Felix Marschall

X-ray full field microscopy at 30 KeV

In our X-ray full field microscopy experiments, we demonstrated a resolution better than 260 nm over the entire field of view of 80 μm × 80 μm at 30 keV. Our experimental setup at PETRA III, P05, had a length of about 5 m consisting of an illumination optics, an imaging lens and a detector. For imaging, we used a compound refractive lens (CLR) consisting of mr-L negative photo resist, which was fabricated by deep X-ray lithography. As illumination optics, we choose a refractive rolled X-ray prism lens, which was adapted to the numerical aperture of the imaging lens.

Increasing the aperture of x-ray mosaic lenses by freeze drying

Point focus x-ray mosaic lenses are limited in aperture by the aspect ratio that can be reached in the micro fabrication process. In lithography based micro fabrication processes, which are used to fabricate the lens pillar structures, the achievable aspect ratio is restricted by structure collapse due to capillary forces which occur during drying after development. Capillary forces can be avoided by freeze drying, hence avoiding the direct phase change from liquid to gas. Substituting conventional drying by freeze drying using cyclohexane at a temperature of  −10 °C, we could increase the achievable aspect ratio for the triangular pillar structures with edge length of 10 to 45 µm of the x-ray mosaic lenses by up to a factor of 2.2 with no further changes in process, material or structural geometry. A maximum aspect ratio of 30 was achieved for pillars with 10 µm edge length. The process can readily be employed to other structures or lithography techniques.

Zone plates as imaging analyzers for resonant inelastic x-ray scattering

We have implemented and successfully tested an off-axis transmission Fresnel zone plate as a novel type of analyzer optics for resonant inelastic x-ray scattering (RIXS). We achieved a spectral resolution of 64 meV at the nitrogen K-edge (E/dE = 6200), closely matching theoretical predictions. The fundamental advantage of transmission optics is the fact that it can provide stigmatic imaging properties. This opens up a variety of advanced RIXS configurations, such as efficient scanning RIXS, parallel detection for varying incident energy and time-resolved measurements.

Low-cost Rolled X-ray Prism Lenses to increase photon flux density in diffractometry experiments

At the Institute of Microstructure Technology (IMT) of the Karlsruhe Institute of Technology (KIT), a new type of refractive X-ray optics has been developed. Owing to its comparably easy fabrication method and the large aperture, the so-called Rolled X-ray Prism Lenses (RXPL) have the potential to be used with X-ray tubes in an industrial environment as a low-cost alternative to existing optics. The lens itself is built out of a micro-structured foil which is cut into shape and rolled around a winding core to form a refracting element for X-rays. The resulting refractive structure can be used as illumination optics. Diffractometry experiments with an NIST 1976a sample were performed and showed up to an 18-fold enhanced integrated intensity compared to that acquired with a steel tube collimator.

Polymer compound refractive lenses for hard X-ray nanofocusing

Compound refractive lenses fabricated out of SU-8 negative photoresist have been used to generate a nanofocused, i.e. sub-µm sized X-ray focal spot at an X-ray nanodiffraction setup. X-ray microscopy and X-ray diffraction techniques have conceptually different demands on nanofocusing optical elements and so with the application of X-ray nanodiffraction in mind, this paper presents the results of an initial characterization of polymer lenses used as primary focusing device at an X-ray nanodiffraction synchrotron beamline. A beam size of ∼ 600 nm was achieved at a photon energy of 13 keV following only a short initial alignment, with the focal spot representing a demagnified, direct image of the undulator source.