フェムト秒ポンプ-プローブ拡散反射吸収分光法による半導体光励起初期過程の追跡 Direct Observation of Initial Processes in Photoexcited Semiconductor by Femtosecond Pump-Probe Diffuse Reflectance Absorption Spectroscopy
Photoirradiation onto semiconducting materials with light of energy greater than their band gap induces creation of pairs of photoexcited electron and positive hole. They react with the species adsorbed on the surface to give redox reactions, otherwise undergo mutual recombination without substantial chemical reactions. Such redox reactions, i.e., heterogeneous electron (or positive hole) transfer triggered by light, at solid/liquid or solid/gas interfaces are called "photoelectrochemical"; or ";photocatalytic"; reactions, and of great importance from both fundamental and applied standpoints. However, mechanism and/or dynamics of such reactions has been poorly understood, because of difficulties of spectroscopic measurement due to heterogeneity of the reaction systems including interfaces, as well as to the rate of electron transfer much faster than the detection limit of conventional time-resolving techniques. Recent progress in laser technology enabled us to measure directly the dynamics of heterogeneous electron transfer with the time resolution even faster than hundred femtosecond. In this article, we show principles of femtosecond pump-probe reflectance absorption spectroscopy and review examples of studies using this promising technique.
表面科学 20(2), 94-101, 1999-02-10
The Surface Science Society of Japan