Xe2 Excimer Lamp Research Articles

Surface loss probability of atomic oxygen on silica under atmospheric-pressure CO2

Abstract The surface loss probability γ O of atomic oxygen was measured for SiO2 in atmospheric-pressure CO2 and Ar/CO2(3.05%) mixture at 300 K. O atoms were produced via the photolysis of CO2 using a 172 nm Xe2 excimer lamp. After irradiation by Xe2 lamp, the working gas flowed through a quartz tube, causing O atoms to be lost on its inner surface. By measuring the density of O atoms at the end of the tube for different tube lengths, we obtained the value of γ O on the inner surface of the tube. The measured value was 5.5 × 10 − 4 ± 50 % , which falls within the range of referred values of γ O ( 1 × 10 − 5 to 1 × 10 − 3 ) at 4 to 1300 Pa measured using low-pressure O2 plasmas. Despite the 2 to 5 orders of magnitude pressure difference, no significant difference in γ O was obtained. The potential influence of the difference in background gas (CO2 and O2) on the value of γ O was also considered.

The comparison of the efficacy of 185/254 nm and 172 nm photolysis for the removal of sulfonamides and trimethoprim from aqueous solutions

The VUV (λ < 200 nm) photolysis can be used to eliminate organic substances without the addition of oxidant due to the efficient generation of OH from water. Two VUV light sources are commercially available: the low-pressure mercury vapor (LPM) and the Xe-excimer lamp, which emit 185/254 nm and 172 nm photons, respectively. This study compares the efficiency of the UV/VUV185nm and VUV172nm photolysis in removing four sulfonamides (SAs) and trimethoprim (TRIM) antibiotics. For the LPM lamp, 254 nm UV radiation ((4.21 ± 0.08) × 10−6 molphoton s−1) can contribute to the transformation of target substances besides the OH generated by the 185 nm VUV light. The VUV photon flux (1.02 × 10−5 molphoton s−1) of the Xe-excimer lamp significantly exceeded that of the LPM lamp (3.97 × 10−7 molphoton s−1); as H2O2 formation in pure water reflected, however, the efficiency of the transformation rate of the target substances was just slightly faster. For the LPM lamp, in addition to the direct UV photolysis of SAs, the 254 nm light enhances the OH formation via H2O2 photolysis, thereby partially compensating for the low VUV185nm photon flux. The high VUV172nm photon flux was primarily manifested in mineralization efficiency and not in the transformation rate of target compounds. The short penetration depth of 172 nm light favors the recombination of primary radicals and decreases the efficiency. The effect of the matrix and matrix components is complex; they act as a radical scavenger or (V)UV filter. The change of radical set and the role of the formed secondary radicals (Cl, Cl2−, and CO3−) in transformation must be considered.

Photoemission-induced atmospheric-pressure DC gas discharge using back-illuminated nano thickness photocathode

Photoemission-induced atmospheric-pressure DC gas discharge was successfully generated using a 9 nm gold thin-film deposited on quartz glass as a photocathode which was back-illuminated with UV light at wavelengths of 172 nm (Xe excimer lamp), 254 nm (Hg lamp), and 265 nm (Deep UV-LED). A stable discharge current of more than 30 μA at 1450 V in Ar and 50 μA at 4000 V in air was achieved by using 172 nm while it was limited by the power densities and quantum efficiencies of other UV sources. The optical emission spectroscopy showed emissions from excited species in both Ar and air plasma.

Degradation of N-nitrosamines and 1,4-dioxane using vacuum ultraviolet irradiation (UV254+185 nm or UV172 nm)

