Wiebe Stolp

In conventional x-ray ptychography, diffraction data are collected by scanning a sample through a monochromatic and spatially coherent x-ray beam. A high-resolution image is then retrieved using an iterative algorithm. Combined with a scan of the incident photon energy, it is also possible to access chemical and elemental information. Although powerful, the high brilliance required currently constrains the method to third and fourth generation synchrotron sources and long scanning times. An alternative approach is to use broadband illumination in combination with an energy resolving detector. These detectors record the data in a series of energy channels simultaneously, creating stacks of coherent data suitable for a ptychographic reconstruction. This approach promises to unlock the full power of the radiation source and provide spectral imaging at a higher rate and in a single acquisition. However, these detectors currently saturate well below reaching the flux rates produced at synchrotrons, which is preventing the uptake of this approach. Furthermore, current monochromatic synchrotron setups typically employ Fresnel zone plates for pre-sample focusing due to their stability, flexibility, and affordability, but these diffractive optics limit the spectral bandwidth that the setup can accept. In this article, we analyze the problem and consider alternative optics that can both maximize the total photon detection rates and broaden the tolerable bandwidth. Broadband x-ray ptychography has the potential to dramatically reduce data collection times at synchrotron sources but also to harness the full power of lower brilliance sources and transition x-ray ptychography into a laboratory technique.

X-ray ptychography is a robust microscopy technique with nanoscale resolution that requires a spatially and temporally coherent illumination. In a typical setup, the temporal coherence requirements are satisfied by monochromating the x-ray source, e.g., using a crystal monochromator. Recent studies have shown that energy resolving, or hyperspectral, detectors can to some extent replace the role of the monochromator to perform, e.g., edge-subtraction ptychographic imaging with broadband radiation in a single acquisition. Scaling this capability from two dimensions (2D) to three dimensions (3D), and from a single absorption edge to multiple edges, is critical for its applications in structural and elemental characterisation. The method is hitherto limited by the inherently lower maximum count rate of hyperspectral detectors and the chromaticity of the optics often used in x-ray ptychography experiments, namely Fresnel zone plates. In this work, we design an optimized broadband spectroscopic ptychography setup and use it to perform 3D hyperspectral imaging of particles of battery material containing various percentages of nickel, manganese, cobalt (NMC). We show that we can identify different compositions based on their spectral response. We discuss the results and provide guidelines for future exploitation of the method in laboratory settings.

Irregular Li heterostructure growth at the interphase between the solid electrolyte and anode reduces solid-state Li metal battery (SSLMB) performance, but the fundamental cause is still elusive. Measuring and imaging Li⁺ ion diffusion in operando inside an SSLMB using a commercially standard cell configuration are extremely challenging because the ultra-light Li element exhibits a minute signal-to-noise ratio using most x-ray-related characterization methods, and the weak x-ray signals of Li⁺ are buried by strong signals of other heavy transition metal elements in the cathode and battery enclosure. Here, we pioneer novel operando correlative imaging of coupling x-ray Compton scattering with computed tomography (XCS-CT), which is able to quantify the interplay between spatially resolved Li⁺ ion diffusion kinetics and Li⁰ metal structure growth at the interphases of both the anode and cathode sides inside a full-cell SSLMB using a solid polymer electrolyte (SPE) and commercially standard cell configuration during (dis)charging. We show a 61% increase in the efficiency of extracting Li⁺ ions from the cathode LiNi_0.6Mn_0.2Co_0.2O₂ to the anode during charging at 0.1 C compared with at 1 C due to restricted Li⁺ ion diffusion at the higher rate inside SSLMB. However, this led to the formation of a more irregular interfacial morphology, consisting not only of Li⁰ dendrites, but also sub-surface pore formation at the anode/SPE interphase. We find that surprisingly, the irregular Li⁰ structure initiation and growth are accelerated during the first Li stripping step, not the Li plating step, and the root cause is the onset imbalance of Li⁺ ion diffusion and redox reactions between the anode and cathode. These insights highlight the benefits of asymmetric charging and discharging rates as a promising solution to improving SSLMB performance with SPEs. The operando correlative XCS-CT imaging technique has the potential to study the relationship between active ion concentrations and buried morphological changes for a variety of battery chemistries.

Laser-plasma accelerators are compact linear accelerators based on the interaction of high-power lasers with plasma to form accelerating structures up to 1000 times smaller than standard radiofrequency cavities, and they come with an embedded X-ray source, namely betatron source, with unique properties: small source size and femtosecond pulse duration. A still unexplored possibility to exploit the betatron source comes from combining it with imaging methods able to encode multiple information like transmission and phase into a single-shot acquisition approach. In this work, we combine edge illumination-beam tracking (EI-BT) with a betatron X-ray source and present the demonstration of multimodal imaging (transmission, refraction, and scattering) with a compact light source down to the femtosecond timescale. The advantage of EI-BT is that it allows multimodal X-ray imaging technique, granting access to transmission, refraction and scattering signals from standard low-coherence laboratory X-ray sources in a single shot.