Periodic Reporting for period 1 - BeamSense (Making more with less: intelligent wavefront design to enable high resolution images of unstable samples.)
Période du rapport: 2020-11-01 au 2022-10-31
In the modern electron microscope, for some materials (typically metals), we can form atomic resolution images relatively easily and and with sufficient clarity to understand atomic positions, bonding and defects to in how the atoms are packed with a crystalline ordering. These atomic scale ordering defects can lead to large scale changes to the properties of the material (such as charge-transfer mechanisms, magnetic structures or strength) - so understanding the atomic structure and ordering of materials is key to understanding global scale properties of materials.
However, many societally important materials (such as photovoltaics - used in solar cells, or battery materials, or pharmacuetical materials) cannot be imaged in this way - the electron beam used to form the images instead damages the sample (damage mechanisms can include heating, localised charging, knocking atoms out of the sample, amongst others). These processes prevent clear images being obtained by using standard electron microscopy imaging protocols. Lacking clear images of these materials hampers our understanding of how their structure and properties are correlated. My overall research objective is to lift this bottleneck, and enable high-resolution, clear images of all materials science samples.
The societal value of this fundamental research comes through in the applications it enables - clearer images of prototypical photovoltaics will enable a more rapid development of efficient sola panels, clearer images of new battery materials will accelerate our understanding of why different options fail to cycle successfully - and so on - materials science progress is built upon progress of accurate materials characterisation.
In this fellowship, I studied a family of algorithms referred to as "ptychography", investigating the potential of these algorithms to enable us to form higher resolution images with a lower electron dose. Ptychographic algorithms (as applied in the scanning transmission electron microscope) make use of every scattered electron that lands on the detector in a diffraction pattern - analysing the position it is scattered to, and how these positions vary with the position of the incoming focussed electron beam can tell us more about the sample, at a higher resolution, than can be interpreted from the conventional bright-field, or dark-field imaging datasets.
Early in this research, it was realised that we lacked verification that these methods can be applied to thick samples, as these scatter the electron beam more than once as it passes through the sample, in a manner not accounted for in the mathematics underlying the algorithm - verifying that these samples could be imaged by using electron ptychography, and verifying the limits of this, became the main focus of this project as the first hurdle to overcome towards the greater goal.
However, many societally important materials (such as photovoltaics - used in solar cells, or battery materials, or pharmacuetical materials) cannot be imaged in this way - the electron beam used to form the images instead damages the sample (damage mechanisms can include heating, localised charging, knocking atoms out of the sample, amongst others). These processes prevent clear images being obtained by using standard electron microscopy imaging protocols. Lacking clear images of these materials hampers our understanding of how their structure and properties are correlated. My overall research objective is to lift this bottleneck, and enable high-resolution, clear images of all materials science samples.
The societal value of this fundamental research comes through in the applications it enables - clearer images of prototypical photovoltaics will enable a more rapid development of efficient sola panels, clearer images of new battery materials will accelerate our understanding of why different options fail to cycle successfully - and so on - materials science progress is built upon progress of accurate materials characterisation.
In this fellowship, I studied a family of algorithms referred to as "ptychography", investigating the potential of these algorithms to enable us to form higher resolution images with a lower electron dose. Ptychographic algorithms (as applied in the scanning transmission electron microscope) make use of every scattered electron that lands on the detector in a diffraction pattern - analysing the position it is scattered to, and how these positions vary with the position of the incoming focussed electron beam can tell us more about the sample, at a higher resolution, than can be interpreted from the conventional bright-field, or dark-field imaging datasets.
Early in this research, it was realised that we lacked verification that these methods can be applied to thick samples, as these scatter the electron beam more than once as it passes through the sample, in a manner not accounted for in the mathematics underlying the algorithm - verifying that these samples could be imaged by using electron ptychography, and verifying the limits of this, became the main focus of this project as the first hurdle to overcome towards the greater goal.
The work performed in this fellowship (1st Nov 2020-31st Oct 2022) differed from that planned due to the global pandemic. Primarily this meant a substantial delay, and then limited access to experimental equipment. This, in turn, meant a pivot to primarily theoretical and computational work.
The headline result of this work, is that it is confirmed that a range of ptychographic and phase imaging algorithms (centre of mass, single sideband, Wigner distribution deconvolution and extended Ptychographic iterative engine) can be used, confidently, to locate atom column positions in samples up to around 12nm thick (depending, of course, on specimen composition and optical settings) - but more usefully, shows that if the STEM ptychographic phase image looks like a map of atoms, it can reasonably be believed to be an accurate representation of the position of those atoms. This is in contrast to many conventional phase imaging methods used in transmission electron microscopy.
