Although ptychography does not require a precise knowledge of the illumination wavefront, common implementations rely upon assumptions such as accurate knowledge of the scan positions and constant ...illumination. Limited validity of these assumptions results in deterioration of the reconstruction quality. We present a generalized ptychography method that optimizes the reconstruction along multiple directions. In our manuscript, we demonstrate that the additional flexibility not only helps to amend imprecisions of the ptychography model in a self-consistent way but additionally leads to faster convergence without a significant increase of the computational cost per iteration.
Both high resolution and high precision are required to quantitatively determine the atomic structure of complex nanostructured materials. However, for conventional imaging methods in scanning ...transmission electron microscopy (STEM), atomic resolution with picometer precision cannot usually be achieved for weakly-scattering samples or radiation-sensitive materials, such as 2D materials. Here, we demonstrate low-dose, sub-angstrom resolution imaging with picometer precision using mixed-state electron ptychography. We show that correctly accounting for the partial coherence of the electron beam is a prerequisite for high-quality structural reconstructions due to the intrinsic partial coherence of the electron beam. The mixed-state reconstruction gains importance especially when simultaneously pursuing high resolution, high precision and large field-of-view imaging. Compared with conventional atomic-resolution STEM imaging techniques, the mixed-state ptychographic approach simultaneously provides a four-times-faster acquisition, with double the information limit at the same dose, or up to a fifty-fold reduction in dose at the same resolution.
We present a systematic study, where effects of the illumination probe design on ptychography reconstruction quality are evaluated under well-controlled conditions. The illumination probe was created ...using Fresnel zone-plate (FZP) optics with locally displaced zones to provide a fine control over perturbations of the illumination wavefront. We show that optimally designed wavefront modulations not only reduce bias and variance in the reconstruction of the lowest spatial frequencies but also lead to improved imaging resolution and reduction of artefacts compared to a conventional FZP. Both these factors are important for quantitative accuracy and resolution of ptychographic tomography. Our work furthers the understanding of the important characteristics of an optimal illumination for high-resolution X-ray ptychography and how to design optimal FZP wavefront modulations for different applications of ptychographic imaging. These findings are applicable and relevant for ptychography using optical, EUV, and X-ray photons as well as electrons.
Ptychography is a coherent diffractive imaging method that can provide a diffraction-limited, robust reconstruction of the sample's complex transmission function without the use of high-quality ...optics. However, the scanning nature of conventional X-ray ptychography unavoidably requires the mechanical motion of either the illumination probe or the sample. In order to avoid overhead related to breaking and acceleration for every scan position, so-called fly-scan methods were developed. Here, we present an improved variant that removes the limitation of continuous scanning along a linear scanning path and allows for ptychographic reconstruction of scans taken along an arbitrary 2D continuous trajectory. We also demonstrate numerically and experimentally that our method provides significantly improved robustness against noise, particularly for larger fly-scan steps, i.e. sample shift during an exposure, which will gain importance with the advent of 4th generation synchrotron sources, where the available coherent flux may be increased by orders of magnitude. Finally, we show that the use of a spiral scan continuous trajectory alleviates significantly raster grid artifacts.
As the resolution of X-ray tomography improves, the limited long-term stability and accuracy of nanoimaging tools does not allow computing artifact-free three-dimensional (3D) reconstructions without ...an additional step of numerical alignment of the measured projections. However, the common iterative alignment methods are significantly more computationally demanding than a simple tomographic reconstruction of the acquired volume. Here, we address this issue and present an alignment toolkit, which exploits methods with deep-subpixel accuracy combined with a multi-resolution scheme. This leads to robust and accurate alignment with significantly reduced computational and memory requirements. The performance of the presented methods is demonstrated on simulated and measured datasets for tomography and also laminography acquisition geometries. A GPU accelerated implementation of our alignment framework is publicly available.
X-ray linear dichroism and X-ray birefringence microscopy are yet to be fully utilized as instruments in the microstructural characterization of crystalline materials. Here, we demonstrate ...analyser-free X-ray linear dichroism microscopy using spectroscopic hard X-ray ptychography. First experiments enabled a spectroscopic and microstructural characterisation of polycrystalline vanadium pentoxide on the nanoscale, outside of diffraction-contrast based methods.
