Vacuum Ultraviolet Spectra Research Articles

Development of double-walled bellows for ITER VUV spectrometer systems

This study describes the design and development of double-walled bellows used in ITER's vacuum ultra-violet (VUV) spectrometer systems. These bellows were designed to accommodate port plug displacement resulting from the thermal expansion of the ITER vacuum vessel and other interface loads. The three VUV spectrometer systems under development—the VUV core survey spectrometer, divertor-VUV spectrometer, and VUV-edge spectrometer—are intended to measure the VUV spectrum to monitor impurity species in the plasma. While the ex-vessel components of ITER VUV spectrometers in the interspace and port cell areas, are fixed to the tokamak building, the closure plate of the port plugs, to which the sight pipes are attached, is expected to move by several centimeters both vertically and radially owing to the vacuum vessel's thermal expansion. As a result, the structural integrity of the system requires a flexible structure that can compensate for displacement caused by thermal expansion. To address this need, two types of double-walled bellows were developed, gimbal bellows for lateral displacement and axial bellows for axial displacement. These were developed in accordance with the ASME SEC.VIII code and EJMA standard to meet ITER's safety and vacuum requirements. A double wall is mandated for vacuum bellows due to their vulnerability in terms of vacuum safety. The structural integrity and functionality of the designed bellows were confirmed through functional tests on the manufactured prototype.

A systematic IR and VUV spectroscopic investigation of ion, electron, and thermally processed ethanolamine ice

ABSTRACT The recent detection of ethanolamine (EtA, HOCH$_2$CH$_2$NH$_2$), a key component of phospholipids, i.e. the building blocks of cell membranes, in the interstellar medium is in line with an exogenous origin of life-relevant molecules. However, the stability and survivability of EtA molecules under inter/circumstellar and Solar System conditions have yet to be demonstrated. Starting from the assumption that EtA mainly forms on interstellar ice grains, we have systematically exposed EtA, pure and mixed with amorphous water (H$_2$O) ice, to electron, ion, and thermal processing, representing ‘energetic’ mechanisms that are known to induce physicochemical changes within the ice material under controlled laboratory conditions. Using infrared (IR) spectroscopy, we have found that heating of pure EtA ice causes a phase change from amorphous to crystalline at 180 K, and further temperature increase of the ice results in sublimation-induced losses until full desorption occurs at about 225 K. IR and vacuum ultraviolet (VUV) spectra of EtA-containing ices deposited and irradiated at 20 K with 1 keV electrons as well as IR spectra of H$_2$O:EtA mixed ice obtained after 1 MeV He$^+$ ion irradiation have been collected at different doses. The main radiolysis products, including H$_2$O, CO, CO$_2$, NH$_3$, and CH$_3$OH, have been identified and their formation pathways are discussed. The measured column density of EtA is demonstrated to undergo exponential decay upon electron and ion bombardment. The half-life doses for electron and He$^+$ ion irradiation of pure EtA and H$_2$O:EtA mixed ice are derived to range between $10.8\!-\!26.3$ eV/16u. Extrapolating these results to space conditions, we conclude that EtA mixed in H$_2$O ice is more stable than in pure form and it should survive throughout the star and planet formation process.

Contactless spectroscopy of photoactive centres in sapphire and nitride layered structures

Spectroscopy of photo-active centres in wide bandgap optical materials with absorption and emission bands in the range close to vacuum ultraviolet spectrum is complicated. In this work, the pulsed photo-ionization (PPI) transients, electron spin resonance (ESR) and proton induced luminescence spectroscopy techniques have been combined to evaluate the origin and parameters of deep centres in crystalline sapphire substrates. Additionally, the layered structures with MOCVD grown thin top layers of GaN, AlGaN and AlN on sapphire substrates were examined in order to clarify origin of emission bands related to the epilayers and sapphire. The sapphire assigned emission bands have been ascribed to the F+ centres, characterized by photo-activation energy of 4.8 eV. Prevailing of F+ centres has been confirmed by ESR spectroscopy results. The covering nitride layers of AlN, AlGaN and GaN led to appearance of the additional PPI spectral peaks ascribed to recombination on the interface between epitaxial material and sapphire substrate.

