Low-pressure Hg Lamp Research Articles

Growth of calcium phosphate thin films by in situ assisted ultraviolet pulsed laser deposition

Calcium phosphate (CaP) thin films including hydroxyapatite were intensively studied in order to optimize the technology of the bone prostheses manufacturing. A drawback in the CaP films processing is the poor mechanical characteristics, especially hardness, tensile strength and adherence to the metallic substrate. We report a new method for the growth of high quality CaP films with substantial improvement of the mechanical properties: pulsed laser deposition (PLD) assisted by in situ ultraviolet (UV) radiation emitted by a low pressure Hg lamp. The depositions were made on Si and Ti-5Al-2.5Fe alloys in very low ambient oxygen at pressures of 10 −2 to 10 −1 Pa with the substrates maintained at 500–600 °C temperature. The films were analyzed by electron microscopy, white light confocal microscopy (WLCM), grazing incidence X-ray diffraction and Berkovich nanoindentation. The films were crystalline and exhibited remarkable mechanical characteristics with values of hardness and Young modulus of 6–8 and 150–170 GPa, respectively, which are uncommonly high for the CaP ceramics. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, while the tensile strength between the film’s grains and the bonding strength at the CaP film-substrate interface were increased.

単結晶二酸化チタンを用いた光触媒作用による油汚れ綿布の洗浄性（原表題は英語）

Cotton garments were coated with titanium dioxide particles consisting of small single crystals. Organic soils such as liquid paraffin, triolein and oleic acid were used as organic dirt coming from human skin. The fabric with titanium dioxide was immersed into aceton solutions of these compounds, withdrawn, and then irradiated with UV with a low pressure Hg lamp. Detergency was calculated from spectral reflectance before and after UV irradiation. In case of liquid paraffin, positive detergency values were obtained in regions with wavelengths of 400 nm or above, but negative ones were obtained in regions with wavelengths of less than 300 nm. On the other hand, positive detergency values were observed in wavelengths of 600 nm or above; however, in regions with wavelengths of less than 400 nm, negative ones were observed for soils such as triolein and oleic acid. A positive value of detergency means that the soil was removed by decomposition from the cotton surface by the titanium dioxide photo-catalytic action. For negative values of detergency, it may be considered that coloration due to changes in chemical structure of soils.

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition.

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti-5Al-2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500-600 degrees C. The UV-assisted PLD films were grown in (10(-2)-10(-1) Pa) oxygen directly on Ti-5Al-2.5Fe substrates heated at 500-600 degrees C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6-7 and 150-170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca(2)P(2)O(7), Ca(2)P(2)O(9) and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.

Ultraviolet-assisted pulsed laser deposition of La0.7Ca0.3MnO3 thin films with improved oxygen content, crystallinity and magnetoresistive properties

Colossal magnetoresistive La0.7Ca0.3MnO3 (LCMO) films with improved magnetoresistance properties have been grown at relatively low temperatures using an ultraviolet-assisted pulsed laser deposition technique. In this technique, a low pressure Hg lamp having a fused silica envelope, which allows more than 85% of the emitted 184.9 nm radiation to be transmitted, is added inside the growth chamber during pulsed laser deposition of LCMO films. Magnetoresistance (MR) measurements carried out on LCMO films grown under identical conditions barring the presence/absence of UV radiation during thin film formation have shown that the MR ratio of UV-assisted grown LCMO films is nearly two orders of magnitude higher than that of LCMO films grown without UV. The improvement in magnetoresistive properties of LCMO film deposited in the presence of UV is assumed to be related with improvement in oxygen content, oxygen homogeneity, and crystallinity. Evidences supporting this assumption are obtained from analysis of spectra recorded using x-ray photoelectron spectroscopy and Rutherford backscattering measurements.

二酸化チタン光触媒作用による綿布に付着した油性汚れの除去（原標題は英語）

Cotton garments were coated with small particles. Liquid paraffin, Triolein and Oleic Acid organic soils served as the sources of produced with human wear. The clothing with titanium dioxide was immersed in aceton solutions of these compounds, withdrawn and irradiated with UV from a low pressure Hg lamp. Spectral reflectance was then measured with a spectrograph and found to increase at more than 400 nm. Detergency and reflectance decrease at less than 400 nm were assessed following irradiation at both these wavelengths, and was found, respectively to be positive and negative. Without titanium dioxide, negative detergency was observed. From these results it may be recognized that changes in model soil materials were occurred by photo catalytic action of titanium dioxide.

