Vacuum Ultraviolet Research Articles

Vacuum Ultraviolet (VUV) Light Photofunctionalization to Induce Human Oral Fibroblast Transmigration on Zirconia.

Soft tissue adhesion and sealing around dental and maxillofacial implants, related prosthetic components, and crowns are a clinical imperative to prevent adverse outcomes of periodontitis and periimplantitis. Zirconia is often used to fabricate implant components and crowns. Here, we hypothesized that UV treatment of zirconia would induce unique behaviors in fibroblasts that favor the establishment of a soft tissue seal. Human oral fibroblasts were cultured on zirconia specimens to confluency before placing a second zirconia specimen (either untreated or treated with one minute of 172 nm vacuum UV (VUV) light) next to the first specimen separated by a gap of 150 µm. After seven days of culture, fibroblasts only transmigrated onto VUV-treated zirconia, forming a 2.36 mm volume zone and 5.30 mm leading edge. Cells migrating on VUV-treated zirconia were enlarged, with robust formation of multidirectional cytoplastic projections, even on day seven. Fibroblasts were also cultured on horizontally placed and 45° and 60° tilted zirconia specimens, with the latter configurations compromising initial attachment and proliferation. However, VUV treatment of zirconia mitigated the negative impact of tilting, with higher tilt angles increasing the difference in cellular behavior between control and VUV-treated specimens. Fibroblast size, perimeter, and diameter on day seven were greater than on day one exclusively on VUV-treated zirconia. VUV treatment reduced surface elemental carbon and induced superhydrophilicity, confirming the removal of the hydrocarbon pellicle. Similar effects of VUV treatment were observed on glazed zirconia specimens with silica surfaces. One-minute VUV photofunctionalization of zirconia and silica therefore promotes human oral fibroblast attachment and proliferation, especially under challenging culture conditions, and induces specimen-to-specimen transmigration and sustainable photofunctionalization for at least seven days.

Vacuum ultraviolet-induced surface modification of polyoxymethylene plates for photo-activation bonding

The surface photoactivation technique using vacuum ultra-violet (VUV) light at 172 nm in wavelength has been applied for adhesive-free bonding of polyoxymethylene (POM) plates. The POM surfaces were photochemically modified via VUV light irradiation in dry air conditions, resulting in the formation of oxygen-containing functionalities. The POM plates were successfully bonded with a practical bonding strength below the melting point. The maximum bonding strength was obtained at an irradiation time of 60 min, while a longer irradiation time resulted in lower bonding strength. Surface morphologies of the photoactivated and fractured POM surfaces were observed by a laser scanning microscope. Due to the VUV irradiation, numerous cracks were formed on the POM surfaces. The fractured surface shows that a cohesive failure occurs at the bonding interface. Atomic force microscopy was used to observe the cross-sectional images of the bonding samples. Around 10 μm width, significant phase contrast between the bonding interface and bulk POM indicates the different mechanical properties, due to VUV irradiation. The modified POM surfaces adhered through thermocompression, and the mechanical interlocking and entanglement of POM molecules can result in successful bonding.

Surface modification of polymers by vacuum ultraviolet Illumination containing low wavelength below 160 nm and microfluidic applications of irradiated polycarbonate

Microfluidic devices are applied in various fields including medicine and drug discovery. Recently, plastics are used for the device due to low cost. One of the challenges is the bonding process. A bonding method that preserves the microstructure is required. Recently, room temperature bonding methods using vacuum ultraviolet (VUV) light have been reported, but the applicable materials are limited. Here, we propose a new method using VUV with a wavelength shorter than 160 nm. As a result of the surface analysis, it was confirmed that the substrate surface becomes hydrophilic upon VUV irradiation. As a result of the bonding test, it was confirmed that it was possible to bond polycarbonate (PC) to each other (maximum bonding force: 2.03 MPa), PC to glass (maximum bonding force: 10.72 MPa), and cyclic olefin polymer to glass (maximum bonding force: 3.51 MPa), which have not been reported so far. The results suggest that one of these bonding mechanisms is the addition of hydrophilicity by VUV irradiation. Based on the results, for the first time, a PC-made microfluidic device was successfully developed using the bonding method. This result greatly contributes to the development of the manufacturing process of plastic microfluidic devices.

