arXiv subjects

Darren Batey

Publications and source records attributed to Darren Batey.

3 recordsLinked to original sources

arXiv2025

Electron volt energy resolution with ptychography using a broadband continuum spectrum

Ptychography is a scanning coherent diffraction imaging technique successfully applied in the electron, visible and x-ray regimes. One of the distinct features of ptychography with respect to other coherent diffraction techniques is its capability of dealing with partial spatial and temporal coherence via the reconstruction algorithm. Here we focus on the temporal and clarify theoretically and with simulations the constraints which affect the energy resolution limits of the ptychographic algorithms. Based on this, we design and perform simulations for a broadband ptychography in the hard x-ray regime, which enables an energy resolution down to 1 eV. We benchmark the simulations against experimental ptychographic data from a nickel test sample, by extracting the x-ray absorption near edge spectrum with energy resolution of 5 eV using a continuum spectrum of 20 eV bandwidth. We review the results, discuss the limitations, and provide guidelines for future broadband ptychography experiments, its prospective applications and potential impact on achieving diffraction limited resolutions.

physics.app-ph↗

arXiv2025

Optics for broadband x-ray ptychography

In conventional x-ray ptychography, diffraction data is 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 3rd and 4th generation synchrotron sources and long scanning times. An alternative approach is to use a broadband illumination in combination with an energy resolving detector. These detectors record the data in a series of energy channels simultaneously, creating a stack 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.

physics.optics↗

arXiv2025

Revealing Nanoscale Ni-Oxidation State Variations in Single-Crystal NMC811 via 2D and 3D Spectro-Ptychography

Enabling lithium (Li)-ion batteries with higher energy densities, longer cycle life, and lower costs will underpin the widespread electrification of the transportation and large-scale energy storage industries. Nickel (Ni)-rich layered oxide cathodes, such as LiNi$_{x}$Mn$_{y}$Co$_{z}$O$_{2}$ (NMC, x > 0.8), have gained popularity due to their high specific capacities and lower cobalt content. However, the standard polycrystalline morphology suffers from accelerated degradation at voltages above 4.2 V versus graphite, due to its increased mechanical and chemical instability. Single-crystal NMC (SC-NMC) has emerged as a promising morphology for suppressing the mechanical instability by preventing intergranular cracking; however, robust methods of understanding its chemical degradation pathways are required. We demonstrate how a high-throughput data collection strategy unlocks the ability to perform 2D and 3D ptychography in minutes, where it currently requires hours, and combine this with X-ray absorption near edge spectroscopy (XANES) to visualise the local Ni oxidation state behaviour in SC-NMC811, with nanometre-scale spatial resolution, and use this as a proxy for state-of-charge. By employing this technique at various stages during lifetime cycling to high voltages (>4.2 V), direct mapping of chemical degradation along the Li channels, identification of nucleation sites, and observation of Ni oxidation state heterogeneities across both electrode and particle scales can be achieved. We further correlate these heterogeneities with the formation and growth of the rocksalt phase and oxygen-induced planar gliding. This methodology will advance the fundamental understanding of how high-Ni layered oxide materials chemically degrade during high-voltage operation, guiding the design of more durable battery materials.

cond-mat.mtrl-sci↗