Advanced oxidation processes (AOPs) play a vital role in attenuating contaminants of emerging concern (CECs) during potable water reuse. AOPs are conventionally performed by irradiating with a 254-nm low-pressure (LP) mercury-vapor (Hg) ultraviolet (UV) lamp along with chemical treatment. Compared with UV-C light treatment (200–280 nm), vacuum-UV (V-UV) light treatment (100–200 nm) is advantageous in terms of hydroxyl radical generation without the requirement for chemical treatment. This study assessed the potential of V-UV (172-nm Xe2 excimer or 185 + 254-nm LP-Hg) lamps on the destruction of two major CECs in potable water reuse, namely N-nitrosodimethylamine (NDMA) and 1,4-dioxane. Direct irradiation using UV254 nm or UV185+254 nm lamps achieved ≥94% removal of N-nitrosamines, including NDMA, at a UV dose of 900 mJ/cm2. In contrast, the Xe2 excimer lamp (UV172 nm) was less effective for N-nitrosamine removal, achieving up to 82% removal of NDMA. The removal of 1,4-dioxane by V-UV lamps at a UV dose of 900 mJ/cm2 reached 51% (UV172 nm) and 28% (UV185+254 nm), both of which results were superior to that obtained using a conventional UV254 nm lamp (10%). The addition of hydrogen peroxide during UV254 nm or UV185+254 nm irradiation was found to enhance the removal of 1,4-dioxane, while UV172 nm irradiation without hydrogen peroxide addition still exhibited greater efficiencies than those UV254 nm lamps-based AOPs. Overall, this study demonstrated that the removal of both NDMA and 1,4-dioxane can be successfully achieved using either a UV254+185 nm lamp with hydrogen peroxide or a UV172 nm Xe2 excimer lamp without hydrogen peroxide.

Photochemical degradation of acrolein using VUV excimer lamp in air at atmospheric pressure

The photochemical degradation of acrolein (C2H3CHO) was investigated in air at atmospheric pressure using a 172-nm Xe2 excimer lamp. When C2H3CHO was decomposed using the side-on type of lamp, HCOOH, CO, CO2, and O3 peaks were observed in FTIR absorption spectra. The dependence of product concentrations on the irradiation time indicated that HCOOH and CO intermediates are finally converted to CO2 via consecutive reactions. The degradation rate coefficient of C2H3CHO in the batch system increased from 8.4 to 19.3 min−1, as the O2 concentration was decreased from 20 to 1%. It increased also from 8.4 to 40.1 min−1 at 20% O2, as the chamber depth was decreased from 3.0 to 0.5 cm. The best energy efficiency of the C2H3CHO degradation was 3.4 g kW−1 h−1 at 1–20% O2 in a flow system. Besides direct VUV photodissociation of C2H3CHO, reactions of O(3P,1D) and O3, produced from photolysis of O2, can contribute to C2H3CHO degradation in the initial stage. Among them, the contribution of O(1D) and O3 was found to be insignificant on the basis of the total pressure dependence of removal amount of C2H3CHO and results obtained from the O3 + C2H3CHO reaction. It was concluded that at first C2H3CHO is decomposed by direct VUV photodissociation of C2H3CHO and the O(3P) + C2H3CHO reaction. It was further decomposed by secondary reactions of O(3P), OH, and O3 with such intermediates as HCOOH and CO and finally oxidized to CO2.

Photochemical removal of NO2 in air at atmospheric pressure using side-on type 172-nm Xe2 excimer lamp

The photochemical removal of NO2 in air (1–20% O2) was studied using a side-on type 172-nm Xe2 excimer lamp. The removal rate of NO2 using the side-on lamp (SL), 37.5 min−1, was faster than that using a head-on lamp (HL), 5.4 min−1, with the same input power of 20 W by a factor of 6.9. The energy efficiency for removal of NO2 using the SL was 3.2 g/kWh, which was 12 times higher than that using the HL. Significant enhancement of the removal rate and the energy efficiency using the SL was attributed to a significant increase in the irradiation volume because of a wider irradiation window. Under the SL irradiation, HNO3 was a major final product that differed from N2O5 obtained under the HL irradiation. To obtain the information related to the conversion mechanism of NO2 to HNO3 under 172-nm photolysis in air, computer simulation of the reaction processes was conducted. Results show that the OH + NO2 reaction is a major pathway for the formation of HNO3 in the SL, where OH radicals are formed by 172-nm photolysis of H2O.

Efficient removal of benzene in air at atmospheric pressure using a side-on type 172nm Xe2 excimer lamp.