Photochemistry of micro-solvated benzonitrile complexes with water/ammonia bordering on the formation of icy grains

Polycyclic aromatic hydrocarbons (PAHs) act as condensation nuclei for water/ammonia molecules forming icy water clusters. In the context of small aromatic rings, we have theoretically examined complexes of benzonitrile with water/ammonia molecules in order to investigate the photochemical kinetics of the icy grain formation. First, we obtain the structure of energetically stable complexes containing different H-bonding patterns and analyze their effects in the infrared (IR) and vacuum ultraviolet (VUV) spectra, before and after ionization. Second, we evaluate the H-bonding reorientation kinetics of the complexes at low temperatures, which indicates that the process involving water occurs faster than the corresponding process involving ammonia. Finally, the thermal rate constants indicate which configurations are the most likely to be ionized under vacuum ultraviolet (VUV) irradiation. Our results are consistent with what has experimentally been observed for related complexes, and are useful as a starting point to investigate the process of the icy grains formation. This study provides insight into possible subsequent photochemical reactions occurring in the interstellar medium (ISM) or in jet-cooled molecular complexes.

Amorphous 1-propanol interstellar ice beyond its melting point

ABSTRACT The recent discovery of 1-propanol (CH3CH2CH2OH) in the interstellar medium (ISM) is of tremendous interest since fatty alcohols have been proposed as constituents of proto-cell membranes. Motivated by this discovery, we present the laboratory mid-infrared (MIR) and vacuum ultraviolet (VUV) absorption spectra of 1-propanol ice under astrochemical conditions, mimicking an icy mantle on cold dust in the ISM. Both MIR and VUV spectra were recorded at ultrahigh vacuum of ∼10-9 mbar and at temperatures ranging from 10 K to sublimation. The morphology of the 1-propanol ice deposited at 10 K was amorphous. By warming the ice to temperatures of 140 K and above, with subsequent recording of IR spectra, we observe complete sublimation of 1-propanol molecules from the substrate around 170 K. No amorphous-to-crystalline phase change was observed upon warming to higher temperatures. Additionally, we observe the IR and VUV signatures of 1-propanol ice on the substrate well beyond its melting point (147 K). To the best of our knowledge, this is the first reported observation of a molecular ice staying well beyond its melting point under such conditions. This result shows that the morphology of icy mantles on ISM cold dust grains is more complex than previously thought. Our atomistic molecular dynamics simulations capture the experimental trends and shed light on the microscopic origin of this unusual phase behaviour of 1-propanol.

The ultraviolet and vacuum ultraviolet absorption spectrum of gamma-pyrone; the singlet states studied by configuration interaction and density functional calculations

A synchrotron based vacuum ultraviolet absorption spectrum for γ-pyrone has been interpreted in terms of singlet excited electronic states using a variety of coupled cluster, configuration interaction, and density functional calculations. The extremely weak spectral onset at 3.557 eV shows eight vibrational peaks, which following previous analyses, are attributed to a forbidden 1A2 state. A contrasting broad peak with a maximum at 5.381 eV has a relatively high cross-section of 30 Mb; this arises from three overlapping states, where a 1A1 state dominates over progressively weaker 1B2 and 1B1 states. After fitting the second band to a polynomial Gaussian function and plotting the regular residuals over 20 vibrational peaks, we have had limited success in analyzing this fine structure. However, the small separation between these three states clearly shows that their vibrational satellites must overlap. Singlet valence and Rydberg state vibrational profiles were determined by configuration interaction using the CAM-B3LYP density functional. Vibrational analysis using both the Franck–Condon and Herzberg–Teller procedures showed that both procedures contributed to the profiles. Theoretical Rydberg states were evaluated by a highly focused CI procedure. The superposition of the lowest photoelectron spectral band on the vacuum ultraviolet spectrum near 6.4 eV shows that the 3s and 3p Rydberg states based on the 2B2 ionic state are present; those based on the other low-lying ionic state (X2B1) are destroyed by broadening; this is a dramatic extension of the broadening previously witnessed in our studies of halogenobenzenes.

