Tomographic reconstruction of a three-dimensional magnetization vector field

Using x-ray magnetic nanotomography the internal magnetization structure within extended samples can be determined with high spatial resolution and element specificity, without the need for assumptions or prior knowledge of the magnetic properties of a sample. Here we present the details of a new algorithm for the reconstruction of a three-dimensional magnetization vector field, discussing both the mathematical description of the problem, and details of the gradient-based iterative reconstruction routine. To test the accuracy of the algorithm the method is demonstrated for a complex simulated magnetization configuration obtained from micromagnetic simulations. The reconstruction of the complex three-dimensional magnetic nanostructure, including the surroundings of magnetic singularities (or Bloch points), exhibits an excellent qualitative and quantitative agreement with the simulated magnetic structure. This method provides a robust route for the reconstruction of internal three-dimensional magnetization structures obtained from x-ray magnetic tomographic datasets, which can be acquired with either hard or soft x-rays, and can be applied to a wide variety of three-dimensional magnetic systems

Three-dimensional magnetization structures revealed with X-ray vector nanotomography

In soft ferromagnetic materials, the smoothly varying magnetization leads to the formation of fundamental patterns such as domains, vortices and domain walls<sup>1</sup>. These have been studied extensively in thin films of thicknesses up to around 200 nanometres, in which the magnetization is accessible with current transmission imaging methods that make use of electrons or soft X-rays. In thicker samples, however, in which the magnetization structure varies throughout the thickness and is intrinsically three dimensional, determining the complex magnetic structure directly still represents a challenge<sup>1, 3</sup>. We have developed hard-X-ray vector nanotomography with which to determine the three-dimensional magnetic configuration at the nanoscale within micrometre-sized samples. We imaged the structure of the magnetization within a soft magnetic pillar of diameter 5 micrometres with a spatial resolution of 100 nanometres and, within the bulk, observed a complex magnetic configuration that consists of vortices and antivortices that form cross-tie walls and vortex walls along intersecting planes. At the intersections of these structures, magnetic singularities—Bloch points—occur. These were predicted more than fifty years ago<sup>4</sup> but have so far not been directly observed. Here we image the three-dimensional magnetic structure in the vicinity of the Bloch points, which until now has been accessible only through micromagnetic simulations, and identify two possible magnetization configurations: a circulating magnetization structure<sup>5</sup> and a twisted state that appears to correspond to an ‘anti-Bloch point’. Our imaging method enables the nanoscale study of topological magnetic structures<sup>6</sup> in systems with sizes of the order of tens of micrometres. Knowledge of internal nanomagnetic textures is critical for understanding macroscopic magnetic properties and for designing bulk magnets for technological applications<sup>7</sup>

4D Early Age Cement Hydration Analysis by Ptychographic X-ray Computed Tomography and Machine Learning Segmentation

Cement manufacturing is responsible for ~7% of the anthropogenic CO2 emissions and hence, decreasing the CO2 footprint, in a sustainable, safe and cost-effective way, is a top priority. To fully understand the binder main properties and to decrease their CO2 footprints, a sound description of their spatially resolved mineralogy is necessary. Developing this knowledge is very challenging as about half of the volume of hydrated cement is a nanocrystalline component, calcium silicate hydrate (C-S-H) gel. Furthermore, other poorly crystalline phases (e.g. iron siliceous hydrogarnet or silica oxide) coexist. Here, we have used ptychographic X-ray computed tomography (PXCT) for understanding the first days of cement hydration with the final goal to improve the mechanical strength performances of low-CO2 cements

3D imaging of clay minerals inside sandstone: pushing the spatial resolution limits using ptychographic tomography

Characterization of microporous, clay-sized particles in natural stone is essential for the understanding of their dynamics. These processes are importand in the fields of oil and gas, groundwater, building stone weathering and soil science. Methods such as X-ray micro-computed tomography is an excellent tool to study features larger than or just under 1 μm, but below the 400 nm limit, the technique falls short. Although destructive methods exists (e.g. FIB/SEM), non-destructive imaging at these very high resolutions has been impossible, until recent developments at synchrotron beam lines. In this study, we use ptychographic tomography at the cSAXS beam line of the PSI in Switzerland, for imaging of clay microstructure at resolutions down to 45 nm, which is the first application of ptychographic tomography for geological samples to our knowledge. During these experiments, relative humidity of the sample’s environment was controlled, in order to asses the influence of R.H. on the analyzed clay minerals. Based on these images, quantitative data on mineral content, porosity, connectivity and behavior under changing environmental conditions of clay mineral clusters was acquired

