Characterization of HAPG mosaic crystals using synchrotron radiation

Abstract

Highly annealed pyrolytic graphite (HAPG) is an advanced type of pyrolytic graphite that, as a mosaic crystal, combines high integral reflectivity with a very low mosaicity of typically less than 0.1°. When used as dispersive X‐ray optics, a high resolving power has been observed, rendering HAPG very suitable for applications in high‐resolution X‐ray spectroscopy, which conventionally relies on ideal crystals. For the design and modelling of HAPG crystals in applications requiring high spectral resolution, the diffraction properties must be known very accurately. To close this gap, a comprehensive characterization of HAPG crystals was performed that allows for modelling of the diffraction properties in different diffraction orders over a broad spectral range. The crystal properties under investigation are the mosaic spread, the peak reflectivity and the intrinsic reflection width. The investigations were carried out for different thickness crystal films, which were mounted adhesively on a substrate. It is shown that the diffraction properties are strongly correlated to the grade of adhesion, which depends crucially on the substrate material and its surface properties. The investigations were performed using monochromated tunable synchrotron radiation of high spectral purity with a high‐precision experimental setup and calibrated detection devices at the electron storage ring BESSY II.

Valence‐to‐core X‐ray emission spectroscopy of Ti, TiO, and TiO2 by means of a double full‐cylinder crystal von Hamos spectrometer

“…Mandic [10] Koster [5] 29.9 (2) 14.6 (6) 15.3 (7) 28. 8 15.8 13.0 29.8 (5) 15.1 (2) 14.7 (5) 30. 4 15.2 15.2…”

“…The experiments were realized using a well‐known polychromatic excitation source. Highly annealed pyrolytic graphite (HAPG) mosaic crystals are used as dispersive elements because this type of crystal offers a high reflectivity at mosaic spreads below 0.1° . We demonstrate that a sufficient spectral resolution for vtc‐XES applications is achieved with a crystal curvature radius of only 50 mm by adding a second crystal to the full‐cylinder spectrometer concept…”

“…Highly annealed pyrolytic graphite (HAPG) mosaic crystals are used as dispersive elements because this type of crystal offers a high reflectivity at mosaic spreads below 0.1°. [8] We demonstrate that a sufficient spectral resolution for vtc-XES applications is achieved with a crystal curvature radius of only 50 mm by adding a second crystal to the full-cylinder spectrometer concept. [9] The von Hamos geometry is associated with a very stable energy axis allowing for a reassessment of chemical energy shifts of TiO and TiO 2 with respect to metallic Ti.…”

X-ray emission as a potential hazard during ultrashort pulse laser material processing

“…Appropriate instruments for spectral measurements of pulsed plasma radiation in a dose relevant photon energy range above 2 up to 50 keV are efficient broadband X-ray crystal spectrometers [12,13], single photon counting semiconductor detectors [14] and TLD based spectrometers [15]. Considering the specific requirements in laser material processing, a single photon counting CdTe spectrometer (X-123CdTe Spectrometer, 3 × 3 × 1 mm 3 , 100 µm Be window, Amptek Inc.) was selected for the spectral measurements in this work.…”

Pyrolitic Graphite Mosaic Crystal Thickness and Mosaicity Optimization for an Extended Source Von Hamos X-ray Spectrometer

“…In the last several decades, the development of the Pyrolitic Graphite mosaic crystals [9][10][11] renewed the interest in Bragg spectrometers as possible candidates also for millimetric isotropic sources' X-ray measurements. Mosaic crystals consist of a large number of nearly perfect small pyrolitic graphite crystallites, randomly misoriented around the lattice main direction; the FWHM of this random angular distribution is called mosaicity (ω FW HM ) and it makes it possible that even a photon not reaching the crystal with the exact Bragg energy-angle relation can find a properly oriented crystallite and be reflected [12]. This, together with a lattice spacing constant of 3514 Å, enables them to be highly efficient in diffraction in the 2-20 keV energy range, for the n = 1 reflection order, while higher energies can be reached at higher reflection orders.…”