UV-VUV absorption spectra of azido-based energetic plasticizer bis(1,3-diazido prop-2-yl)malonate in gas phase.

Ultraviolet and vacuum ultraviolet photo-absorption spectra of azido (-N3)-based energetic plasticizer, bis(1,3-diazido-prop-2-yl)-malonate (abbreviated as BDAzPM), in the gas phase is recorded at room temperature and in the photon energy range of 5.5-9.9eV using a synchrotron radiation source. Complementary computational results obtained using the time-dependent density functional theory document the vertical transition energies and oscillator strengths. Comparison of the simulated spectra with the experimental absorption spectrum of BDAzPM reveals that the early part of the absorption spectrum of BDAzPM is of pure valence excitation character, whereas the later intense part of the absorption spectrum is dominated by mixed Rydberg and valence electronic excitations.

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.

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.

High-level studies of the singlet states of quadricyclane, including analysis of a new experimental vacuum ultraviolet absorption spectrum by configuration interaction and density functional calculations.

A synchrotron-based vacuum ultraviolet absorption spectrum (VUV) of quadricyclane (QC) is reported with energies up to 10.8eV. Extensive vibrational structure has been extracted from the broad maxima by fitting short energy ranges of the VUV spectrum to high level polynomial functions and processing the regular residuals. Comparison of these data with our recent high-resolution photoelectron spectral of QC showed that this structure must be attributed to Rydberg states (RS). Several of these appear before the valence states at higher energies. Both types of states have been calculated by configuration interaction, including symmetry-adapted cluster studies (SAC-CI) and time dependent density functional theoretical methods (TDDFT). There is a close correlation between the SAC-CI vertical excitation energies (VEE) and both Becke 3-parameter hybrid functional (B3LYP), especially Coulomb-attenuating method-B3LYP determined ones. The VEE for several low-lying s-, p, d-, and f-RS have been determined by SAC-CI and adiabatic excitation energies by TDDFT methods. Searches for equilibrium structures for 11,3A2 and 11B1 states for QC led to rearrangement to a norbornadiene structure. Determination of the experimental 00 band positions, which show extremely low cross-sections, has been assisted by matching features in the spectra with Franck-Condon (FC) fits. Herzberg-Teller (HT) vibrational profiles for the RS are more intense than the FC ones, but only at high energy, and are attributed to up to ten quanta. The vibrational fine structure of the RS calculated by both FC and HT procedures gives an easy route to generating HT profiles for ionic states, which usually require non-standard procedures.

Limits of identification using VUV spectroscopy applied to C8H18 isomers isolated by GC×GC.

The vacuum ultraviolet detector for gas chromatography can be used to identify structural differences between isomers with similar chromatographic elution times, which adds detail to characterization, valuable for prescreening of sustainable aviation fuel candidates. Although this capability has been introduced elsewhere, vacuum ultraviolet spectroscopy for saturated hydrocarbons has been examined minimally, as the similarities between their spectra are much less significant than their aromatic counterparts. The fidelity with which structural differences can be identified has been unclear. In this work, all possible structural isomers of C8H18 are measured and determined to have unambiguously unique vacuum ultraviolet spectra. Using a statistically based residual comparison approach, the concentration limits at which the spectral differences are interpretable are tested in both a controlled study and a real fuel application. The concentration limit at which the spectral differences between C8H18 isomers are unambiguous is below 0.40% by mass and less than 0.20% with human discretion in our experimental configuration.