The photochemical removal of benzene was studied in air at atmospheric pressure using a side-on type 172nm Xe2 excimer lamp with a wide irradiation area. After 1.5min photoirradiation, C6H6 (1000ppm) in air was completely converted to HCOOH, CO, and CO2 at a total flow rate of 1000mL/min. The initial decomposition rate of C6H6 was determined to be 1.18min-1. By using a flow system, C6H6 (200ppm) was completely removed at a total flow rate of 250mL/min. The conversion of C6H6 and the energy efficiency in the removal of C6H6 changed in the 31-100% and 0.48-1.2g/kWh range, respectively, depending on the flow rate, the O2 concentration, and the chamber volume. On the basis of kinetic model simulation, dominant reaction pathways were discussed. Results show that the O(3P) + C6H6 reaction plays a significant role in the initial stage of the C6H6 decomposition. Important experimental parameters required for further improvement of the C6H6 removal apparatus using a 172 excimer lamp were discussed based on model calculations.

An UV-C/B emitting Xe excimer discharge lamp comprising BaZrSi3O9 – A lamp performance and phosphor degradation analysis

This work concerns a highly efficient UV-C emitting phosphor, viz. BaZrSi3O9, which photoluminescence is suitable for a number of photochemical processes, e.g. for air, surface, or water disinfection as well as oxidative purification processes of water. The latter imply direct photolysis as well as photooxidation involving auxiliary components like H2O2. The material was investigated with respect to its application as a conversion layer in Xe excimer discharge lamps (λEm = 172 nm). To this end, substitution of Zr4+ by Hf4+ was performed aiming at an optimization of the preparative process and the resulting VUV conversion efficiency.As-prepared powder samples were consecutively employed in state-of-the-art dielectric barrier Xe excimer discharge lamps and their performance was compared to YPO4:Bi3+ as a UV-C emitting commercially available reference material (Phillips GmbH). Even the non-optimized BaZr0.8Hf0.2Si3O9 succeeded the standard in terms of long term stability of its luminous flux. Detailed analysis of the material was secured by crystallographic as well as extensive optical and spectroscopic measurements. The latter was supplemented by EPR studies in order to further examine the underlying aging mechanism which governs the phosphor decay during Xe excimer lamp operation.

Performance Enhancement of a Dielectric Barrier Discharge Vacuum-Ultraviolet Photon Source Using Short-Pulsed Electrical Excitation

We have studied the electrical and optical characteristics of an air-cooled argon excimer vacuum-ultraviolet lamp ( $\lambda \sim 126$ nm) excited by a dielectric barrier discharge powered by: 1) pulsed or 2) sinusoidal high-voltage drivers from 32 to 100 kHz. Compared to sinusoidal excitation, pulsed excitation gives nearly $\sim 2\times $ higher vacuum-ultraviolet (VUV) output and electrical-to-VUV conversion efficiency at high pressure (800–900 mbar). Visually, the pulse-driven plasma is spatially homogeneous, whereas for sinusoidal excitation the plasma becomes filamentary at higher pressure and/or frequency. Spectral emission is highly monochromatic with most of the output in the desired VUV band ( $\lambda = 115$ –140 nm). With the lamp running at pressure >700 mbar and power loadings >1.6 W/cm3, a sharp spike in VUV output was consistently seen at turn-on. We believe that transient phenomena or favorable initial conditions may be partly responsible for this VUV spike, although the equilibrium VUV output appears to be limited due to thermal dissipation, gas heating, and associated loss of gas from the active region. We propose that we may be observing the same intrinsic VUV spiking phenomena as reported in liquid nitrogen-cooled Xe, Kr, and Ar excimer lamps by Gerasimov et al. More importantly, we believe ours is the first such observation reported for an excimer VUV lamp operating near room temperature. This VUV spiking behavior raises the prospect that designs with improved thermal management may achieve even higher VUV power and efficiency.

