Projects

Condensed Matter Science Created by Hyper-ordered Structures

The "Hyper-ordered structures science" that are the subject of this research in this area of scientific innovation refer to unique nanostructures formed by dopants, vacancies, and voids. Examples of such structures include composite defects of different elements and vacancies instead of lattice defects, which are regarded as points, and nanoscale atomic arrangements that show topological order even in amorphous materials. Such nanoscale order or "Hyper-ordered structure" can be viewed as an intermediate structural state between "perfect order" and "perfect disorder. Hyper-ordered structure" is an important key factor for imparting high functionality to crystals and amorphous materials, in other words, it can be a treasure house of material functionality, and therefore, infinite possibilities can be created by highly controlling the structure. In this research area, we will explore new approaches to materials design and search for highly functional materials by working on the observation, understanding, and control of "hyper-ordered structures.

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Photoelectron holography using synchrotron radiation

In the fabrication of functional materials, methods to add small amounts of elements to base materials (doping) or to adsorb and deposit atoms on surfaces are often used. Since the atomic arrangement structure formed by these doped atoms has a great influence on physical properties, visualization of the atomic structure is the key to material development. However, it is not possible to see them only with conventional measurement methods. In our laboratory, we are conducting research to develop and apply experimental devices to visualize the structure of these small amounts of added atoms in order to bring about technological innovation in materials science. The research will be conducted using external research facilities such as SPring-8 and J-PARC.

Theoretical study of stereoscopic atomic image reproduction from atomic resolution holograms

In addition to photoelectron holography, atomic resolution holography includes X-ray fluorescence holography and neutron holography. The atomic arrangement around a dopant can be recorded in these holograms. In this laboratory, we are investigating an original theory that combines machine learning and the quantum theory of scattering to reproduce stereo atomic arrays from atomic resolution holograms. We study the visualization of stereo atomic arrays around dopants to reveal the mechanism of functional expression of advanced materials.

Surface structure analysis by reciprocal lattice space mapping

Quantum dots are being widely applied to displays, lasers, solar cells, and other devices, and it is important to evaluate and control the crystal phase, size, orientation, and strain. However, the existing experimental and analytical methods such as X-ray diffraction and microscopy are complicated and time-consuming. In this laboratory, we propose an azimuthal scan RHEED method to generate a three-dimensional reciprocal space map from multiple reflection high-energy electron diffraction (RHEED) transmission patterns, and develop a simple and quick algorithm to find the agreement with the crystal phase and orientation.

Atomic structure analysis by STM, LEED, and mass spectrometry

The fusion of MOS technology with a control mechanism in which molecular chemical reactions are induced by electronic excitation is a fundamental concept for dream catalytic reaction devices. We have succeeded in injecting hot electron and hole carriers generated by applying gate voltage to MOS (Fe/wet-SiO2/Si) and MOS (Ti/wet-SiO2/Si) structures into metallic nanofilm layers for electronic excitation and desorption. Since the defect density in insulating oxide films is one of the keys to elucidate the mechanism of electron excitation/desorption by MOS, we are currently studying the gate voltage excitation/desorption behavior of MOS structures with modified insulating oxide films by various methods.

Electronic structure analysis by electron spectroscopy and emission spectroscopy

Electronic states are fundamental information for clarifying the mechanisms of physical properties and solid-state device characteristics. In this research theme, we investigate how the electronic state is affected by low-dimensional structural confinement, distortion, and electron-lattice interactions by angle-resolved photoemission spectroscopy and calculations. We will also develop new measurement techniques such as depth-resolved emission spectroscopy and UHV Raman spectroscopy to quantitatively investigate defects and distortions that affect the electronic structure.

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Dynamic processes of atoms adsorbed on crystal surfaces

Atoms adsorbed on a crystal surface move on the surface or are incorporated into the crystal in various ways. In this research theme, we use electron diffraction and other experimental techniques to clarify how atoms move when different atoms are supplied to a crystal surface.

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Development of a new holography experimental apparatus

The development of original experimental equipment is essential for observing new physics, but a wide range of knowledge is required from conception to design, development, and implementation. We aim to develop all-rounders by exchanging knowledge with each other through collaborative work with members from diverse backgrounds. Currently, we are planning to develop a photoelectron holography system and a soft X-ray fluorescence holography system based on a blocking potential type electron energy analyzer.