Radiation Effect of Vacuum Ultraviolet on the Performance of Polyimide Films

Polyimide (PI) films equipped on the surface of spacecraft are susceptible to ultraviolet damage. Herein, the performance of two kinds of polyimide films i.e. 3,3′,4,4′-biphenyl dianhydride-p-phenylenediamine (BPDA-PDA) and pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA) under vacuum ultraviolet (VUV, 172 nm) irradiation was studied. The failure behavior of the PI films was studied by tensile tests, thermogravimetry (TGA), thermomechanical analysis (TMA), electric breakdown, UV–visible transmittance and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the molecular structure. The results indicated that the tensile strength of BPDA-PDA PI and PMDA-ODA PI films decreased by 10.4 and 7.4% under VUV irradiation, respectively; the breakdown strength and UV-transmittance also deteriorated. Besides, the surface morphology of the PI films showed a large number of microcracks after VUV irradiation, which we ascribe to the breakage of imide rings (C-N-C) and ether bonds (C-O-C) of the PI films. However, the thermal stability (residual weight) of both PI films remained constant compared to the initial level; this can be explained by the combined effect of bond breaking and cross-linking of the polyimide films.

Unraveling the Conformational Preference of Morpholine: Insights from Infrared Resonant Vacuum Ultraviolet Photoionization Mass Spectroscopy.

The preference for different conformations in morpholine has a notable effect on its behavior and reactivity in organic synthesis. Herein, we explored the intricate conformational properties of morpholines through a combination of advanced mass spectrometric techniques and theoretical calculations. Notably, we employed infrared (IR) resonant vacuum ultraviolet (VUV) mass-analyzed threshold ionization spectroscopy to measure the unique vibrational spectra of the distinct conformers (Chair-Eq and Chair-Ax) in morpholine for the first time. Through precise VUV photon energy adjustments to coincide with the vibrational excitation via IR absorption, we effectively pinpointed the adiabatic ionization thresholds corresponding to the Chair-Eq (65 442 ± 4 cm-1) and Chair-Ax (65 333 ± 4 cm-1) conformers. This allowed us to accurately determine the conformational stability between the two conformers (109 ± 4 cm-1). By shedding light on the conformational properties of morpholine, this study brings far-reaching implications to the fields of organic synthesis and pharmaceutical research.

Atmospheric Hydroxyl Radical Reaction Rate Coefficient and Total Environmental Lifetime of α-Endosulfan.

Endosulfan is a persistent organochlorine pesticide that was globally distributed before it was banned and continues to cycle in the Earth system. The chemical kinetics of the gas-phase reaction of α-endosulfan with the hydroxyl radical (OH) was studied by means of pulsed vacuum UV flash photolysis and time-resolved resonance fluorescence (FP-RF) as a function of temperature in the range of 348-395 K and led to a second-order rate coefficient kOH = 5.8 × 10-11 exp(-1960K/T) cm3 s-1 with an uncertainty range of 7 × 10-12 exp(-1210K/T) to 4 × 10-10 exp(-2710K/T) cm3 s-1. This corresponds to an estimated photochemical atmospheric half-life in the range of 3-12 months, which is much longer than previously assumed (days to weeks). Comparing the atmospheric concentrations observed after the global ban of endosulfan with environmental multimedia model predictions, we find that photochemical degradation in the atmosphere is slower than the model-estimated biodegradation in soil or water and that the latter limits the total environmental lifetime of endosulfan. We conclude that the lifetimes typically assumed for soil and aquatic systems are likely underestimated and should be revisited, in particular, for temperate and warm climates.

Conformational effects in the vibrational and electronic spectra of propionaldehyde: Experimental and theoretical studies.

