Vacuum Ultraviolet Radiation Research Articles

Barrier Discharge Excilamps with a Small-Diameter Exit Window and Their Application

The principle of operation and technical parameters of excilamps with a small-diameter output window from a series of portable narrow-band ultraviolet and vacuum ultraviolet radiation sources are described. An example of using a KrCl excilamp to excite photoluminescence of crystalline materials is given.

Thermo-Optical Property Degradation of ITO-Coated Aluminized Polyimide Thin Films Under VUV and Low-Energy Proton Radiation

We studied thermo-optical property degradation of indium tin oxide (ITO)-coated aluminized polyimide thin films under exposure to vacuum ultraviolet radiation and low-energy (3 and 5 keV) protons during ground tests using the Complex Irradiation Facility at the DLR site in Bremen. Changes in solar absorption and thermal emission coefficients caused by the irradiation were analyzed. We report a significant increase in solar absorptance of the samples irradiated by protons. We also attempted to identify any defects on the surface of the samples. The study was motivated by a unique opportunity that is provided by the Complex Irradiation Facility to study the degradation effects induced by exposure to protons with an energy below 10 keV and short-wavelength light below 115 nm.

Effect of Vacuum-Ultraviolet Light Irradiation on Thermal Fusion Bonding Strength of Carbon Fiber-Reinforced Polyimide Composite with Thermoplastic Polyimide Film

Effect of Vacuum-Ultraviolet Light Irradiation on Thermal Fusion Bonding Strength of Carbon Fiber-Reinforced Polyimide Composite with Thermoplastic Polyimide Film

Nuclear Excitation of the ^{229}Th Isomer via Defect States in Doped Crystals.

When Th nuclei are doped in CaF_{2} crystals, a set of electronic defect states appear in the crystal band gap which would otherwise provide complete transparency to vacuum-ultraviolet radiation. The coupling of these defect states to the 8eV ^{229m}Th nuclear isomer in the CaF_{2} crystal is investigated theoretically. We show that although previously viewed as a nuisance, the defect states provide a starting point for nuclear excitation via electronic bridge mechanisms involving stimulated emission or absorption using an optical laser. The rates of these processes are at least 2 orders of magnitude larger than direct photoexcitation of the isomeric state using available light sources. The nuclear isomer population can also undergo quenching when triggered by the reverse mechanism, leading to a fast and controlled decay via the electronic shell. These findings are relevant for a possible solid-state nuclear clock based on the ^{229m}Th isomeric transition.

Photon-stimulated Desorption Processes of Polymethylmethacrylate by Vacuum Ultraviolet Irradiations

Photon-stimulated Desorption Processes of Polymethylmethacrylate by Vacuum Ultraviolet Irradiations

Efficient removal of halogenated phenols by vacuum-UV system through combined photolysis and OH oxidation: Efficiency, mechanism and economic analysis

In this study, efficient simultaneous degradation and dechlorination of the photo-recalcitrant emerging disinfection byproduct, 2-chlorophenol (2-CP), was achieved by vacuum-ultraviolet (VUV) system for the first time. Different from the conventional UV system, the combined action of direct photolysis and OH oxidation in VUV system led to a significantly higher removal efficiency for 2-CP. In UV system, 2-CP degradation rate constants was independent of the initial 2-CP concentration, and was increased with enhancing pH. To the contrary, in VUV system, higher initial concentration of 2-CP resulted in lower rate constant, and the degradation rates of 2-CP under both acidic and alkaline conditions were higher than that at the neutral pH. Moreover, humic acid could inhibit 2-CP degradation more prominently in VUV system than in UV system, owing to the scavenging effect of OH by it. The degradation pathways of 2-CP were proposed based on the identified main degradation products by GC–MS/MS. Furthermore, degradation of the other seven typical halogenated phenols by VUV irradiation in tap water, ultrafiltrated water and Mill-Q water were investigated to verify the feasibility of the system. Based on the systematic economic analysis, VUV process is economically feasible for the advanced treatment of tap water to remove halogenated phenols.