Direct Evidence of Ozone as the Active Oxidant in “Photooxidation” of Alkanethiols on SERS-Active Silver

Surface-enhanced Raman spectroscopy (SERS) has been used to study the mechanism of “photooxidation” of decanethiol self-assembled on roughened Ag. Direct exposure of self-assembled decanethiol to light from a low-pressure Hg lamp under ambient conditions results in adsorbed oxidized sulfur species. Absorbance spectroscopy was used to quantify ozone levels (∼ 20 ppm) generated by the Hg lamp. When decanethiol samples were exposed to the same amount of 254 nm light from the lamp but were environmentally isolated, so that oxygen was present but ozone generated by the lamp could not diffuse to the surface, no oxidation was observed. In addition, when decanethiol samples were exposed to an equivalent amount of electrically generated ozone in the absence of light, the SERS oxidation product spectra were identical to those generated by the lamp under ambient conditions. Quantitative investigation of the kinetics of oxidation yielded second-order rate constants of 0.0029 ± 0.0005 ppm−1 s−1 and 0.0024 ± 0.0006 ppm−1 s−1, for electrically generated ozone and the lamp, respectively. The two rate constants are the same within error, indicating that under the conditions of our experiment the mechanism of oxidation is dominated by ozone and not light.

Atmospheric chemistry of toluene-1,2-oxide/2-methyloxepin

A kinetic and product study of the atmospheric chemistry of toluene-1,2-oxide/2-methyloxepin, a possible intermediate in the OH-initiated oxidation of toluene, was conducted in a 1080 l quartz glass reaction chamber. The compound was found to be unstable, with a thermal decomposition lifetime of (333±83) min. Photolysis with superactinic lamps (320 nm<λ<460 nm, λmax=360 nm) was found to be slow, while that with low-pressure Hg lamps (λmax=254 nm) proceeded rapidly. For clear sky conditions at noon on July 1 at a latitude of 40°N, an atmospheric photolytic lifetime of (26±4) min can be extrapolated from the experimental data using the superactinic lamps. For the reaction with OH radicals, a reaction rate constant of (2.1±0.1)×10−10 cm3 molecule−1 s−1 was determined; the main products were E/Z-isomers of 6-oxohepta-2,4-dienal. Reaction with NO3 radicals was observed to proceed with a rate constant of (1.27±0.10)×10−11 cm3 molecule−1 s−1; the main products were unidentified nitrogen-containing compounds. In addition, 2E,4Z-6-oxohexa-2,4-dienal was identified; other isomers are probably formed as well. The results suggest that under atmospheric conditions both photolysis and reaction with OH radicals will be important sinks for toluene-1,2-oxide/2-methyloxepin, while reaction with NO3 radicals will become important under laboratory conditions at high concentrations of NOx, possibly also in heavily polluted tropospheric air masses.

Ultraviolet Photochemistry and ex Situ Ozonolysis of Alkanethiol Self-Assembled Monolayers on Gold

The ultraviolet (UV)-photoinduced chemistry at low irradiances in O2 and the O3 thermal chemistry of alkanethiolate SAMs have been studied. At the low irradiances typical of low-pressure Hg lamps, UV photolytic generation of products soluble in polar solvents from hexadecanethiol (HDT) SAMs requires both O2 and irradiation below 200 nm. Significantly, exposure of HDT SAMs to ex situ generated O3 in the dark produced the same results as UV irradiation of HDT SAMs in the presence of O2. Both of these facts suggest a leading role for photogenerated O3 in the UV photochemistry of alkanethiol SAMs. Further, O3 was found to be at least an order of magnitude more effective than other active oxygen-containing species at generating labile products under the conditions employed. The products of reaction from either O3 exposure or UV irradiation in O2 appear to be oxidized sulfur headgroups, which are easily removed by subsequent rinsing in a polar solvent. The heterogeneous reaction of O3 with alkanethiols is remar...

Ablative photodegradation of poly(methyl methacrylate) and its homologues by 185- nm light

Photodegradation of poly(methyl methacrylate), poly(n-butyl methacrylate), poly(t-butyl methacrylate) and poly(isopropyl methacrylate) was studied under high vacuum using 185 nm light from a low-pressure Hg lamp. UV and FT-IR spectroscopies, GPC and quartz crystal microbalance were used to study the degradation. The efficiency of photodegradation of the polymers was dependent on the structure of the ester units in the side chain. The polymer with low glass transition temperature was easily decomposed. The ablation of the polymer films was observed, if irradiated at elevated temperatures (50–130°C). The temperature at which the ablation began to occur was strongly dependent on the polymer structure.