Reaching the full potential of X-ray nanotomography, in particular for biological samples, is limited by many factors, of which one of the most serious is radiation damage. Although sample ...deformation caused by radiation damage can be partly mitigated by cryogenic protection, it is still present in these conditions and, as we exemplify here using a specimen extracted from scales of the Cyphochilus beetle, it will pose a limit to the achievable imaging resolution. We demonstrate a generalized tomographic model, which optimally follows the sample morphological changes and attempts to recover the original sample structure close to the ideal, damage-free reconstruction. Whereas our demonstration was performed using ptychographic X-ray tomography, the method can be adopted for any tomographic imaging modality. Our application demonstrates improved reconstruction quality of radiation-sensitive samples, which will be of increasing relevance with the higher brightness of 4th generation synchrotron sources.
Ptychography is a lensless imaging technique that is aberration-free and capable of imaging both the amplitude and the phase of radiation reflected or transmitted from an object using iterative ...algorithms. Working with extreme ultraviolet (EUV) light, ptychography can provide better resolution than conventional optical microscopy and deeper penetration than scanning electron microscope. As a compact lab-scale EUV light sources, high harmonic generation meets the high coherence requirement of ptychography and gives more flexibilities in both budget and experimental time compared to synchrotrons. The ability to measure phase makes reflection-mode ptychography a good choice for characterising both the surface topography and the internal structural changes in EUV multilayer mirrors. This paper describes the use of reflection-mode ptychography with a lab-scale high harmonic generation based EUV light source to perform quantitative measurement of the amplitude and phase reflection from EUV multilayer mirrors with engineered substrate defects. Using EUV light at 29.6nm from a tabletop high harmonic generation light source, a lateral resolution down to ∼88nm and a phase resolution of 0.08rad (equivalent to topographic height variation of 0.27nm) are achieved. The effect of surface distortion and roughness on EUV reflectivity is compared to topographic properties of the mirror defects measured using both atomic force microscopy and scanning transmission electron microscopy. Modelling of reflection properties from multilayer mirrors is used to predict the potential of a combination of on-resonance, actinic ptychographic imaging at 13.5nm and atomic force microscopy for characterising the changes in multilayered structures.
Scanning X‐ray microscopy such as X‐ray ptychography requires accurate and fast positioning of samples in the X‐ray beam. Sample stages often have a high mobile mass as they may carry additional ...mechanics or mirrors for position measurements. The high mobile mass of a piezo stage can introduce vibrations in the setup that will lead to imaging quality deterioration. Sample stages also require a large travel range which results in a slow positioning step response and thus high positioning overhead. Moving lightweight X‐ray optics, such as focusing Fresnel zone plates, instead of the sample can improve the situation but it may lead to undesired variations in the illumination probe which may result in reconstruction artifacts. This paper presents a combined approach in which a slow sample stage mechanism covers the long distance range for a large field of view, and a light‐weight optics scanner with a small travel range creates a superimposed motion to achieve a fast step response. The step response in the ptychographic tomography instrument used was thereby improved by an order of magnitude, allowing for efficient measurement without loss of imaging quality.
A novel approach for fast ptychography scans over an extended field of view by means of simultaneous Fresnel zone plate and sample motion is presented.
Across all branches of science, medicine and engineering, high‐resolution microscopy is required to understand functionality. Although optical methods have been developed to `defeat' the diffraction ...limit and produce 3D images, and electrons have proven ever more useful in creating pictures of small objects or thin sections, so far there is no substitute for X‐ray microscopy in providing multiscale 3D images of objects with a single instrument and minimal labeling and preparation. A powerful technique proven to continuously access length scales from 10 nm to 10 µm is ptychographic X‐ray computed tomography, which, on account of the orthogonality of the tomographic rotation axis to the illuminating beam, still has the limitation of necessitating pillar‐shaped samples of small (ca 10 µm) diameter. Large‐area planar samples are common in science and engineering, and it is therefore highly desirable to create an X‐ray microscope that can examine such samples without the extraction of pillars. Computed laminography, where the axis of rotation is not perpendicular to the illumination direction, solves this problem. This entailed the development of a new instrument, LamNI, dedicated to high‐resolution 3D scanning X‐ray microscopy via hard X‐ray ptychographic laminography. Scanning precision is achieved by a dedicated interferometry scheme and the instrument covers a scan range of 12 mm × 12 mm with a position stability of 2 nm and positioning errors below 5 nm. A new feature of LamNI is a pair of counter‐rotating stages carrying the sample and interferometric mirrors, respectively.
A technical description of an instrument that allows 3D nano‐imaging via ptychographic X‐ray laminography is presented.
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