Development of a high-precision XYZ translator and estimation of beam profile of the vacuum ultraviolet and soft X-ray undulator beamline BL-13B at the Photon Factory.

A high-precision XYZ translator was developed for the microanalysis of electronic structures and chemical compositions on material surfaces by electron spectroscopy techniques, such as photoelectron spectroscopy and absorption spectroscopy, utilizing the vacuum ultraviolet and soft X-ray synchrotron radiation at an undulator beamline BL-13B at the Photon Factory. Using the high-precision translator, the profile and size of the undulator beam were estimated. They were found to strongly depend on the photon energy but were less affected by the polarization direction. To demonstrate the microscopic measurement capability of an experimental apparatus incorporating a high-precision XYZ translator, the homogeneities of an SnO film and a naturally grown anatase TiO2 single crystal were investigated using X-ray absorption and photoemission spectroscopies. The upgraded system can be used for elemental analyses and electronic structure studies at a spatial resolution in the order of the beam size.

Synchrotron-based VUV excitation-induced ultrahigh quality cool white light luminescence from Sm-doped ZnO.

We report that the rare-earth (RE) ion, Sm-doped ZnO, acts as white light emitting vacuum ultraviolet (VUV) phosphors and possesses an ultrahigh color rendering index (CRI) and color quality scale (CQS). The VUV-excited emission spectra measured from the synchrotron source reveal the emergence of multi-color emission bands in the visible-IR region and substantially depend on the concentration of Sm3+ ions. A mechanism is proposed to elucidate the origin behind the high-energy bandgap excitation of the host charge carrier and subsequent energy transfer to the Sm3+ states leading to additional green-yellow-orange emission bands of Sm3+(4G5/2→6HJ(J=5/2,7/2,and9/2)). High-quality cool white light (correlated color temperature 5600 K) having CIE coordinates (0.33, 0.35) with a CRI as high as 95.89 and a CQS value of 94.49 is achieved for Zn0.985Sm0.015O under synchrotron VUV radiations. This Letter demonstrates that RE activated ZnO-based phosphors are expected to be a promising candidate in solid state lighting, as well as plasma display devices.

Room temperature direct patterning of nanocrystalline zinc oxide on flexible polymer substrates through vacuum ultraviolet light irradiation

This paper describes a 172-nm vacuum ultraviolet (VUV) light treatment in ambient air towards the formation of nanocrystalline zinc oxide (ZnO) micropatterns. Thin layers of zinc acetate (Zn(OAc)2) as a precursor are spun on substrates, and subsequently treated by the VUV irradiation. The VUV treatments lead to an organic-free ZnO films with wurtzite crystalline structures, determined by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The nanocrystalline ZnO patterns with a fine feature of 1 μm are fabricated on cycloolefin polymer (COP) substrates via the precise VUV lithography. This one-step ZnO crystallizing and patterning process is suited for polymer substrates because the potentially damaging procedures involving acidic etchants and thermal treatments are no longer needed. The present method proves to be a simple, effective, controllable patterning approach, which might be recommended for the future fabrication of flexible devices.

Decay Kinetics of CeF3 under VUV and X-ray Synchrotron Radiation

Characteristic dimensions and evolution times of regions of secondary electronic excitations created by the interaction of ionizing radiation with matter cannot be measured directly. At the same time these are essential parameters both for engineering of nanostructured composite materials defining optimal layer thickness and nanoparticles radii and for the development of optimized scintillators. The paper demonstrates how such spatial and temporal data can be extracted from luminescence decay kinetics excited by vacuum ultraviolet (VUV) and X-ray photons at modern sources of synchrotron radiation MAX IV and PETRA III. Specific features of energy-band structure of self-activated crystal CeF3 are discussed, and its potential for a super-fast detection of ionizing radiation evaluated. Diffusion-controlled dipole–dipole interaction of Frenkel excitons is demonstrated to account well for the luminescence non-exponential decay kinetics providing information on the scales of excited regions created by photons of different energy. For 20 eV photons the radius of excited regions is estimated to be 10 nm, and for 200 eV photons it increases to 18 nm. Effective radius of excited regions of complicated shape created by 19 keV is as large as 80 nm and the diffusion length of Frenkel excitons over radiative time is 14 nm.