Inactivation of Bacillus atrophaeus by OH radicals

The inactivation of Bacillus atrophaeus by OH radicals is measured. This study aims to evaluate the bactericidal effects of OH radicals produced by atmospheric-pressure nonthermal plasma widely used for plasma medicine; however, in this study, OH radicals are produced by vacuum ultraviolet (VUV) photolysis of water vapor instead of plasma to allow the production of OH radicals with almost no other reactive species. A 172 nm VUV light from a Xe2 excimer lamp irradiates a He–H2O mixture flowing in a quartz tube to photodissociate H2O to produce OH, H, O, HO2, H2O2, and O3. The produced reactive oxygen species (ROS) flow out of the quartz tube nozzle to the bacteria on an agar plate and cause inactivation. The inactivation by OH radicals among the six ROS is observed by properly setting the experimental conditions with the help of simulations calculating the ROS densities. A 30 s treatment with approximately 0.1 ppm OH radicals causes visible inactivation.

Photochemically induced deposition of protective alumina coatings onto UV emitting phosphors for Xe excimer discharge lamps

This work concerns the particle coating of the UV-C emitting phosphor YPO4:Bi, targeting a stability enhancement of the phosphor material for Xe excimer lamp operation. To this end, the material is coated by the wide band gap material Al2O3. In order to obtain a thin and homogeneous coating layer, a novel process based on the photochemical cleavage of NaN3 in water was developed. This results in a slow and continuous enhancement of the pH value due to ongoing NaOH formation, which results in the precipitation of Al(OH)3 from an Al2(SO4)3×18H2O solution. It turned out that the obtained particle coatings are of much better quality, i.e. homogeneity, compared to coatings made from a wet-chemical homogeneous precipitation process. The morphology and electrochemical properties of Al2O3 coated YPO4:Bi are discussed on the basis of optical spectroscopy, ESA measurements, and SEM/EDX investigations.

Trench Filling Properties of Low k Insulated Layer Using Vacuum Ultraviolet Light-CVD

Photo-induced deposition of SiOCH thin films and their trench filling properties are discussed. Octamethyl-cycloterasiloxan (OMCTS) was used as a precursor and Xe2 excimer lamp was used as a light source. The deposition temperature was 80°C and the reactor pressure was maintained at 38.5 Pa. The relative permittivity of as-deposited film was 7.9. Due to the UV cure process, those OH-related bonds in the film were significantly decreased. The k-value of the UV cure film was 2.1. Photo-induced SiOCH was employed to achieve bottom-up filling of high-aspect-ratio features (A/S > 7.5).

Thermal decomposition of tungsten hexacarbonyl: CVD of W‐containing films under Pd codeposition and VUV assistance

AbstractExperiments on chemical vapor deposition of W(CO)6‐derived films on silicon substrates were carried out at total pressure of 5‐10 Torr within the temperature range of 250‐350 °C; in Ar or H2 flow. Metallic, carbide and oxide phases composed the obtained films. Deposition in presence of hydrogen results in the increase of the metal content in the film. Sublimed palladium hexafluoracetylacetonate Pd(hfa)2 was used for Pd catalytic promotion of the deposition process. Codeposition with Pd(hfa)2 in hydrogen increases W‐metal fraction and oxygen content while the Pd content is up to 10 at.%. Influence of vacuum ultraviolet (VUV) radiation from Xe excimer lamp (λ ∼172 nm) on the quality of the obtained films was investigated. It was found that VUV irradiation can reduce the oxygen‐content in the film while W‐metal fraction slightly increases. In all films, oxygen was in the form of WO3 and carbon was mainly incorporated as a graphite metastable phase. The influence of other chemical additives is discussed. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Production of reactive species using vacuum ultraviolet photodissociation as a tool for studying their effects in plasma medicine: simulations and measurements

We propose a method for producing OH, H, O, O3, and O2(a1Δg) using the vacuum ultraviolet photodissociation of H2O and O2 as a tool for studying the reaction processes of plasma medicine. For photodissociation, an H2O/He or O2/He mixture flowing in a quartz tube is irradiated by a Xe2 or Kr2 excimer lamp. The effluent can be applied to a target. Simulations show that the Xe2 lamp method can produce OH radicals within 0.1–1 ppm in the effluent at 5 mm from a quartz tube nozzle. This is comparable to those produced by a helium atmospheric-pressure plasma jet (He-APPJ) currently used in plasma medicine. The Xe2 lamp method also produces H atoms of, at most, 6 ppm. In contrast, the maximum O densities produced by the Xe2 and Kr2 lamp methods are 0.15 ppm and 2.5 ppm, respectively; these are much lower than those from He-APPJ (several tens of ppm). Both lamp methods can produce ozone at concentrations above 1000 ppm and O2(a1Δg) at tens of ppm. The validity of the simulations is verified by measuring the O3 and OH densities produced by the Xe2 lamp method using ultraviolet absorption and laser-induced fluorescence. The differences between the measured and simulated densities for O3 and OH are 20% and factors of 3–4, respectively.

