VUV Beamline Research Articles

DESIRS : a state-of-the-art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL

DESIRS is a new undulator-based VUV beamline at SOLEIL (France) optimized for the study of gas phase matter in the 5-40 eV range. It is equipped with two dedicated endstations: a VUV Fourier-Transform Spectrometer (FTS) for ultra-high resolution absorption spectroscopy (resolving power up to 106) and an electron/ion imaging coincidence spectrometer. The photon source is a 10 m-long pure electromagnetic variable polarization undulator providing, at the sample location, fully calibrated quasi-perfect horizontal, vertical and circular polarizations. The optical design includes a beam waist allowing the implementation of a gas filter to suppress the undulator higher harmonics. The 6.65 m Eagle off-plane Normal Incidence Monochromator equipped with four gratings allows the tuning of the flux-to-resolution trade-off. Measured ultimate instrumental resolving powers are 124000 (174 μeV) around 21 eV and 250000 (54 μeV) around 13 eV, while the typical measured flux is in the 1010−1011 ph/sec range in a 1/50000 bandwidth and 1012-1013 ph/sec in a 1/1000 bandwidth.

A robust link between the thermochemistry of urea and isocyanic acid by dissociative photoionization

Dissociative photoionization reactions of internal energy selected urea cations were studied by vacuum ultraviolet threshold photoionization at the imaging photoelectron photoion coincidence (iPEPICO) endstation of the VUV beamline at the Swiss Light Source. An accurate T=0K appearance energy could be determined for the lowest energy channel, the formation of isocyanic acid (HNCO) and ammonia cation (NH3+). This process is analogous to the thermolysis of urea in selective catalytic reduction (SCR) for which ΔrHo0K=(62.9±1.0)kJ·mol−1 is derived. The next higher energy channel leading to H2NCO+ and NH2 is also discussed. The parent ion was found to dissociative quickly to HNCO+NH3+ even at threshold, indicating a loose transition state. The potential energy surface of a roaming H atom around the urea core shows lower H-transfer barriers in the cation than in the neutral molecule, and the measured dissociative photoionization energy is lower than expected based on the literature enthalpies of formation. Consequently, the threshold for HNCO loss corresponds to the dissociative photoionization energy and not to a prior H-transfer barrier. A significant, 5.1kJ·mol−1 discrepancy between the dissociation energy and the reaction energy calculated with the latest published values of the enthalpy of formation warrants a revision of the urea and isocyanic acid thermochemistry. This discrepancy is assigned to enthalpies of formation with the help of W1 and CBS-APNO ab initio calculations. The isocyanic acid enthalpy of formation at T=0K and that of gas phase urea at T=298K are, thus, revised to ΔfHo0K(HNCO, g)=–(116.2±1.4)kJ·mol−1 and ΔfHo298K(CO(NH2)2, g)=–(235.7±1.4)kJ·mol−1, respectively.

A new UV and VUV beamline for angular resolved photoemission with high resolution and at low energy

A new 5-m normal-incidence monochromator at the third generation synchrotron source BESSY II of the Helmholz-Zentrum Berlin (HZB) has been constructed with the emphasis on angle-resolved photoelectron spectroscopy with high-resolution and at low energy utilizing photons from 5eV to 40eV. Optical design and preliminary performance results of the beamline and the photoemission endstation are presented and match the design goals.

DESIRS: a state-of-the-art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL

DESIRS is a new undulator-based VUV beamline on the 2.75 GeV storage ring SOLEIL (France) optimized for gas-phase studies of molecular and electronic structures, reactivity and polarization-dependent photodynamics on model or actual systems encountered in the universe, atmosphere and biosphere. It is equipped with two dedicated endstations: a VUV Fourier-transform spectrometer (FTS) for ultra-high-resolution absorption spectroscopy (resolving power up to 10(6)) and an electron/ion imaging coincidence spectrometer. The photon characteristics necessary to fulfill its scientific mission are: high flux in the 5-40 eV range, high spectral purity, high resolution, and variable and well calibrated polarizations. The photon source is a 10 m-long pure electromagnetic variable-polarization undulator producing light from the very near UV up to 40 eV on the fundamental emission with tailored elliptical polarization allowing fully calibrated quasi-perfect horizontal, vertical and circular polarizations, as measured with an in situ VUV polarimeter with absolute polarization rates close to unity, to be obtained at the sample location. The optical design includes a beam waist allowing the implementation of a gas filter to suppress the undulator high harmonics. This harmonic-free radiation can be steered toward the FTS for absorption experiments, or go through a highly efficient pre-focusing optical system, based on a toroidal mirror and a reflective corrector plate similar to a Schmidt plate. The synchrotron radiation then enters a 6.65 m Eagle off-plane normal-incidence monochromator equipped with four gratings with different groove densities, from 200 to 4300 lines mm(-1), allowing the flux-to-resolution trade-off to be smoothly adjusted. The measured ultimate instrumental resolving powers are 124000 (174 µeV) around 21 eV and 250000 (54 µeV) around 13 eV, while the typical measured flux is in the 10(10)-10(11) photons s(-1) range in a 1/50000 bandwidth, and 10(12)-10(13) photons s(-1) in a 1/1000 bandwidth, which is very satisfactory although slightly below optical simulations. All of these features make DESIRS a state-of-the-art VUV beamline for spectroscopy and dichroism open to a broad scientific community.