Publications:
(published) Clark et al - The effect of dynamical scattering on single-plane phase retrieval in electron ptychography, Microscopy and Microanalysis, https://academic.oup.com/mam/advance-article/doi/10.1093/micmic/ozac022/6948181(s’ouvre dans une nouvelle fenêtre)
(published) Mawson et al - https://doi.org/10.1016/j.ultramic.2021.113457(s’ouvre dans une nouvelle fenêtre)
Dissemination has occurred at multiple conferences and congresses during the funded period, including
EMAG2021 (virtual)
M&M 2022 (Portland, US)
PICO 2022 (Vaals, Netherlands)
And events floowing the conclusion of the funded period, including:
Invited advanced school lecture at IOP Magnetism Winter School - Dec 2022, Abingdon UK
Invited conference presentation MRS fall 2022 - Nov/Dec 2022, Boston US
Exploitation of these advances will enable future research, including developments in Leeds (new ptychographic microscope to be installed in the coming months), York (new microscope installation underway, my new host institute), and ptychographic work with collaborators at the ePSIC and RFI national UK microscopy facilities, the dept of Materials at Oxford University and MCEM at Monash University Australia.
The headline result of this work, is that it is confirmed that a range of ptychographic and phase imaging algorithms (centre of mass, single sideband, Wigner distribution deconvolution and extended Ptychographic iterative engine) can be used, confidently, to locate atom column positions in samples up to around 12nm thick (depending, of course, on specimen composition and optical settings) - but more usefully, shows that if the STEM ptychographic phase image looks like a map of atoms, it can reasonably be believed to be an accurate representation of the position of those atoms. This is in contrast to many conventional phase imaging methods used in transmission electron microscopy.
Publications:
(published) Clark et al - The effect of dynamical scattering on single-plane phase retrieval in electron ptychography, Microscopy and Microanalysis, https://academic.oup.com/mam/advance-article/doi/10.1093/micmic/ozac022/6948181(s’ouvre dans une nouvelle fenêtre)
(published) Mawson et al - https://doi.org/10.1016/j.ultramic.2021.113457(s’ouvre dans une nouvelle fenêtre)
Dissemination has occurred at multiple conferences and congresses during the funded period, including
EMAG2021 (virtual)
M&M 2022 (Portland, US)
PICO 2022 (Vaals, Netherlands)
And events floowing the conclusion of the funded period, including:
Invited advanced school lecture at IOP Magnetism Winter School - Dec 2022, Abingdon UK
Invited conference presentation MRS fall 2022 - Nov/Dec 2022, Boston US
Exploitation of these advances will enable future research, including developments in Leeds (new ptychographic microscope to be installed in the coming months), York (new microscope installation underway, my new host institute), and ptychographic work with collaborators at the ePSIC and RFI national UK microscopy facilities, the dept of Materials at Oxford University and MCEM at Monash University Australia.
As a project developing fundamental science, the impact will follow on a rather longer timescale than the 24month fellowship. However, the results generated in this work have set the course for my next fellowship (a Royal Society University Research Fellowship) in which the next steps towards widespread application of these new methodologies will be made.
The primary progress beyond state of the art was the confirmation that ptychographic algorithms in electron microscopy can be applied to samples of realistic thicknesses, even though the algorithms are mathematically founded on a thinner sample regime (known as the phase object approximation). This will scaffold the validity of future experimental applications and means that the upcoming experimental results can be interpreted with confidence (that a bright dot in the image will be in the correct position to accurately reflect the position of the atoms).
This will enable robust development of the rapidly growing field of electron ptychography - which in turn, as a high resolution materials characterisation technique, will enable accellerated developments across materials science (photovoltaics, battery materials, pharmaceutical materials, amongst others) due to it's clear resolution of lighter atoms amongst heavier atoms, and better dose efficiency vs conventional imaging methods.
The primary progress beyond state of the art was the confirmation that ptychographic algorithms in electron microscopy can be applied to samples of realistic thicknesses, even though the algorithms are mathematically founded on a thinner sample regime (known as the phase object approximation). This will scaffold the validity of future experimental applications and means that the upcoming experimental results can be interpreted with confidence (that a bright dot in the image will be in the correct position to accurately reflect the position of the atoms).
This will enable robust development of the rapidly growing field of electron ptychography - which in turn, as a high resolution materials characterisation technique, will enable accellerated developments across materials science (photovoltaics, battery materials, pharmaceutical materials, amongst others) due to it's clear resolution of lighter atoms amongst heavier atoms, and better dose efficiency vs conventional imaging methods.