Microscopic Study of Atomic Layer Deposition of TiO2 on GaAs and Its Photocatalytic Application

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• 作者：Jing Qiu ; Guangtong Zeng ; Mai-Anh Ha ; Bingya Hou ; Matthew Mecklenburg ; Haotian Shi ; Anastassia N. Alexandrova ; Stephen B. Cronin
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：December 8, 2015
• 年：2015
• 卷：27
• 期：23
• 页码：7977-7981
• 全文大小：379K
• ISSN：1520-5002

文摘

We report a microscopic study of p-GaAs/TiO₂ heterojunctions using cross-sectional high resolution transmission electron microscopy (HRTEM). The photocatalytic performance for both H₂ evolution and CO₂ reduction of these heterostructures shows a very strong dependence on the thickness of the TiO₂ over the range of 0鈥?5 nm. Thinner films (1鈥?0 nm) are amorphous and show enhanced catalytic performance with respect to bare GaAs. HRTEM images and electron energy loss spectroscopy (EELS) maps show that the native oxide of GaAs is removed by the TiCl₄ atomic layer deposition (ALD) precursor, which is corrosive. Ti³⁺ defect states (i.e., O vacancies) in the TiO₂ film provide catalytically active sites, which improve the photocatalytic efficiency. Density functional theory (DFT) calculations show that water molecules and CO₂ molecules bind stably to these Ti³⁺ states. Thicker TiO₂ films (15 nm) are crystalline and have poor charge transfer due to their insulating nature, while thinner amorphous TiO₂ films are conducting.