Vacuum Ultraviolet Spectral Range Research Articles

New infrared undulator beamline at FLASH

At the vacuum ultraviolet (VUV) free electron laser in Hamburg (FLASH) an infrared (IR) beamline is being built to allow novel pump-and-probe experiments combining coherent IR pulses with the FEL radiation in the VUV spectral range. It will provide useful IR radiation generated by a purpose built undulator over the wavelength range from 200μm to 10μm and possibly even shorter. The commissioning of the beamline has started this summer and first light will be delivered to the experimental hall by autumn 2007. Another important application of the beamline will be electron diagnostics of the longitudinal charge distribution of the electron bunches.

Photochemical processes in doped argon-neon core-shell clusters: The effect of cage size on the dissociation of molecular oxygen

The caging effect of the host environment on photochemical reactions of molecular oxygen is investigated using monochromatic synchrotron radiation and spectrally resolved fluorescence. Oxygen doped clusters are formed by coexpansion of argon and oxygen, by pickup of molecular oxygen or by multiple pickup of argon and oxygen by neon clusters. Sequential pickup provides radially ordered core-shell structures in which a central oxygen molecule is surrounded by argon layers of variable thickness inside large neon clusters. Pure argon and core-shell argon-neon clusters excited with approximately 12 eV monochromatic synchrotron radiation show strong fluorescence in the vacuum ultraviolet (vuv) spectral range. When the clusters are doped with O2, fluorescence in the visible (vis) spectral range is observed and the vuv radiation is found to be quenched. Energy-resolved vis fluorescence spectra show the 2 1Sigma+-->1 1Sigma+(ArO(1S)-->ArO(1D)) transition from argon oxide as well as the vibrational progression A '3Delta u(nu'=0)-->X 3Sigmag*(nu") of O2 indicating that molecular oxygen dissociates and occasionally recombines depending on the experimental conditions. Both the emission from ArO and O2 as well the vuv quenching by oxygen are found to depend on the excitation energy, providing evidence that the energy transfer from the photoexcited cluster to the embedded oxygen proceeds via the O2+ ground state. The O2+ decays via dissociative recombination and either reacts with Ar resulting in electronically excited ArO or it recombines to O2 within the Ar cage. Variation of the Ar layer thickness in O2-Ar-Ne core-shell clusters shows that a stable cage is formed by two solvation layers.

Vacuum-ultraviolet spectroscopy measurement of poly(methylphenylsilylene) photosensitivity

Photoinduced optical absorption changes in the vacuum-ultraviolet (VUV) spectral range have been measured in poly(methylphenylsilylene) thin films under varied excitation photon energies and local atmospheric environments. Spectral changes in resonances associated with both the linear chain Si–Si backbone and the side groups of the hybrid structure are consistent with the photodisruption of backbone topology. These effects are more pronounced under a higher energy photon exposure (5.10eV) resonant with the fundamental π-π* transition of the phenyl moiety. An aerobic environment also favors more dramatic bleaching of VUV absorption in these materials. Finally, the present study enables a Kramers-Kronig analysis of absorption change from the visible to the VUV. These results do not adequately describe the photoinduced refractive index changes measured at 632.8nm via ellipsometry, indicating the presence of other contributions to the index modifications observed.

A windowless VUV excilamp

An open windowless excilamp capable of operating on argon (λ ∼ 126 nm), krypton (∼146 nm), and xenon (∼172 nm) dimers is described. The lamp has a total radiating surface area of 23 × 23 = 529 cm2. At a total power of ∼0.8 W radiated through this area, the average output power density at λ ∼ 126 nm is ∼1.6 mW/cm2 at a distance of 2 cm from the emitting surface. A pulsed discharge between insulator-coated anode and thin wire cathode ensures a high efficiency of the proposed radiation source operating in the vacuum ultraviolet spectral range.

A high-power xenon dimer excilamp

A high-power sealed-off excilamp operating on xenon dimers excited by a barrier discharge and emitting in the vacuum ultraviolet spectral range (λ ∼ 172 nm) has been designed, constructed, and tested. The lamp comprises six quartz tubes (emitters) and has a total radiating surface area of 20 × 20 = 400 cm2. The average output power density radiated from the surface of each emitter exceeds 120 mW/cm2. The total output power of the excilamp immediately upon discharge ignition exceeds 50 W.

