INDUCTION OF LAMBDA PROPHAGE NEAR THE SITE OF FOCUSED UV LASER RADIATION

DNA damage from photon scatter or beam spread during UV excimer laser irradiation was investigated using the induction of bacteriophage lambda in E. coli BR339. Prophage induction in these cells leads to the production of beta-galactosidase which can be detected colorimetrically by the application of appropriate substrates. An agar surface overlayed with BR339 cells was placed at various distances from the focal point of a converging lens and exposed to either 193 or 248 nm laser radiation. Energy densities ranging from approximately 5 mJ/cm2 to 30 J/cm2 were used. Ablation with 193 nm laser radiation produced an 800 microns wide clear 'trench' surrounded by a 500 microns zone of cells in which lambda had been induced. Following ablation with 248 nm laser radiation, the zone of induction was several millimeters wide. Exposures to 193 nm radiation at 170 mJ/cm2/pulse produced visible ablation of the agar surface at 1.7 J/cm2. Lambda induction was observed surrounding cleared ablation areas. The presence of induction in this system suggests that both 248 and 193 nm excimer laser radiation delivered at high energy densities has sufficient spread or scatter to damage DNA in cells surrounding areas of ablation.     

A comparative study of the polyaniline thin films produced by the cluster beam deposition and laser ablation methods

Polyaniline (PANI) thin films have been prepared by applying the novel neutral and ionized cluster beam deposition (NCBD and ICBD) methods and the pulsed laser deposition (PLD) technique to the PANI samples of half-oxidized emeraldine base (EB-PANI) and protoemeraldine base forms in a high-vacuum condition. Characterization of the oxidation states and structural changes of pristine and doped thin films has been performed by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, and x-ray photoelectron spectroscopy. Spectroscopic measurements demonstrate that the dominant structure of NCBD and ICBD thin films corresponds to the reduced leucoemeraldine base state, whereas the chemical composition of PLD thin films depends critically on the laser fluence and the molecular weight of PANI target. The congruent deposition is only obtained for the PLD films deposited by the laser-induced decomposition of the low-molecular-weight targets in the low to intermediate fluence regime (below 100 mJ/cm2 with a pulse duration of 7 ns). The surface morphology examined by atomic force microscopy measurements shows that the cluster and laser beams are effective in producing smooth, uniform polymeric thin films. After I2 and HCl doping, the electrical conductivities of the NCBD, ICBD, and particularly PLD thin films are increased significantly. The higher conductivity of PLD films is ascribed to higher amounts of quinoid di-imine doping sites in the EB-PANI state, and the overall structure-conductivity characteristics are consistent with the spectroscopic observations.     

X-ray microfocussing combined with microfluidics for on-chip X-ray scattering measurements

This work describes the fabrication of thin microfluidic devices in Kapton (polyimide). These chips are well-suited to perform X-ray scattering experiments using intense microfocussed beams, as Kapton is both relatively resistant to the high intensities generated by a synchrotron, and almost transparent to X-rays. We show networks of microchannels obtained using laser ablation of Kapton films, and we also present a simple way to perform fusion bonding between two Kapton films. The possibilities offered using such devices are illustrated with X-ray scattering experiments. These experiments demonstrate that structural measurements in the 1 A-20 nm range can be obtained with spatial resolutions of a few microns in a microchannel.     

Ultraviolet-Laser-Induced Crystallization of Sol-Gel Derived Indium Oxide Films

Modification of sol-gel derived indium oxide thin films using ultraviolet lasers was investigated. Irradiation by an ArF excimer (6.4 eV) and the fourth harmonic generation of a Nd : YAG laser (4.7 eV) was found to be effective in crystallization with a loss of hydroxyl groups and a decrease in the sheet resistance of the sol-gel films. Transparent crystalline indium oxide films were successfully obtained by 6.4 eV laser irradiation at fluences below 20 mJ/(cm2·shot), whereas degradation of the films was induced by a relatively high-fluence beam.     

Low-Temperature Synthesis of ITO Thin Films Using an Ultraviolet Laser for Conductive Coating on Organic Polymer Substrates

The resistivity of sol-gel-derived indium tin oxide (ITO) films effectively decreased with crystallization by exposure to a low fluence UV beam (10–20 mJ/cm²) from an ArF laser. The increase in temperature at the surface of the films was below 10°C under the irradiation condition. Thus, conductive and transparent ITO coatings were successfully obtained on polyethylene terephthalate and polyimide sheets using a sol-gel route assisted with an ultraviolet laser beam.     

