Characterization of sub-monolayer coatings as novel calibration samples for X-ray spectroscopy

With the advent of both modern X-ray fluorescence (XRF) methods and improved analytical reliability requirements the demand for suitable reference samples has increased. Especially in nanotechnology with the very low areal mass depositions, quantification becomes considerably more difficult. However, the availability of suited reference samples is drastically lower than the demand. Physical vapor deposition (PVD) techniques have been enhanced significantly in the last decade driven by the need for extremely precise film parameters in multilayer production. We have applied those techniques for the development of layer-like reference samples with mass depositions in the ng-range and well below. Several types of reference samples were fabricated: multi-elemental layer and extremely low (sub-monolayer) samples for various applications in XRF and total-reflection XRF (TXRF) analysis. Those samples were characterized and compared at three different synchrotron radiation beamlines at the BESSY II electron storage ring employing the reference-free XRF approach based on physically calibrated instrumentation. In addition, the homogeneity of the multi-elemental coatings was checked at the P04 beamline at DESY. The measurements demonstrate the high precision achieved in the manufacturing process as well as the versatility of application fields for the presented reference samples

Note: Reflection zone plates as highly resolving broadband optics for soft X-ray laboratory spectrometers

The resolving power and relative efficiency of two off-axis reflection zone plates (RZPs) in the soft X-ray range between 1 nm and 5 nm were investigated. RZPs focus only a very narrow bandwidth around the design wavelength. By misaligning the RZP, the focused wavelength can be tuned through a much wider spectral range. Using a laser-produced plasma source, we demonstrate that a single RZP can be efficiently used for spectroscopy at arbitrary wavelengths in the investigated soft X-ray range.DFG, 313838950, Neuartiges Laborspektrometer für Pump-Probe NEXAFS-Untersuchungen an Biomolekülen in wässriger Lösun

Towards Poisson noise limited optical pump soft X-ray probe NEXAFS spectroscopy using a laser-produced plasma source

We present a laboratory setup for near edge X-ray absorption spectroscopy (NEXAFS) in the soft X-ray regime between 284 eV to 1303 eV with a resolving power of up to 1370. Based on a laser-produced plasma source, a pair of identical reflection zone plates and an X-ray CCD camera, the setup is intended for optical pump X-ray probe NEXAFS measurements with a detectable change in absorption of the excited sample down to 10-4 and 500 ps time resolution. Because of the high stability of the source the statistical error only depends on the detector response and the number of photons detected and can reach the detector noise limit after a couple of thousands single shots. Thus, structure-function relationship investigations of bio-molecules are rendered feasible in the laboratory

Old traces, read anew - 'The Reading Hermit' painting in the light of X-ray fluorescence

There exist several very similar looking versions of the painting ‘The Reading Hermit’, all allegedly painted by Rembrandt Harmenszoon van Rijn (approx. in ∼1630 A.D., Leiden). The classification of Rembrandt's paintings, which were produced by Rembrandt himself, in his academy by his students and the ones being mere copies is a crucial and difficult task. We gathered background evidence and performed elemental analyses by non-destructive micro-X-ray fluorescence (micro-XRF) in order to elucidate the painting's provenance. Elemental distributions of Ca, Mn, Fe and Cu show that the painting was presumably changed during the painting process, which indicates, together with neutron autoradiography (NAR) investigations, that this version of ‘The Reading Hermit’ is not a copy

Laboratory quick near edge x-ray absorption fine structure spectroscopy in the soft x-ray range with 100 Hz frame rate using CMOS technology

In laboratory based x-ray absorption fine structure (XAFS) spectroscopy, the slow readout speed of conventional CCD cameras can prolong the measuring times by multiple orders of magnitude. Using pulsed sources, e.g., laser-based x-ray sources, the pulse repetition rate often exceeds the frame rate of the CCD camera. We report the use of a scientific CMOS (sCMOS) camera for XAFS spectroscopy with a laser-produced plasma source facilitating measurements at 100 Hz. With this technological improvement, a new class of experiments becomes possible, starting from the time consuming analysis of samples with small absorption to pump-probe investigations. Furthermore, laboratory quick soft x-ray absorption fine structure (QXAFS) measurements with 10 ms time resolution are rendered feasible. We present the characterization of the sCMOS camera concerning noise characteristics and a comparison to conventional CCD camera performance. The feasibility of time resolved QXAFS measurements is shown by analyzing the statistical uncertainty of single shot spectra. Finally, XAFS spectroscopy on a complex sandwich structure with minute amounts of NiO exemplifies the additional merits of fast detectors.DFG, 313838950, Neuartiges Laborspektrometer für Pump-Probe NEXAFS-Untersuchungen an Biomolekülen in wässriger LösungEC/H2020/654148/EU/The Integrated Initiative of European Laser Research Infrastructures/LASERLAB-EUROP