Towards Sic-Based VUV Pin-Photodiodes - Investigations on 4H-SiC Photodiodes with Shallow Implanted Al Emitters

4H silicon carbide (SiC) based pin photodiodes with a sensitivity in the vacuum ultraviolet spectrum (VUV) demand newly developed emitter doping profiles. This work features the first ever reported 4H-SiC pin photodiodes with an implanted p-emitter and a noticeable sensitivity at a wavelength of 200 nm. As a first step, Aluminum doping profiles produced by low energy ion implantation in 4H-SiC were characterized by secondary-ion mass spectrometry (SIMS). Photodiodes using these shallow emitters are compared to one with a deep p-emitter doping profile employing IV characteristics and the spectral response. SIMS results demonstrate the possibility of shallow Alimplantation profiles using low implantation energies with all emitter profiles featuring characteristic I-V results. For some shallow doping profiles, a meassurable signal at the upper limit of the VUV spectrum could be demonstrated, paving the way towards 4H-SiC pin photodiodes with sensitivities for wavelengths below 200 nm.

Experimental study on n-hexane pyrolysis initiated by 1-nitropropane in a low-pressure flow reactor

In order to investigate the species pool and primary channels of initiated pyrolysis of n-hexane, the low-pressure (30 Torr, 4.0 kPa) flow reactor pyrolysis of n-hexane initiated by 5% 1-nitropropane (1-NP) was studied experimentally in a wide range of temperature from 623 K to 1223 K. Combined with synchrotron vacuum ultraviolet (SVUV) photoionization mass spectra scanned at photon energies ranging from 9.0 to 14.7 eV and near-threshold photoionization efficiency (PIE) spectra, 29 pyrolysis species, covering C1–C6 hydrocarbons and several pyrolysis species containing O or N atoms, were identified. Based on the ion signal intensities of the visible peaks in the mass spectra, the mole fraction profiles of all the experimental species were evaluated. The experimental results suggested that the initial pyrolysis temperature of n-hexane was reduced by approximately 275–325 K. On the basis of the mole fraction profiles and the initial formation temperatures reported in this work and rate coefficients proposed in previous studies, the 1-NP-initiated pyrolysis mechanisms of n-hexane were discussed. It was suggested that n-hexane was dominantly consumed by the H-abstraction reactions by the attack of OH radical in this work. The 1-NP-initiated pyrolysis of n-hexane mainly proceeded via reactions to produce C3H6 + C3H7, or 1-C4H8 + C2H5, or 1-C5H10 + CH3.

Luminescence properties of Mg4Ta2O9:M (M= Hf4+, Zr4+, W6+, Mo6+) with vacuum ultraviolet light and X-ray excitation

Mg4Ta2O9:x at % M (M = Hf4+, Zr4+, W6+, Mo6+; x = 0, 1, 2, 3, 4, 5) with single phase were synthesized via the conventional solid-state reactions in air. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), vacuum ultraviolet (VUV) light excited spectra and X-rays excited luminescence (XEL). Structural characterization and Rietveld refinement show that more than 60% of 5 at % Hf4+, Zr4+, W6+ and Mo6+ doped ions enter into the Ta sites and less than 40% ions into the Mg(1) and Mg(2) sites. They can be excited efficiently by VUV light at 160 nm, and emit wide UV-A or blue light at 355∼458 nm depending on the doping ion and its concentration. XEL spectra and decay time data indicate that Mg4Ta2O9:1 at % Hf4+ has excellent X-ray excited scintillation performance typically with light yield of 13469 ph/MeV and decay time of 5.28 μs. Thus, it has potential application in optical conversion devices and security inspection.

Vacuum UV photoabsorption spectroscopic and photoionization mass spectrometric study of geminal dibromoethylene (1,1-Br2C2H2) in the 5–15eV range. Experiment and theory

