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

Talgat Mamyrbayev,Yanlin Wu,Hidekazu Takano,Kenji Kimura,Katsumasa Ikematsu,Pascal Meyer,Arndt Last,Patrick Doll,Atsushi Momose

doi:10.1107/s1600577521001521

Talgat Mamyrbayev, Yanlin Wu + Show 7 more

Open Access

https://doi.org/10.1107/s1600577521001521

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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.

Highlights

X-ray focusing optics are key elements for increasing the performance of X-ray beams at synchrotron sources
The fabricated refractive multi-lenses (RMLs) present the same geometry, which leads to different focal distances in a staircase arrangement; the lens geometry from RML1 to RMLN could be designed in such a way to obtain an identical focal position for all RMLs by changing the radius of curvature
As a possible application of the developed technique, we demonstrated pixel super-resolution’ (PSR)-STHXM of a dental implant abutment made of titanium alloy

Summary

Introduction

X-ray focusing optics are key elements for increasing the performance of X-ray beams at synchrotron sources. The sub-10 nm-sized X-ray probe can be reached at high-brilliance synchrotron sources using photon energies below 20 keV (Mimura et al, 2010; Yamauchi et al, 2011; Doring et al, 2013). As a consequence, owing to the high penetration depth of X-rays, X-ray microscopy techniques are widely used for non-destructive testing and visualization of the inner structure of specimens, providing extremely high spatial resolution equal to the X-ray nanoprobe size, though at the expense of the FOV (Sakdinawat & Attwood, 2010). X-ray microscopy of centimetre-sized specimens with sub-micrometre spatial resolution will need an extremely long data acquisition time

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