We report here investigations on conformational effects in the vibrational and electronic spectra of the propionaldehyde (propanal) molecule using FTIR (600-3200cm-1) and vacuum ultraviolet (VUV) synchrotron radiation photoabsorption (52 500-85 000cm-1) spectroscopy respectively. Detailed theoretical calculations (using DFT and TDDFT methodologies) on ground and excited states of the cis and gauche conformers of propanal are performed; a comprehensive spectral analysis of the IR and VUV spectra is presented. A reinvestigation of the IR spectrum reveals several new bands assigned to the gauche conformer based on theoretical calculations. The VUV spectrum exhibits rich Rydberg series structure assigned to ns, np and nd series converging to the first ionization potentials of the two conformers. Earlier assignments of the 3s cis and gauche origins are revised in addition to extending Rydberg series analysis to several higher members. Vibronic bands accompanying the 3s, 4s and 4p Rydberg states are assigned using estimated vibrational frequencies of cis and gauche conformers in the cationic ground state. Simulated potential energy curves of the first few excited states (singlets and triplets) of cis and gauche conformers of propanal help in gaining insights into photodissociation mechanisms and possible conformational effects therein.

Wind turbine contaminant classification using machine learning techniques

It has been well established in the literature that surface contamination can adversely affect the aerodynamic performance of aerofoils and hence the efficiency with which turbines can convert wind to electrical power. Hence it is critical to ensure that turbine blades are kept as free as possible of contaminants. In this manuscript, we discuss LIBS and machine learning techniques on contaminated wind turbine blades with a view to the possibility of integrating these methods into a standoff laser ablation setup in the future. A LIBS signal will be a key step in the decision process, i.e., to determine if a wind turbine blade has been fouled in the first place. Relatedly one must also determine the point at which the laser has adequately removed contaminants from the current Area of Irradiation (AoI) before moving to the adjacent AoI, i.e., interim end-point-detection. For both steps (presence / absence of fouling) we are investigating laser-induced breakdown spectroscopy (LIBS) to discriminate clean from fouled wind turbine blade samples. In particular we have performed LIBS in both the Vacuum Ultraviolet (VUV) and Ultraviolet Visible (UV–Vis) spectral ranges. Analysis of the spectra showed only slight variations in the constituent materials between clean and contaminated blade samples. In order to address this challenge, the efficacy of a number of machine learning and statistical methods for clean versus contaminated blade classification was investigated. Four methods (Partial Least Squares Discriminant Analysis (PLS-DA), Support Vector Machines (SVM), Competitive Learning (CL), and Convolutional Neural Networks (CNN)) were evaluated. The spectral regions where machine learning algorithms were applied was determined via a volumetric ellipsoid overlap test based on Principal Component Analysis (PCA). It was found that SVMs provided the most accurate methodology for binary classification of clean vs contaminated blades whilst also yielding the shortest run time.

UV-Induced Synthesis of Hybrid HMDSO/SiO2 Thin Films with Compositional Gradients for High-Performance Atomic Oxygen Resistance.

A flexible, dense, defect-free, highly adhesive, and highly dissociation energy-rich protective coating is essential to enhance the atomic oxygen (AO) resistance of polymeric materials in a low Earth orbit (LEO). In this work, a dense, defect-free hybrid HMDSO/SiO2 thin film coating with compositional gradients on the surface of polyimide was synthesized using vacuum-ultraviolet (VUV) irradiation. The effects of VUV irradiation on the morphology, optical transmittance, and chemical components of plasma-polymerized HMDSO (pp-HMDSO) thin-film coatings deposited on the polyimide surface were investigated in depth. There were no defects such as cracks and holes in the surface morphology of pp-HMDSO films after VUV irradiation, but the surface roughness increased slightly, and the corresponding optical transmittance decreased slightly. The chemical components of pp-HMDSO films were changed in the depth direction starting from the top of the surface, forming hybrid HMDSO/SiO2 thin films with compositional gradients. The component gradient HMDSO/SiO2 composite coating further enhanced the atomic oxygen resistance of the polyimide due to the surface layer of the UV-modified coating enriched with high dissociation energy SiOx material. Therefore, this work provides a facile UV-induced synthesis method to prepare dense, defect-free, and highly dissociation energy-rich protective gradient coatings, which are promising not only for excellent AO protection in LEO but also for potential application in water-oxygen barrier films.

