Research

Theory for 3D Atomic Imaging from Atomic-Resolution Holograms

Atomic-resolution holography includes photoelectron holography as well as X-ray fluorescence holography and neutron holography. These techniques can record the local atomic arrangement around dopants in holograms. In our laboratory, we develop original theories that combine machine learning with quantum scattering theory to reconstruct 3D atomic structures from atomic-resolution holograms. By visualizing the 3D atomic configuration around dopants, we aim to uncover the mechanisms behind functional properties in advanced materials.

Synchrotron-Based Photoelectron Holography

In functional materials, it is common to introduce trace amounts of elements (doping) or to adsorb/deposit atoms on surfaces. The atomic structures formed by such added atoms strongly influence physical properties, making structural visualization a key to materials design. However, conventional techniques often cannot directly observe these dilute structures. Our lab develops and applies experimental instrumentation to visualize the structure of dilute dopants and adsorbates, aiming to innovate materials science. We conduct experiments using large-scale facilities such as SPring-8 and J-PARC, in collaboration with external research organizations.

Surface Structure Analysis by Reciprocal Space Mapping

Quantum dots, widely used in displays, lasers, and solar cells, require careful evaluation and control of crystal phase, size, orientation, and strain. Yet experimental/analytical workflows based on conventional X-ray diffraction and microscopy can be complex and time-consuming. We propose an azimuthal-scan RHEED method that constructs a 3D reciprocal-space map from multiple RHEED patterns. We also develop algorithms to efficiently search for the best match to crystal phase and orientation in a simple and rapid manner.

Atomic Structure Analysis by STM, LEED, and Mass Spectrometry

Combining electronically driven chemical reactions with MOS technology is a foundational concept toward “catalysis-on-a-chip” devices. Our group has demonstrated electron-stimulated desorption triggered by injecting hot electron/hole carriers generated in MOS (Fe/wet-SiO2/Si) and MOS (Ti/wet-SiO2/Si) structures into metal nanothin films under gate bias. Since defect density in insulating oxides is considered a key factor in understanding the MOS desorption mechanism, we are currently investigating gate-bias-induced desorption behavior in MOS structures with oxides modified by various methods.

Electronic-State Analysis by Photoelectron and Luminescence Spectroscopy

Electronic structure is fundamental to understanding physical-property mechanisms and solid-state device characteristics. In this topic, we investigate how electronic states change due to low-dimensional confinement, strain, and electron–phonon coupling using angle-resolved photoemission spectroscopy and calculations. We also develop new measurement methodologies such as depth-resolved luminescence spectroscopy and ultra-high-vacuum Raman spectroscopy to quantitatively evaluate defects and strain that affect electronic states.

Details: here.

Dynamics of Atoms Adsorbed on Crystal Surfaces

Atoms adsorbed on crystal surfaces exhibit rich dynamics: they diffuse across surfaces, incorporate into crystals, and undergo various transformations. In this topic, we clarify how atoms move when foreign atoms are supplied to a crystal surface, using experimental techniques such as electron diffraction.

Details: here.

Development of New Experimental Instruments for Holography

To observe new physics, developing original experimental instruments is essential. From concept to design, development, and implementation, it requires broad expertise. We aim to nurture versatile researchers through collaborative work among members with diverse backgrounds, sharing knowledge and skills across disciplines. We are currently planning to develop photoelectron holography and soft X-ray fluorescence holography instruments based on a retarding-field-type electron energy analyzer.