Vacuum Ultraviolet Research Articles

Vacuum Ultraviolet Spectroscopic Properties in Gd3+-Eu3+ Ions Pair Doped MYF4 (M = Li, Na, and K)

LiYF4, NaYF4, and KYF4 doped with Gd3+-Eu3+ ion pairs synthesised by soft route (wet) chemical technique tracked by Reactive Atmosphere Process (RAP). The phase purity of every synthesized material is verified using the X-ray Diffraction (XRD) method. The photoluminescence excitation (PLE) and photoluminescence emission (PL) properties are examined in ultra-violet (UV) and vacuum ultraviolet (VUV) regions. A new type of photon harvesting (cutting) process is studied in the synthesized phosphors. The Quantum Cutting (QC) is observed only in host LiYF4 doped with Gd3+-Eu3+ Phosphor.

Efficient removal of per- and polyfluoroalkyl substances from biochar composites: Cyclic adsorption and spent regenerant degradation

In order to solve the problem of efficient desorption of per- and polyfluoroalkyl substances (PFAS) and regeneration of adsorbents, a novel biochar composite was prepared based on the quaternary ammonium groups and hydrophobicity of sulfobetaine polymer, which can be used for the efficient removal of various PFASs and has great regeneration ability. Through adsorption, regeneration and degradation experiment, the comprehensive effect of the novel biochar composite on the whole process of removal of PFAS was systematically investigated. The results showed that the maximum adsorption capacity of PFOS, PFOA, PFBS, and PFBA reached 634 mg/g, 536 mg/g, 301 mg/g and 264 mg/g, respectively. The adsorption process involved hydrophobicity, electrostatic, pore diffusion and complexation. The NaI + NaOH solution was used at 50 °C to achieve efficient regeneration of the adsorbent, which can be recycled more than 4 times. When the vacuum-ultraviolet (VUV)/sulfite reduction system was used for deep degradation of the regenerated solution, the effect of hydrated electrons on PFAS was enhanced due to the inclusion of NaI and NaOH in the regeneration reagent, resulting in an increase in the degradation efficiency (89.1%–99.9%) and defluorination efficiency (63.3%–84.1%). Based on the performance of BC-P(SB-co-AM) and the treatment efficiency of PFAS, the design idea of the whole process treatment technology of PFAS proposed in this work is expected to hold great promise in environmental applications. This work provides a novel idea and system for the efficient adsorption removal and desorption of PFAS, and subsequent deep degradation.

Diamond Immersion Photodetector for 193 nm Lithography

AbstractAt present, most photodetectors work in atmospheric or vacuum environments, which leaves a large gap for detection under liquid conditions. However, this kind of research is of great significance, especially for the monitoring of 193 nm vacuum UV (VUV) light in the immersion lithography system underwater. Here, the p‐type diamond single crystal (PDSC) is applied as the photoelectrode for the construction of a VUV immersion photodetector with a PDSC‐ultra‐pure water‐Pt structure and a high response to 193 nm light. Under 193 nm excitation (@8 µW) and at 0 V, the PDSC immersion photodetector demonstrates a favorable characteristic of having a high responsivity of 5 mA·W−1. Due to its exceptional performance, this device has been proven to function as a highly‐sensitive and self‐powered VUV detector, with significant potential for utilization in the monitoring of 193 nm light in immersion lithography systems.

Pulsewidth-switchable ultrafast source at 114 nm.

Femtosecond laser sources with high repetition rate in the ultraviolet (UV) and vacuum UV (VUV) are fundamental tools enabling tabletop time-resolved and angle-resolved photoemission spectroscopy in solids. We describe a VUV source at 114 nm (10.8 eV) based on an industrial grade ytterbium-doped ultrafast laser, a nonlinear pulse width selection stage, and two cascaded frequency tripling stages, first in crystals, second in xenon. The role of ionization in gas-based perturbative third harmonic generation phase-matching is analyzed using a simple theory, numerical simulations, and experimental data. The source features high photon flux, high repetition rate, and adjustable time resolutions. Thereby, in combination with a state-of-the-art angle-resolved photoemission spectroscopy (ARPES) apparatus it enables the study of the electronic dynamics of the whole Brillouin zone in a large number of materials.

