force microscopy (AFM), is below 0.5 nm. The optical properties (refractive index, birefringence, and optical loss at 1310 nm and 1550 nm, respectively) of the PSQ‐Ls films are investigated by a prism coupler. The refractive index of PSQ‐Ls can be exactly tuned from 1.4483 to 1.5212 by blending PSQ‐LH (n_TE=1.5212 @ 1310 nm) and PSQ‐LL (n_TE=1.4483 @ 1310 nm). The maximum refractive index contrast is about 4.8%. After post‐baking, birefringences of the films are below 0.0005 and optical losses are about 0.2 dB · cm^?1 at 1310 nm, 0.7 dB · cm^?1 at 1550 nm, respectively. Furthermore, the PSQ‐Ls films also show outstanding thermal stability in air atmospheres.     

Ultraviolet nanosecond laser ablation behavior of silver nanoparticle and melamine–formaldehyde resin-coated short sisal fiber-modified PLA composites

Nd:YAG laser (355 nm) induced surface modifications in polylactic acid (PLA), and its composites with silver nanoparticles (AgNPs, size range between 120 and 150 nm) with and without additional melamine–formaldehyde-coated short sisal fibers were studied as a function of laser pulse numbers. The AgNP content was varied (100, 300 and 500 ppm), whereas the sisal content kept as constant (9 mass%). The PLA-based systems with a fully amorphous matrix were irradiated with 1–256 laser pulses at a constant fluence of 0.32 µJ µm^?2. Changes in the irradiated surfaces were assessed and quantified by light and scanning electron microscopic pictures. Protrusion with bubbling, bubbled protrusion with cratering and crater formation with more or less bubbled ridges were found as characteristic ablation features. Bubbling was traced to entrapped gaseous products of PLA degradation, while the onset of ridges was ascribed to the melt flow of the PLA matrix caused by laser shock waves. The laser irradiation caused damage and ablation highly depended on the actual composition, which influenced the UV absorption at 355 nm, which was measured as well.