VUV Excimer Research Articles

Simulation study of excimer VUV emission from xenon microhollow cathode discharge in the self-pulsing regime

A volume-averaged model is employed to study the dynamics of a microhollow cathode discharge in xenon operating in the self-pulsing regime. The numerical results revealed that the discharge voltage initially increases during the abnormal mode when the discharge current is quite low. Then, the discharge is transferred to a normal mode in which the current shows a steep growth to extremely high values. The results also indicated that the self-pulsing frequency increases with an increase in the input voltage at constant pressure. However, an increase in pressure at a constant input voltage leads to a reduced self-pulsing frequency. The strongest vacuum ultraviolet emission is attributed to xenon triplet excimers at a wavelength of 173 nm. An increase in the input voltage enhances the average densities of the xenon excimers, but has almost no effect on the maximum densities. Compared to the input voltage, an increase of the pressure has a much stronger effect on both the maximum and average densities, such that the maximum density of the triplet excimer is increased from 1.48×1017 m−3 at P = 30 Torr to 2×1021 m−3 at P = 250 Torr. A comparison between the self-pulsing and stationary regimes shows that the maximum densities of the excimers at the self-pulsing regime are an order of magnitude higher than those of the stationary regime. Furthermore, the average densities of the excimers in the self-pulsing regime are higher than those of the stationary regime at higher input voltages. However, the reverse is true for lower voltages.

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.

Effect of VUV Excimer Lamps on Microorganisms

Effect of VUV Excimer Lamps on Microorganisms

Surface analysis of VUV irradiated mulberry silk through carbonyl group estimation

Surface irradiation of mulberry silk fabric is carried out using a VUV excimer lamp. Change in surface chemistry is studied through carbonyl group estimation and surface morphological changes are analyzed in high resolution scanning electron microscope. Significant development in carbonyl groups is observed upon irradiation. Mechanism of carbonyl groups formation has been proposed. Further, VUV light penetration effect, with an irradiation power of 50 mW/cm2, in the irradiation atmosphere is studied through degree of modification at different points of the irradiated sample for various timings from 1 min to 30 min. Up to an irradiation time of 10 min, the rate of change is noticeable at all the points particularly just below the lamp boundary points i.e. between −20 mm to +20 mm (lamp ϕ: 40 mm, center of the lamp is considered to be 0). The fabric points lied outside the lamp boundaries (−40 mm to −20 mm and 20 mm to 40 mm) has undergone less intense surface modifications. This has been evidenced through carbonyl group analysis, wetting time measurements, and SEM results.

Topographical changes in polyester after chemical, physical and enzymatic hydrolysis

Polyester was treated with alkali, VUV excimer, and a hydrolytic enzyme. The effect of each treatment on the physicochemical properties of polyester (PET) was studied and compared by qualitative and quantitative methods. Scanning electron microscopy and atomic force microscopy analysis show that alkali treatment causes severe fiber degradation with formation of pits on the fabric surface. In contrast, excimer treatment results in uniform pitting at nanometer level, which is restricted to the surface. In case of enzyme-treated samples, non-uniform roughness was observed due to deposition of residual protein formed due to enzyme hydrolysis. K/S value and moisture regain value of excimer-treated samples were found to be higher than alkali- or enzyme-treated PET. Out of the three methods, excimer treatment appears to be the best method for PET modification with maximum number of polar groups being created on hydrolysis with marginal loss in strength and weight.

Synergistic Water-Treatment Reactors Using a TiO2-Modified Ti-Mesh Filter

The recent applications of a TiO2-modified Ti-mesh filter (TMiP™) for water purification are summarized with newly collected data including biological assays as well as sewage water treatment. The water purification reactors consist of the combination of a TMiP, a UV lamp, an excimer VUV lamp, and an ozonation unit. The water purification abilities of the reactor were evaluated by decomposition of organic contaminants, inactivation of waterborne pathogens, and treatment efficiency for sewage water. The UV-C/TMiP/O3 reactor disinfected E. coli in aqueous suspension in approximately 1 min completely, and also decreased the number of E. coli in sewage water in 15 min dramatically. The observed rate constants of 7.5 L/min and 1.3 L/min were calculated by pseudo-first-order kinetic analysis respectively. Although organic substances in sewage water were supposed to prevent the UV-C/TMiP/O3 reactor from purifying water, the reactor reduced E. coli in sewage water continuously. On the other hand, although much higher efficiencies for decomposition of organic pollutants in water were achieved in the excimer/TMiP reactor, the disinfection activity of the reactor for waterborne pathogens was not as effective as the other reactors. The difference of efficiency between organic pollutants and waterborne pathogens in the excimer/TMiP reactor may be due to the size, the structure, and the decomposition mechanism of the organic pollutants and waterborne pathogens. These results show that a suitable system assisted by synergy of photocatalysts and other technologies such as ozonation has a huge potential as a practical wastewater purification system.

