Scanning Hard X-Ray Microscopy Based on Be CRLs

Andreas Schropp, Dennis Bruckner, Jessica Bulda, Gerald Falkenberg, Jan Garrevoet, Frank Seiboth, Felix Wittwer, Frieder Koch, Christian David, Christian G. Schroer
2018 Microscopy and Microanalysis  
It was demonstrated in recent experiments that aberration-free nano-focusing of X rays is possible with a stack of Beryllium compound refractive lenses (Be CRLs) in combination with a corrective phase plate [1, 2] . The phase plate operates like an eyeglass rectifying residual errors of the main optics. In this way, diffraction-limited X-ray focusing can be achieved, enhancing the performance of scanning X-ray microscopy based on, e. g., Be CRLs to ultimate limits. We implemented this approach
more » ... t beamline P06 at PETRA III (DESY, Hamburg) making use of additive manufacturing for phase plate fabrication in order to provide a versatile and easy-to-use nano-focusing platform. In this contribution, we demonstrate the high performance of these optics, which can now produce very clean Gaussian X-ray foci with a size smaller than 100 nm (FWHM) at moderate working distances larger than 10 cm. This development is especially interesting if larger sample environments are required. For example, in-situ or operando setups often need more infrastructure in the vicinity of a sample to adjust temperature, pressure or gas flow [3] . With a new optical setup at beamline P06 combining the micro-(optics and sample) and nanohutch (diffraction detector), we recently investigated a thin section of a Clunio-larva eye (see G. Falkenberg, et al. [4] and references therein) by scanning X-ray microscopy employing X-ray fluorescence (XRF) and coherent diffraction contrast (ptychography). In this case, a stack of 50 Be CRLs with radius of curvature of R = 50 µm and geometric aperture of D = 300 µm was used to focus hard X rays (E = 12 keV) to slightly below 100 nm (FWHM) at a focal length of f = 22 cm. In a first step the optics were characterized by ptychography using a nano-structured sample having finest lateral structures of 50 nm. It consists of an array of Siemens-stars structured into a 1 µm thick tungsten layer on a CVD-diamond substrate. This sample was scanned through the nanofocused X-ray beam over an area of 2 µm in horizontal and vertical direction. Far-field diffraction patterns were recorded at each scan point by an Eiger X 4M-detector (Dectris Ltd.), positioned at a distance of L = 6850 mm behind the sample. From this data set the full information about the nano-focused X-ray beam can be retrieved [5] . By implementing a polymer phase plate the performance could be considerably improved as illustrated in Fig. 1 a) , showing a comparison between the X-ray beam caustic with and without the phase plate. Here, the polymer phase plate [cf. inset of Fig. 1 a) ] was fabricated using a Nanoscribe 3D-printer. Using this corrective optics the maximum intensity in side lobes surrounding the main focal spot could be decreased to the 1 %-level. Some results of the XRF-experiment on the Clunio-larva eye are summarized in Fig. 1 b) , demonstrating that we could image an arrangement of pigments with high spatial resolution at a moderate photon flux of 3 × 10 9 ph/s. The size of these pigments is typically a few hundred nanometers, https://doi.
doi:10.1017/s1431927618013284 fatcat:fux2bghc6fbphjnsvrxuwwcnye