Highly reflecting aluminum-protected optical coatings for the vacuum-ultraviolet spectral range

We discuss the approaches to preserve the high-reflectance aluminum mirror for the vacuum-ultraviolet spectral region. Single fluoride and oxide layers, a homogeneous multilayer, and hybrid multilayer solutions are put forward. Single fluoride and oxide materials have achieved reflectance above 90% at 193 nm. Multilayer capping can provide reflectance of 93.4% at 193 nm, and a hybrid multilayer of fluoride and oxide can achieve reflectance above 90% to 160 nm.

Ellipsometry from infrared to vacuum ultraviolet: Structural properties of thin anisotropic guanine films on silicon

AbstractBio‐molecular films of the DNA base guanine were characterized by ellipsometry from the Infrared (IR) to Vacuum Ultraviolet (VUV) spectral range, X‐ray diffraction (XRD) and atomic force microscopy (AFM). In this study we in particular focus on the contact‐less and reference‐free characterization of thin anisotropic bio‐molecular films by ellipsometry. Ellipsometric spectra in the IR as well as in the UV–VUV spectral range are molecule specific and the absorption bands could be used to identify molecules deposited on a substrate, since both the vibrational and electronic excitations are molecule specific. Especially we demonstrate that the measured pseudo‐dielectric function in the mid infrared (MIR) spectral range can be used as a characteristic “fingerprint” for DNA base molecules and their orientation in a thin film. Moreover an interpretation of the ellipsometric spectra in an optical model delivers the dielectric function and could give information about the molecular structure, orientation and conductivity. The determination of average molecular orientations from IR and UV/VUV ellipsometry spectra is discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental Investigation of the Reflectivity of Refractory Dielectric Materials in the Vacuum Ultraviolet Spectral Region

The paper deals with the results of experimental investigation of spectrally averaged group reflectivities R(Δλ) in a vacuum ultraviolet (hν ∼ 10 to 70 eV) spectral range of commercial samples of high-temperature dielectric materials (α-Al2O3, SiO2, BNC) under conditions of a prethreshold (prior to the beginning of developed surface evaporation) power density of probing radiation.

Optical phonon modes and interband transitions in cubicAlxGa1−xNfilms

We present a comprehensive study of the phonon mode behavior and the optical interband transitions of cubic ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ films $(0<~x<~0.20)$ using spectroscopic ellipsometry from the midinfrared to the vacuum-ultraviolet spectral range (0.05--8.5 eV). The $\ensuremath{\approx}0.5\ensuremath{-}\ensuremath{\mu}\mathrm{m}$-thick ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ layers were grown by radio-frequency plasma-assisted molecular-beam epitaxy and possess free-electron concentrations in the range of $6\ifmmode\times\else\texttimes\fi{}{10}^{19}--1\ifmmode\times\else\texttimes\fi{}{10}^{20} {\mathrm{cm}}^{\ensuremath{-}3}.$ A two-mode behavior for the transverse-optical phonon of ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ is observed, which is consistent with theoretical predictions. Due to the high free-electron concentration, the observed ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ fundamental band-gap energy ${E}_{0}$ is subject to a strong Burstein-Moss shift and band-gap renormalization. We quantify the amount of both band-gap shifting mechanisms, and provide an estimate for the composition dependence of the ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ band-gap energy ${E}_{0},$ which depends approximately linearly on the alloy composition with ${E}_{0} (\mathrm{eV})=3.19+2.77x$ at room temperature and for carrier-depleted material. For cubic GaN, the L-point interband transition ${E}_{1}$ shifts to lower energies with increasing free-electron concentration, whereas the interband transition ${E}_{2}$ remains unshifted. Increasing Al content induces a blueshift (redshift) of the ${E}_{1}$ ${(E}_{2})$ transition of ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ for $x<~0.12.$ Due to strong broadening effects, both transitions cannot be differentiated anymore for $x>~0.16.$

