Investigating ptychography for light-element imaging in the STEM and CTEM

Lead Research Organisation: University of Oxford
Department Name: Materials

Abstract

The research proposed here aims to develop entirely new ways of imaging in the scanning transmission electron microscope (STEM) and conventional transmission electron microscope (CTEM), and to use these methods to study materials problems. The overarching aim that forms the basis of the project is to use recently developed fast pixelated detectors to record two-dimensional diffraction patterns as a function of the position of a focused, atomic-scale, electron beam performing a two-dimensional scan in STEM. By the principle of reciprocity, an equivalent data set can be recorded using a tilt series in CTEM. The resulting four-dimensional data contains information about the phase shift that results from transmission through the sample.

Using an approach similar to holography, the project will develop new methods to retrieve information about the composition of the sample, the strain in the sample and the three-dimensional ordering in the sample can be measured. These developments will allow new types of materials to be observed at atomic resolution and new types of measurements about materials to be made. The project will involve developing skills ranging from fundamental studies of electron scattering processes to statistical methods and parallel computing along with developing the appropriate experiments on the microscope.

Although ptychography has become established in light and X-ray optics, its application to electron imaging has been more limited. The current project makes use of developments in fast pixelated detectors to unlock the potential of electron ptychography, and to combine it with existing electron imaging methods.

The project is partially supported by JEOL UK Ltd, and has the potential to unlock new applications for transmission electron microscopy, including to light and radiation sensitive materials, to materials containing a wide range of atomic numbers, and to measure 3D sample information. It aligns with existing EPSRC funding under grant number EP/M010708/1, and both the Physical Sciences and Research Infrastructures themes of the EPSRC. It will support a wide range of EPSRC research areas, in particular energy materials (catalysts, Li battery materials), functional ceramics and biomaterials.

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
1801646 Studentship EP/N509711/1 01/10/2016 30/09/2019 Colum O'Leary
 
Description When imaging materials that are light or easily damaged during the imaging process, one must have a powerful imaging method. Ptychography is a very powerful imaging method in electron microscopy. The research done under this project has further pushed the boundaries of this imaging method. For example, the minimum intensity usable for a given experiment has been determined. In addition to this, the optical properties of ptychography have been enhanced such that more information can be retrieved from biological samples.
Not only has new knowledge been generated from this research, but more methods of imaging have been developed. We have implemented a technique of collecting ptychography data from an electron microscope using a binary counting mode (i.e. when a camera can only count ones and zeros). This allows much faster recording speeds, allowing imaging of materials which could never be imaged before using a scanning transmission electron microscope (STEM).

Optimisation of ptychography for conventional transmission electron microscopy (CTEM) has also been (and is currently being) developed, although the progress in this area is hindered by experimental instabilities and aligning of the acquired image series.

Now that the optimisation of ptychography to light materials has been successful, this has opened-up a new question: how successfully can we image in three dimensions using ptychography? It is known that 3D information can be obtained from such experiments which allow access to information from different depths. Such 3D information is of tremendous importance to manufacturing, pharmaceutical and biomedical industries.

Collaborations which have developed from this research include those with Diamond Light Source, University of Cambridge and University of Liverpool. These collaborations will hopefully lead to the development of further techniques, imaging of novel materials which have not yet been imaged on an atomic scale, and the implementation of the developed methods throughout the materials science community.

In summary, the research undertaken has made significant progress in maximizing information available while using as little intensity as possible to image materials in a scanning transmission electron microscope (STEM). There is still further work to be done, but the base of findings will make further research much more streamlined. The collaborations developed will help to communicate my research throughout the academic community.
Exploitation Route The research which I have undertaken will hopefully be implemented not only throughout the electron microscopy research facility in Oxford, but at the electron Physical Sciences Imaging Centre (ePSIC) at Diamond Light Source. ePSIC is the largest national centre for electron microscopy, serving academic research groups both throughout the UK and across the world. Due to the strong collaboration between Oxford and ePSIC, I envisage that the methods developed within my research can be used for research throughout the global academic community. Materials science research groups will often be closely linked to industry, which will in turn make use of my research.
Sectors Aerospace, Defence and Marine,Chemicals,Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology,Transport

 
Description The development of my research has shown the applications of fast pixelated detectors for electron microscopy, which has led to an increasing demand for these detectors across the UK and abroad. This has caused a number of companies, such as UK-based Quantum Detectors Ltd, to develop and improve their camera technology, creating a higher demand for technology jobs across the UK.
First Year Of Impact 2017
Sector Aerospace, Defence and Marine,Chemicals,Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology
Impact Types Economic

 
Description Hertford College Senior Scholarship
Amount £8,000 (GBP)
Organisation University of Oxford 
Sector Academic/University
Country United Kingdom
Start 09/2018 
End 07/2020
 
Description Worshipful Company of Scientific Instrument Makers Scholarship
Amount £2,000 (GBP)
Organisation Worshipful Company of Scientific Instrument Makers 
Sector Charity/Non Profit
Country United Kingdom
Start 09/2018 
End 07/2019
 
Description Worshipful Company of Armouerers and Brasiers Networking Event 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Supporters
Results and Impact 100 people, ranging from students, to teachers to industrial and academic staff attended a networking event setup by the Worshipful Company of Armourers and Brasiers (educational charity). I participated in an 'elevator pitch' competition where I described the impact of my research to an audience.
Year(s) Of Engagement Activity 2018