ORCID Profile
0000-0001-8245-162X
Current Organisation
University of York
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Publisher: American Association for the Advancement of Science (AAAS)
Date: 30-10-2020
Abstract: The optoelectronic and photovoltaic applications of polycrystalline hybrid metal halide perovskite films are notable because grain boundaries in most materials cause scattering of charge carriers that decreases performance. Electron microscopy studies of these materials have been hindered by their rapid structural degradation under intense electron beams. Rothmann et al. now present an atomic crystallographic structure of formamidinium lead triiodide (FAPbI 3 ) polycrystalline thin films obtained by low-electron-dose scanning transmission electron microscopy with advanced image processing. The crystal structure sustains substoichiometry in the A-site cation, has a nearly perfect crystallographic alignment between PbI 2 impurity phases and the FAPbI 3 perovskite, and has atomically clean grain boundaries between polycrystalline domains. These features help to explain the films' surprising regenerative ability, their benign grain boundaries where strain and dislocations appear mostly absent, and why excess lead-iodide precursor can be counterintuitively beneficial. Science , this issue p. eabb5940
Publisher: American Physical Society (APS)
Date: 18-04-2018
Publisher: Elsevier BV
Date: 03-2022
DOI: 10.1016/J.ULTRAMIC.2021.113457
Abstract: Quantitative differential phase contrast imaging of materials in atomic-resolution scanning transmission electron microscopy using segmented detectors is limited by various factors, including coherent and incoherent aberrations, detector positioning and uniformity, and scan-distortion. By comparing experimental case studies of monolayer and few-layer graphene with image simulations, we explore which parameters require the most precise characterisation for reliable and quantitative interpretation of the reconstructed phases. Coherent and incoherent lens aberrations are found to have the most significant impact. For images over a large field of view, the impact of noise and non-periodic boundary conditions are appreciable, but in this case study have less of an impact than artefacts introduced by beam deflections coupling to beam scanning (imperfect tilt-shift purity).
Publisher: Oxford University Press (OUP)
Date: 30-07-2020
Publisher: Elsevier BV
Date: 09-2019
DOI: 10.1016/J.MICRON.2019.102701
Abstract: For many soft-matter specimens, transmission electron microscopists face the double-bind of low contrast images, due to weakly-scattering specimens, alongside severe limits on the electron dose that can be used before the specimen is damaged by the electron beam. The combination of these effects causes the resultant micrographs to have very low signal-to-noise. It is well known that varying the defocus aberration can enhance image contrast in electron microscopy. For single-material objects where the variation of absorption and phase contrast are functions of one another, since both are governed by the variation in thickness profile, we show that the thickness profile can be reconstructed at very low dose. The algorithm, first established in X-ray imaging, requires some a priori information but only a single defocussed image of the region of interest, making it more dose efficient than either a conventional transport-of-intensity phase reconstruction (which would require two images and tends to lify noise), or an absorption-contrast analysis of a single in-focus image recorded at the same electron dose (which does not benefit from the significant signal-to-noise enhancement of the present algorithm). These findings are presented through both simulations and experimental data.
Publisher: Oxford University Press (OUP)
Date: 20-12-2022
Abstract: Segmented and pixelated detectors on scanning transmission electron microscopes enable the complex specimen transmission function to be reconstructed. Imaging the transmission function is key to interpreting the electric and magnetic properties of the specimen, and as such four-dimensional scanning transmission electron microscopy (4D-STEM) imaging techniques are crucial for our understanding of functional materials. Many of the algorithms used in the reconstruction of the transmission function rely on the multiplicative approximation and the (weak) phase object approximation, which are not valid for many materials, particularly at high resolution. Herein, we study the breakdown of simple phase imaging in thicker s les. We demonstrate the behavior of integrated center of mass imaging, single-side band ptychography, and Wigner distribution deconvolution over a thickness series of simulated GaN 4D-STEM datasets. We further give guidance as to the optimal focal conditions for obtaining a more interpretable dataset using these algorithms.
Publisher: Elsevier BV
Date: 05-2017
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Laura Clark.