Topography of an electron cyclotron resonance plasma in the vacuum-ultraviolet spectral range

The plasma topography of the vacuum-ultraviolet (VUV) radiation source ELISA (electron cyclotron resonance light source assembly) was investigated. ELISA is operated at a VUV spectrometer which allows two-dimensional images of the axially observable plasma shape to be taken with a spatial resolution of 150 μm in the spectral range from 40 to 400 nm. The VUV radiance profile of the electron cyclotron resonance plasma was investigated for different working conditions of the source, with the source operated with nitrogen and krypton. Under specific operating conditions, the observed plasma radiance profile shows a structure similar to calculations performed by the group of Andrä. It was shown for the first time that the plasma topography can be interpreted by an electron density distribution as simulated there for a monomode electron cyclotron resonance ion source.

High Energetic Transitions in Pr3 + -Doped Polycrystalline LiCaAlF6 and LiSrAlF6

-doped and polycrystalline samples were prepared and investigated by means of high energetic excitation with synchrotron radiation. In the emission spectra, bands due to the intraconfigurational transitions were observed. Simultaneously observed emission bands due to transitions in and are assigned to residual phases of and respectively, in the samples. In the excitation spectra in the ultraviolet to vacuum-ultraviolet spectral range weak lines due to the transition as well as strong broad bands due to the parity- and spin-allowed interconfigurational transitions are observed. © 2001 The Electrochemical Society. All rights reserved.

Analysis of biodiesel by argon–oxygen mixed-gas inductively coupled plasma optical emission spectrometry

The determination of Ca, Cl, K, Mg, Na and P in biodiesel samples by ICP optical emission spectrometry was investigated using a new ICP spectrometer with CCD detectors and radial plasma viewing. Prior to analysis the samples were diluted 1∶4 (m/m) with kerosene. The effect of added oxygen to the intermediate gas, outer gas and nebulizer gas was studied. An overall increase of the signal to background ratios for Na I 588.995 nm, Na I 589.592 and K I 766.490 nm was observed due to reduced background emission of carbon and carbon compounds when oxygen was added. The addition of 0.35 l min−1 oxygen and 0.8 l min−1 argon to the nebulizer gas flow was found to be the most efficient in order to improve the detection limits for Na and K. The application of this cold argon–oxygen plasma enables Na and K determination at µg kg−1 concentrations in biodiesel. The limits of detection for Na I 588.995 nm, Na I 589.592 nm and K I 766.490 nm after the dilution of biodiesel with kerosene are 1.6, 1.4 and 7.1 µg kg−1, respectively, compared with 59, 74 and 220 µg kg−1, respectively, calculated for typical ICP operating conditions. The determination of environmentally relevant organic chlorine at low mg kg−1 levels is possible using the intense spectral lines in the vacuum ultraviolet spectral range at 134.724 or 135.166 nm. Limits of detection for these lines are 0.4 and 0.9 mg kg−1, respectively, after sample dilution as described above.

Phonon Modes and Critical Points of GaPN

Spectroscopic ellipsometry in the mid-infrared and near-infrared to vacuum-ultra violet spectral range is employed to study the phonon properties and critical points of a GaP 0.977 N 0.023 layer grown on GaP. We observe a two-mode phonon behaviour, i.e., a GaN-like and a GaP-like phonon. We detect six critical-point structures, which we assign as E dir 0 , E' 0 , E 1 , E' 1 , E 1 2 and E 2 2 transitions. We observe a blueshift of the direct band gap E dir 0 and of the E 1 transition in contrast to the redshift of the photoluminescence peak and the absorption tail, which we observed on the same sample. The critical-point energies Eg, E' 1 , and E 2 do not show any significant composition dependence.

Application of prominent spectral lines in the 125-180 nm range for inductively coupled plasma optical emission spectrometry.

