Development of Novel Electron Microscopy Based on Integrated Approach of New Experimental Tools & Machine Learning
Microstructure and local chemical composition analysis using scanning electron microscopy and transmission electron microscopy is an indispensable analytical method for searching for new materials and for research and development of highly functional materials, and is routinely used in the fields of science, technology, and medicine. In particular, the “in-situ observation” method, in which the microstructure and functional/mechanical properties of a material are observed in real time by applying heat, light, or external force to the material, is a method that makes the most of the characteristics of the electron microscope, which allows us to see phenomena with our own eyes. Using this technique, it is possible to directly observe the functional properties of new materials such as graphene and carbon nanotubes, the mechanical properties of structural metals and ceramics, the compositional deformation behavior of rocks that leads to the mechanism of earthquakes, and the vibration modes of polymers at the nanometer scale. Our research group has a research level comparable to the world’s top groups, especially in in-situ observation using transmission electron microscopy. In the U.S. and Europe, the development of operando electron microscopy, which enables the exploration of unknown materials and the evaluation of their functional properties, is now being actively pursued by further evolving the in-situ observation method and integrating it with data science and computational science methods. This is expected to bring about a dramatic change in materials analysis, as well as in the research and development of substances and materials, similar to the change from a five-year-old cell phone to a state-of-the-art smartphone. Our research group routinely collaborates with Professor Satoshi Hata’s group at the Graduate School of Science and Engineering and the Center for Ultramicroscopy at the Ito Campus to establish next-generation microscopic analysis methods, such as Operando electron microscopy, and to elucidate physical and chemical phenomena using these methods. At the same time, we are conducting research and education to acquire the fundamentals for understanding the “correlation between microstructure and functional/mechanical properties,” which is indispensable for the next generation of physics and materials research through these advanced projects.
Exploring Unique Nanophotonic Phenomena by Electron Beam
Since the electron beam itself is an external force that excites the electronic system in a material, we can take advantage of the atomic-level spatial resolution of the electron microscope to analyze the electronic state spectroscopically. Using electron energy loss spectroscopy (EELS), which is equivalent to absorption spectroscopy, and cathodoluminescence (CL), which analyzes the emission, we are searching for novel surface plasmon modes in nanostructures.
Recent microfabrication techniques allow us to design and fabricate artificial crystals with periodic arrays of nanostructures, and to use electronic state control based on band theory of solid state physics to control plasmon propagation. For example, properties derived from the geometry of crystal structures, such as topological insulators and valley polarization, are concepts that can be applied to all kinds of waves, including light waves, and we aim to create new degrees of freedom in light propagation at the nanoscale by utilizing these properties, and to create new optical functional devices in combination with material systems.
Although electron beams are effectively used as “ultra-fine probes” as typified by electron microscopes, there are still many unknown aspects of their interaction with materials. However, there are still many unknowns in the interaction with materials. For example, it is possible to excite excitons locally and densely, which may lead to an unprecedented approach to explore the physical properties of nano-condensed systems. The discovery of new aspects of the excitation source of electron beams, which will lead to the discovery of such new functional materials, is also an important basic subject of this laboratory.