Microcystin-LR Removal by Ozone (O3) and Vacuum-UV (VUV): The Effect of Chloride Ions

ABSTRACT Removal of microcystin-LR (MC-LR) by ozone (O3), vacuum-UV (VUV), and their combination was investigated in the presence of chloride as one of the main solutes present in water. In general, the combined VUV/O3 process provided the greatest MC-LR removal, with the presence of chloride enhancing the removal efficacy. Formation of chlorine radical species was the primary reason for the observed improvement. The order of MC-LR removal by different processes using UV fluence of around 300 mJ cm−2, ozone dose of 0.1 mg L−1, and chloride concentration of 120 mg L−1 was as follows: VUV/O3/Chloride > VUV/O3 > VUV/Chloride > VUV > O3. Comparing MC-LR removal by O3, VUV and VUV/O3 in synthetic lab samples, spiked with Suwannee River NOM and natural water samples of the same organic concentration, showed the significance of background organics in scavenging ozone in the process. For a given ozone dosage, MC-LR removal by O3 or VUV/O3 in natural water was lower than that in the synthetic water samples. The standalone VUV was not affected and the MC-LR removals were identical in both synthetic and natural waters.

Immobilization protects enzymes from plasma-mediated inactivation.

Non-thermal plasmas are used in various applications to inactivate biological agents or biomolecules. A complex cocktail of reactive species, (vacuum) UV radiation and in some cases exposure to an electric field together cause the detrimental effects. In contrast to this disruptive property of technical plasmas, we have shown previously that it is possible to use non-thermal plasma-generated species such as H2O2 as cosubstrates in biocatalytic reactions. One of the main limitations in plasma-driven biocatalysis is the relatively short enzyme lifetime under plasma-operating conditions. This challenge could be overcome by immobilizing the enzymes on inert carrier materials. Here, we tested whether immobilization is suited to protect proteins from inactivation by plasma. To this end, using a dielectric barrier discharge device (PlasmaDerm), plasma stability was tested for five enzymes immobilized on ten different carrier materials. A comparative analysis of the treatment times needed to reduce enzyme activity of immobilized and free enzyme by 30% showed a maximum increase by a factor of 44. Covalent immobilization on a partly hydrophobic carrier surface proved most effective. We conclude from the study, that immobilization universally protects enzymes under plasma-operating conditions, paving the way for new emerging applications.

Emission of Shock-Heated Air in the Vacuum Ultraviolet Spectral Region

Emission of Shock-Heated Air in the Vacuum Ultraviolet Spectral Region

Single-Photon Ionization Induced New Covalent Bond Formation in Acrylonitrile(AN)-Pyrrole(Py) Clusters.

The formation of nitrogen-containing organic compounds is crucial for understanding chemical evolution and the origin of life in the interstellar medium (ISM). In this study, we explore whether acrylonitrile (AN) and pyrrole (Py) can form new nitrogen-containing compounds after single-photon ionization in their gaseous clusters by vacuum ultraviolet (VUV)-infrared (IR) spectroscopy and theoretical calculations. The results show that a strong linear H-bond is formed in neutral AN-Py, while cyclic or bicyclic H-bonded networks are formed in the neutral AN-Py2 cluster. It is found that the structure containing a new C-C covalent bond between two moieties in (AN-Py)+ is formed besides the formation of H-bonded structures after AN-Py is ionized by VUV light. In (AN-Py2)+ cluster cations, new C-C or C-N covalent bonds tend to be formed between two Py, with (Py)2+ as the core in the cluster. The results reveal that new covalent bonds are more likely to be formed between two Py species when AN and Py are present in the cationic clusters. These results provide spectroscopic evidence of the formation of new nitrogen-containing organic compounds from AN and Py induced by VUV, which are helpful for our understanding of the formation of diverse prebiotic molecules in interstellar space.