A new axially viewed ICP optical emission spectrometer featuring an argon-filled optic and CCD detectors was evaluated for the application of prominent spectral lines in the 125-180 nm range. This wavelength range was investigated for several analytical applications of inductively coupled plasma optical emission spectrometry (ICP-OES). There are different advantages for the application of spectral lines below 180 nm. A number of elements, such as Al, Br, Cl, Ga, Ge, I, In, N, P, Pb, Pt, S and Te, were found to have the most intense spectral lines in the wavelength range from 125-180 nm. Compared with lines above 180 nm higher signal-to-background ratios were found. Low limits of detection using pneumatic nebulization of aqueous solutions for sample introduction were calculated for Al II 167.080 nm (0.04 microg L(-1)), Br I 154.065 nm (9 microg L(-1)), Cl I 134.724 nm (19 microg L(-1)), Ga II 141.444 nm (0.8 microg L(-1)), Ge II 164.919 nm (1.3 microg L(-1)), II 142.549 nm (13 microg L(-1)), In II 158.583 nm (0.2 microg L(-1)), P I 177.500 nm (0.9 microg L(-1)), Pb II 168.215 nm (1.5 microg L(-1)), Pt II 177.709 nm (2.6 microg L(-1)), S I 180.731 nm (1.9 microg L(-1)) and Te I 170.00 nm (4.6 microg L(-1)). Numerous application examples for the use of those lines and other important spectral lines below 180 nm are given. Because of fewer emission lines from transition elements, such as Fe, Co, Cr, lines below 180 nm often offer freedom from spectral interferences. Additional lines of lower intensity for the determination of higher elemental concentrations are also available in the vacuum ultraviolet spectral range. This is specially useful when the concentrations are not in the linear range of calibration curves obtained with commonly used lines.

Applications of ICP-OES with a New Argon-Filled CCD Spectrometer Using Spectral Lines in the Vacuum Ultraviolet Spectral Range

It is shown that the use of analytical lines in the spectral range between 125 and 195 nm opens new analytical possibilities for inductively coupled plasma optical emission spectrometry (ICP-OES). Prominent emission lines in the vacuum ultraviolet (VUV) spectral region were used for different analytical applications with a new ICP optical emission spectrometer with charge-coupled device detectors (CCDs). These applications include the determination of Cl and S in organic samples (oil and gasoline), the determination of Al, Br, I, and P in high-saline 200 g/L NaCl solutions, and the determination of Pb, Sn, and In in highly pure 99.9% (m/m) Pd and Pt. The superiority of the VUV emission lines of Al 167, Br 148, Cl 134, Cl 135, Ga 141, I 161, In 158, P 177, Pb 168, Sn 140, and Sn 147 nm in these applications with respect to power of detection and freedom from spectral interferences is shown. The limits of detection (LODs) are tabulated for a series of further elements with prominent spectral lines in the 125–195 nm range using pneumatic nebulization of aqueous solutions for sample introduction. These results are compared with those for lines above 195 nm. In some cases VUV lines are superior to commonly used lines; for example, calculated LODs for Al(II) 167.080 nm, In(II) 158.637 nm, and Ga(II) 141.444 nm are 0.07, 0.2, and 0.8 μg/L, respectively, compared to 1.1, 7.1, and 5.9 μg/L for Al(I) 396.152, In(I) 230.606, and Ga I 417.204 nm, respectively. In other cases LODs in the μg/L range are possible only with VUV lines, such as for Cl(I) 134.724 or Br(I) 154.065 nm.

VUV spectroscopy of a new fluoride system NaF–(Er,Y)F3

Abstract Emission and excitation spectra as well as luminescence decay kinetics of a new complex fluoride system Na 0.4 (Y 1− x Er x ) 0.6 F 2.2 ( x =0.01, 0.1, 1) have been studied in the vacuum ultraviolet (VUV) spectral range. It has been shown that these crystals have intense VUV luminescence due to the interconfiguration 5d–4f transitions in Er 3+ ion. The spin-allowed 5d–4f luminescence of Er 3+ in this system is very weak, i.e., in these crystals there exists an efficient non-radiative relaxation from higher-lying 5d states of Er 3+ to the lowest 5d level responsible for spin-forbidden luminescence. This makes the studied new fluoride system a promising active medium for the production of VUV solid state laser with optical pumping. Due to rather large bandwidth of Er 3+ 5d–4f luminescence in this system there is a possibility for the construction of tuneable VUV laser.

