High-resolution Soft X-ray Spectrometer Research Articles

Readout electronics for a high-resolution soft X-ray spectrometer based on silicon drift detector

The readout electronics for a prototype soft X-ray spectrometer based on silicon drift detector (SDD), for precisely measuring the energy and arrival time of X-ray photons is presented in this paper. The system mainly consists of two parts, i.e., an analog electronics section (including a pre-amplifier, a signal shaper and filter, a constant fraction timing circuit, and a peak hold circuit) and a digital electronics section (including an ADC and a TDC). Test results with X-ray sources show that an energy dynamic range of 1–10 keV with an integral nonlinearity of less than 0.1% can be achieved, and the energy resolution is better than 160 eV @ 5.9 keV FWHM. Using a waveform generator, test results also indicate that time resolution of the electronics system is about 3.7 ns, which is much less than the transit time spread of SDD (<100 ns) and satisfies the requirements of future applications.

A portable high-resolution soft x-ray and extreme ultraviolet spectrometer designed for the Shanghai EBIT and the Shanghai low energy EBITs.

A portable high resolution soft x-ray and extreme ultraviolet (EUV) spectrometer has been developed for spectroscopic research at the Shanghai Electron Beam Ion Trap (EBIT) laboratory. A unique way of aligning the grazing incidence spectrometer using the zero order of the grating is introduced. This method is realized by extending the range of the movement of the CCD detector to cover the zero order. The alignment can be done in a few minutes, thus leading to a portable spectrometer. The high vacuum needed to be compatible with the EBITs is reached by mounting most of the translation and rotation stages outside the chamber. Only one high vacuum compatible linear guide is mounted inside the chamber. This is to ensure the convenient interchange of the gratings needed to enable wavelength coverage of the whole range of 10 to 500 Å. Spectra recorded with one of our low energy EBITs shows that a resolving power of above 800 can be achieved. In the slitless configuration used in this work, we found the resolving power to be limited by the width of the EBIT plasma. When mounted on the Shanghai EBIT which is a high energy EBIT and has a narrower EBIT plasma width, the estimated resolving power will be around 1400 at 221.15 Å.

Design and performance of AERHA, a high acceptance high resolution soft x-ray spectrometer.

A soft x-ray spectrometer based on the use of an elliptical focusing mirror and a plane varied line spacing grating is described. It achieves both high resolution and high overall efficiency while remaining relatively compact. The instrument is dedicated to resonant inelastic x-ray scattering studies. We set out how this optical arrangement was judged best able to guarantee performance for the 50 - 1000 eV range within achievable fabrication targets. The AERHA (adjustable energy resolution high acceptance) spectrometer operates with an effective angular acceptance between 100 and 250 μsr (energy dependent) and a resolving power well in excess of 5000 according to the Rayleigh criterion. The high angular acceptance is obtained by means of a collecting pre-mirror. Three scattering geometries are available to enable momentum dependent measurements with 135°, 90°, and 50° scattering angles. The instrument operates on the Synchrotron SOLEIL SEXTANTS beamline which serves as a high photon flux 2 × 200 μm(2) focal spot source with full polarization control.

RIXS investigations of liquids, solutions, and liquid/solid interfaces

We summarize our development of instrumentation for the study of liquids, aqueous solutions, and liquid/solid interfaces using resonant inelastic soft X-ray scattering (RIXS) and illustrate the value of the experimental approach with a few instructional examples. Using a high-transmission, high-resolution soft X-ray spectrometer, we are able to measure complete RIXS maps, i.e., record the soft X-ray emission intensity as a function of emission and absorption energy. As a first example, we show that a comparison of RIXS maps of “normal” and deuterated liquid and gas-phase water allows us to identify dissociation processes on the time scale of the oxygen 1 s core-hole lifetime. Similar dissociation effects are found for aqueous solutions of ammonia and amino acids. For the latter, the pH value has a strong influence on the nitrogen K emission spectra, which can thus be used to identify protonation and deprotonation processes in the solution. Finally, we review the investigation of the interface between liquid water and a CuIn(S,Se)2 thin-film solar cell absorber, demonstrating the power of the technique to study liquid–solid interfaces in real-world systems. Under X-ray irradiation, the formation of sulfate on the absorber surface can be found.

Resonant X-ray emission spectroscopy of liquid water: Novel instrumentation, high resolution, and the “map” approach

Techniques to study the electronic structure of liquids are rare. Most recently, resonant X-ray emission spectroscopy (XES) has been shown to be an extremely versatile spectroscopy to study both occupied and unoccupied electronic states for liquids in thermodynamic equilibrium. However, XES requires high-brilliance soft X-ray synchrotron radiation and poses significant technical challenges to maintain a liquid sample in an ultra-high vacuum environment. Our group has therefore developed and constructed a novel experimental setup for the study of liquids, with the long-term goal of investigating the electronic structure of biological systems in aqueous environments. We have developed a flow-through liquid cell in which the liquid is separated from vacuum by a thin Si 3N 4 or SiC window and which allows a precise control of temperature. This approach has significant advantages compared to static liquids cells used in the past. Furthermore, we have designed a dedicated high-transmission, high-resolution soft X-ray spectrometer. The high transmission makes it possible to measure complete resonant XES “maps” in less than an hour, giving unprecedented detailed insight into the electronic structure of the investigated sample. Using this new equipment we have investigated the electronic structure of liquid water. Furthermore, our XES spectra and maps give information about ultra-fast dissociation on the timescale of the O 1s core hole lifetime, which is strongly affected by the initial state hydrogen bonding configuration.