Competitive and synergistic effects between excimer VUV radiation and O radicals on the etching mechanisms of polyethylene and fluoropolymer surfaces treated by an atmospheric He–O2 post-discharge

Among various surface modification techniques, plasma can be used as a source for tailoring the surface properties of diverse materials. HDPE and fluoropolymer surfaces have been treated by the post-discharge of an atmospheric RF-plasma torch supplied with helium and oxygen gases. The plasma-treated surfaces were characterized by measurements of mass losses, water contact angles, x-ray photoelectron spectroscopy and atomic force microscopy. This experimental approach correlated with an optical characterization of the plasma phase allowed us to propose etching mechanisms occurring at the post-discharge/polymer interface. We discuss how competitive and synergistic effects can result from the oxidation and/or the roughening of the surface but also from the excimer VUV radiation, the He metastable species and the O radicals reaching the plasma-polymer interface.

Development of a hybrid environmental purification unit by using of excimer VUV lamps with TiO2 coated titanium mesh filter

A versatile photocatalyst-excimer-lamp hybrid unit for both air- and water-purification at practical scale was investigated. The unit consisted of a xenon filled quartz tube (20mm i.d.×300mm length) and TiO2 nanoparticles-modified Ti-mesh sheet (TMiP™). Emission at 172nm from a xenon excimer (Xe2∗) was able to produce reactive species by direct photolysis of water or air. At the same time, the emission was able to excite TiO2 on TMiP surface. Therefore, the unit decomposes organic contaminants by synergy of photocatalysis and photolysis. Air- and water-purification efficiency of the unit was examined by high concentration of acetaldehyde and phenol decomposition test, respectively. The disinfection activity of the units for waterborne pathogens was also investigated. For comparison, the purification units using excimer-lamp alone or UV lamps with TMiP and/or ozone treatment were evaluated in the same methods. The photocatalyst-excimer-lamp hybrid unit was able to decompose acetaldehyde and phenol effectively, compared with the other units. On the other hand, disinfection activity of the unit for waterborne pathogens was strongly affected by the kind of the waterborne pathogens. The difference of efficiency between organic pollutants and waterborne pathogens by the unit may be due to the molecular or bacterial size and the surface composition of bacteria and viruses, critical wavelength for disinfection, and the permeation ability of the outer wall of bacterial cells or virus particles for reactive species. Taken together, the photocatalyst-excimer-lamp hybrid unit has wide potentials for environmental purification by the synergy of photocatalysis and photolysis. These results would be attractive to develop a practical environmental purification system such as sewage water treatment.

Ultraviolet excimer radiation from nonequilibrium gas discharges and its application in photophysics, photochemistry and photobiology

Narrowband UV and VUV excimer radiation can be generated in a variety of nonequilibrium gas discharges: dielectric barrier discharges, microhollow cathode discharges, arrays of microplasmas, corona discharges. Excimer lamps (excilamps) are now available for a large number of wavelengths and in various geometrical shapes. The availability of nearly monochromatic photon fluxes ranging in energy up to 15 eV resulted in a number of innovative photo-induced processes in photophysics, photochemistry and photobiology. This report focuses on progress made in the last decade.