The vacuum UV photoabsorption spectrum (PAS) of 1,1-C2H2Br2 has been examined between 5 eV and 15 eV using the vacuum UV light of synchrotron radiation. For the first time the photoionization mass spectroscopy and efficiency of 1,1-C2H2Br2+ has been measured in the same energy range. A quantum chemical calculation is proposed for the investigation of the neutral and ionized states. The photoionization efficiency curve (PIEC) of 1,1-C2H2Br2+ provided the IEad(X˜2B1)= 9.617±0.005 eV. A vibrational structure gave ω3+=1336 cm−1 and most likely ω4+=483 cm−1. The PIEC of C2H2Br+ shows the lowest appearance energy to be at 11.14±0.02 eV. The onset at 11.56±0.01 eV likely corresponds to the excitation of Br in the 2P1/2 spin-orbit state. In the vacuum UV-PAS the broad band observed at 6.231 eV includes nσ→Rs, 2b1(π)→π* valence transitions and the 2b1→3 s Rydberg transition in agreement with the present calculations. An isolated weak continuum at 7.15 eV is assigned to the nπ→π* transition. The 2b1→3 s Rydberg transition is characterized by a short progression starting at 6.583 eV. A series of long progressions observed between 7.364 eV and 9.666 eV has been analyzed in terms of vibrational transitions to np- (δ= 0.544) and nd-type (δ= -0.04) Rydberg states all converging to the X˜2B1 ionic ground state. An analysis has been attempted providing average values of the vibrational wavenumbers ω3≈1300 cm−1 (or 162 meV), ω4≈480 cm−1 (or 60 meV) and ω5≈145 cm−1 (or 18 meV). By the same way several other Rydberg states were analyzed. For the first time the vacuum UV spectrum of 1,1-C2H2Br2 has been recorded above 10 eV and up to 15 eV. Several broad bands are tentatively assigned to transitions to Rydberg states converging to excited ionic states of 1,1-C2H2Br2+. For one of these a vibrational structure is observed and a tentative assignment is proposed.

Elemental Fluctuation in Gd3Al2Ga3O12:Ce Crystals Imposed by Li+ and Mg2+ Co-Doping: The Impact on Defects, Luminescence, and Scintillation Properties

This research revealed the response of Ga and Al sublattices to the incorporation of mismatching substituents in Gd3Al2Ga3O12:Ce single crystals. Incompatible in size and charge, Li+ and Mg2+ substituents violated configurational entropy. This led to lattice distortion and triggered structural rearrangements. The radial fluctuation of the Ga and Al elements was proven by multi-elemental energy-dispersive X-ray spectroscopy mapping and elemental composition analysis. Further evidence was observed by the shift of the exciton creation energy toward higher energy in the vacuum ultraviolet excitation spectra recorded with synchrotron radiation. In the Li+ and Mg2+ co-doped samples, the crystal core was depleted with Ga atoms and enriched with Al elements. The crystal rim showed the opposite behavior. The change in thermoluminescence peak positions revealed a different mechanism for the formation of localized traps. As a result, Li+ co-doping slightly improved the light yield value, but at the same time decelerated the scintillation decay time. On the contrary, Mg2+ co-doping markedly diminished scintillation parameters.

A portable diagnostic system for the quantification of VUV fluxes emitted from low-temperature plasmas

Vacuum-ultraviolet (VUV) spectroscopy is linked to a huge effort, in particular if absolute numbers are required. To overcome this, a flexible device is developed based on a photodiode and optical filters for wavelength selection. Characterization of the diagnostic is performed against a VUV spectrometer that is radiometrically calibrated down to 46 nm. In the first instance, the latter is used for an analysis of VUV spectra of inductively coupled low-temperature plasmas for a variety of discharge gases and mixtures. The measured photon fluxes can easily have comparable magnitude as the occurring ion flux, and it is demonstrated that the photonic energy distribution can change drastically with varying external parameters (pressure, RF power). This highlights the need for energy resolution for VUV flux detection and a set of ten optical filters was selected for the VUV diode system according to the respective prominent emission ranges of typical discharge gases for plasma processing. Recommended filter combinations for each of the discharge gases and mixtures are given. The developed diagnostic is calibrated in-house against the VUV spectrometer, which makes energy-resolved absolute VUV flux measurements up to photon energies of 27 eV possible. The calibration is performed individually for all the investigated discharge gases and the corresponding filter combinations, and an accuracy of better than 25% compared to the VUV spectrometer is attested for the investigated parameter space (0.3–10 Pa, 200–1100 W RF power). Its applicability is demonstrated by measuring VUV fluxes at two further low-temperature plasma setups.

