arXiv subjects

Angus I Kirkland

Publications and source records attributed to Angus I Kirkland.

3 recordsLinked to original sources

arXiv2025

Atomic resolution imaging of the strength and 3D direction of atomic displacements in functional oxide thin films

Atomic resolution imaging is key to understanding thin film growth and how a particular set of conditions influences properties. Whilst such imaging in the scanning transmission electron microscope (STEM) has had transformative impact in nanoscience, it forms projection images and provides no direct information about displacements perpendicular to the image plane. In this article we show that it is possible to make atomic resolution maps of the direction and magnitude of La displacements at ~30° to the imaging plane in a La2CoMnO6 thin film on (111) LSAT (LaAlO3-La(Sr,Ta)O3) using a 4-dimensional STEM (4DSTEM) methodology. This reveals that the La modulation lies preferentially in the interface plane, and is strongly suppressed close to the epitaxial interface, and further reveals how the modulation varies with distance from the interface with unit cell resolution. These details would be completely invisible to all prior techniques in electron microscopy and this sheds light on why this particular substrate in this orientation best promotes double perovskite cation ordering, and the consequent optimal magnetic ordering for this thin film system. The approach used herein of fitting atomic resolution 4DSTEM data to determine crystal parameters opens the door for a new era of atomic-resolution crystallography.

cond-mat.mtrl-sci↗

arXiv2024

A high-performance reconstruction method for partially coherent ptychography

Ptychography is now integrated as a tool in mainstream microscopy allowing quantitative and high-resolution imaging capabilities over a wide field of view. However, its ultimate performance is inevitably limited by the available coherent flux when implemented using electrons or laboratory X-ray sources. We present a universal reconstruction algorithm with high tolerance to low coherence for both far-field and near-field ptychography. The approach is practical for partial temporal and spatial coherence and requires no prior knowledge of the source properties. Our initial visible-light and electron data show that the method can dramatically improve the reconstruction quality and accelerate the convergence rate of the reconstruction. The approach also integrates well into existing ptychographic engines. It can also improve mixed-state and numerical monochromatisation methods, requiring a smaller number of coherent modes or lower dimensionality of Krylov subspace while providing more stable and faster convergence. We propose that this approach could have significant impact on ptychography of weakly scattering samples.

physics.comp-ph↗

arXiv2021

Oleylamine aging of PtNi nanoparticles giving enhanced functionality for the oxygen reduction reaction

We report a rapid solution-phase strategy to synthesize alloyed PtNi nanoparticles which demonstrate outstanding functionality for the oxygen reduction reaction (ORR). This one-pot co-reduction colloidal synthesis results in a monodisperse population of single-crystal nanoparticles of rhombic dodecahedral morphology, with Pt enriched edges and compositions close to Pt1Ni2. We use nanoscale 3D compositional analysis to reveal for the first time that oleylamine (OAm)-aging of the rhombic dodecahedral Pt1Ni2 particles results in Ni leaching from surface facets, producing aged particles with concave faceting, an exceptionally high surface area and a composition of Pt2Ni1. We show that the modified atomic nanostructures catalytically outperform the original PtNi rhombic dodecahedral particles by more than 2-fold and also yield improved cycling durability. Their functionality for the ORR far exceeds commercially available Pt/C nanoparticle electrocatalysts, both in terms of mass-specific activities (up to a 25-fold increase) and intrinsic area-specific activities (up to a 27-fold increase).

cond-mat.mtrl-sci↗