Matrix-assisted pulsed laser evaporation of polyimide thin films and the XPS study

Compared with the traditional thin film techniques, the matrix-assisted pulsed laser evaporation (MAPLE) technique has many advantages in the deposition of polymer and organic thin films. It has a wide range of applications in many fields, such as non-linear optics, luminescent devices, electronics, various sensors. We have successfully deposited polyimide thin films by using the MAPLE technique. These films were characterized with XPS. The XPS spectra showed that the single-photon effect is ob-vious at low laser fluence and the chemical bonds will be broken, resulting in decomposition of the films. Contrarily, the single-photon effect will decrease and the multi-photon effect and the photothermal effect will increase at high laser fluence, resulting in the protection of the structure of the polyimide thin films and the obvious decrease in decomposition. High laser fluence is more suitable for the deposition of polymer and organic thin films than low laser fluence.     

Spectroscopic characterization of carbon chains in nanostructured tetrahedral carbon films synthesized by femtosecond pulsed laser deposition

A comparative study of carbon bonding states and Raman spectra is reported for amorphous diamondlike carbon films deposited using 120 fs and 30 ns pulsed laser ablation of graphite. The presence of sp(1) chains in femtosecond carbon films is confirmed by the appearance of a broad excitation band at 2000-2200 cm(-1) in UV-Raman spectra. Analysis of Raman spectra indicates that the concentrations of sp(1)-, sp(2)-, and sp(3)-bonded carbon are approximately 6%, approximately 43%, and approximately 51%, respectively, in carbon films prepared by femtosecond laser ablation. Using surface enhanced Raman spectroscopy, specific vibrational frequencies associated with polycumulene, polyyne, and trans-polyacetylene chains have been identified. The present study provides further insight into the composition and structure of tetrahedral carbon films containing both sp(2) clusters and sp(1) chains.     

Ablative photodecomposition of polymer films by pulsed far-ultraviolet (193 nm) laser radiation: Dependence of etch depth on experimental conditions

Data on the ablative photodecomposition of three condensation polymers [polyimide, poly(ethylene terephthalate), and polycarbonate] and one addition polymer (polymethyl methacrylate) by laser pulses at 193 nm are presented. The etch depth/pulse is a linear function of the number of pulses at constant laser fluence. It varies with the logarithm of the fluence in a linear manner at different fluences. The etch depth is independent of the atmosphere above the film, whether it is air at 1 atm, or a vacuum. The etching of PMMA at fluences > 100 mJ/cm² is believed to follow a mechanism different from the process at lower fluences. Etching of polyimide and polyethylene terephthalate at 248 and 308 nm is also reported. The mechanism of etching by laser radiation may receive greater contribution from a thermal process with increasing wavelength. This is manifested in the etch depth versus log fluence plot by sharp changes in slope.     

Surface characterization, modification chemistry, and separation performance of polyimide and polyamidoamine dendrimer composite films

6FDA-polyimide films modified by polyamidoamine (PAMAM) dendrimers with generations of 0, 1, and 2 are reported in this article. The actual molecular conformation and bulk size of these three generation dendrimers immobilized on polyimide surface were characterized by atomic force microscopy. After comparing with the results of dynamic simulation, we believe that the disk-shape cluster structure of dendrimers has been developed on the polymer surfaces. The amidation and cross-linking reaction between dendrimers and polyimide were examined and quantified by X-ray photoelectron spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, and gel content measurements. Modification time and the generations of PAMAM dendrimer have been verified as two important factors in determining the properties of modified polyimide films. These modified polyimide films exhibit excellent gas separation performance. The ideal selectivity of He/N(2) increases tremendously to about 200% as compared to that of the original polyimide film. Particularly, the separation performance of CO(2)/CH(4) gas pair can be improved beyond the upper bond limit possibly due to the strong interactions of dendrimer molecules with CO(2), which was verified by sorption tests.     

Analysis of blackbody-like radiation from laser-heated gas-phase tungsten nanoparticles

Thermal (blackbody-like) radiation that originated from laser-heated tungsten nanoparticles was measured using optical emission spectroscopy. The nanoparticles were generated via ArF excimer laser-assisted photolytic decomposition of WF6/H2/Ar gas mixtures, and the laser heating was applied parallel to the deposition. The temperature of the nanoparticles was determined, and its dependence on time, with respect to the 15-ns laser pulse (full width at half-maximum, fwhm) and laser fluence (phi), has been presented. At phi > 90 mJ/cm2, the particles reached the melting point (shortly after the laser pulse). Dominant cooling mechanisms, such as evaporation (above approximately 3000 K) and a combination of heat transfer by the ambient gas and radiative cooling (below approximately 3000 K), were observed for the nanoparticles, which were approximately 10 nm in diameter. The degree of inelasticity for the (predominantly) argon-gas collisions and the total emissivity of the particles (in the 2500-3000 K temperature region) could also be derived. The measured cooling rate and temperature data indicate that, depending on experimental parameters, evaporation and surface reactions can have a definite effect on the growth of particles.     

