Staircase array of inclined refractive multi-lenses for large field of view pixel super-resolution scanning transmission hard X-ray microscopy

Abstract

Owing to the development of X-ray focusing optics during the past decades, synchrotron-based X-ray microscopy techniques allow the study of specimens with unprecedented spatial resolution, down to 10 nm, using soft and medium X-ray photon energies, though at the expense of the field of view (FOV). One of the approaches to increase the FOV to square millimetres is raster-scanning of the specimen using a single nanoprobe; however, this results in a long data acquisition time. This work employs an array of inclined biconcave parabolic refractive multi-lenses (RMLs), fabricated by deep X-ray lithography and electroplating to generate a large number of long X-ray foci. Since the FOV is limited by the pattern height if a single RML is used by impinging X-rays parallel to the substrate, many RMLs at regular intervals in the orthogonal direction were fabricated by tilted exposure. By inclining the substrate correspondingly to the tilted exposure, 378000 X-ray line foci were generated with a length in the centimetre range and constant intervals in the sub-micrometre range. The capability of this new X-ray focusing device was first confirmed using ray-tracing simulations and then using synchrotron radiation at BL20B2 of SPring-8, Japan. Taking account of the fact that the refractive lens is effective for focusing high-energy X-rays, the experiment was performed with 35 keV X-rays. Next, by scanning a specimen through the line foci, this device was used to perform large FOV pixel super-resolution scanning transmission hard X-ray microscopy (PSR-STHXM) with a 780 ± 40 nm spatial resolution within an FOV of 1.64 cm × 1.64 cm (limited by the detector area) and a total scanning time of 4 min. Biomedical implant abutments fabricated via selective laser melting using Ti–6Al–4V medical alloy were measured by PSR-STHXM, suggesting its unique potential for studying extended and thick specimens. Although the super-resolution function was realized in one dimension in this study, it can be expanded to two dimensions by aligning a pair of presented devices orthogonally.

Parabolic gratings enhance the X-ray sensitivity of Talbot interferograms

“…The FoV of our biconcave-plano-convex system under plane wave illumination was limited to a nickel structure height of 60 µm, and an array length of 10.24 mm, which was sufficient to confirm the sensitivity enhancement concept. However, the FoV can be increased up to tens of squared centimeters using inclined staircase lens arrays such as the structures demonstrated for super-resolution X-ray transmission microscopy 28 .…”

Parabolic gratings enhance the X-ray sensitivity of Talbot interferograms

“…The FoV of our biconcave-plano-convex system under plane wave illumination was limited to a nickel structure height of 60 μm, and an array length of 10.24 mm, which was sufficient to confirm the sensitivity enhancement concept. However, the FoV can be increased up to tens of squared centimeters using inclined staircase lens arrays such as the structures demonstrated for super-resolution X-ray transmission microscopy 28 .…”