Consideration of Improved Adhesion of Direct Copper Seed Layer by Medium-Vacuum Sputtering Using Vacuum Ultraviolet Light

A sputtering method is used to form the seed layer for copper electric plating. In general, copper spatter has weak adhesion to resin, so titanium spatter is combined to increase the adhesion strength. However, etching in the lithography process requires two types of processes, titanium and copper metal. We have reported the improvement of adhesion of copper sputter to glass epoxy resin by medium vacuum sputtering equipment in 242nd ECS meeting. Adhesion strength was improved by performing vacuum ultraviolet treatment as a pretreatment for medium-vacuum sputtering. We discovered the relationship between the hydroxyl groups on the resin surface and the adhesion force by the chemical modification XPS method. Furthermore, by XPS analysis of the peeled copper interface, the adhesion mechanism between the resin and copper due to UV irradiation was estimated. We evaluated the absorption properties in the vacuum ultraviolet region of a thinly processed glass epoxy resin. We investigated the behavior of functional groups at the interface and considered the effect of vacuum ultraviolet rays in the depth direction.

Stark control of multiphoton ionization through Freeman resonances in alkyl iodides.

Multiphoton ionization (MPI) of alkyl iodides (RI, R = CnH2n+1, n = 1-4) has been investigated with femtosecond laser pulses centered at 800 and 400nm along with photoelectron imaging detection. In addition, the ultraviolet (UV)-vacuum ultraviolet (VUV) absorption spectra of gas-phase RIs have been measured in the photon energy range of 5-11eV using the VUV Fourier transform spectrometer at the VUV DESIRS beamline of the synchrotron SOLEIL facility. The use of high-laser-field strengths in matter-radiation interaction generates highly non-linear phenomena, such as the Stark shift effect, which distorts the potential energy surfaces of molecules by varying both the energy of electronic and rovibrational states and their ionization energies. The Stark shift can then generate resonances between intermediate states and an integer number of laser photons of a given wavelength, which are commonly known as Freeman resonances. Here, we study how the molecular structure of linear and branched alkyl iodides affects the UV-VUV absorption spectrum, the MPI process, and the generation of Freeman resonances. The obtained results reveal a dominant resonance in the experiments at 800nm, which counter-intuitively appears at the same photoelectron kinetic energy in the whole alkyl iodide series. The ionization pathways of this resonance strongly involve the 6p(2E3/2) Rydberg state with different degrees of vibrational excitation, revealing an energy compensation effect as the R-chain complexity increases.

Manipulation of Ion Conversion in Dichloromethane-Enhanced Vacuum Ultraviolet Photoionization Mass Spectrometry of Oxygenated Volatile Organic Compounds.

The ion conversion processes in CH2Cl2-enhanced vacuum ultraviolet photoionization of oxygenated volatile organic compounds (OVOCs) have been systematically studied by regulating the pressure, humidity, and reaction time in the ionization source of a time-of-flight mass spectrometer. As the ionization source pressure increased from 100 to 1100 Pa, the main characteristic ions changed from CH2Cl+ to CH2Cl+(H2O), CH2OH+, and C2H4OH+ and then to the hydrated hydronium ions H3O+(H2O)n (n = 1, 2, 3). The total ion current (TIC) almost remained unchanged even if the humidity increased from 44 to 3120 ppmv, indicating interconversion between ions through ion-molecule reactions. The intensity of protonated methanol/ethanol (sample S) ion was almost linearly correlated with the intensity of H3O+(H2O)n, which pointed to the proton transfer reaction (PTR) mechanism. The reaction time was regulated by the electric field strength in the ionization region. The intensity variation trends of different ions with the reaction time indicated that a series of step-by-step ion-molecule reactions occurred in the ionization source, i.e., the primary ion CH2Cl+ reacted with H2O and converted to the intermediate product ions CH2OH+ and C2H4OH+, which then further reacted with H2O and led to the production of H3O+, and finally, the protonated sample ion SH+ was obtained through PTR with H3O+, as the ion-molecule reactions progressed. This study provides valuable insights into understanding the formation mechanism of some unexpected intermediate product ions and hydrated hydronium ions in dopant-enhanced VUV photoionization and also helps to optimize experimental conditions to enhance the sensitivity of OVOCs.