The superconducting high-resolution soft X-ray spectrometer at the advanced biological and environmental X-ray facility

We have built a 36-pixel superconducting tunnel junction X-ray spectrometer for chemical analysis of dilute samples in the soft X-ray band. It offers an energy resolution of ∼10–20 eV FWHM below 1 keV, a solid angle coverage of ∼10 −3, and can be operated at total rates of up to ∼10 6 counts/s. Here, we describe the spectrometer performance in speciation measurements by fluorescence-detected X-ray absorption spectroscopy at the Advanced Biological and Environmental X-ray facility at the ALS synchrotron.

Preliminary results from the soft x-ray crystal spectrometer on Alcator C-Mod

A high resolution (λ∕Δλ∼2000) soft x-ray spectrometer has been installed on the Alcator C-Mod tokamak. The system was designed to measure emission line spectra from heliumlike neon (1s12p1→1s2) in a narrow spectral band centered on λ=13.5Å (920eV). The instrument is mounted with a poloidal view 20cm below the midplane (r∕a∼0.85). In addition to the neon emission lines, strong fluorine, xenon, iron, and manganese lines have been observed.

A high-resolution soft x-ray spectrometer on the MAST tokamak

A curved crystal spectrometer in Johann configuration has been implemented on MAST to obtain values for electron temperature, ion temperature and toroidal velocity. The spectrometer is used to examine medium Z impurities in the soft x-ray region by utilising a Silicon (111) crystal, bent using a 4 pin bending jig, and a CCD detector (Δt=8 ms). Helium-like Argon emissions from 3.94 to 4.00 Å have been examined using a crystal radius of 859.77 mm. The Bragg angle and crystal radius can be adjusted with relative ease. The spectrometer can be scanned toroidally and poloidally to include a radial view which facilitates absolute velocity measurements by assuming radial velocity =0. Doppler shifts of 2.3×10−5 Å (1.8 kms−1) can be measured. The line of sight is shared with a neutral particle analyzer, which enables in situ ion temperature comparisons. Ray tracing has been used for the development of new imaging spectrometers, using spherical/toroidal crystals, planned to be implemented on MAST.

A multichannel superconducting tunnel junction detector for high-resolution X-ray spectroscopy of magnesium diboride films

We have built a high-resolution soft X-ray spectrometer using a 3 /spl times/ 3 array of superconducting Nb-Al-AlO/sub x/-Al-Nb tunnel junctions. The detector is cooled to /spl sim/0.1 K by a two-stage adiabatic demagnetization refrigerator while being held at the end of a 40-cm-long detector snout that can be inserted into an experimental chamber. The 0.6 mm /spl times/ 0.6 mm array has an energy resolution of 10-15 eV FWHM for X-ray energies below 1 keV and total count rate capabilities above 100 000 counts/s. We demonstrate the capabilities of the instrument in a study of anisotropy in c-axis oriented MgB/sub 2/ films by near edge X-ray absorption spectroscopy. The absorption fine structure at the B K-edge differs for excitation with X-rays polarized along the c-axis and in the ab-plane of the MgB/sub 2/ film. We discuss the implications of the anisotropy for the density of states in MgB/sub 2/ at the Fermi surface.

High-resolution soft x-ray spectrometer for the NSTX tokamak

A high-resolution spectrometer for measuring the soft x-ray emission (7–24 Å) has been implemented on the National Spherical Tokamak Experiment (NSTX). The instrument will be used to study the K-shell spectra of O, Ne, and Mg as well as the L-shell spectra of Fe and Ni and to calibrate spectral diagnostics of fusion and astrophysical plasmas. The spectrometer employs a spherically bent crystal for dispersion and two microchannel-plate intensified 1D charged-coupled devices for recording the x rays. The temporal resolution is 25 ms per spectrum.

High-resolution soft X-ray spectroscopy of 2.3 keV/u N 7+ ions through a microcapillary target

X-rays emitted from 2.3 keV/u 15N 7+ ions transmitted through a highly ordered Ni microcapillary were measured with a high-resolution soft X-ray spectrometer. The highly ordered microcapillary has recently become available employing a nano-lithographic technique. A transmission ratio and charge state distribution of ions through the microcapillary target were found to be consistent with theoretical predictions. A preliminary analysis showed that a series of X-rays from np–1s transitions with n as high as 8 were identified, which is consistent with the classical over barrier model.

