Dynamic in-situ microscopy relating structure and function

Complex, electron-beam sensitive systems include organic crystals, hybrid organic-inorganic materials, some inorganic materials such as hydrates as well as multiphase solid/liquid and solid/gas materials. Arguably they constitute the majority of systems of current interest across a wide range of scientific and engineering disciplines including chemistry and chemical engineering, engineering materials, food science, biology and increasingly physics and electronic engineering.

For the purposes of this presentation Professor Brydson defines in-situ as the native-state analysis of such complex, beam sensitive materials and systems, in that they remain unmodified by interaction with the electron beam which is well-known to alter both the structure and chemistry of the specimen. Here, he also concentrates almost exclusively on transmission electron microscopy (TEM) of thin specimens. 

Electron dose is related to the energy absorbed by the specimen during electron irradiation and can be a function of both the electron fluence and fluence rate in the TEM. Professor Brydson discusses a number of useful concepts for TEM imaging and/or chemical analysis, including a dose budget for experiments and also a dose-limited resolution. We also highlight the current state-of-the-art in dose control during imaging and spectroscopy including the use of scanning TEM (STEM) as opposed to conventional TEM (CTEM), compressed sensing methods and the cryo-preservation of samples.

Finally, he also discusses dynamic studies of such complex materials and systems including the use of in-situ liquid and gas cells TEM holders, which have their own additional limitations due to dose, as well as the use of time-resolved cryo-methods to provide snapshots of dynamic systems.

Catalysts are operating far from thermodynamic equilibrium in an open system that exchanges heat and matter with the surrounding. In their active state, they are supposed to repeatably facilitate sequences of reaction steps of a catalytic cycle. The combination of non-equilibrium conditions and cyclic behaviour can result in complex dynamics and formation of dissipative structures. Such structures are difficult to study because they only exist under reactive conditions. Furthermore, they are difficult to predict using computational methods because of the non-linearity of the underlying kinetics. Structure-function relationships have thus to be studied under relevant reaction conditions. While in situ TEM enables observation of atomistic details under conditions of slow kinetics, in situ SEM delivers complementary information about catalyst dynamics at reduced lateral resolution and provides insight about collective phenomena that are controlled by heat and mass transport. As will be shown in the presentation, the combination of in situ SEM with in situ TEM enables a multi-scale approach for the study of catalyst dynamics from the Å to the mm range and across pressures ranging from 10^-5 to 10⁺⁵ Pa. Combined with simultaneous detection of reaction products by RGA it is possible to correlate structural dynamics with catalytic activity.

Recent advances in using noble metals to confine light to the sub-nm³ scale through advanced plasmonics is opening up a new realm of 'picoscopy'. Professor Baumberg will show how a wide range of dynamic motions of atoms and molecules can be studied on microsecond timescales under ambient conditions. This explores crucial realms of catalytic surface reconstructions and electrochemical interfaces that have been inaccessible.

Professor Baumberg will show how simple nano-architectures enable such trapping of visible light, and how elastic and inelastic light scattering reveal detailed spectral information about extremely small volumes of space. A few examples will highlight the light-induced motion of individual gold atoms, of flickering defects in metal interfaces, and of individual bonds in single molecules moving in real time.

Pearl Jam’s hit, 'The Light Years', declares "We were but stones, light made us stars". Bringing light to the transmission electron microscope (TEM) promises to transform our understanding of materials, enabling both direct observation of light-mediated processes and detection of optical emission with atomic scale resolution. To help achieve this goal, Professor Dionne's lab is developing capabilities for concurrent optical and electron microscopy within an environmental TEM. This presentation will describe their efforts to visualise a variety of plasmonic processes in situ with nanometre-to-atomic scale resolution. The group focuses in particular on i) observing plasmon-driven chemical transformations in nanoparticles; ii) detecting quantum light emission from two-dimensional materials; and iii) developing TEM-Raman with nanometre-scale resolution. First, they study the photocatalytic dehydrogenation of Au-Pd systems, in which the Au acts as a plasmonic light absorber and Pd serves as the catalyst. They find that plasmons modify the rate of distinct reaction steps differently, increasing the overall rate more than ten-fold. Plasmons also open a new reaction pathway that is not observed without illumination, laying a foundation for site-selective and product-specific photocatalysts. Secondly, the group uses scanning transmission electron microscopy and cathodoluminescence spectroscopy to investigate colour centres in two-dimensional hexagonal boron nitride, a wide bandgap material capable of room-temperature, high-brightness visible quantum emission. They find that sharp, single-photon emission peaks are usually associated with regions of multiple fork dislocations, facilitating design of next-generation two-dimensional materials and devices. Finally, they describe a new technique for high-resolution spectroscopy in the TEM: electron-and-light-induced stimulated Raman scattering (ELISR). In particular, theyleverage the electron beam as a highly-localised Angstrom-scale source to locally excite the plasmonic resonances of individual nanoparticles, which stimulate local Raman scattering. They show how ELISR can be used to map molecular signatures with nanometre-scale resolution. 

Environmental transmission electron microscopy (E-TEM) attracts a strong interest of materials scientists, particularly, those of batteries and catalysts, because the actual chemical reaction processes in gases and liquids should be clarified in real space and in atomic level. E-TEM observations of thick samples also become important for cutting-edge materials in practical use. 3D observation is also necessary for clarifying morphologies of practical catalysts.