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.     

Structural stability and phase transitions in WO3 thin films

Tungsten oxide (WO3) thin films have been produced by KrF excimer laser (lambda = 248 nm) ablation of bulk ceramic WO3 targets. The crystal structure, surface morphology, chemical composition, and structural stability of the WO3 thin films have been studied in detail. Characterization of freshly grown WO3 thin films has been performed using X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) measurements. The results indicate that the freshly grown WO3 thin films are nearly stoichiometric and well crystallized as monoclinic WO3. The surface morphology of the resulting WO3 thin film has grains of approximately 60 nm in size with a root-mean-square (rms) surface roughness of 10 nm. The phase transformations in the WO3 thin films were investigated by annealing in the TEM column at 30-500 degrees C. The phase transitions in the WO3 thin films occur in sequence as the temperature is increased: monoclinic --> orthorhombic --> hexagonal. Distortion and tilting of the WO6 octahedra occurs with the phase transitions and significantly affects the electronic properties and, hence, the electrochemical device applications of WO3.     

The importance of the plume ejection time for the fragmentation yields observed in the UV ablation of molecular van der Waals films. Ablation of chlorobenzene films at 248 nm

The efficiency of photolysis in the ablation of thick C₆H₅Cl films at 248 nm is probed over 40–300 mJ/cm² by means of time-of-flight quadrupole mass spectrometry. Up to ≈ 150 mJ/cm², the photolysis yield is considerably smaller than that in the gas-phase. We argue that because of plume ejection well after the laser pulse, photolysis occurs exclusively in the film, and as a result, permanent dissociation is limited by the operation of efficient recombination processes characteristic of condensed phases. Fragmentation starts being important only at higher fluences, at which desorption during the laser pulse is indicated to be significant.     

Particle formation by infrared laser ablation of glycerol: implications for ion formation

The quantity and size distribution of micrometer-sized particles ejected from thin films of glycerol were measured using light scattering particle sizing. Thin glycerol films were irradiated at atmospheric pressure with an infrared optical parametric oscillator at wavelengths between 2.95 and 3.1 microm. Particulate material resulting from the ablation was sampled directly into a particle-sizing instrument and particles with diameters greater than 500 nm were detected and sized by light scattering. The fluence threshold for particle formation was between 2000 and 3000 J/m2 for all laser wavelengths. At threshold, fewer than 100 particles/cm3 were detected and this value increased to several thousand particles/cm3 at twice the threshold fluence. The average size of the coarse particles ranged from 900 nm to 1.6 microm at threshold and decreased by 10-20% at twice the threshold fluence. The coarse particle formation observations were compared with ion formation behavior in matrix-assisted laser desorption ionization and interpreted in terms of a photomechanical mechanism for material ablation and ion formation.     

Histamine detection using functionalized porphyrin as electrochemical mediator

This study reports on deposition of asymmetrical substituted meso-phenyl porphyrin, 5-(4-carboxyphenyl)-10,15,20-triphenylporphyrin (CPTPP) thin films by matrix-assisted pulsed laser evaporation (MAPLE) on screen-printed electrodes, aiming for histamine detection. Raman spectrometry confirmed that CPTPP chemical structure was preserved in MAPLE-deposited thin films at 200 mJ/cm² laser fluence. Atomic force microscopy topography revealed that MAPLE-deposited thin films have a better coverage on the working electrode made of carbon compared to the ones obtained by dropcasting. Cyclic voltammetry demonstrated that CPTPP is an appropriate mediator for histamine detection in trichloroacetic acid solution. We proved that MAPLE serves as a soft technique in fabrication of porphyrin thin films and patterns.     

On the copper oxide neutral cluster distribution in the gas phase: detection through 355 nm and 193 nm multiphoton and 118 nm single photon ionization

The distribution of neutral copper oxide clusters in the gas phase created by laser ablation is detected and characterized through time-of-flight mass spectroscopy (TOFMS). The neutral copper oxide clusters are ionized by two different approaches: Multiphoton absorption of 355 and 193 nm radiation; and single photon absorption of 118 nm radiation. Based on the observed cluster patterns as a function of experimental conditions (e.g., copper oxide or metal sample, ablation laser power, expansion gas, etc.) and on the width of the TOFMS features, one can uncover the true neutral cluster distribution of CumOn species following laser ablation of the sample. Ablation of a metal sample generates only small neutral CumOn clusters for m less, similar 4 and n approximately 1, 2. Ablation of copper oxide samples generates neutral clusters of the form CumOm (m < or = 4) and CumO(m-1) (m > 4). These clusters are directly detected without fragmentation using single photon, photoionization with 118 nm laser radiation. Using 355 and 193 nm multiphoton ionization, the observed cluster ions are mostly of the form Cu2mOm+ for 4 < or = m < or = 10 (193 nm ionization) and CumO1,2 (355 nm ionization) for copper oxide samples. Neutral cluster fragmentation due to multiphoton processes seems mainly to be of the form CumO(m,m-1) --> CumO(m/2,m/2+1). Neutral cluster growth mechanisms are discussed based on the cluster yield from different samples (e.g., Cu metal, CuO powder, and Cu2O powder).     

