- We are a solid state physics and surface chemistry group specializing in atomic-scale characterization techniques.
Contributing to Green Technology
Green technology is one of the keys to establishing a sustainable society.
From the standpoint of materials science, contributing to green technology entails establishing fundamental techniques
for the development of functional materials and devices which can help save energy and resources.
Additionally, green research also aims to make these devices more ecologically friendly, mainly by replacing rare elements
and environmentally harmful substances which are often used in their manufacture. Some examples of current issues
which need to be tackled include the development of materials for energy (e.g., materials for energy generation and storage,
high-performance catalysts), the design of environmental sensors which improve energy and material efficiency,
improving material lifetimes by investigating specific properties, and recycling.
Surface and Interface Science
Active sites are located at the surfaces and interfaces of many functional materials and devices such as solar cells,
semiconductor devices, heterogeneous catalysts, and multilayer magnetic thin films.
In order to develop these materials and devices, it is important to establish methods to evaluate atomic site-specific surface and interfacial phenomena,
and to devise techniques to design and construct interfaces at an atomic level. Our laboratory strives to understand the novel properties
that can arise at interfaces in functional materials and devices, especially in the context of green nanosystems,
by using surface science and electron spectroscopy techniques. In particular, photoelectron diffraction spectroscopy is a unique, non-destructive local analysis method
which can be used to study both the atomic structure and properties of material surfaces and interfaces.
Surface and Interface Science
Nanostructures lie at the intersection of several fields - materials, information, environment, and energy.
These functional structures have attracted research in a variety of disciplines as their properties may enable numerous next-generation technologies;
for example, novel surface and interfacial phenomena arising from local electronic states can confer unique functional properties onto these materials.
Therefore, we are working both to understand the mechanisms behind these phenomena, and how to control them in the context of specific applications.
For example, in the interfacial region between two dissimilar solids, local anisotropic structural strain and compositional changes
(which are not observed in the bulk) can generate unique local electronic states in the material, and give rise to functional properties such as polarization, rectification,
light emission, photothermoelectric effects, interface magnetization, and electronic conductivity.
Establishing atomic site-specific characterization methods and atomic-scale techniques for the design and
construction of interfaces is of utmost importance for the development of functional materials and devices,
which depend on the properties arising from interfacial phenomena.
Photoelectron Diffraction Spectroscopye
In our new laboratory, we focus on the development of photoelectron diffraction spectroscopy - a unique,
nondestructive method for visualizing the atomic structure of surfaces and interfaces.
Non-destructive methods which examine the response of a sample to light or to magnetic fields can be extremely effective for the analysis of a material's physical properties;
these can largely be divided into spectroscopy, microscopy, diffractometry, and time-resolved measurements.
Due to the continuous advancement in detector technology, the resolution of these techniques (energy, spatial, angular, and time resolution) has improved greatly,
enabling high-precision analysis.
Furthermore, new methods, which examine samples from different perspectives, can be created by combining these four classes of non-destructive analytical techniques -
for example, time-resolved spectroscopy and microscopic spectroscopy are now commonly used, with time-resolved microscopy also gaining popularity.
In contrast, combinations involving diffractometry are rarely used due to the comparatively long time required for diffraction measurements.
We began developing diffraction spectroscopy while trying to find a new way to analyze the electronic state of individual atoms. Our techniques combine two well-established analytical methods, photoelectron spectroscopy and electron diffractometry. Photoelectron spectroscopy analyzes electrons emitted from solid surfaces and adsorbates in response to light irradiation, and has been proven to be an effective method for the direct observation of electronic states which determine physical properties; meanwhile, electron diffractometry is frequently used as an element-specific method for analyzing atomic structures. Our research has been aided by the availability of third-generation light sources, which produce light with high energy resolution, ultra-short beam pulses, and tunable polarization. These technological breakthroughs have enabled scientists around the world to initiate projects for devising new analytical methods that combine microscopy, spectroscopy, and time-resolved measurements. However, for the next step in the development of diffraction spectroscopy, improvements in multi-channel, high-speed detection are needed.
Diffraction spectroscopy studies typically require a detector that can detect emissions from all angles of a light-irradiated sample. In our lab, we have combined multiple techniques - photoelectron diffraction, Auger electron diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy - to analyze the electronic states and magnetic structure of magnetic thin films and superconductor surfaces in a site-selective or layer-resolved manner. We are also in the process of developing an algorithm for analyzing single-energy electron holography data. By taking advantage of being able to obtain photoelectron diffraction patterns in one measurement, we aim to study the structure of microcrystalline and heterogeneous systems with 2D focused beam scanning, and to track reaction and phase transition dynamics with time- and temperature-dependent measurements. The key focus of our research is atomic site-specific, 3D analysis of electronic states and magnetic structures. We can obtain unique information on atomic trajectory directly from the analysis of transition matrix elements and the polarization dependence of transition processes, which can lead to the discovery of new physics; we have discovered several exciting phenomena using this approach, and it has been shown that this technique can be extremely effective for understanding novel phenomena which occur at buried interfaces.
New Display-Type Analyzer
In our new laboratory, as an independent research project, we are developing a new display-type analyzer.
We applied for a domestic patent in 2015, and for an international patent in 2016, and we plan to launch a compact, user-friendly analyzer this academic year.
We would welcome those with skills in electronic circuits, design, and precision machining for this project.
Evaluation of Green Devices
Recent developments at the Graduate School of Materials Science have allowed close integration of interface analysis and device fabrication techniques.
In the past, the lack of adequate methods for the direct observation of local atomic structure and electronic states at device interfaces was
a significant hindrance to research, but we have now developed strategies to overcome this challenge,
namely through creative sample preparation and the development of photoelectron diffraction spectroscopy.
We are currently preparing a proposal for a joint research project aiming to elucidate the atomic structure of functional materials and device interfaces, and the mechanisms behind their local electronic properties - specifically, we will pursue the following themes in green nanosystems.
1. SiC-based power devices: we will analyze the interfacial atomic structure and electronic states, providing feedback to the heterostructure fabrication process.
2. Graphene-substrate interactions: we will conduct a layer-by-layer analysis of the structure and electronic states of graphene laminates, and identify which interactions are most beneficial for device performance.
3. Depth-resolved compositional analysis of amorphous thin films, and microscopic diffraction spectroscopy of polycrystalline surfaces.
4. Magnetic thin films: we will develop methods for atomic, layer-resolved magnetic structure analysis, with the aim of controlling the perpendicular magnetic switching which occurs with phase transitions.