High-Resolution Soft X-Ray Emission Spectra of Crystalline Carbon Nitride Films Deposited by Electron Cyclotron Resonance Sputtering

The X-ray emission spectra of crystalline carbon nitride films deposited by electron-cyclotron-resonance (ECR) plasma sputtering were observed using a high-resolution soft X-ray spectrometer at the Advanced Light Source to investigate the electronic structure of carbon nitride crystals. The spectral features in C K and N K X-ray emissions from the ECR-deposited carbon nitride films represent the highly degenerated valence orbitals and their highly pure crystalline form. The C K and N K X-ray emission spectra were approximately explained based on the C2p and N2p density of states in the hybridized C–N bonds. The absence of significant peak shifting in selectively excited C K and N K X-ray emission spectra showed that there is a fairly nondispersive structure between valence and conduction bands in ECR-deposited carbon nitride films.

Wide-band, high-resolution soft x-ray spectrometer for the Electron Beam Ion Trap

We have constructed two wide-band, high-resolution vacuum flat crystal spectrometers and implemented them on the Electron Beam Ion Trap located at the Lawrence Livermore National Laboratory. Working in unison, these spectrometers can measure an x-ray bandwidth ⩽9 Å in the soft x-ray region below 21 Å. In order to achieve this large bandwidth each spectrometer houses either two 125 mm × 13 mm × 2 mm RAP (rubidium acid phthalate, 2d=26.121 Å), two 114 mm × 13 mm × 2 mm TlAP (thallium acid phthalate, 2d=25.75 Å) crystals, or some combination thereof, for dispersion and two position sensitive proportional counters for detection of x rays. The spectrometers are used to measure wavelengths and relative intensities of the L-shell line emission from Fe XVII–XXIV for comparison with spectra obtained from astrophysical and laboratory plasmas. The wide wavelength coverage attainable by these spectrometers makes it possible to measure all the L-shell emission from a given iron ion species simultaneously.

End station for polarization and excitation energy selective soft x-ray fluorescence spectroscopy

An end station for soft x-ray fluorescence spectroscopy has been constructed, which includes an experiment chamber, rotatable 90° under ultrahigh vacuum conditions around the incoming synchrotron radiation beam, which is provided with a high-resolution soft x-ray spectrometer. A manipulator allowing three axes of rotation, three directions of translation, as well as LN2 cooling and resistive heating is mounted to the chamber and serves as the sample holder. Samples can be transferred under vacuum between the experiment chamber and two other chambers, one for sample preparation and another for introducing new samples and for sample storage. The end station has been used at two different synchrotron radiation laboratories (beamline BW3) at HASYLAB in Hamburg and at ALS (beamline 7.0) in Berkeley. Polarization-dependent and angular resolved, selectively excited x-ray emission studies have been made on ordered as well as nonordered systems, e.g., high-Tc superconducting systems, diamond, fullerenes, and molecular ices. The experimental system will be presented along with some recent scientific results.

Nickel Lα spectra measured by a high resolution particle induced X-ray emission (PIXE) spectrometer

The satellite spectra of Ni Lα X-rays induced by 21.0 MeV/amu N 2+ ion bombardment were measured using a high-resolution soft X-ray spectrometer which was specially designed for the chemical state analysis by PIXE. We succeeded in observing two distinguished satellite lines, whose energies were estimated by the use of a relativistic self-consistent field program. Relative intensities of the satellites observed here were also well reproduced by theoretical values estimated from the semiclassical approximation after correcting the X-ray selfabsorption. The satellites were confirmed to originate from the multiply ionized states with one L 3 and n M electron vacancies.

High-resolution duo-multichannel soft x-ray spectrometer for tokamak plasma diagnostics

A high-resolution, time-resolving soft x-ray multichannel spectrometer (SOXMOS) that permits the simultaneous measurement of emission in two different spectral ranges has been developed and tested extensively for tokamak plasma diagnostics. The basic instrument is a high-resolution, interferometrically adjusted, extreme grazing incidence Schwob–Fraenkel duochromator. The instrument is equipped with two multichannel detectors that are adjusted interferometrically and scan along the Rowland circle. Each consists of an MgF2 coated, funneled microchannel plate, associated with a phosphor screen image intensifier that is coupled to a 1024-element photodiode array by a flexible fiber-optic conduit. The total wavelength coverage of the instrument is 5–340 Å with a measured resolution (FWHM) of about 0.2 Å when equipped with a 600-g/mm grating, and 5–85 Å with a resolution of about 0.06 Å using a 2400-g/mm grating. The simultaneous spectral coverage of each detector varies from 15 Å at the short wavelength limit to 70 Å at the long wavelength limit with the lower dispersion grating. The minimum readout time for a full spectral portion is 16 ms, but several individual lines can be measured with 1-ms time resolution by selected pixel readout. Higher time resolution can be achieved by replacing one multichannel detector with a single channel electron multiplier detector. Examples of data from the PLT and TFTR tokamaks are presented to illustrate the instrument’s versatility, high spectral resolution, and high signal-to-noise ratio even in the 10-Å region.