Discovery of deep and shallow trap states from step structures of rutile TiO2 vicinal surfaces by second harmonic and sum frequency generation spectroscopy.
Discovery of deep and shallow trap states from step structures of rutile TiO2 vicinal surfaces by second harmonic and sum frequency generation spectroscopy.
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DOI：
10.1063/1.3578178
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发表时间：
2011-04
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通讯作者：
Hiroaki Takahashi;R. Watanabe;Y. Miyauchi;G. Mizutani
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文献类型：
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作者：
Hiroaki Takahashi;R. Watanabe;Y. Miyauchi;G. Mizutani
在本报告中，通过二次谐波和和频发生（SHG∕SFG）光谱研究了金红石TiO(2)单晶面上台阶和台阶的局域电子结构。我们使用最近开发的阶跃选择性探测技术实现了对邻近 (17 18 1) 和 (15 13 0) 表面上形成的阶跃束的局部电子态的选择性测量。还讨论了平坦的(110)-(1×1)(邻近表面的平台面)和(011)-(2×1)表面的电子结构。 SHG∕SFG 谱表明，阶梯结构主要负责陷阱态的形成，因为仅从邻近表面观察到陷阱态的显着共振。我们从邻近表面的阶梯束中选择性地检测到深空穴陷阱（DHT）态和浅电子陷阱（SET）态。对 SHG∕SFG 谱的详细分析表明，DHT 和 SET 态更有可能在阶梯束的顶部边缘而不是在其山坡上引起。与SET态不同，DHT态仅在平行于[1 1 1]的阶梯束处观察到[相当于在(17 18 1)表面上形成的阶梯束]。还通过亚甲基蓝光降解反应测量了每个 TiO(2) 样品的光催化活性，发现其遵循以下顺序：(110) < (17 18 1) < (15 13 0) < (011)，表明沿 [0 0 1] 的步骤比沿 [1 1 1] 的步骤更具反应性。该结果意味着从与 [1 1 1] 平行的阶梯束中观察到的 DHT 态的存在并没有有效地促进亚甲基蓝光降解反应。
In this report, local electronic structures of steps and terraces on rutile TiO(2) single crystal faces were studied by second harmonic and sum frequency generation (SHG∕SFG) spectroscopy. We attained selective measurement of the local electronic states of the step bunches formed on the vicinal (17 18 1) and (15 13 0) surfaces using a recently developed step-selective probing technique. The electronic structures of the flat (110)-(1×1) (the terrace face of the vicinal surfaces) and (011)-(2×1) surfaces were also discussed. The SHG∕SFG spectra showed that step structures are mainly responsible for the formation of trap states, since significant resonances from the trap states were observed only from the vicinal surfaces. We detected deep hole trap (DHT) states and shallow electron trap (SET) states selectively from the step bunches on the vicinal surfaces. Detailed analysis of the SHG∕SFG spectra showed that the DHT and SET states are more likely to be induced at the top edges of the step bunches than on their hillsides. Unlike the SET states, the DHT states were observed only at the step bunches parallel to [1 1 1] [equivalent to the step bunches formed on the (17 18 1) surface]. Photocatalytic activity for each TiO(2) sample was also measured through methylene blue photodegradation reactions and was found to follow the sequence: (110) < (17 18 1) < (15 13 0) < (011), indicating that steps along [0 0 1] are more reactive than steps along [1 1 1]. This result implies that the presence of the DHT states observed from the step bunches parallel to [1 1 1] did not effectively contribute to the methylene blue photodegradation reactions.