High-quality gate oxide formed at 150 °C for flexible electronics

This study describes the low temperature process to form the gate oxide of MOSFETs using a SiO nano-powder and post UV oxidation. The high-quality SiO2 gate oxide was successfully formed on a silicon substrate by vacuum evaporation of the SiO nano-powder followed by the post UV oxidation in steam at 200 °C. However, further lowering of the oxidation temperature to 150 °C degraded the insulating property and increased the interface trap density. In order to improve the SiO2/Si interface quality, the Si surface was irradiated by vacuum UV (VUV) using a Xe excimer lamp before evaporation of the SiO nano-powder. This substrate treatment has substantially improved the SiO2/Si interface quality. The physical mechanisms of the VUV and UV oxidation are discussed in order to understand the low-temperature formation of the SiO2.

Low-temperature synthesis of diamond films by photoemission-assisted plasma-enhanced chemical vapor deposition

Photoemission-assisted plasma-enhanced chemical vapor deposition (PA-PECVD), a process in which photoelectrons emitted from a substrate irradiated with ultraviolet light are utilized as a trigger for DC discharge, was investigated in this study; specifically, the DC discharge characteristics of PA-PECVD were examined for an Si substrate deposited in advance through hot-filament chemical vapor deposition with a nitrogen-doped diamond layer of thickness ∼1 μm. Using a commercially available Xe excimer lamp (hν = 7.2 eV) to illuminate the diamond surface with and without hydrogen termination, the photocurrents were found to be 3.17 × 1012 and 2.11 × 1011 electrons/cm2/s, respectively. The 15-fold increase in photocurrent was ascribed to negative electron affinity (NEA) caused by hydrogen termination on the diamond surfaces. The DC discharge characteristics revealed that a transition bias voltage from a Townsend-to-glow discharge was considerably decreased because of NEA (from 490 to 373 V for H2 gas and from 330 to 200 V for Ar gas), enabling a reduction in electric power consumption needed to synthesize diamond films through PA-PECVD. In fact, the authors have succeeded in growing high-quality diamond films of area 2.0 cm2 at 540 °C with a discharge power of only 1.8 W, plasma voltage of 156.4 V, and discharge current of 11.7 mA under the glow discharge of CH4/H2/Ar mixed gases. In addition to having only negligible amounts of graphite and amorphous carbon, the diamond films exhibit a relatively high diamond growth rate of 0.5 μm/h at temperatures as low as 540 °C, which is attributed to Ar+ ions impinging on the diamond surface, and causing the removal of hydrogen atoms from the surface through sputtering. This process leads to enhanced CHx radical adsorption, because the sample was applied with a negative potential to accelerate photoelectrons in PA-PECVD.

シクロオレフィンポリマーの酸素増感VUV表面改質によるパラジウム吸着表面層の形成

A photochemical process was applied to form an active surface layer on cyclo-olefine polymer (COP) for improved immobilization of palladium. A Xe excimer lamp irradiating vacuum ultraviolet (VUV) light of 172 nm wavelength was used as a light source for surface modification. COP samples placed in dry air with atmospheric pressure were irradiated with VUV light. Because of the dissociative excitation of oxygen molecules, atomic oxygen species were generated along with ozone molecules formed through the following chemical reactions of the oxygen atoms. These active oxygen species served as oxidants for COP surface modification. Based on VUV photochemistry assisted with oxygen, known as the oxygen-amplified VUV process, an oxidized COP layer with thickness of several tens of nanometers was formed on each COP sample. The layer, which contained highly concentrated hydrophilic functional groups such as -OH, -CHO, and -COOH, functioned as an adsorbing site for palladium catalysts. Consequently, this technique has been found to be effective as a pre-treatment of Ni-P electroless plating. Electroless Ni films with sufficient adhesion to pass the cross-cut tape test were deposited on the VUV-modified COP substrates. Direct patterning without photolithography has been demonstrated for fabricated Ni micropatterns.