Mechanistic insights into toluene degradation under VUV irradiation coupled with photocatalytic oxidation

Volatile organic compounds (VOCs) exists ubiquitously in chemical industries and were regarded as major contributors to air pollution, which should be strictly regulated. Vacuum ultraviolet irradiation coupled with photocatalytic oxidation (VUV-PCO) has been considered as an efficient approach to VOCs removal due to high-energy photons which could break down VOCs directly and be absorbed by photocatalysts to generate free radicals for further oxidation. However, the photochemical transformation mechanisms of VOCs have not been fully revealed. Herein, we systematically analyzed the intermediates using proton-transfer-reaction mass spectrometer (PTR-MS) to explore the transformation mechanisms of toluene degradation in VUV and VUV-PCO processes. VUV-PCO process displayed superior toluene degradation efficiency (50 %) and mineralization efficiency (65 %) compared with single VUV photolysis (35 %) and UV photocatalysis (5 %). TiO2 was deeply involved into CO2 generalization by amplifying the advantages of VUV system and further mineralizing the intermediates. In VUV and VUV-PCO processes, O2 participation changed the intermediates distribution by increasing multiple oxygenated products, while the introduction of water contributed to the formation and degradation of most intermediates. A possible degradation mechanism of toluene under VUV irradiation combined with TiO2 was proposed. This study provides a deep mechanistic insight into VOCs degradation by VUV-PCO process.

VUV radiation flux from argon DC magnetron plasma

Vacuum ultraviolet (VUV) flux of argon plasma radiation in a DC magnetron discharge with a plane circular titanium cathode is measured. It is found that the intensity of VUV radiation, mainly indicated by the resonance lines of argon atoms at 104.8 and 106.7 nm and ions at 92 and 93.2 nm, is proportional to the discharge current and decreases with pressure. Following the results of the measurements, a numerical model of resonance radiation transport is developed to determine the VUV flux to the substrate placed near the sputtering cathode where direct measurements are impossible due to the fast contamination of the detector by sputtered atoms. In the case of a substrate located 10 cm opposite the cathode surface, the upper limit of estimated VUV flux is of the order of 1015 photons cm−2 s−1 at a coating deposition rate of 1.5 nm s−1 for 2 and 12 mTorr gas pressures. Based on the measurements, the damage to a porous low-k dielectric by VUV radiation during the deposition of barrier layers in the DC magnetron discharge is first estimated.

Proton transfer processes in interstellar molecular clusters under synchrotron VUV radiation: Taking acrylonitrile and acetonitrile dimers as example

Acrylonitrile (ALN) and acetonitrile (ATN) are two important interstellar molecules that contain nitrogen atoms. Herein, we explore the proton transfer processes occurring in gaseous clusters of ALN and ATN molecules with the aid of synchrotron vacuum ultraviolet radiation. We investigated the proton transfer phenomenon by use of time-of-flight mass spectrometry as well as theoretical calculations. We observe that the mass spectra of ALN and ATN clusters are apparently different from each other. In the mass spectrum of ALN clusters, the peaks related to un-protonated cluster cations are dominant. Unlike the ALN clusters, the protonated cluster cations are dominant in the mass spectrum of ATN clusters. These results are attributed to the different conjugate and hyperconjugate molecular structures in ALN and ATN, respectively. Theoretical calculations show that the conjugation effect between the πC=C orbital and πC≡N orbital in ALN induces a high proton transfer barrier that determines the dominant peaks of its non-protonated clusters cations. Conversely, the hyperconjugation between the σCα-H and πC≡N orbital in the ATN molecule determines that the proton transfer process in ATN is a low-barrier or even a no-barrier process. This favors the formation of protonated clusters. The present results reveal that ALN clusters are more aprotic than those consisting of ATN, and a relative high energy barrier is needed to surmount the proton transfer process of ALN clusters. This property of ALN makes it an appropriate candidate molecule to form the membrane alternative in the liquid methane lakes of Titan. ATN is not an appropriate candidate.

