What Determines the Lifetime of Photoexcited Carriers on TiO2 Surfaces?

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• 作者：Kenichi OzawaSusumu Yamamoto ; Ryu YukawaRoya Liu ; Masato Emori ; Koki Inoue ; Taku Higuchi ; Hiroshi Sakama ; Kazuhiko Mase ; Iwao Matsuda
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：December 29, 2016
• 年：2016
• 卷：120
• 期：51
• 页码：29283-29289
• 全文大小：444K
• ISSN：1932-7455

文摘

Pump–probe time-resolved X-ray photoelectron spectroscopy measurements have been carried out to comparatively assess the relaxation process of the photoexcited states on pristine and Ar⁺-sputtered TiO₂(110) surfaces and a TiO₂(011)-2 × 1 surface, on which the accumulation-type space charge layers are developed. Ultraviolet laser irradiation induces a surface photovoltage (SPV) of around 0.1 eV. The SPV relaxation time on pristine TiO₂(110) is determined to be approximately 100 ns and is doubled on the sputtered surface. In contrast, a much shorter time of 1 ns is observed on TiO₂(011)-2 × 1. The difference in the relaxation time on the two TiO₂(110) surfaces is explained by differences in the O vacancy density on the surface as well as the barrier height of the surface potential for the photoexcited holes. A large hole capture cross section of a state characteristic of TiO₂(011)-2 × 1 is, on the other hand, responsible for the fast SPV relaxation on this surface.