瞬態吸收光譜探討磊晶釩酸鉍電荷載子動力學及其各向異性

Abstract

在半導體催化反應中，缺陷與晶軸方向對材料在能階的形成、電荷載子的複合、電荷載子的有效質量等方面有所影響。相較於粉末樣品，固態薄膜可以透過生長基材的選擇來控制薄膜中的晶軸方向或缺陷分布，且在光催化、光電催化後易與反應溶液分離，因此受到重視。基於此原因，本論文以瞬態吸收光譜研究具磊晶（epitaxial）性質的釩酸鉍薄膜在電荷載子複合過程的各向異性以及不同實驗製程下的載子行為。

通過系統性的討論我們探討了三個關鍵因素在飛秒至皮秒時間尺度下對電荷載子動力學的影響。激發脈衝強度的調控說明了電荷載子濃度與複合機制的關聯；磊晶薄膜的光極化方向研究展現了電子－聲子耦合的方向依賴性；快速熱退火與鉬摻雜的製程優化則改善了電荷載子的傳輸特性。

瞬態吸收光譜結果顯示，在飛秒時間尺度下，電荷載子的複合行為展現出晶向依賴性，特別是在電子－聲子耦合過程中。此外，通過優化製程參數，如快速熱退火和鉬摻雜，能夠有效延長電荷載子的壽命，這對提升材料的光催化效率具有重要意義。

綜上所述，本研究結果有助於理解釩酸鉍，此半導體光催化材料的電荷載子動力學，揭示晶軸方向和缺陷控制對光催化性能的影響機制，為優化高效光催化材料的設計和應用提供相關實驗數據與解釋。

In semiconductor photocatalysis, defects and crystallographic orientation significantly affect charge carrier dynamics. This thesis employs transient absorption spectroscopy to investigate the anisotropy of charge carrier recombination processes and carrier behavior under different experimental conditions in epitaxial bismuth vanadate thin films.

Through systematic investigation, we explored three key factors affecting charge carrier dynamics in the femtosecond to picosecond time scale. The control of excitation pulse intensity revealed the correlation between carrier concentration and recombination mechanisms; the study of pump pulse polarization direction in epitaxial films demonstrated the directional dependence of electron-phonon coupling; while process optimization through rapid thermal annealing and molybdenum doping improved charge carrier transport properties.

Transient absorption spectroscopy results show that charge carrier recombination behavior exhibits significant crystallographic orientation dependence at the femtosecond time scale, particularly in electron-phonon coupling processes. Moreover, optimizing process parameters, such as rapid thermal annealing and molybdenum doping, effectively extended charge carrier lifetime, which is crucial for enhancing the material's photocatalytic efficiency. In conclusion, this study advances our understanding of charge carrier dynamics in bismuth vanadate, a semiconductor photocatalytic material, revealing how crystallographic orientation and defect control influence photocatalytic performance, thereby providing experimental data and insights for optimizing the design and application of efficient photocatalytic materials.