Vacuum-UV Radiation at 185 nm for Disinfecting Water

Vacuum-UV Radiation at 185 nm for Disinfecting Water

Quantum efficiency of black silicon photodiodes at VUV wavelengths.

Black silicon (b-Si) is an emerging material made by modifying silicon with nanostructures for improved photon detection. It has been demonstrated that when used in photodetectors b-Si significantly improves photon detection and extends spectral sensitivity from NIR to the visible wavelengths. However, no data have been reported in the Vacuum Ultraviolet (VUV) range, which is increasingly becoming important for many applications. Here, we have measured the spectral response of n-type b-Si light-trapping photodiodes under VUV radiation at ambient and cryogenic temperatures. The device exhibited a near-unity quantum efficiency above the 1.1 eV intrinsic bandgap of silicon. Quantum efficiency increased linearly with photon energy above the electron-hole pair creation energy of silicon ∼3.6 eV and the device had a responsivity of 0.2 A/W at 175 nm at room temperature in vacuum. These results demonstrate new technology in UV detection and could pave way for the development of a high quantum efficiency black silicon photomultiplier device (b-SiPM) needed for direct VUV photon detection in noble gas and liquid scintillating detectors.

Vacuum ultraviolet irradiation for mitigating dissolved organic nitrogen and formation of haloacetonitriles

The main objective of this work was to investigate the feasibility of using vacuum ultraviolet (VUV, 185 + 254 nm) and ultraviolet (UV, 254 nm) for the reduction of dissolved organic nitrogen (DON) and haloacetonitrile formation potential (HANFP) of surface water and treated effluent wastewater samples. The results showed that the reduction of dissolved organic carbon (DOC), DON, hydrophobicity (HPO), absorbance at 254 nm (UV254), and fluorescence excitation-emission matrix (FEEM) of both water samples by VUV was higher compared to using UV. The addition of H2O2 remarkably improved the performances of VUV and UV. VUV/H2O2 exhibited the highest removal efficiency for DOC and DON. Even though HANFP increased at the early stage, its concentration decreased (19–72%) at the end of treatment (60 min). Decreases in DON (30–41%) and DOC (51–57%) led to HANFP reduction (53–72%). Moreover, FEEM revealed that substantial reduction in soluble microbial product-like compounds (nitrogen-rich organic) had a strong correlation with HANFP reduction, implying that this group of compounds act as a main precursor of HANs. The VUV/H2O2 system significantly reduced HANFP more than UV/H2O2 and therefore is suitable for controlling HAN precursors and HAN formation in drinking water and reclaimed wastewater.

Synchrotron Photoionization Study of the Diisopropyl Ether Oxidation.

Scientific evidence has shown oxygenates help to reduce dangerous pollutants arising from burning fossil fuel in the automotive sector. For this reason, their use as additives has spread widely. The aim of this work consists in providing a comprehensive identification of the main primary oxidation products of diisopropyl ether (DIPE), one of the most promising among etheric oxygenates. The Cl-initiated oxidation of DIPE is examinated by using a vacuum ultraviolet (VUV) synchrotron radiation at the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory (LBNL). Products are identified on the basis of their mass-to-charge ratio, shape of photoionization spectra, adiabatic ionization energies, and chemical kinetic profiles, at three different temperatures (298, 550, and 650 K). Acetone, propanal, propene, and isopropyl acetate have been identified as major reaction products. Acetone is the main primary product. Theoretical calculations using the composite CBS-QB3 method provided useful tools to validate the postulated reaction mechanisms leading to experimentally observed species. The formation of other species is also discussed.