Excitation and fragmentation of the dielectric gas C4F7N: Electrons vs photons.

C4F7N is a promising candidate for the replacement of sulfur hexafluoride as an insulating medium, and it is important to understand the chemical changes initiated in the molecule by collision with free electrons, specifically the formation of neutral fragments. The first step of neutral fragmentation is electronic excitation, yet neither the absorption spectrum in the vacuum ultraviolet (VUV) region nor the electron energy loss spectrum have previously been reported. Here, we experimentally probed the excited states by VUV photoabsorption spectroscopy and electron energy loss spectroscopy (EELS). We found that the distribution of states populated upon electron impact with low-energy electrons is significantly different from that following photoabsorption. This difference was confirmed and interpreted with ab initio modeling of both VUV and EELS spectra. We propose here a new computational protocol for the simulation of EELS spectra combining the Born approximation with approximate forms of correlated wave functions, which allows us to calculate the (usually very expensive) scattering cross sections at a cost similar to the calculation of oscillator strengths. Finally, we perform semi-classical non-adiabatic dynamics simulations to investigate the possible neutral fragments of the molecule formed through electron-induced neutral dissociation. We show that the product distribution is highly non-statistical.

Electronically excited states of formic acid investigated by theoretical and experimental methods

Absolute cross-section values are reported from high-resolution vacuum ultraviolet (VUV) photoabsorption measurements of gas-phase formic acid (HCOOH) in the photon energy range 4.7–10.8 eV (265–115 nm), together with quantum chemical calculations to provide vertical energies and oscillator strengths. The combination of experimental and theoretical methods has allowed a comprehensive assignment of the electronic transitions. The VUV spectrum reveals various vibronic features not previously reported in the literature, notably associated with (3pa′←10a′), (3p′a′←10a′), (3sa′←2a″) and (3pa′←2a″) Rydberg transitions. The assignment of vibrational features in the absorption bands reveal that the C=O stretching, v3′a′, the H′–O–C′ deformation, v5′a′, the C–O stretching, v6′a′, and the O=C–O′ deformation, v7′a′ modes are mainly active. The measured absolute photoabsorption cross sections have also been used to estimate the photolysis lifetime of HCOOH in the upper stratosphere (30–50 km), showing that solar photolysis is an important sink at altitudes above 30 km but not in the troposphere. Potential energy curves for the lowest-lying electronic excited states, as a function of the C=O coordinate, are obtained employing time dependent density functional theory (TD-DFT). These calculations have shown the relevance of internal conversion from Rydberg to valence character governing the nuclear dynamics, yielding clear evidence of the rather complex multidimensional nature of the potential energy surfaces involved.

Soliton dynamics in a piecewise gas-filled hollow-core fiber for efficient dispersive wave emission in the vacuum-ultraviolet range

Table-top coherent vacuum-ultraviolet (VUV) sources are important in many researches. Dispersive wave (DW) emission in a gas-filled hollow-core fiber (HCF) is an efficient way to obtain tunable VUV source with microjoule-level pulse energy. However, the shortest VUV wavelength is limited above 110 nm. This work investigated a method using a piecewise HCF in order to push the shortest VUV DW emission below 110 nm efficiently. The rich and complex spatiotemporal soliton dynamics in the HCF is revealed through rigorous numerical simulations and quantitative analysis. It is found that both the generation of VUV light below 110 nm and the overall conversion efficiencies below 150 nm can be significantly improved if the piecewise gas-filled HCF system is properly designed. As a result, the whole VUV spectrum (200--100 nm) can now be accessed efficiently, with single pulse energy of microjoule level. Different from other widely used intense VUV sources, this source has broad spectrum along with femtosecond time width. These unique characteristics in the VUV spectrum can lead to new research opportunities in various areas.