Photochemistry simulation of planetary atmosphere using synchrotron radiation at soleil. Application to Titan’s atmosphere

We report here on the coupling of a gas reactor with a VUV beamline at the SOLEIL synchrotron radiation facility. The reactor may be irradiated window-less with gas pressure up to the atmosphere. The photochemistry is monitored by a mass spectrometer gas analyzer. This set up, termed APSIS for Atmospheric Photochemistry SImulated by Synchrotron, has been used to simulate the atmosphere of Titan and to study the formation of the photochemical smog and the formation of tholins.

Status of the Center for Advanced Microstructures and Devices (CAMD)—2010

The J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices (CAMD) is a 1.3 GeV synchrotron-radiation facility owned and operated by the State of Louisiana. Fifteen beamlines provide radiation for CAMD users and cover the spectral range from the far IR to X-rays of ca. 40 keV. Eleven of them receive radiation from bending magnets and four from a 7 T wavelength shifter. A wide range of basic and applied scientific experiments as well as microfabrication are performed at these beamlines. The nanomaterial synthesis and characterization laboratory at CAMD continues to add new instruments such as SQUID magnetometer (Quantum Deign MPMS XL5) and high precision microfluidic-based nanomaterials synthesis equipment complementing already available facilities. We have recently received NSF MRI funding for a multipole 7.5 T wiggler that will become operational in 2012. Generous equipment donations from the University of California at Riverside (Professor Jory Yarmoff) and the University of Bonn (ELSA facility) will provide users with two additional VUV beamlines in the near future.

Absorption cross section of molecular oxygen in the transition E3Σu-v= 0 – X3Σg-v= 0 at 38 K

Aims. This investigation was undertaken to determine the absorption cross sections of oxygen in the VUV region at temperatures <50 K. Methods. The absorption spectra of gaseous samples cooled with a slit jet and near 300 K were measured with the same absorption system coupled to the VUV beam line of a synchrotron. Results. The maximum absorption cross section for the transition from X 3 Σ − v = 0 to state E 3 Σ − v = 0f or 16 O2 at 38 K was determined to be 98.7 Mb (or 9.87 × 10 −18 cm 2 ). The value of this maximum absorption cross section at 38 K is 1.7 times the value at 303.7 K.

Dissociation Dynamics of Energy Selected, Propane, and i-C3H7X+ Ions by iPEPICO: Accurate Heats of Formation of i-C3H7+, i-C3H7Cl, i-C3H7Br, and i-C3H7I

The dissociation dynamics of energy selected i-C(3)H(7)X (X = H, Cl, Br, and I) ions have been investigated by imaging photoelectron-photoion coincidence (iPEPICO) spectroscopy using synchrotron radiation from the X04DB VUV beamline in the Swiss Light Source of the Paul Scherrer Institut. The 0 K dissociation energy (E(0)) for i-C(3)H(8) was determined to be 11.624 ± 0.002 eV. This leads to a 298 K isopropyl ion heat of formation of 805.9 ± 0.5 kJ mol(-1). The Δ(f)H(298K)°(i-C(3)H(7)(+)) combined with the measured 0 K onsets for i-C(3)H(7)(+) formation from isopropyl chloride (11.065 ± 0.004 eV), isopropyl bromide (10.454 ± 0.008 eV), and isopropyl iodide (9.812 ± 0.008 eV) yields the 298 K isopropyl chloride, bromide, and iodide heats of formation of -145.7 ± 0.7, -95.6 ± 0.9, and -38.5 ± 0.9 kJ mol(-1), respectively. These values provide a significant correction to literature values and reduce the error limits. Finally, the new i-C(3)H(7)(+) heat of formation leads to a predicted adiabatic ionization energy for the isopropyl radical of 7.430 ± 0.012 eV and a 298 K proton affinity for propene of 744.1 ± 0.8 kJ mol(-1).

