The electronic structures of Anatase TiO2 studied by photoemission spectroscopy using synchrotron light and laser

2019 Fiscal Year Final Research Report

• Project/Area Number: 16K05406
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Condensed matter physics I
• Research Institution: Saga University
• Principal Investigator: Azuma Junpei 佐賀大学, シンクロトロン光応用研究センター, 准教授 (40372768)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 光電子分光 / 放射光 / レーザー / 光触媒 / 二酸化チタン / 電子状態

Outline of Final Research Achievements

Clean surfaces of (100), (110) and (001) surfaces of anatase-type TiO2 natural single crystals, known as photocatalysts, were prepared and measured by three-dimensional angle-resolved photoemission spectroscopy using synchrotron radiation. The experimental results have revealed a detailed three-dimensional band structure. It is found that the valence band maximum is located just above the M point, whereas that has been predicted to be near the M point along the Γ-M line by theoretical calculations. It is directly observed that the conduction band minimum, which is electron-doped by the oxygen vacancies, is at Γ point and that the indirect band gap is 3.2 eV. The surface elecronic states due to the surface oxyzen defects were found by the laser-based two-photon photoemission spectroscopy, which are derived from the Ti 3d orbitals.

Free Research Field

数物系科学

Academic Significance and Societal Importance of the Research Achievements

アナターゼ型二酸化チタンTiO2は光触媒として既に実用化されているが、バンド構造について実験的にほとんど確かめられていなかった。これは二酸化チタン結晶が劈開性を持たないので、角度分解光電子分光測定が可能な清浄表面を得ることが困難であることに由来する。本研究では、二酸化チタン結晶の清浄表面を複数の面方位で作製する事に成功した。また得られた清浄表面について、複数の面方位で三次元角度分解光電子分光測定を行う事で、アナターゼTiO2の三次元バンド構造に関する詳細な知見が得られた。この成果は光触媒の詳細なメカニズムを明らかにし、光による水素発生などのクリーンエネルギー技術の発展に寄与すると考えられる。