Modification of Polydimethylsiloxane Coatings by H2 RF Plasma, Xe2* Excimer VUV Radiation, and Low‐Energy Electron Beams

AbstractThe crosslinking of thin liquid PDMS layers by three different technically relevant processes, H2 radio‐frequency plasma treatment, Xe2* excimer VUV irradiation, and low‐energy electron beam processing is investigated. The modifications to the layers due to the processing are monitored by means of RAIRS. Plasma processing of liquid PDMS leads to a direct conversion to a SiOx‐like material of the topmost layers, whereas a gradual transition from PDMS to the same product is observed upon VUV irradiation. Electron exposure does not induce oxidation. The initiating steps of the conversion induced by the interaction with VUV photons, low‐energy electrons, or their combined effect with ions and H atoms in the plasma are discussed. The latter creates a high density of damage sites. magnified image

Discharge diagnosis of high Xe concentration and high‐γ protective layer in PDPs

Abstract— The high‐Xe‐concentration and high‐γ (ion‐induced secondary‐electron emission coefficient) protective layer have been diagnosed from both experimentation and simulation. The experimental results show that there is a great increase in luminance and luminous efficacy, while the breakdown voltage decreases in the high‐Xe and high‐γ discharge. In the high‐Xe discharge, the great increase in VUV radiation mainly results from an increase in excimer VUV emission. The application of high‐Xe concentration can greatly increase the luminous efficacy, while the high‐γ protective layer can promote it further. Considering that the total discharge efficiency can be divided into the electron heating efficiency, the Xe excitation efficiency, and the VUV radiation efficiency, both the electron heating efficiency and Xe excitation efficiency increased for a high‐Xe discharge; while for a high‐γ discharge, the increase in electron heating efficiency contributes to the improvement in discharge efficiency.

Prospects for the nuclear pumping of a VUV laser

The possibility of using nuclear emissions (in particular, uranium-fission fragments) to create a powerful source of stimulated VUV radiation is analyzed. The starting point in the analysis is provided by the results of recent investigations of a krypton–xenon mixture in an extended dc discharge, which indicate that continuous lasing is possible in the VUV region. Experience in transforming the kinetic energy of nuclear particles into the laser radiation of inert gases (in the visible and near-IR regions) makes it possible to homogeneously pump extended volumes of inert gases at atmospheric pressures and to transfer 20–30% of the embedded energy into spontaneous VUV excimer radiation. According to our estimates, the power of the quasi-continuous laser VUV radiation can reach 1–2kW∕L in this case.

Surface Treatment with VUV Excimer Lamp

Surface Treatment with VUV Excimer Lamp

High frequency excitation waveform for efficient operation of a xenon excimer dielectric barrier discharge lamp

The application of a high frequency (∼2.5 MHz) burst (amplitude-modulated sinusoidal) excitation voltage waveform is investigated for driving a fluorescent dielectric barrier discharge (DBD) light source. The excitation waveform presents a novel method for generating spatially stable homogeneous Xe DBD possessing a high conversion efficiency from electrical energy to VUV excimer radiation (∼172 nm), even at a significantly higher electrical energy deposition than realized by pulsed excitation. Simulation and experimental results predict discharge efficiencies around 60%. Lamp efficacy above 74 lm W−1 has been achieved. VUV emission and loss mechanisms are investigated extensively and the performance of burst and pulsed waveforms is compared both theoretically and experimentally.

Eliminating carbon contamination on oxidized Si surfaces using a VUV excimer lamp

In the VUV spectrum we see a significant decrease in reflection due to organic contamination on the surface of mirrors. To study VUV mirrors it is requisite to have calibration standards. Such standards are useless as calibration tools if the surface has organic contamination. For our standard, we use a thermally oxidized silicon wafer with a 27 nm oxide overlayer. We found that silicon wafer samples capped with native oxide acquire 0.1 to 0.2 nm of organic contamination within two hours of being cleaned with stored in closed, but nonvacuum, conditions. After a week there is an additional 0.2 to 0.5 nm deposition after which no further significant deposition is measured up to 90 days. We place the samples in air within one cm of a xenon excimer lamp that radiates 7.2 eV photons which remove half of the remaining contamination every minute. Five minutes exposure is sufficient to clean both fresh and stored samples. Data are determined using spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS). Additionally this paper addresses the need to ensure that these characterization tools are not a source of organic contamination. We determined that the antechamber of our XPS was contaminating samples at a rate of 0.6 nm/30 min as they waited for transfer to the analysis chamber. This contamination was virtually eliminated by attaching an oxygen radical source (ORS) device (Evactron® C De-Contaminator RF Plasma Cleaning System) directly to the antechamber.