Spectral response measurement of FUV image intensifier

It is possible to obtain some space weather parameters such as the electron flux and mean energy of the precipitating electrons from the far ultraviolet (FUV) radiance of the aurora observed in a nadir viewing geometry, and the FUV image intensifier is one of the key equipment that used for observation the FUV radiance of the aurora in a nadir viewing geometry. The capability of this equipment will affect the whole purpose of the detection. And the responsibility to the wavelength is the most important parameter of image intensifier. Using the VUV beamline f rom synchrotron radiation as optical source, with PMT and Si-photodiode to detect the optical signal from synchrotron radiation and image intensifier separately, the authors measured the relatively spectral response distribution of our FUV image intensifier from 135 to 250 nm. The measurement result shows that the equipment can work well between 140 and 190 nm and the peak response is near 160 nm, and it can be used for our FUV aurora camera.

High-resolution photoemission study of organic systems at the CAMD 3 m NIM beamline

The 3 m normal incidence monochromator (NIM) VUV beamline at CAMD was designed for novel high-resolution photoemission experiments. Both solid-state samples and gas phase resolution tests demonstrate that high-resolution photoemission is possible below 10 meV, and vibronic fine structure in the photoemission final state from the crystalline copolymer poly-vinylidenefluoride with trifluoroethylene can be observed: the first direct experimental identification of symmetry dependence in electron–phonon coupling in photoemission from a solid-state system.

Optimization of the 3 m TGM beamline, at CAMD, for constant initial state spectroscopy

The 3 m toroidal grating monochromator (TGM) VUV beamline at CAMD/LSU was realigned to achieve better illumination of the monochromator gratings with the goal of substantially increasing the flux at the higher photon energies. This is partly accomplished through a tilting of the monochromator (by about of 13.5°), with respect to the plane defined by the synchrotron, providing a smaller grazing angle at the initial mirrors. The improved performance of the beamline permits resonant photoemission studies at Gd 4d core threshold without resorting to second order light, which we demonstrate for Gd doped HfO 2.

An energy-dispersive VUV beamline for NEXAFS and other CFS/CIS studies

By combining the photon energy dispersion of a plane-grating XUV monochromator with the imaging properties of a hemispherical electron energy analyzer, energy-dispersive electron spectroscopy is possible. This multiplex technique allows the utilization of various electron spectroscopies, such as near-edge X-ray absorption (NEXAFS), photoemission (XPS) and Auger/autoionization spectroscopy, without time-consuming scanning of the photon energy. Thus, changes on short time scales may be monitored with full spectroscopic information. We present the design for an upgrade of the existing BESSY UE52-PGM beamline and the results of a pilot energy-dispersive experiment on condensed C 60 molecules.

New approach to monitoring photon beam using visible light on VUV beamlines of compact storage ring HiSOR

A simple method to monitor the motion of photon beams using the visible component of synchrotron radiation (SR) is proposed, in which visible SR diagnostics are effectively extended. A preliminary test of the measurement principle was performed. We obtained a reasonable position response from photon beam fluctuation due to electron beam instability. With the aim of beam monitoring in user's beamlines of small storage rings, we discuss appropriate monitor assembly along with the advantages of the extension of visible diagnostics because the conventional photo–current method in VUV and X-ray regions is not applicable at the beamlines.

Quantum cutting in Gd2SiO5︰Eu3+ by VUV excitation

The emission and excitation spectra of Gd2SiO5 : Eu3+ were investigated using the VUV beam line of the Beijing Synchrotron Radiation Facility (BSRF). The experimental results were discussed in the frame of visible quantum cutting process involved in Gd3+ -Eu3+ system. Upon direct excitation into the (6)G(J) states of Gd3+, two visible photon emissions from Eu3+ were observed. Cursory evaluation proved that Gd2SiO5 : Eu3+ is an efficient visible quantum cutter.