Role of pinch in Argon impurity transport in ohmic discharges of Aditya-U Tokamak

We present experimental results of the trace argon impurity puffing in the ohmic plasmas of Aditya-U tokamak performed to study the argon transport behaviour. Argon line emissions in visible and Vacuum Ultra Violet (VUV) spectral ranges arising from the plasma edge and core respectively are measured simultaneously. During the experiments, space resolved brightness profile of Ar1+ line emissions at 472.69 nm (3p44s 2P3/2–3p44p 2D3/2), 473.59 nm (3p44s 4P5/2–3p44p 4P3/2), 476.49 nm (3p44s 2P1/2–3p44p 2P3/2), 480.60 nm (3p44s 4P5/2–3p44p 4P5/2) are recorded using a high resolution visible spectrometer. Also, a VUV spectrometer has been used to simultaneously observe Ar13+ line emission at 18.79 nm (2s22p 2P3/2–2s2p22P3/2) and Ar14+ line emission at 22.11 nm (2s21S0–2s2p 1P1). The diffusivity and convective velocity of Ar are obtained by comparing the measured radial emissivity profile of Ar1+ emission and the line intensity ratio of Ar13+ and Ar14+ ions, with those simulated using the impurity transport code, STRAHL. Argon diffusivities ~ 12 m2/s and ~ 0.3 m2/s have been observed in the edge (ρ > 0.85) and core region of the Aditya-U, respectively. The diffusivity values both in the edge and core region are found to be higher than the neo-classical values suggesting that the argon impurity transport is mainly anomalous in the Aditya-U tokamak. Also, an inward pinch of ~ 10 m/s mainly driven by Ware pinch is required to match the measured and simulated data. The measured peaked profile of Ar density suggests impurity accumulation in these discharges.

Vacuum UV studies of protonated serine clusters

In a recent work, we have shown that photon absorption can cause a chemical bond to be created between the two monomers within a protonated serine dimer, a process known as intra-cluster bond formation, despite this process not occurring following thermal excitation via low energy collision-induced dissociation (LE-CID). Here we show further evidence for non-statistical photon-induced dissociation (PID) of the protonated serine dimer. In addition we discuss LE-CID and PID studies of the protonated serine octamer, showing that in this case as well, PID leads to non-statistical fragmentation and to the formation of two bonds between three neighboring monomers.

Vacuum Ultraviolet Fingerprints as a New Way of Disentangling Tropylium/Benzylium Isomers.

The two inseparable companions, tropylium (Tr+) and benzylium (Bz+), were interrogated by vacuum ultraviolet (VUV) radiation from 4.5 to 7.0 eV in an ion trap. These new fingerprints provide a new means of distinguishing these two intertwined C7H7+ isomers. In particular, the singular spectral signature of Tr+ in the VUV consists of a single strong electronic transition at ≈6 eV. To illustrate this diagnostic tool, we shed light on the structure of the C7H7+ intermediate that is ubiquitous when using commercial atmospheric pressure photoionization (APPI) sources. We have identified its structure as the 7-membered ring Tr+, which contradicts some previous beliefs.

In search of universalities in the dissociative photoionization of PANHs via isomerizations.

In search of the cause behind the similarities often seen in the fragmentation of PANHs, vacuum ultraviolet (VUV) photodissociation of two pairs of isomers quinoline-isoquinoline and 2-naphthylamine-3-methyl-quinoline are studied using the velocity map imaging technique. The internal energy dependence of all primary fragmentation channels is obtained for all four target molecules. The decay dynamics of the four molecules is studied by comparing their various experimental signatures. The dominant channel for the first pair of isomers is found to be hydrogen cyanide (HCN) neutral loss, while the second pair of isomers lose HCNH neutral as its dominant channel. Despite this difference in their primary decay products and the differences in the structures of the four targets, various similarities in their experimental signatures are found, which could be explained by isomerization mechanisms to common structures. The fundamental role of these isomerization in controlling different dissociative channels is explored via a detailed analysis of the experimental photoelectron-photoion coincidences and the investigation of the theoretical potential energy surface. These results add to the notion of a universal PANH fragmentation mechanism and suggests the seven member isomerization as a key candidate for this universal mechanism. The balance between isomerization, dissociation, and other key mechanistic processes in the reaction pathways, such as hydrogen migrations, is also highlighted for the four molecules.

Development and Application of a Chemical Ionization Focusing Integrated Ionization Source TOFMS for Online Detection of OVOCs in the Atmosphere.