Comparative study of UV/chlorine and VUV/chlorine as ultrafiltration membrane pretreatment techniques: Performance, mechanisms and DBPs formation

Membrane fouling, primarily resulting from natural organic matter (NOM) widely existing in water sources, has always been a chief hindrance for the prevalent application of ultrafiltration (UF). Thus, vacuum ultraviolet (VUV)/chlorine process was proposed as a strategy for UF membrane fouling control and ultraviolet (UV)/chlorine process was used for comparison. VUV/chlorine process exhibited more excellent performance on NOM removal than UV/chlorine process. [HO•]ss and [Cl•]ss were calculated as 1.26 × 10−13 and 3.06 × 10−14 M, respectively, and ClO• might not exist under the conditions of 0.08 mM chlorine and 30 min VUV irradiation. [HO•]ss, [Cl•]ss and [ClO•]ss were not available and the formation of reactive radicals was unsustainable in UV/chlorine system. Moreover, VUV/chlorine pretreatment also showed better performance on the reversible and irreversible membrane fouling control than UV/chlorine pretreatment. The dominated fouling mechanism in the final stage of filtration was cake filtration. Additionally, the amount of detected disinfection by-products (DBPs) in VUV/chlorine system was significantly lower than that in UV/chlorine system. During subsequent chlorination disinfection, the yield of DBPs with VUV/chorine pretreatment was higher than that with UV/chlorine pretreatment. VUV/chlorine pretreatment could effectively control DBPs formation when the pretreatment time was extended to 120 min. In summary, VUV/chlorine system presented a most excellent performance on membrane fouling control, NOM degradation and DBPs control.

Vibrational spectroscopy of neutral and cationic 2-Methoxyethanol

Hydrogen bonding interactions, such as the O-H···O interaction, play a crucial role in stabilizing conformations of both organic and biological molecules. In this study, we employed the infrared (IR)–vacuum-ultraviolet (VUV) non-resonant ionization detected IR spectroscopy (NRID-IR) method to investigate the molecular structure of neutral and cationic 2-methoxyethanol (CH3OCH2CH2OH, 2-ME). The stable structures and anharmonic IR spectra of neutral and cationic 2-ME were calculated using density functional theory (DFT) at the B3LYP-D3(BJ)/def2-TZVPP level. Our results revealed that the two most stable conformers of neutral 2-ME exhibit a weak O-H···O intramolecular hydrogen bond, while the cationic 2-ME lacks the O-H···O interaction but contains a C-H···O intramolecular hydrogen bond. A comparison of the experimental and theoretical IR absorption spectra reveals that the most stable conformer (gauche-(anti-gauche)-trans) is the primary contributor to the observed IR spectra of neutral 2-ME in the 2700–7250 cm−1 range. Similarly, the second stable conformer is found to be the dominant contributor to the observed IR spectra of cationic 2-ME in the range of 2700–7100 cm−1. Additionally, the C-H fundamental stretching mode of cationic 2-ME is found to be blue-shifted by approximately 100 cm−1 compared to that of neutral 2-ME. Furthermore, the natural bond orbital (NBO) analysis suggests that in neutral 2-ME, the n(O)→σ*(CαH) interactions result in significant negative hyperconjugation, leading to the weakening of CαH bonds and a subsequent reduction in vibrational energy.