Quantitative disentanglement of nanocrystalline phases in cement pastes by synchrotron ptychographic X-ray tomography

Mortars and concretes are ubiquitous materials with very complex hierarchical microstructures. To fully understand their main properties and to decrease their CO2 footprint, a sound description of their spatially resolved mineralogy is necessary. Developing this knowledge is very challenging as about half of the volume of hydrated cement is a nanocrystalline component, calcium silicate hydrate (C-S-H) gel. Furthermore, other poorly crystalline phases (e.g. iron siliceous hydrogarnet or silica oxide) may coexist, which are even more difficult to characterize. Traditional spatially resolved techniques such as electron microscopy involve complex sample preparation steps that often lead to artefacts (e.g. dehydration and microstructural changes). Here, synchrotron ptychographic tomography has been used to obtain spatially resolved information on three unaltered representative samples: neat Portland paste, Portland–calcite and Portland–fly-ash blend pastes with a spatial resolution below 100 nm in samples with a volume of up to 5 x 104 mm3. For the neat Portland paste, the ptychotomographic study gave densities of 2.11 and 2.52 g cm -3 and a content of 41.1 and 6.4 vol% for nanocrystalline C-S-H gel and poorly crystalline iron siliceous hydrogarnet, respectively. Furthermore, the spatially resolved volumetric mass-density information has allowed characterization of inner-product and outer-product C-S-H gels. The average density of the inner-product C-S-H is smaller than that of the outer product and its variability is larger. Full characterization of the pastes, including segmentation of the different components, is reported and the contents are compared with the results obtained by thermodynamic modelling.This work has been supported by MINECO through BIA2014-57658 and BIA2017-82391-R research grants, which are cofunded by FEDER. Instrumentation development was supported by SNF (R’EQUIP, No. 145056,‘OMNY’) and the Competence Centre for Materials Science and Technology (CCMX) of the ETH-Board, Switzerland

Ab initio nonrigid X-ray nanotomography

Abstract: 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

Accelerated deep self-supervised ptycho-laminography for three-dimensional nanoscale imaging of integrated circuits

Three-dimensional inspection of nanostructures such as integrated circuits is important for security and reliability assurance. Two scanning operations are required: ptychographic to recover the complex transmissivity of the specimen; and rotation of the specimen to acquire multiple projections covering the 3D spatial frequency domain. Two types of rotational scanning are possible: tomographic and laminographic. For flat, extended samples, for which the full 180 degree coverage is not possible, the latter is preferable because it provides better coverage of the 3D spatial frequency domain compared to limited-angle tomography. It is also because the amount of attenuation through the sample is approximately the same for all projections. However, both techniques are time consuming because of extensive acquisition and computation time. Here, we demonstrate the acceleration of ptycho-laminographic reconstruction of integrated circuits with 16-times fewer angular samples and 4.67-times faster computation by using a physics-regularized deep self-supervised learning architecture. We check the fidelity of our reconstruction against a densely sampled reconstruction that uses full scanning and no learning. As already reported elsewhere [Zhou and Horstmeyer, Opt. Express, 28(9), pp. 12872-12896], we observe improvement of reconstruction quality even over the densely sampled reconstruction, due to the ability of the self-supervised learning kernel to fill the missing cone.Comment: 13 pages, 5 figures, 1 tabl

A lathe system for micrometre-sized cylindrical sample preparation at room and cryogenic temperatures

A simple two-spindle based lathe system for the preparation of cylindrical samples intended for X-ray tomography is presented. The setup can operate at room temperature as well as under cryogenic conditions, allowing the preparation of samples down to 20 and 50 µm in diameter, respectively, within minutes. Case studies are presented involving the preparation of a brittle biomineral brachiopod shell and cryogenically fixed soft brain tissue, and their examination by means of ptychographic X-ray computed tomography reveals the preparation method to be mainly free from causing artefacts. Since this lathe system easily yields near-cylindrical samples ideal for tomography, a usage for a wide variety of otherwise challenging specimens is anticipated, in addition to potential use as a time- and cost-saving tool prior to focused ion-beam milling. Fast sample preparation becomes especially important in relation to shorter measurement times expected in next-generation synchrotron sources