Formation of novel cage compounds via photoreaction of [3.3.3](1,3,5)cyclophane

Photoirradiation of [3 3](1,3,5)cyclophane 11 with a low pressure Hg lamp in CH 2Cl 2 in the presence or absence of water afforded new polycyclic cage compounds of chlorinated tribridged hexacyclododecane 12 or its hydroxy analogue 14 and tribridged tetracyclic olefin 13.

Xe&lt;SUB&gt;2&lt;/SUB&gt;*エキシマランプを用いたUV/O&lt;SUB&gt;3&lt;/SUB&gt;洗浄の検討

UV/O3 cleaning by an Xe2*excimer lamp was investigated under various experimental conditions. We found that UV/O3 cleaning was caused by excited atomic oxygen {O (1D)} and that the cleaning speed was about six times faster than that using a low-pressure Hg lamp.

Hydrogen bromide photochemistry: actinometry for determination of absolute power outputs of xenon excimer and other UV/VUV light sources

This work describes convenient and accurate power measurements of UV/VUV light sources by HBr actinometry. The absolute power output of a high-intensity excimer lamp is determined and is compared with the UV/VUV output of conventional low-pressure Hg lamps. The absolute radiant power is extracted from experimental yields which are measured by absorption spectroscopy at 450 nm. A novel computer program calculates the fraction of UV/VUV photons emitted by the lamp at a specific wavelength which result in photodissociation of HBr.

Synthesis, Structure, and Reactivity of a Bis(silylene)carbonylruthenium Complex and a Novel Addition Reaction of Photochemically Generated Dimethylsilylene to Bis(silylene) Complexes Cp(OC)M{SiMe2···O(Me)···SiMe2} (M = Ru, Fe)

Photolysis of CpRu(CO)2SiMe2SiMe3 (1a) with a low- or medium-pressure Hg lamp for a long time caused the loss of a SiMe2 moiety to give CpRu(CO)2SiMe3 (2), perhaps through the photochemical dissociation of a CO ligand. This mechanism was supported by the quantitative formation of the bis(silylene)ruthenium complex Cp(OC)Ru{SiMe2···O(Me)··· SiMe2} (3a) by photolysis of the (methoxydisilanyl)ruthenium complex CpRu(CO)2SiMe2SiMe2OMe (1b). The X-ray crystal structure analysis of 3a revealed that 3a has an almost planar Ru−Si−O−Si four-membered chelate ring with short Ru−Si bonds (2.316(3) and 2.311(3) Å) and long Si···O bonds (1.801(7) and 1.793(7) Å). 3a reacts with MeOH instantaneously to give Cp(OC)Ru(H)(SiMe2OMe)2 (4) quantitatively. Photolysis of CpM(CO)2SiMe2SiMe2OMe (1b, M = Ru; 1c, M = Fe) or Cp(OC)M{SiMe2···O(Me)···SiMe2} (3a, M = Ru; 3b, M = Fe) with the photochemical silylene precursor (SiMe2)6 by means of a low-pressure Hg lamp afforded a mixture of 3a or 3b, disilanyl−silylene complexes Cp(OC)M{SiMe2←O(Me)SiMe2SiMe2} (5a, M = Ru; 5b, M = Fe), and (SiMe2)5. Two possible mechanisms for the addition of dimethylsilylene to 3 to give 5 were proposed.

Highly selective photochemical synthesis of perfluoroalkyl bromides and iodides

Highly fluorinated alkyl iodides are conveniently synthesized by telomerization of a fluoroalkyl-iodide, RI, with, e.g., C 2F 4. Normally, the reaction, often carried out in the liquid phase with a radical initiator, gives products with a broad distribution of molecular weights. In this work, we report a method that obtains selectively products of a desired molecular weight: this method is a photochemically induced reaction in the gas phase; the gas is circulated through a trap or a rectification still which continuously removes the heavier products, whereas the more volatile molecules return to the photoreactor. An analysis by rate equations shows which control parameters are important, and by a suitable choice of these parameters, we obtained a better selectivity for, e.g., C 8F 17I than previously. This method also works with BrC 2F 4Br instead of an iodide. In this case, we demonstrated in a small laboratory setup with simple low-pressure Hg lamps (5 × 30 W), a productivity of more than 0.5 kg/day. In the telomerization of CF 3Br or HC 2F 4Br with C 2F 4 we found, however, a few percent of dibromide side products which are sometimes difficult to separate because of similar boiling points. For this case, it is better to synthesize the iodides instead, and then exchange the I for Br, if desired.