Progress in coupling MPGD-based photon detectors with nanodiamond photocathodes

The next generation of gaseous photon detectors is requested to overcome the limitations of the available technology, in terms of resolution and robustness. The quest for a novel photocathode, sensitive in the far vacuum ultra violet wavelength range and more robust than present ones, motivated an R&D programme to explore nanodiamond based photoconverters, which represent the most promising alternative to cesium iodine. A procedure for producing the novel photocathodes has been defined and applied on THGEMs samples. Systematic measurements of the photo emission in different Ar/CH4 and Ar/CO2 gas mixtures with various types of nanodiamond powders have been performed. A comparative study of the response of THGEMs before and after coating demonstrated their full compatibility with the novel photocathodes.

Interaction Study of Energetic Protons and Electrons with the Vacuum Ultra Violet Source used in the Complex Irradiation Facility

Context: One important factor to be considered for space missions is the radiation environment. It is composed of energetic particles, such as protons, electrons and ions, and electromagnetic radiation, photons ranging from Vacuum Ultra Violet (VUV) to Far Infrared (FIR). Each of these radiation sources have an unique energy spectrum that further depends on the location inside the solar system, e. g. Earth orbits or interplanetary space.For material qualification and material engineering, individual irradiation is considered and their effects are superimposed. However, effects occurring when two and more radiation types simultaneously are present have barely been investigated yet. Further complexity is added, when additional interactions take place due to laboratory hardware. Aims: This publication reports on the efforts made to analyse and measure the interaction of a VUV and corpuscular radiation sources. The aim is to quantify the deviations due to interactions and conclude consequences for the simultaneous operation of these radiation sources. Methods: In order to quantify the effects, the Complex Irradiation Facility (CIF), located at the DLR Bremen has been used. It connects proton and electron accelerators together with VUV and UV light sources to an ultra high vacuum chamber. The corpuscular and VUV radiation sources have been operated simultaneously. The reaction of the operation parameters, such as current measured with Faraday Cups (FC) has been tracked and post-processed. Results: It has been discovered, that protons considerably interact with the gas mixture used to operate the VUV source. This interaction decreases for higher beam intensities of the corpuscular irradiation. It was found, that this is likely due to protons ionizing gas atoms which are then measured by the FC as current. For electrons, this phenomena was not observed due to their smaller stopping power. The discovery restricts the acceleration factor of the CIF for proton together with VUV irradiation, but does not necessarily limit the range of application of the CIF depending on the requirements of the material and/or qualification test. Energy range of electrons stays unrestricted.

Vacuum-ultraviolet laser source for spectroscopy of trapped thorium ions

A tunable vacuum-ultraviolet (VUV) laser source based on four-wave frequency mixing in xenon is presented. Using seed radiation from two continuous-wave lasers, the system allows for precise control of the VUV frequency and is developed for the resonant laser excitation of the Th-229 nucleus to its low-energy isomeric state. The system is prepared to operate in a wide scanning range from 148 nm to 155 nm. The source produces pulses of 6–10 ns duration with up to 40 µJ energy and is coupled via a vacuum beamline to a linear radiofrequency ion trap. In a first implementation of VUV laser spectroscopy of trapped Th+ ions we excite three previously unknown resonance lines near 149 nm wavelength to electronic levels that are close to the Th-229 isomer energy. The resonances are detected and analyzed via fluorescence of the excited Th+ ions. An analysis of the lineshape is used to estimate the linewidth of the VUV radiation to be in the range of 6 GHz, dominated by phase noise that is enhanced in harmonic generation and in the four-wave mixing process. The prospects for the use of the system in nuclear laser spectroscopy of Th-229 are discussed.

Generation of Soft X-Ray and Vacuum Ultraviolet Radiation during the Interaction of a Hydrogen Plasma Flow with a Gas Jet

Generation of Soft X-Ray and Vacuum Ultraviolet Radiation during the Interaction of a Hydrogen Plasma Flow with a Gas Jet

Efficient removal of electroneutral carbonyls by combined vacuum–UV oxidation and anion-exchange resin adsorption: mechanism, model simulation, and optimization