New developments in the radiance calibration of deuterium lamps in the UV and VUV spectral range at the PTB

The Physikalisch-Technische Bundesanstalt (PTB) operates a unique beam line for the radiometric calibration of ultraviolet (UV) and vacuum-ultraviolet (VUV) radiation sources by direct comparison of their unknown spectral radiant flux with the calculable spectral radiant flux of the electron storage ring BESSY I in the spectral range 40 nm to 400 nm. At this beam line the relative standard uncertainty of the calculated spectral radiant flux of the synchrotron radiation is u = 3 × 10−3 and it allows the calibration of the spectral radiance of deuterium lamps with a relative standard uncertainty of 2.5 × 10−2 above 165 nm. The high-accuracy beam line is now complemented by new instrumentation specially designed for the dissemination of the spectral radiance and radiant intensity scale using deuterium lamps as transfer source standards. This instrumentation allows the calibration of radiation sources in the 115 nm to 400 nm spectral range without significant loss in accuracy and the measurement of spectrally and spatially resolved radiance profiles such as to image the plasma topography of the discharge. The new instrumentation is described. Results for the radiometric long-term stability of selected deuterium lamps are shown. The radiance and radiant intensity as well as the radiance profile of different types of commercially available deuterium lamp are presented.

Electron cyclotron resonance light source assembly—A vacuum-ultraviolet radiation source based on an electron cyclotron resonance plasma

A vacuum-ultraviolet radiation source based on an electron cyclotron resonance plasma was developed. Electron cyclotron resonance light source assembly (ELISA) is a 10 GHz monomode source of compact design featuring a tunable cavity and permanent magnets which can be axially positioned. The radiation emission of the source can be detected simultaneously in the vacuum-ultraviolet spectral range via a toroidal grating monochromator and in the x-ray spectral range via a Si(Li) detector. Spectroscopic investigations of a krypton and a neon plasma in the 9–27 nm spectral range show that ELISA produces complex line spectra of highly ionized atoms by applying only 12 W microwave power.

IR-VUV Dielectric Function of Al1−xInxN determined by Spectroscopic Ellipsometry

ABSTRACTSpectroscopic Ellipsometry from the mid-infrared (mid-ir) to the vacuum-ultraviolet (vuv) spectral range (350 cm−1 … 8.8 eV) is used to study the optical properties of hexagonal MOVPE-grown Al1−xInxN films for 0.11 ≤ × ≤ 0.21. The AlInN E1(TO) phonon shows a onemode behavior in contrast to recent theoretical predictions [H. Grille, Ch. Schnittler, and F. Bechstedt, Phys. Rev. B 61, 6091 (2000)]. Approximately 120 nm thick Al1−xInxN films grown on slightly compressively strained hexagonal GaN buffer layers reveal the influence of in-plane strain on the E1(TO) phonon mode frequencies. Al1−xInxN deposited directly on [0001] sapphire substrate possesses E1(TO) mode frequency which indicate fully relaxed film growth. For highquality Al0.890In0.110N one A1(LO) phonon mode was observed. Furthermore, we present the complex dielectric function of hexagonal Al0.872In0.128N from the mid-ir to vuv spectral range.

Performance of the new monomode 10 GHz ECR radiation source ELISA

Abstract A new vacuum-ultraviolet radiation source based on an electron cyclotron resonance plasma was developed. Electron Cyclotron Resonance Light Source Assembly (ELISA) is a 10 GHz monomode source of a compact design featuring a tunable cavity and axially positionable permanent magnets. The radiation emission of the source can be detected simultaneously in the vacuum-ultraviolet (VUV) spectral range via a toroidal grating monochromator from 5 to 105 nm and in the X-ray spectral range via a Si(Li) detector. Systematic investigations of the microwave characteristics of ELISA and of the radiation emission of a krypton plasma were performed at a low absorbed microwave power of about 13 W. The dependence on the cavity tuning, on the magnet position and on pressure is presented.