UV Radiation-Induced Degradation of Poly(n-Propylmethylsilane-Co-Isopropylmethylsilane) in Solution

The photodegradation of poly(n-propylmethylsilane-co-isopropylmethylsilane) (NPIPSC) in solution was investigated. The results obtained indicate that a low-pressure Hg lamp photoinduces degradation. Therefore, this light source can be used as an acceptable radiation source for the photobleaching of NPIPSC. Gel permeation chromatography/light scattering (GPC/LS) measurements indicate that two photodegradation stages exist in this process. The first occurs at less than 6 s of exposure, where scission is very rapid. The second occurs between 6 and 12 s of exposure. The latter does not result in a significant loss of molecular weight. A change of slope in the plot of molecular weight as a function of elution volume is observed in the degradation process. This result indicates the presence of at least two species with different conformations. The ratio of scissions to cross-linking related to photodegradation was calculated and revealed that the scission process predominates over cross-linking. The presence of isopropylmethylsilane (IPMS) units in the copolymer appears to induce a decrease in the NPIPSC degradation efficiency. The linear plot of degradation degree as a function of exposure time suggests that there are no weak links in the copolymer. This result can be correlated with the chemical composition of the copolymer, which was nearly the same between 0 and 10 s of UV exposure. After 12 s of exposure, the IPMS was removed from the NPIPSC.

Red-band holographic storage in azo dye sensitized by noncoherent light

Biphoton holographic storage recorded with 633-nm He-Ne beams has been investigated in Methyl Yellowdoped polystyrene film sensitized by weak noncoherent light from a low-pressure Hg lamp. It is demonstrated that the holography in the sample is erasable without fading. The dynamic behavior of the hologram is dependent on the cis-trans isomerization by noncoherent light and 633-nm beams and photoinduced heat.

ULSI dielectrics: low-temperature silicon dioxides

The use of ultraviolet (UV) and vacuum ultraviolet light generated from low-pressure Hg lamps and also a new type of excimer lamp to stimulate the growth and/or deposition of ultrathin dielectric films is described. Growth enhancement of more than 50 times is found for UV oxidation of Si at 550 °C, providing growth rates of around 0.5 Å min −1. Even higher enhancement factors (but relatively lower growth rates) are obtained at lower temperatures. Compared with other commonly used lamps, the novel excimer sources are pseudo-continuous and produce high photon fluxes (more than a few watts) over large areas. Oxide, nitride and oxynitride layers have been deposited using such sources. The film growth rates and initial physical properties were determined using ellipsometry and Fourier transform infrared spectroscopy. A layered combination of silicon oxide, silicon nitride and silicon oxynitride has also been produced in the same reactor at temperatures below 300 °C using this deposition method.

Perfluoroalkylation of Benzene by 185 nm Photolysis of Perfluoroazooctane

Abstract Perfluoroazooctane was photolyzed in benzene upon low pressure Hg lamp irradiation to generate perfluorooctyl radicals, which reacted with an excess of benzene to afford perfluorooctylbenzene. The investigation on the wavelength and light intensity dependence revealed that this photolysis proceeded effectively upon 185 nm irradiation by two photon absorption.

Photo-CVD of Al 2O 3 thin films using a D 2 lamp

Al 2O 3 thin films have been deposited by reduced-pressure photo-CVD for the first time using a D 2 lamp as excitation source and aluminum-tri-isopropoxide as source material. The measured absorption band of the source material vapor overlaps the emission lines of the D 2 lamp in the vacuum ultraviolet region. At deposition temperatures below 270°C, the deposition rate was enhanced and the film qualities such as tan δ and the refractive index were improved. Above 270°C, in contrast, the effect of the D 2 lamp irradiation is not so clear. These results are discussed compared with the previous photo-CVD results obtained using low-pressure Hg lamps as light source.

Gas phase reactions diagnosed by mass analysis in photo-assisted chemical vapor deposition of silicon nitride

Silicon nitride (SiN x ) films have been deposited at lower substrate temperature (≦ 500°C) by direct photo-chemical vapor deposition (photo-CVD) with a low-pressure Hg lamp without Hg sensitization using SiH 4 and NH 3. Results from transient mass analysis suggest that NH 3 is photo-decomposed into H and NH 2, SiH 4 is decomposed in reactions with H or NH 2, which were confirmed by a reaction simulation. Following the decomposition reactions, intermediate species at 47 and 77 amu were formed, and they contributed to the film deposition. The decomposition of SiH 4 is controlled by the decomposition of NH 3, less decomposable in a plasma process, in photo-CVD.