14:15 〜 14:30
▲ [23p-E106-4] Electronic structure of the Bi4V2O11 (001) surface by ARPES
キーワード：semiconductor, ARPES, Photocatalysis
BiVO4 is one of the most widely investigated photoanode catalysts for water splitting to produce O2. Bi4V2O11 is composed of the same elements as BiVO4 but exhibits different photocatalytic performance. To elucidate the factors that play an essential role in the photocatalytic process, the electronic-structure understanding of the Bi4V2O11 surface is adequate. Until now, the theoretical study based on the density functional theory has predicted a direct bandgap nature of Bi4V2O11. However, since experimental verification of the Bi4V2O11 surface is insufficient, the current study provides a basis for understanding the relationship between the surface electronic structure and photocatalysis.
A single-domain Bi4V2O11 film was deposited on the Nb-doped STO (001) substrate by RF-sputtering. We characterized the Bi4V2O11 (001) surface by low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES) at BL-3B of the Photon Factory. The results show that the clean crystal surface exhibits a √2/2×√2/2 R45° pattern, consistent with the (001) orientation of the surface. The valance band maximum (VBM) is composed of a hybrid state between the Bi 6s lone pair states and O 2p states. This antibonding state is remarkable in Bi4V2O11, which causes the shift of VBM to a lower binding energy position compared with BiVO4. The ARPES results reveal that the Γ point is the local maximum of the VBM, which is consistent with the theoretical calculation. By fitting the dispersion, the effective mass of the hole was obtained as 7.13 ± 0.60 me. This huge effective mass could be considered as one reason for unsatisfactory photocatalytic performance.
A single-domain Bi4V2O11 film was deposited on the Nb-doped STO (001) substrate by RF-sputtering. We characterized the Bi4V2O11 (001) surface by low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES) at BL-3B of the Photon Factory. The results show that the clean crystal surface exhibits a √2/2×√2/2 R45° pattern, consistent with the (001) orientation of the surface. The valance band maximum (VBM) is composed of a hybrid state between the Bi 6s lone pair states and O 2p states. This antibonding state is remarkable in Bi4V2O11, which causes the shift of VBM to a lower binding energy position compared with BiVO4. The ARPES results reveal that the Γ point is the local maximum of the VBM, which is consistent with the theoretical calculation. By fitting the dispersion, the effective mass of the hole was obtained as 7.13 ± 0.60 me. This huge effective mass could be considered as one reason for unsatisfactory photocatalytic performance.