Single photon ionization (SPI) based on vacuum ultraviolet (VUV) lamps has been extensively investigated and applied due to its clean mass spectra as a soft ionization method. However, the photon energy of 10.6 eV and photon flux of 1011 photons s-1 of a commercial VUV lamp limits its range of ionizable analytes as well as its sensitivity. This work designs a chemical ionization focusing integrated (CIFI) ionization source time-of-flight mass spectrometry (TOFMS) based on a VUV lamp for the detection of volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs). The photoelectrons obtained from the VUV lamp via the photoelectric effect ionized the oxygen and water in the air to obtain the reagent ions. The ion-molecule-reaction region (IMR) is constituted by a segmented quadrupole that radially focuses the ions using a radio-frequency electric field. This significantly enhances the yield and transport efficiency of the product ions leading to a great improvement in sensitivity. As a result, a 44-fold and 1154-fold increase in the signal response for benzene and pentanal were achieved, respectively. To verify the reliability of the ionization source, the linear correspondence and repeatability of benzene and pentanal were investigated. Satisfactory dynamic linearity was obtained in the mixing ratio range of 5-50 ppbv, and the relative standard deviation (RSD) of inter-day reached 3.91% and 6.26%, respectively. Finally, the CIFI-TOFMS was applied to the determination of OVOCs, and the LOD of 12 types of OVOCs reached the pptv level, indicating that the ionization source has the potential for accurate and sensitive online monitoring of atmospheric OVOCs.

Origin of Homochirality in Amino Acids Induced by Lyman-α Irradiation in the Early Stage of the Milky Way.

The enantiomeric excess (ee) of l-form amino acids found in the Murchison meteorite poses some issues about the cosmic origin of their chirality. Circular dichroism (CD) spectra of amino acids in the far-ultraviolet (FUV) at around 6.8 eV (182 nm) indicate that the circularly polarized light can induce ee through photochemical reactions. Here, we resort to ab initio calculations to extract the CD spectra up to the vacuum-ultraviolet (VUV) region (∼11 eV), and we propose a novel equation to compute the ee applicable to a wider range of light frequency than what is available to date. This allows us to show that the strength of the induced ee (|ee|) in the 10 eV VUV region is comparable to the one in the 6.8 eV FUV region. This feature is common for some key amino acids (alanine, 2-aminobutyric acid, and valine). In space, intense Lyman-α (Lyα) light of 10.2 eV is emitted from star forming regions. This study provides a theoretical basis that Lyα emitter from an early starburst in the Milky Way plays a crucial role in initiating the ee of amino acids.

Fate of low molecular weight organic matters in reverse osmosis and vacuum ultraviolet process for high-quality ultrapure water production in the semiconductor industry

Ultrapure water (UPW) is essential in the semiconductor industry for rinsing and cleaning products. With the growing demand for UPW, various feed water sources such as tap water, surface water, and wastewater are utilized to produce UPW. However, these feed water sources contain various low molecular weight organic matters (LMWOMs), which can adversely affect the quality of semiconductors when present in treated UPW. Therefore, achieving the complete removal of LMWOMs is crucial in the UPW production process. However, the current reverse osmosis (RO) and vacuum ultraviolet (VUV) processes employed for UPW production have limitations in achieving complete LMWOM removal. Therefore, this study is conducted to investigate the mechanisms of LMWOM removal in RO and the performance of VUV for high-quality UPW production. Six LMWOMs found in the semiconductor industry were tested for lab- and pilot-scale experiments. The result showed that size exclusion is the main mechanism of LMWOM removal in the RO process. However, methanol, ethanol, and urea were not efficiently removed by RO membranes. In addition, a lab-scale VUV experiment was performed under accelerated conditions to examine the oxidation mechanism of LMWOM. The LMWOM with low reactivity to hydroxyl radicals, such as tetramethylammonium hydroxide (TMAH) and urea, were not removed perfectly within 60 min and 180 min, respectively. Furthermore, a pilot-scale VUV experiment was performed to examine the oxidation of LMWOM under real UPW production conditions. Despite observing a correlation in the pseudo-first-order rate constants between the lab-scale and pilot-scale experiments, the removal of TMAH and urea was still not achieved even with a lamp power of 320 W. As urea was not completely removed by either RO or VUV, strategies for UPW production using current water sources are discussed to develop future UPW technologies.