Degradation of 2,4-dihydroxibenzoic acid by vacuum UV process in aqueous solution: Kinetic, identification of intermediates and reaction pathway

2,4-Dihydroxybenzoic acid (2,4-DHBA) is found frequently as a pollutant in natural waters and represents a threat to water quality because it is a precursor to the formation of quinones which are highly toxic. The degradation of 2,4-DHBA using the vacuum UV photolysis of water has been investigated. Irradiation was carried out in an annular photoreactor equipped with a Xe-excimer lamp situated in the centre and emitting at 172nm. The degradation kinetic followed a pseudo first order and the reaction has been found to be very heterogeneous, especially at low concentration. Impacts of oxygen or temperature have also been investigated but no effect has been shown. LC–MS and HPLC-UV combined with other analytical techniques allowed the identification of the formation of trihydroxybenzoïc acids and trihydroxybenzenes which underwent a ring opening, conducting to the formation of aliphatic products named α, β, δ and γ. These products were in turn degraded successively into maleïc acid, malic and succinic acid, malonic acid, glyoxalic acid and oxalic acid before reaching the complete mineralization in about 180min. The proposed reaction pathway has shown to be very different from the one observed for the TiO2 photocatalysis which involves only holes (h+) without any formation of aromatic intermediates. The different behaviours of 2,4-DHBA towards the h+ and HO make it a good probe to identify involved entities.

Photo-oxidized Coating on the Optical Materials for High Power Laser Resistance and Waterproof

ABSTRACTA photo-oxidized thin film, which transformed the organic silicone oil into inorganic glass, was coated on optical materials surface by using Xe2 excimer lamp at room temperature. This technique has enabled an optical thin coating capable of transmitting ultraviolet rays [UV] of wavelengths under 200 nm and possessing the characteristics of hardness, strain-free, resistance to high power laser, and resistance to water. UV and IR spectroscopic analysis was carried out for investigation of the oxidized silicone oil. The results revealed that the absorption peak of the CH3 group at 2900 cm-1 decreased as the irradiation time of the excimer lamp increased, and the transmittance of the light in the 172 nm wavelengths conversely became high. The UV transmittance of the silicone oil was 29.2 % before the lamp irradiation; and it improved to 90.6 % after the irradiation for 120 minutes. Moreover, in order to evaluate for resistance to laser damage [J/cm2/10 ns], the films were further irradiated with the Nd: YAG laser of ω [1.06 μm] or 2ω [0.503 μm]. The silica glass substrate had almost same laser tolerance in ω and 2ω, 112 J/cm2 and 113 J/cm2, respectively. The laser damage threshold of the photo-oxidized 100 nm thick film formed on the fused silica substrate was 72 J/cm2 in ω and 107 J/cm2 in 2ω.

Photochemical Removal of Benzene Using 172 nm Xe2 Excimer Lamp in N2/O2 Mixtures at Atmospheric Pressure

Abstract The photochemical removal of benzene was investigated in N2/O2 mixtures (0–20% O2) using a 172 nm Xe2 excimer lamp at atmospheric pressure. After 20 min photoirradiation, about 97% of C6H6 (1000 ppm) in N2/O2 mixtures (10–20% O2) was converted to HCOOH, CO, and CO2. In the 172 nm photolysis of C6H6, not only direct photolysis by VUV photons but also reactions of O(3P,1D) and O3 can take part in the decomposition of C6H6. To examine effects of direct photolysis, C6H6 was decomposed in N2, whereas the contribution of O3 was studied by observing the O3 + C6H6 reaction. The contribution of O(1D) was examined by reducing the total pressure to suppress the collisional quenching of O(1D) by N2/O2 mixtures. It was found that the O(3P) + C6H6 reaction plays a significant role in the initial stage of the removal reaction of C6H6.