Thermogravimetry Coupled to Single Photon Ionization Quadrupole Mass Spectrometry: A Tool To Investigate the Chemical Signature of Thermal Decomposition of Polymeric Materials

Mass spectrometry (MS) is an established analytical technique to analyze evolved gas in thermogravimetry (TG). In this study, for the first time a novel SPI-MS technique using an electron beam pumped VUV excimer lamp as photon source (lambda = 126 nm) was employed in conjunction with thermogravimetry. The coupling was achieved with an improved heated interface and adjacent transfer capillary between TG and ion source of a quadrupole mass spectrometer. The feasibility of this approach was proven by investigating semivolatile substances such as long-chain alkanes (heptadecane C17H36), polymers, e.g., polystyrene, polycarbonate, and acrylonitrile-butadiene-styrene, polymer mixtures and blends. Mass spectra with almost no fragmentation were obtained, and quantification of selected substances could be achieved. Polymer mixtures could be distinguished by their SPI mass spectra, and the effect of premixing of polymers has been accessed. Its unique attributes render the TA-SPI-MS method a promising new tool for quantitative and qualitative evaluation of complex organic thermal degradation products.

Radiation resistance of optical materials for windows of UV and VUV excimer lasers

The behaviour of modern quartz glasses and fluo-rite is studied experimentally under a prolonged action of the 280-keV electron beam pulses and an overall fluence of up to ∼30 kJ cm-2. The induced absorption in all investigated mate-rials saturates with increasing the fluence. The maximum variation of transmission in high-purity CaF2 samples does not exceed 5%–10% in the wavelength range 120–1000 nm. Quasi-stationary absorption in the region of ∼180–300 nm in the KS-4V quartz glass sample is approximately four times smaller than that in the KU-1 quartz glass and half the value for Corning 7980 glasses.

Modification of one side of mulberry silk fabric by monochromatic VUV excimer lamp

One side of mulberry silk fabric surface was irradiated with monochromatic VUV excimer lamp (172 nm). Change in surface morphology due to one side (I) and two side (II) irradiation was analyzed using high resolution scanning electron microscope (SEM) and atomic force microscope (AFM). The irradiated samples were further characterized through measurement of wetting time, vertical and horizontal wicking. Surface nanopores of 100 nm × 10 nm were formed on the irradiated side, however, on back side change in morphology was not observed. Upon one side irradiation the wettability and wickability improved significantly. One side irradiated silk surface (I) showed average wetting time of 14.7 s and 7.2 s while the two side irradiated silk surface (II) showed a wetting time of 9.3 s and 3.1 s for irradiation period of 1 min and 5 min, respectively. Beyond 5 min of irradiation the wettability of both the surfaces stabilized. Mechanism responsible for wetting behaviour of one side irradiated sample has been proposed. The influence of lamp geometry on irradiation effect was found to be noticeable for irradiation timings <5 min.

Preparation of a multifunctional mulberry silk fabric having hydrophobic and hydrophilic surfaces using VUV excimer lamp

A multifunctional silk fabric has been prepared with one face having hydrophobic and another having hydrophilic properties. Fluorocarbon based finish was used to impart hydrophobicity, followed by irradiation on one side of the fabric with 172 nm UV excimer lamp for imparting hydrophilicity. Treated samples were characterised by contact angle measurements, horizontal wicking, air permeability, bending length, and crease recovery angle. Qualitative and quantitative analysis of the treated surface was carried out by atomic force microscope (AFM). The contact angle decreased with irradiation time on the irradiated surface, without affecting the hydrophobic effect on the other side of the fabric. The wickability of the samples was improved significantly at higher irradiation time of 5 min and 10 min. Upon hydrophobic finish application, the fabric properties such as air permeability, bending length were least affected while the crease recovery was improved noticeably.

Nanoscale surface roughening of mulberry silk by monochromatic VUV excimer lamp

AbstractSurface treatment of mulberry silk was carried out using a VUV excimer lamp (172 nm). The changes occurring in morphology and physical properties of silk were studied. The nanopores created on the surface of treated samples were quantitatively analyzed using a high resolution scanning electron microscope. The physical and chemical changes taking place in silk fabric on irradiation were studied through measurement of wetting and wicking time, weight loss, crystallinity, and strength. Effect of irradiation time and distance from the lamp on these properties was also studied. Results show that wettability and wickability of silk improved significantly on exposure before stabilizing at 5 min irradiation time while the weight loss continued to increase. The effect of irradiation was negligible when the distance of the sample from the lamp became &gt;15 mm. The effect of irradiation on tensile strength was found to be insignificant. Presence of moisture in silk hindered the effect of irradiation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 4102–4106, 2007