【公開日：2025.06.10】【最終更新日：2025.05.19】

課題データ / Project Data

課題番号 / Project Issue Number

24HK0022

利用課題名 / Title

Improve Charge Transfer under Strong Coupling Condition via Interfacial modification

利用した実施機関 / Support Institute

北海道大学 / Hokkaido Univ.

機関外・機関内の利用 / External or Internal Use

内部利用（ARIM事業参画者以外）/Internal Use (by non ARIM members)

技術領域 / Technology Area

【横断技術領域 / Cross-Technology Area】（主 / Main）計測・分析/Advanced Characterization（副 / Sub）-

【重要技術領域 / Important Technology Area】（主 / Main）量子・電子制御により革新的な機能を発現するマテリアル/Materials using quantum and electronic control to perform innovative functions（副 / Sub）-

キーワード / Keywords

原子薄膜/ Atomic thin film,光学顕微鏡/ Optical microscope,電子顕微鏡/ Electronic microscope,走査プローブ顕微鏡/ Scanning probe microscope

利用者と利用形態 / User and Support Type

利用者名（課題申請者）/ User Name (Project Applicant)

曹 恩

所属名 / Affiliation

北海道大学 電子科学研究所

共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes

ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes

利用形態 / Support Type

（主 / Main）機器利用/Equipment Utilization（副 / Sub）-

利用した主な設備 / Equipment Used in This Project

HK-609：ヘリコンスパッタリング装置
HK-603：超高速スキャン電子線描画装置(130kV)
HK-404：超高分解能電界放出形走査電子顕微鏡
HK-611：多元スパッタ装置
HK-617：原子層堆積装置（粉末対応型）

報告書データ / Report

概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)

 Recently, we developed an Au nanoparticle (NP)/ titanium dioxide (TiO2)/ Au mirror (ATA) structure that utilized strong coupling between localized surface plasmon resonance (LSPR) and Fabry-Pérot (FP) nanocavity to overcome challenges associated with plasmonic water splitting. We demonstrated that under the modal strong coupling conditions, the absorption intensity is enhanced, the absorption wavelength range is broadened, and the quantum yield of water oxidation is also improved as compared to those of conventional LSPR systems without strong coupling. [1,2] Under modal strong coupling conditions, it has been reported that the quantum coherence among Au nanostructures contributes to enhancing the apparent quantum efficiency (AQE) of electron injection into the conduction band (CB) of TiO₂. [3] Moreover, activation energy was the minimum energy that was required to activation atoms and molecules chemical transformation or physical transport. Therefore, it was an important indicator for evaluating the performance of catalytic water splitting.  on the other hand, little is known about the activation energy in the electron transfer process in Au NP/TiO2 system. To further elucidate the mechanism underlying the quantum efficiency enhancement under modal strong coupling, in this study, we measured activation energy of the electron transfer process of electrons injected into TiO₂ from Au NP in both modal strong coupling ATA structures and non-coupling AT structures. From the transient absorption (TA) measurements, the activation energy of electron transfer in TiO₂ was estimated from the decay rate of electron-hole recombination measured with variable temperature range (293-353K). ATA structures indicate a smaller activation energy value compared to the AT structure without a cavity, suggesting that high electron transfer efficiency occurs in the ATA system. Additionally, the activation energy obtained from the temperature dependence of the incident photon-to-current conversion efficiency (IPCE) showed larger value in both ATA and AT structures, suggesting that recombination from deeper electron trap sites in TiO₂ was observed. These results demonstrate that the activation energy can play a role in enhancing the charge transfer efficiency.

実験 / Experimental

ATA and AT structures were fabricated according to the following procedures. A 100-nm-Au-film and 30-nm-TiO₂ film was deposited on the SiO₂ substrate by sputtering and atomic layer deposition (ALD). A 4 nm Au thin film was evaporated by a thermal evaporator and annealed in air at 300^oC for 2h to form AuNPs with an average diameter of ~12 nm. To fabricate the partially inlaid Au NPs, a thin layer TiO₂ was deposited on the AuNP/TiO₂/Au film and AuNPs/TiO₂ by ALD. Ultrahigh resolution scanning electron microscopy and photonic multichannel analyzer were used to characterize the morphologies and far-field spectral properties of the sample. During the transient absorption measurement, the fundamental output from a regenerative amplified Ti: sapphire laser (800 nm femtosecond pulses with a repetition rate of 1000 Hz and a pulse duration of 25 fs) is split into two parts as pump and probe pulses. To obtain the IPCE of samples, in a three-electrode system, the I-t curves were measured in KOH solution at a working electrode potential of + 0.3 V vs. saturated calomel electrode (SCE). 

結果と考察 / Results and Discussion

The absorption spectra of ATA structures are increased dramatically to nearly one and the absorption bandwidth is broadened compared to AT structure without cavity. We examined the temperature dependence TA measurements and observed an improvement in the AQE of the electron injection into TiO₂ as increasing of temperature. We also estimated the decay rate of electron-hole recombination within 20 ps measured with variable temperature, and an Arrhenius plot was created to estimated the activation energy of electron transfer in TiO₂. The calculated average activation energy of ATA was 5.7 kJ/mol, which is comparable to the activation energy (8.5 kJ/mol) of AT structure, suggesting the activation energy of electron transfer in TiO₂ independence electron injection into TiO₂. 

図・表・数式 / Figures, Tables and Equations

その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)

Reference[1] X. Shi, K. Ueno, T. Oshikiri, Q. Sun, K. Sasaki and H. Misawa, Nat. Nanotechnol., 2018, 13, 953-958.[2] Y. Suganami, T. Oshikiri, X. Shi and H. Misawa, Angew. Chem., Int. Ed., 2021, 60, 18438−18442. [3] X. Shi, T. Yokoyama, S. Inoue, Y. Sunaba, T. Oshikiri, Q. Sun, M. Tamura, H. Ishihara, K. Sasaki and H. Misawa, ACS Nano., 2023, 17, 8315-8323. AcknowledgeThey acknowledge financial support from The Japan Society for the Promotion of Science (JSPS) KAKENHI, Grant Numbers JP23H05464, JP23H01916, JP23K04902, JP22K19003, JP22H05136, JP22H05131 (a Grant-in-Aid for Transformative Research Areas “Evolution of Chiral Materials Science using Helical Light Fields”), and JP18H05205. (A part of). This work was supported by “Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM)” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT). Proposal Number JPMXP1224HK0022. This work was also supported by “Crossover Alliance to Create the Future with People, Intelligence and Materials” from MEXT, Japan.  

成果発表・成果利用 / Publication and Patents

論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)

1. En Cao, Activation Energy in the Electron Transfer Process and Water Oxidation Intermediate Generation under Plasmon–Nanocavity Strong Coupling, The Journal of Physical Chemistry C, 129, 1590-1597(2025).
   DOI: doi/10.1021/acs.jpcc.4c07398
   
2. En Cao, Improving Charge Transfer under Strong Coupling Conditions via Interfacial Modulation, ACS Photonics, 11, 1205-1212(2024).
   DOI: doi/10.1021/acsphotonics.3c01733
   

口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.

特許 / Patents

特許出願件数 / Number of Patent Applications：0件
特許登録件数 / Number of Registered Patents：0件