Amorphous iron phase formation in swift heavy ion irradiated electrodeposited iron thin films

⁵⁷Fe conversion electron Mössbauer spectroscopy, SEM, EDAX, XRD and AFM measurements were used to study the radiation effect of 246 MeV Kr ions on electrochemically deposited ⁵⁷Fe thin films. Amorphous iron phase formation has been shown to occur for the first time in electrodeposited iron thin films due to the irradiation with swift heavy ions.     

Trace gas detection of molecular hydrogen H(2) by photoacoustic stimulated Raman spectroscopy (PARS)

Photoacoustic stimulated Raman spectroscopy (PARS) has been used for sensitive and selective trace gas detection of molecular hydrogen under ambient conditions. In one experiment, 532 nm output of a seeded pulsed Nd:YAG laser is employed as Raman pump source and a Raman shifter filled with gaseous H(2) to obtain Stokes shifted radiation at 683 nm, suitable to stimulate H(2) Raman detection in a photoacoustic cell. A noise equivalent detection limit of 40 ppm by volume H(2) in 1 atm N(2) is obtained (14 mJ at 532 nm, 18 mJ at 683 nm, 10 Hz repetition rate, 58 s measurement time). Another experiment employs a dye laser for stimulating Raman radiation between 681-684 nm, allowing tuneable PARS. A Gaussian spectral fitting procedure has been applied giving a noise equivalent detection limit of 4.6 ppm by volume H(2) in 1 atm N(2) (35 mJ pulse energy at 532 nm, 45 mJ at 681-684 nm, 10 Hz repetition rate, 256 s measurement time). Spectroscopic detection offers the advantage of high selectivity along with the ability to obtain temperature and dynamic information from the rotational population and a line shape analysis, and also allows the discrimination between ortho- and para-H(2).     

Different susceptibility of cells of porcine skin and internal organs to ultraviolet A-induced breaking of nuclear DNA

There is a continuously growing interest in medical applications of ultraviolet radiation (UV-A and long-wavelength UV-B) especially for laser surgery, phototherapy and photodiagnostics of human internal organs. UV-B and UV-A radiation is potentially mutagenic, however, there has been very little information published to date concerning the significance of possible deleterious action of such photons on cells of internal tissues. The aim of this study is to compare the sensitivities of skin cells to those of internal organs upon exposure to UV-A. To assess this sensitivity we have determined the UV-A dose-dependent frequency of nuclear DNA breaks detected with the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) technique. The materials for the study were macroscopic samples of porcine skin, colon and esophagus. The UV-A dose ranged from 0.1 to 1000 mJ/cm2, which is similar to doses received by cells in regions examined with laser-induced fluorescence or by cells surrounding areas subject to a laser ablation. To reduce the influence of DNA repair processes the tissue samples were kept at a low temperature during the irradiation and were deep frozen immediately after completing the irradiation procedure. The cells of the internal organs are much more susceptible to UV-A-induced breaking of DNA than the skin cells. The percentage fractions and the spatial distributions of the damaged cells and the characteristics of the UV-A dose dependence seem to vary by type of internal organ.     

Preparation and adhesion of ultrathin polyimide films on polycrystalline silver

4.4-oxydianiline (ODA) and 1,2,3,5-benzenetetracarboxylic anhydride (PMDA) were deposited from the vapor phase onto a polycrystalline silver substrate and polymerization of the two components to form ultrathin polyimide films (d≈ 11 Å) was followed by X-ray photoelectron spectroscopy. Both PMDA and ODA chemisorb on the clean surface under partial fragmentation. Co-deposition of ODA and PMDA followed by heating of the substrate led to formation of thermally stable (T<450°C) polyimide films. Our data indicate that adhesion of the polyimide film to the surface involves chemical bonding to fragmented PMDA and/or ODA chemisorbed on the substrate. Our experiments show that polyimide films can be prepared sufficiently thin to allow the application of surface sensitive techniques to probe the substrate-polymer interface and to study the basic physics and chemistry of adhesion.