Professor Tanaka and colleagues have developed 1MV TEM/STEM equipped with an open-type environmental cell which enables observations in 100 Torr of hydrogen, oxygen, nitrogen and carbon mono-oxide(CO) gases, named 'Reaction Science HVEM'(RSHVEM).

In this talk, Professor Tanaka would like to present new data obtained by the instrument such as (1) in-situ observation of porous gold catalysts, whose inner surfaces with zigzag atom arrangement enhance oxidation of CO gas, (2) observation of diesel soot oxidized in air, and (3) in-situ observation of fractures related to 'hydrogen brittleness' for a Cu/Si interface and  grain boundaries in Ni3Al alloys. Observation of lithium battery materials is also available using a non-exposure transfer holder as well as QMAS ability. Finally, advantages and future prospects of E-HVEM are discussed.

Many heterogeneous chemical reactions utilise gas-solid catalyst reactions at elevated temperatures and they play a pivotal role in the production of energy, healthcare, pollution control and food. The dynamic catalytic chemical reactions take place at the atom level. Understanding atomic structure evolution and the ensuing catalyst function are vital to developing novel materials and improved chemical processes. However due to limitations of the instrumentation these atomic processes were not well understood. The development of the first atomic resolution-Environmental Transmission Electron Microscope (atomic resolution-ETEM) [Boyes and Gai, Ultramicroscopy 67 (1997) 197], enables the visualisation and analysis of gas-solid catalyst reactions at the atomic level leading to key discoveries and the development is used globally. The ETEM has been advanced to analytical environmental scanning TEM (ESTEM) with single atom resolution and full analytical capabilities. Novel E(S)TEM imaging and analysis in real-time in controlled real-world reaction environments reveal single atom dynamics in fuel cell catalysts, fuels including sustainable biofuels, healthcare applications and ammonia synthesis for agricultural products in food production. The development of a liquid holder enables imaging and analysis of chemical reactions in liquid environments. The dynamic studies, in combination with chemical methods, provide unique insights into atoms in action and atomic scale reaction pathways in chemical reactions, opening new opportunities for the control of the dynamic atomic structure for beneficial catalytic and functional properties. Smarter synthesis leading to improved materials and processes with significantly enhanced performance are possible. Benefits include new knowledge and cleaner processes for renewable energy and healthcare as well as improved or replacement mainstream technologies in the chemical and energy industries.

The atomic-scale structure of a catalyst under reaction conditions determines its activity, selectivity, and stability. Recently it has become clear that essential differences can exist between the behaviour of catalysts under industrial conditions (high pressure and temperature) and the (ultra)high vacuum conditions of traditional laboratory experiments. Differences in structure, composition, reaction mechanism, activity, and selectivity have been observed. These observations made it clear that meaningful results can only be obtained at high pressures and temperatures. Therefore, the last years have seen a tremendous effort in designing new instruments and adapting existing ones to be able to investigate catalysts in situ under industrially relevant conditions.

In this talk, Professor Groot will give an overview of the in situ imaging techniques the group uses to study the structure of model catalysts under atmospheric pressures and elevated temperatures. The group has developed set-ups that combine an ultrahigh vacuum environment for model catalyst preparation and characterisation with a high-pressure flow reactor cell, integrated with either a scanning tunneling microscope or an atomic force microscope. With these set-ups the group is able to perform atomic-scale investigations of well-defined model catalysts under industrial conditions. Additionally, they combine the structural information from scanning probe microscopy with mass spectrometry measurements. In this way, the group can correlate structural changes of the catalyst due to the gas composition with its catalytic performance. Furthermore, they use other in situ imaging techniques such as transmission electron microscopy, surface X-ray diffraction, and optical microscopy, all combined with mass spectrometry.

The rapid advances in understanding and treatment of common human brain diseases have (arguably) been made possible by advances in development of in vivo diagnostic imaging technologies in the last few decades. The human brain is complex, with no truly comparable model species, limiting the ultimate clinical value of many rodent models. Advances in non-invasive medical imaging technologies particularly magnetic resonance imaging, mean that detailed data on brain structure and function and pathological changes in disease can now be determined and tracked in large human samples including population studies and disease cohorts. However, these methods also have limitations of resolution, and tissue often only becomes available post mortem, reflecting end stage disease. Hence, to tackle a complex disorder that develops insidiously in life requires a multimodal approach that includes in vivo MRI and related ‘macroscopic’ methods in patients and volunteers, and parallel and complementary microscopic methods applied to post-mortem brain tissue and in vivo and in vitro static and dynamic imaging methods in rodent models such as MRI, 2-PI, histological and electron microscopic methods. This lecture will illustrate these principles using the example of cerebral small vessel disease, a major cause of both stroke and dementia and of ageing-related multimorbidities.

Structure prediction is a long standing challenge in solid state and nano-science, with a variety of approaches including the use of topological principles and the search of energy landscapes employing a range of procedures and algorithms. Professor Catlow will review briefly the methodologies currently in use and illustrate both their efficacy and the current challenges by describing recent applications, concentrating mainly on inorganic materials and their surfaces and on both metallic and oxide nano-particles. He will discuss how computational structure modelling and prediction can guide and assist the interpretation of experimental studies.