Multi-Dimensional Electron Microscope

In the past decade or so, there has been something of a revolution in electron microscopy, a technique central to much of materials science, and parts of solid state chemistry and condensed matter physics. That revolution has been based around developments both in hardware, improving electron optics, monochromation, camera sensitivity and spectrometer efficiency, and in software, with code now able to process vast data sets in a robust and speedy fashion to extract the key information. This proposal, for a 'multi-dimensional electron microscope', or MDEM, brings together many of these development into a single instrument that is dedicated to analysing materials at the atomic- and nano-scales in two and three dimensions. The flexibility and power of modern microscopy resides also in the ability to use multiple detectors, cameras and spectrometers simultaneously so that multiple signals can be acquired from a single electron beam position - this is known as 'multi-modal' microscopy and when combined with the MDEM approach leads to a remarkable detailed investigation of structure and composition, crystallography and physico-chemical behaviour.

The MDEM is based around a scanning electron microscope that can operate from low voltages (e.g. 60kV) to high voltages (e.g. 300kV), the former being used for the study of samples with low atomic number and/or of low dimension, such as graphene, where knock-on damage may be predominant, the latter for organic crystals where radiolysis can be hugely detrimental. The MDEM is designed to investigate samples that have previously been considered too beam-sensitive to examine with conventional methods. By using the latest generation of direct electron detectors, with remarkably sensitive and linear response, we are able to record diffraction patterns from organic crystals in just a few milliseconds, before the crystal degrades under the beam. We will apply this method to study the nanoscale defect structure in pharmaceutical crystals, the development of dislocations, stacking faults and twins and importantly the interfaces between dissimilar organic crystals. Remarkably little is known about the microstructure of processed 'semi-crystalline' polymers, especially aliphatic polymers such as polyethylene and related alkanes. By using scanning electron diffraction methods we will use the MDEM to reveal hitherto unseen polymer nano-structure.

Electron tomography, or 3D imaging, can now be extended to a huge range of nanoscale materials and can be combined with diffraction, x-ray and energy loss spectroscopy to provide a full 3D picture of the materials' structure, composition and crystallography. The method is almost universally applicable and the range of materials science enabled by this method is huge. The multi-modal multi-dimensional aspect of the MDEM means we are able to acquire vast amounts of information and new software algorithms will be developed to process the data in a robust, efficient and meaningful fashion. These algorithms use the latest ideas in machine learning and in compressed sensing, where prior information is built into any reconstruction or interpretation of the image, tomogram or spectrum.

There are numerous material systems and devices that will benefit from the MDEM approach and, in addition to those already mentioned, we present a few more examples: perovskite solar cells, nitride semiconductors, engineering alloys such as nano-structured steels and Ni-base superalloys, low-dimensional dichalcogenides , magnetic skyrmionic materials, heterogeneous catalysts, MOFs and metallic glasses.

MDEM is a research-enabling platform which combines complementary electron microscopy techniques to build a detailed understanding of structure, composition and properties of materials. MDEM's multi-dimensional approach relies on efficient acquisition of images, diffraction patterns and spectroscopic data, that allow to reconstruct 3D, 4D and even 6D data sets, and closely monitor the evolution of specimens under the influence of external stimuli. It will be managed within an existing Cambridge University facility, WEMS, to guarantee access and support to as wide a user-base as possible. User fees, both from internal and external users, will be directed to the maintenance and upgrade of the microscope and ancillary equipment, to ensure continuous and reliable operation throughout the lifetime of the instrument.

Research projects in all areas of Materials Science will benefit from access to MDEM and to the suite of analysis software developed for interpretation and visualisation of multidimensional datasets. Among the most likely academic beneficiaries are the graduates from the CDTs in Graphene Technology and Sustainable and Functional Nano, and researchers involved in advanced materials research or solid state physics and chemistry.

We believe that MDEM will strongly enhance the capability of UK microscopy, through a robust and flexible analytical platform. The characterization techniques available on MDEM are highly relevant to industry, but are not normally accessible within one instrument and therefore are seldom used to their full potential, given that the strict cost/benefit constrains industry faces. Competitive markets require both innovation and strict quality control, and MDEM is ideally placed to support both, and hence to enhance the eco-system. Proactive engagement with industry, in turn, will benefit the academic community, creating opportunities for longer term projects and collaborations.

As well as attracting academic and industrial collaborations, MDEM will generate data that will interest and inspire young scientists, as well as the general public. In line with the Open Data ideal, datasets acquired with MDEM will be shared online, together with analysis software and tutorials aimed at high school and college students, to develop an understanding of Materials Science through practical data analysis.