Molecular Aggregation Structure and Surface Properties of Biomimetic Catechol-Bearing Poly[2-(perfluorooctyl)ethyl acrylate] and Its Application to Superamphiphobic Coatings.

The molecular aggregation structure and surface properties of a catechol-bearing fluoropolymer, P(FAC8-co-DOPAm), which was synthesized by conventional radical copolymerization of 2-(perfluorooctyl)ethyl acrylate (FAC8) and N-(3,4-dihydroxyphenethyl)acrylamide (DOPAm), and its application to the superamphiphobic surfaces are presented. The crystallinity of P(FAC8-co-DOPAm) was lower than that of poly[2-(perfluorooctyl)ethyl acrylate] (PFAC8). The perfluoroalkyl (Rf) groups were ordered on the surface with CF3 terminals exposed to air, and the Rf ordering was influenced by thermal history: the thermally annealed film exhibited higher Rf ordering than the unannealed one. The surface free energy was estimated to be γ = 7.32 mJ m–2 for both the unannealed and annealed films. Based on contact angle measurement, various interfacial structures of water and oils in accordance with the surface aggregation structure of Rf groups were proposed. Dewetting of the PFAC8 film at elevated temperature was suppressed by the introduction of catechol groups in the backbone. The degradation temperature of PFAC8 was improved significantly, and the evaporation of the low molar mass-polymer was inhibited by the introduction of catechol groups under both nitrogen and air atmospheres. The hydrophobicity of the copolymer films could be healed after the surface was damaged by vacuum ultraviolet (VUV) irradiation. This copolymer was used to create superamphiphobic fabrics and halloysite nanotube (HNT)-based organic/inorganic hybrid coatings successfully. Wetting behaviors of the superamphiphobic fabrics and coatings both follow the Cassie–Baxter wetting model.

Room temperature bonding of cycloolefin polymer by vacuum ultraviolet surface photoactivation

We have applied vacuum ultraviolet (VUV) irradiation to room temperature bonding (RTB) of cyclo-olefin polymer (COP). The COP surface was oxidized into oxygen functional groups through the VUV irradiation in air. The extent of oxygenation was evaluated by water contact angle (WCA), X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The obtained results showed that the concentration of oxygen functional groups increased with VUV-irradiation time. The VUV-irradiation conditions for RTB were optimized based on our finding that prolonged irradiation resulted in a decrease in bonding strength. Observation of the fractured surfaces indicated that cohesive failure occurred after the appropriate irradiation time, but deterioration of the surface layer occurred with longer irradiation times.

Degradation of sodium dodecyl benzenesulfonate by vacuum ultraviolet irradiation

Sodium dodecyl benzenesulfonate (SDBS) is a common anionic surfactant used in detergents, and a major household pollutant. SDBS released with bathing and laundry wastewater causes eutrophication of water bodies and toxicity in aquatic organisms. We compared the degradation of SDBS in aqueous solution, by vacuum ultraviolet (VUV, 254 nm and 185 nm) and ultraviolet irradiation (UV, 254 nm). Using lab-scale reactors, VUV degraded SDBS more efficiently than UV, also achieving a higher mineralization rate. HO was the main reactive oxygen species produced by VUV. SDBS concentration affected the distribution of absorbed VUV and UV photons, and influenced the reaction triggered. VUV was more efficient at lower concentrations, when indirect oxidation by HO was prevalent. The UV process, relied mostly on direct photolysis, and was affected slightly by initial concentration. VUV was more efficient at solution pH of 5 and 9, while UV performed better at alkaline conditions. Temperature increased the degradation rates for both processes. The addition of SO42− slightly promoted SDBS degradation in the VUV process, while Cl− and HCO3− inhibited it. For UV, SO42− and Cl− illustrated no significant difference on the degradation, while HCO3− had a positive impact on the system. We identified the four photoproducts of SDBS degradation by VUV, and proposed a degradation pathway. Finally, the fact the VUV could be efficiently used to remove anionic surfactant from real wastewater, proved that it can be applied efficiently with low energetic consumption.