Electroneutral carbonyls (ENCs) with low molecular weights (e.g., aldehydes and ketones) are recalcitrant to single water treatment process to achieve ultralow concentration. Residual ENCs are present in reverse osmosis permeate and pose risks to human health during potable use or industrial application in manufacturing processes. Herein, a combined vacuum–UV (VUV) oxidation and anion-exchange resin (AER) adsorption method was developed to treat the ENCs and reduce total organic carbon (TOC) to an ultralow concentration (< 5 μg/L) with high efficiency and at low cost. VUV-AER was 2.1–2.4 times more efficient than VUV alone for the removal of TOC. VUV oxidized the ENCs to electronegative carboxylic acids, which were adsorbed by the AER through electrostatic interactions and hydrogen bonding. When the VUV fluence was lower than 643 mJ cm−2, the AER could not achieve ultralow TOC removal of ENCs. The treat capacity of 1500–2900 valid bed volume (BVs) was achieved after increasing the VUV fluence to 1929 mJ cm−2. The AER could more efficiently adsorb carboxylic acids that contained more carboxylic groups or shorter carbon chain. Acetate was identified as the primary breakthrough product at relatively low VUV fluence, and oxalate was the main byproduct at relatively high VUV fluence. A mathematical model to predict TOC breakthrough was developed considering the VUV–oxidation kinetics and the AER breakthrough curve. The model was used to optimize the method to maximize TOC removal and minimize energy consumption. These results imply that VUV-AER is technically feasible and economically applicable to eliminate recalcitrant ENCs to ultralow concentration for the production of water requires high quality (e.g., potable water or electronic-grade ultrapure water).

A Simple High-Flux Switchable VUV Lamp Based on an Electrodeless Fluorescent Lamp for SPI/PAI Mass Spectrometry.

Single-photon ionization (SPI) is a unique soft ionization technique for organic analysis. A convenient high-flux vacuum ultraviolet (VUV) light source is a key precondition for wide application of SPI techniques. In this study, we present a novel VUV lamp by simply modifying an ordinary electrodeless fluorescent lamp. By replacing the glass bulb with a stainless steel bulb and introducing 5% Kr/He (v/v) as the excitation gas, an excellent VUV photon flux over 4.0 × 1014 photons s-1 was obtained. Due to its rapid glow characteristics, the VUV lamp can be switched on and off instantly as required by detection, ensuring the stability and service life of the lamp. To demonstrate the performance of the new lamp, the switchable VUV lamp was coupled with an SPI-mass spectrometer, which could be changed to photoinduced associative ionization (PAI) mode by doping gaseous CH2Cl2 to initiate an associative ionization reaction. Two types of volatile organic compounds sensitive to SPI and PAI, typically benzene series and oxygenated organics, respectively, were selected as samples. The instrument exhibited a high detection sensitivity for the tested compounds. With a measurement time of 11 s, the 3σ limits of detection ranged from 0.33 to 0.75 pptv in SPI mode and from 0.03 to 0.12 pptv in PAI mode. This study provides an extremely simple method to assemble a VUV lamp with many merits, e.g., portability, robustness, durability, low cost, and high flux. The VUV lamp may contribute to the development of SPI-related highly sensitive detection technologies.

Momentum-Space Imaging of Ultra-Thin Electron Liquids in δ-Doped Silicon.

Two-dimensional dopant layers (δ-layers) in semiconductors provide the high-mobility electron liquids (2DELs) needed for nanoscale quantum-electronic devices. Key parameters such as carrier densities, effective masses, and confinement thicknesses for 2DELs have traditionally been extracted from quantum magnetotransport. In principle, the parameters are immediately readable from the one-electron spectral function that can be measured by angle-resolved photoemission spectroscopy (ARPES). Here, buried 2DEL δ-layers in silicon are measured with soft X-ray (SX) ARPES to obtain detailed information about their filled conduction bands and extract device-relevant properties. This study takes advantage of the larger probing depth and photon energy range of SX-ARPES relative to vacuum ultraviolet (VUV) ARPES to accurately measure the δ-layer electronic confinement. The measurements are made on ambient-exposed samples and yield extremely thin (< 1nm) and dense (≈1014 cm-2 ) 2DELs. Critically, this method is used to show that δ-layers of arsenic exhibit better electronic confinement than δ-layers of phosphorus fabricated under identical conditions.