Transient laboratory X-ray absorption fine structure spectroscopy on thin films demonstrated with F8BT

We present advanced instrumentation for the investigation of thin organic films offered by a laboratory X-ray absorption fine structure (XAFS) spectrometer for the soft X-ray range. The transmission spectrometer is based on a laser-produced plasma source in combination with a twin-arm reflection zone plate spectrometer. The efficiency and stability of the spectrometer allow for single shot measurements within 500 ps with a resolving power of E/ΔE ~ 900 in a range between 200 eV and 1300 eV. Through the implementation of an optical pump beam, also transient absorption measurements can be performed. The merits of the spectrometer are demonstrated through the investigation of poly[(9,9-dioctylfluorenyl- 2,7-diyl)-alt-co-(1,4-benzo-{2,1‘,3}-thiadiazole)] (F8BT), a polyfluorene copolymer. Transient optical pump soft X-ray probe spectroscopy with 500 ps time resolution detects changes in the C K edge spectrum which can be attributed to the lowest unoccupied molecular orbitals of the molecules in the benzothiadiazole unit

Metadata Fields and Quality Criteria - XAS Reference Database under DAPHNE4NFDI

X-ray absorption spectroscopy is important to analyse solid materials, in particular amorphous materials, disordered or multicomponent materials. Due to its vast application in diverse fields XAS has become an essential tool for studying, e.g., catalytic reactions or battery materials to mention just a few. In the field of XAS, data are often evaluated by comparing them to previously measured or calculated reference spectra [1]. This sets the high requirements concerning both spectral quality and documentation of the measurements. Under DAPHNE4NFDI, we have been working on to set up a XAS reference database including raw and processed data with an interface developed for uploading and evaluating the data. In this context, defining metadata fields about an XAS experiments and documenting this information along with data is essential to make the measured data reusable by any researcher in a similar field and beyond. Another important aspect of a curated database is that users should be able to easily judge the quality and the usability of each data set by looking at the mentioned quality criteria. In the present work, we have discussed and highlighted the importance of metadata fields and quality criteria for the data to be uploaded at the XAS database

Towards Poisson noise limited optical pump soft X-ray probe NEXAFS spectroscopy using a laser-produced plasma source

We present a laboratory setup for near edge X-ray absorption spectroscopy (NEXAFS) in the soft X-ray regime between 284 eV to 1303 eV with a resolving power of up to 1370. Based on a laser-produced plasma source, a pair of identical reflection zone plates and an X-ray CCD camera, the setup is intended for optical pump X-ray probe NEXAFS measurements with a detectable change in absorption of the excited sample down to 10−4 and 500 ps time resolution. Because of the high stability of the source the statistical error only depends on the detector response and the number of photons detected and can reach the detector noise limit after a couple of thousands single shots. Thus, structure-function relationship investigations of bio-molecules are rendered feasible in the laboratory.DFG, 313838950, Neuartiges Laborspektrometer für Pump-Probe NEXAFS-Untersuchungen an Biomolekülen in wässriger Lösun

RefXAS: an open access database of X-ray absorption spectra

Under DAPHNE4NFDI, the X-ray absorption spectroscopy (XAS) reference database, RefXAS, has been set up. For this purpose, we developed a method to enable users to submit a raw dataset, with its associated metadata, via a dedi- cated website for inclusion in the database. Implementation of the database includes an upload of metadata to the scientific catalogue and an upload of files via object storage, with automated query capabilities through a web server and visualization of the data and files. Based on the mode of measurements, quality criteria have been formulated for the automated check of any uploaded data. In the present work, the significant metadata fields for reusability, as well as reproducibility of results (FAIR data principles), are discussed. Quality criteria for the data uploaded to the database have been formulated and assessed. Moreover, the usability and interoperability of available XAS data/file formats have been explored. The first version of the RefXAS database prototype is presented, which features a human verification procedure, currently being tested with a new user interface designed specifically for curators; a user-friendly landing page; a full list of datasets; advanced search capabilities; a streamlined upload process; and, finally, a server-side automatic authentication and (meta-) data storage via MongoDB, PostgreSQL and (data-) files via relevant APIs