Hard X-ray ptychography at Taiwan Photon Source at 11–20 nm spatial resolution

Abstract

X-ray ptychography, a technique based on scanning and processing of coherent diffraction patterns, is a non-destructive imaging technique with a high spatial resolution far beyond the focused beam size. Earlier demonstrations of hard X-ray ptychography at Taiwan Photon Source (TPS) using an in-house program successfully recorded the ptychographic diffraction patterns from a gold-made Siemens star as a test sample and retrieved the finest inner features of 25 nm. Ptychography was performed at two beamlines with different focusing optics: a pair of Kirkpatrick–Baez mirrors and a pair of nested Montel mirrors, for which the beam sizes on the focal planes were 3 µm and 200 nm and the photon energies were from 5.1 keV to 9 keV. The retrieved spatial resolutions are 20 nm to 11 nm determined by the 10–90% line-cut method and half-bit threshold of Fourier shell correlation. This article describes the experimental conditions and compensation methods, including position correction, mixture state-of-probe, and probe extension methods, of the aforementioned experiments. The discussions will highlight the criteria of ptychographic experiments at TPS as well as the opportunity to characterize beamlines by measuring factors such as the drift or instability of beams or stages and the coherence of beams. Besides, probe functions, the full complex fields illuminated on samples, can be recovered simultaneously using ptychography. Theoretically, the wavefield at any arbitrary position can be estimated from one recovered probe function undergoing wave-propagating. The verification of probe-propagating has been carried out by comparing the probe functions obtained by ptychography and undergoing wave-propagating located at 0, 500 and 1000 µm relative to the focal plane.

Synchrotron X-ray Studies of the Structural and Functional Hierarchies in Mineralised Human Dental Enamel: A State-of-the-Art Review

“…Studies have been performed using a transmission X-ray microscope [ 630 ] and using a technique moving beyond the limitation of the optics in 2D and in 3D [ 631 ]. The latter requires retrieving the sample’s phase and the amplitude of sample using a technique referred to as ptychography [ 632 ] without a lens [ 633 , 634 ], and which can be carried out in 2D, 3D, and 4D [ 635 ] and has been used in various fields using X-ray or electron microscopy [ 292 , 636 ]. In dental research, the technique is limited [ 78 , 413 , 637 , 638 ] and X-ray ptychography ( Figure 8 f) has made it possible to characterise human dentine (energy of 6.2 keV) with a spatial resolution of 158 nm [ 413 ] using 3D ptychography and recently to map carious enamel from a lamella with soft X-ray (energy of 1 keV and reconstruction performed with a pixel size of 8 nm) [ 78 ].…”

Ptychography at the Taiwan Photon Source

“…Earlier test of hard X-ray ptychography has been performed in the beamlines TPS 25A and TPS 23A at Taiwan Photon Source (TPS), where the hard X-rays were focused by a pair of Kirkpatrick-Baez mirrors and a pair of nested Montel mirrors. The specimen for the test was a gold-made Siemens star with the finest feature of 25 nm, and the spatial resolution of the retrieved images determined by half-bit threshold of Fourier shell correlation is 11 nm [1]. We apply the optimized Fermat spiral trajectory [2] during the scanning of the ptychography, ePIE [3] as the phase retrieving algorism, position correction [4] and mixture-state [5] method to extend the tolerance of errors arising from the non-ideal sources and the beam-pointing instabilities.…”