Yu-Shan Huang

Following our initial demonstration of ptychography at the Taiwan Photon Source (TPS), the system has been substantially upgraded. This article details the design and performance of the new hard X-ray 2D ptychography endstation, TPS 25A2. A zone-plate focusing system has been inserted downstream of the previous Kirkpatrick–Baez mirror optics at the TPS 25A2 beamline. Operating at a photon energy of 8.979 keV, the endstation routinely achieves a spatial resolution of sub-10 nm in 2D, with a highest achieved resolution of 6.9 nm on a standard Siemens star test pattern. We present the full instrumental specifications and performance benchmarks, and showcase the endstation's capabilities with imaging examples of inorganic nanoparticles and a complex biological structure. The establishment of TPS 25A2 provides the scientific community with a powerful and accessible tool for nanoscale imaging.

The TPS Phase III soft x-ray beamlines, designated as 33, 35, and 43, employ bendable mirrors to achieve the required optical performance across a broad energy range. All mirrors, except for the grating mirrors, are designed with adjustable height and position to optimize alignment. The mirrors are secured to the bending mechanism using specially designed clips and bolt joints. During bending, the mirror surface deformation can be approximated by second- and third-order polynomial terms, which must be removed to minimize optical aberrations. After applying these corrections, the residual slope error in the useful optical area must remain below ±1.5 × 10−6 rad to meet performance criteria. Therefore, the design of the mirror clip and the precise application of bolt joint forces are critical to achieving high-accuracy figure control. This study systematically investigates how varying bolt joint forces at the mirror clip can compensate for high-order residual deformations. Finite element method simulations were conducted to determine optimal force distributions, providing guidance for experimental setup and safe mounting conditions. In experiments, the bolt joint forces were adjusted using a calibrated torque wrench, while the long trace profiler continuously measured the slope error to identify the configuration yielding the widest functional optical area with minimal residual error.

Coherent diffraction microscopy (CDM) is a robust direct imaging method due to its unique 2D/3D phase retrieval capacity. Nonetheless, its resolution faces limitations due to a diminished signal-to-noise ratio (SNR) in high-frequency regions. Addressing this challenge, X-ray ensemble diffraction microscopy (XEDM) emerges as a viable solution, ensuring an adequate SNR in high-frequency regions and effectively surmounting resolution constraints. In this article, two experiments were conducted to underscore XEDM's superior spatial resolution capabilities. These experiments employed 55 nm-sized silicon–gold nanoparticles (NPs) and 19 nm-sized nodavirus-like particles (NV-LPs) on the coherent X-ray scattering beamline of the Taiwan Photon Source. The core–shell density distribution of the silicon–gold NPs was successfully obtained with a radial resolution of 3.4 nm per pixel, while NV-LPs in solution were reconstructed at a radial resolution of 1.3 nm per pixel. The structural information was directly retrieved from the diffraction intensities without prior knowledge and was subsequently confirmed through transmission electron microscopy.

The inherent ambiguity in reconstructed images from coherent diffraction imaging (CDI) poses an intrinsic challenge, as images derived from the same dataset under varying initial conditions often display inconsistencies. This study introduces a method that employs the Noise2Noise approach combined with neural networks to effectively mitigate these ambiguities. We applied this methodology to hundreds of ambiguous reconstructed images retrieved from a single diffraction pattern using a conventional retrieval algorithm. Our results demonstrate that ambiguous features in these reconstructions are effectively treated as inter-reconstruction noise and are significantly reduced. The post-Noise2Noise treated images closely approximate the average and singular value decomposition analysis of various reconstructions, providing consistent and reliable reconstructions.

Coherent diffraction microscopy (CDM) is a potential approach to image micromaterials at atomic resolution without crystals. Due to the lack of high-angle scattering, the achieved resolution is limited to several nanometers. Small-angle scattering allows researchers to reveal high-resolution 3D structures of specimens by fitting 1D diffraction signals. However, prerequisite 3D models and non-unique solutions restrict the potential to image general specimens. Under the assumption of an ensemble containing large amounts of identical specimens with the same orientation, the intensity distribution of the diffraction pattern of the whole ensemble is approximated to the form factor of a single specimen multiplied by the number of identical specimens. Since the diffraction intensities are contributed from the whole ensemble, the signal can be significantly extended to high-frequency regions. The feasibility of ensemble diffraction microscopy (EDM) was demonstrated by a designed sample using both totally and partially coherent x-ray sources at Taiwan Photon Source (TPS). The reconstructed images show excellent consistency with the image of a scanning electron microscope. This work represents a new protocol for directly characterizing the structures of nanomaterials, or potentially biomacromolecules, from accumulated x-ray scattering data.

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.