Electron transfer dynamics from organic adsorbate to a semiconductor surface:: Zinc phthalocyanine on TiO2(110)
Electron transfer dynamics from organic adsorbate to a semiconductor surface:: Zinc phthalocyanine on TiO2(110)
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DOI：
10.1021/jp052078d
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发表时间：
2005-09-29
影响因子：
3.3
通讯作者：
Matsumoto, Y
中科院分区：
文献类型：
--
作者：
Ino, D;Watanabe, K;Matsumoto, Y
利用时间分辨双光子光电子能谱（TR-2 PPE）研究了酞菁锌（ZnPC）薄膜及其与TiO 2（110）界面激发态的飞秒时间演化.激发态在具有过量振动能的第一单重激发态（SI）中制备。两种不同的膜进行检查：单层（单层）和厚膜的厚度类似于30埃。衰减行为取决于膜的厚度。在厚膜的情况下，TR-2 PPE光谱由来自膜中的ZnPC的信号主导。激发态衰减τ = 118 fs，主要通过分子内振动弛豫。在激发态级联下降到接近底部的S，歧管，它们衰减缓慢（τ = 56 ps），虽然状态位于以上的散装TiO 2的导带最小值。厚膜中的激子迁移是电子从薄膜向体相TiO 2转移的速率决定步骤。在薄膜的情况下，电子转移的贡献更明显。激发态的衰减速度比那些在厚膜中，因为电子转移与分子内弛豫过程的竞争。电子与TiO 2导带空带的耦合在电子转移中起着重要作用。电子转移速率的下限估计为1/296 fs（-1）。在激发态弛豫到其能量低于TiO 2的导带最小值的状态后，它们衰减得慢得多，因为电子转移通道对于这些状态不可用。
The femtosecond time evolutions of excited states in zinc phthalocyanine (ZnPC) films and at the interface with TiO2(110) have been studied by using time-resolved two-photon photoelectron spectroscopy (TR-2PPE). The excited states are prepared in the first singlet excited state (SI) with excess vibrational energy. Two different films are examined: ultrathin (monolayer) and thick films of similar to 30 angstrom in thickness. The decay behavior depends on the thickness of the film. In the case of the thick film, TR-2PPE spectra are dominated by the signals from ZnPC in the film. The excited states decay with tau = 118 fs mainly by intramolecular vibrational relaxation. After the excited states cascaded down to near the bottom of the S, manifold, they decay slowly (tau = 56 ps) although the states are located at above the conduction band minimum of the bulk TiO2. The exciton migration in the thick film is the rate-determining step for the electron transfer from the film to the bulk TiO2. In the case of the ultrathin film, the contribution of electron transfer is more evident. The excited states decay faster than those in the thick film, because the electron transfer competes with the intramolecular relaxation processes. The electronic coupling with empty bands in the conduction band of TiO2 plays an important role in the electron transfer. The lower limit of the electron- transfer rate was estimated to be 1/296 fs(-1). After the excited states relax to the states whose energy is below the conduction band minimum of TiO2, they decay much more slowly because the electron-transfer channel is not available for these states.