Excited states of trans-stilbene and 1,4-diphenylbutadiene. Near and vacuum UV polarization spectroscopy

The UV absorbance spectra of trans-stilbene ((E)-1,2-diphenylethene, DPE) and (E,E’)-1,4-diphenyl-1,3-butadiene (DPB) are investigated by Synchrotron Radiation Linear Dichroism (SRLD) spectroscopy using stretched polyethylene as an anisotropic solvent. The investigation covers the range 58,000–25,000 cm–1 (172–400 nm). The observed polarization data provide information on the transition moment directions of the observed spectral features. The wavenumbers, intensities, and polarization directions of the observed spectral bands are compared with the results of quantum chemical calculations using the semiempirical all-valence-electrons method LCOAO and Time-Dependent Density Functional Theory (TD–DFT) with the functional CAM-B3LYP.

Magic Numbers and Stabilities of Photoionized Water Clusters: Computational and Experimental Characterization of the Nanosolvated Hydronium Ion.

The stability and distributions of small water clusters generated in a supersonic beam expansion are interrogated by tunable vacuum ultraviolet (VUV) radiation generated at a synchrotron. Time-of-flight mass spectrometry reveals enhanced population of various protonated water clusters (H+(H2O)n) based upon ionization energy and photoionization distance from source, suggesting there are "magic" numbers below the traditional n = 21 that predominates in the literature. These intensity distributions suggest that VUV threshold photoionization (11.0-11.5 eV) of neutral water clusters close to the nozzle exit leads to a different nonequilibrium state compared to a skimmed molecular beam. This results in the appearance of a new magic number at 14. Metadynamics conformer searches coupled with modern density functional calculations are used to identify the global minimum energy structures of protonated water clusters between n = 2 and 21, as well as the manifold of low-lying metastable minima. New lowest energy structures are reported for the cases of n = 5, 6, 11, 12, 16, and 18, and special stability is identified by several measures. These theoretical results are in agreement with the experiments performed in this work in that n = 14 is shown to exhibit additional stability, based on the computed second-order stabilization energy relative to most cluster sizes, though not to the extent of the well-known n = 21 cluster. Other cluster sizes that show some additional energetic stability are n = 7, 9, 12, 17, and 19. To gain insight into the balance between ion-water and water-water interactions as a function of the cluster size, an analysis of the effective two-body interactions (which sum exactly to the total interaction energy) was performed. This analysis reveals a crossover as a function of cluster size between a water-hydronium-dominated regime for small clusters and a water-water-dominated regime for larger clusters around n = 17.

Vacuum UV Photolysis of Benzene in Solid Nitrogen

Vacuum UV Photolysis of Benzene in Solid Nitrogen

Photodissociation and photoionization of molecules of astronomical interest

Context. Vacuum-ultraviolet (VUV) photons are important drivers of chemical processes in space. Thus, it is important to accurately characterize and constrain photorates in different radiation fields, via the photodissociation and photoionization cross sections of individual atoms and molecules. These have been available in the Leiden VUV photodissocation and photoionization cross section database. Aims. Experimental and theoretical advances in the past decade or so have allowed multiple new cross sections to be obtained, particularly photoionization cross sections of radicals. The database is hereby updated by including these more recent cross sections and is also expanded with several astronomically relevant species. Methods. The cross sections have been used to calculate photodissociation and photoionization rates in several different radiation fields as well as from cosmic-ray-induced VUV fluxes. The reduction of rates in shielded regions was calculated as a function of dust, molecular and atomic hydrogen, atomic carbon, and self-shielding column densities. The relative importance of these shielding types is molecule and atom dependent, as well as the assumed dust absorbance. All the data are publicly available from the Leiden VUV cross section database. Results. The Leiden VUV cross section database has been updated with 14 new astrophysically relevant molecular species and 16 updates to previous entries. The database update is accompanied by a brief review of the basic physical processes, particularly photoionization processes which have not been reviewed in the context of previous database updates.