Beamlines at Siam photon laboratory

This report provides the up-to-date information on the present and future beamlines at the Siam Photon Laboratory. The first two beamlines, BL-4 and BL-6, have already been installed, and are now in commissioning. BL-4 is a VUV beamline to be used for investigating the electronic structures of solids and solid surfaces using the angle-resolved photoemission experimental technique. BL-6 is a beamline for electron beam monitoring. Future beamlines utilizing synchrotron light generated by a planar undulator and a superconducting magnet wiggler are discussed.

Automated angle-scanning photoemission end-station with molecular beam epitaxy at KEK-PF BL-1C

In order to satisfy demands to study the electronic structure of quantum nanostructures, a VUV beamline and a high-resolution and high-throughput photoemission end-station combined with a molecular beam epitaxy (MBE) system have been constructed at the BL-1C of the Photon Factory. An angle-resolved photoemission spectrometer, having high energy- and angular-resolutions; VG Microtech ARUPS10, was installed. The total energy resolution of 31 meV at the 60 eV of photon energy is achieved. For the automated angle-scanning photoemission, the electron spectrometer mounted on a two-axis goniometer can be rotated in vacuum by the computer-controlled stepping motors. Another distinctive feature of this end-station is a connection to a MBE chamber in ultahigh vacuum (UHV). In this system, MBE-grown samples can be transferred into the photoemission chamber without breaking UHV. Photoemission spectra of MBE-grown GaAs(0 0 1) surfaces were measured with high-resolution and bulk and surface components are clearly resolved.

Complete characterization of SU5:: a VUV high resolution beamline with variable polarizations

The SU5 VUV beamline aims towards a dual scientific program: high resolution spectroscopy on dilute targets and linear/circular dichroism on anisotropic systems. A crossed planar/helicoidal electromagnetic undulator has been designed and built, providing both flux and variable polarizations. We have shown a complete versatility of the polarization state of the emitted light with high polarization rates. Besides, the harmonics of the undulator can be suppressed owing to a gas filter, acting as a low-energy pass filter, with rejection factors above 10 5. The beamline is centered around a 6.65 m off-plane Eagle normal incidence monochromator which has shown unprecedented raw resolving powers (117 000 at 21.6 eV, 133 000 at 15.8 eV) with typical flux in a 1/50 000 bandwidth of 10 10–10 9 photons/s between 6 and 30 eV.

NEXAFS multiple scattering calculations of KO2.

Since many years the oxidation of alkali metals has being attracted much interest due to the catalytic properties of metal promoters and the simple electronic structure of alkali atoms. The alkali-oxides phase diagram indicates that the interaction of oxygen with alkali metals can lead to the formation of different atomic O2- ions and molecular O2(-) and O(2)2- ions. Potassium superoxide has been prepared in situ and high resolution O k-edge absorption NEXAFS spectra have been measured at the VUV beam-line at ELETTRA facility. The experimental data have been analyzed by multiple scattering approach deriving many geometrical and electronic details. In particular, we have found that the growth material structure is of the KO2 type with an O-O distance of about 1.35A and that the transition involving single pi molecular empty state of the superoxide O2(-) anion has a fine structure. Multiple Scattering self consistent calculation indicates that the bond between oxygen anion and K atom is totally ionic and that the fine structure is essentially due to solid state effects.

Applications of UV-storage ring free electron lasers: the case of super-ACO

The potential of UV-storage ring free electron lasers (SRFELs) for the performance of original application experiments is shown with a special emphasis concerning their combination with the naturally synchronized synchrotron radiation (SR). The first two-color FEL+SR experiment, performed in surface science at Super-ACO is reported. The experimental parameters found to be the most important as gathered from the acquired experience, are underlined and discussed. Finally, future prospects for the scientific program of the Super-ACO FEL are presented with two-color experiments combining the FEL with SR undulator-based XUV and VUV beamlines as well as with a SR white light bending magnet beamline emiting in the IR-UV ( 20 μm – 0.25 μm) .

A plasma light source for the VUV spectral region

The 5-50-eV spectral range appears to be absent from the planned third generation synchrotron radiation sources (SRS) and the science requiring this radiation can be jeopardized once the second generation SRS light sources are switched off worldwide. Molecular photochemistry, photobiology, atomic physics, solid-state physics are but a few sciences requiring powerful VUV sources. We demonstrate that a compact, laser heated plasma light source can generate efficiently radiation in this spectral region, and that this radiation can be coupled very efficiently from the plasma to the exposure cell, by three simple VUV beam-lines, each providing a different spectral bandwidth.