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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Ultrafast Charge Transfer Dynamics in Polycrystalline CdSe/TiO2 Nanorods Prepared by Oblique Angle Codeposition
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Ultrafast Charge Transfer Dynamics in Polycrystalline CdSe/TiO2 Nanorods Prepared by Oblique Angle Codeposition

机译：斜角编码沉积制备的多晶CdSe/TiO2纳米棒的超快电荷转移动力学

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摘要

Ultrafast exciton dynamics of aligned polycrystalline nanorod arrays composed of CdSe or CdSe/TiO2 grown on conductive glass substrates using oblique angle deposition/codeposition, have been studied using femtosecond transient absorption (TA) spectroscopy. Scanning electron microscopy images show that the morphology of the two samples are comparable in height, width, and tilt angle. X-ray diffraction and Raman spectroscopy indicate that the as-deposited CdSe nanorod arrays are in the hexagonal phase, while the TiO2 is amorphous. In the TA studies, a pump wavelength of 580 nm was used to determine the exciton lifetimes of CdSe in the two samples. Transient bleach dynamics probed at 695 nm can be fit with triple exponential functions with lifetimes of 7 ps, 84 ps, and ～1.0 ns for CdSe nanorods versus 0.5 ps, 3 ps, and 24 ps for the CdSe/TiO2 composite-nanorods. These lifetimes are independent of the pump power, indicating that nonlinear processes are not involved. For CdSe nanorods, the two fast decays are mainly due to nonradiative electron—hole recombination or exciton relaxation mediated by trap states. The overall much faster decay in CdSe/TiO2 nanorods is due to electron transfer from the conduction band of CdSe to the conduction band of TiO2. The electron injection rate from CdSe into TiO2 was calculated to be 1,7 X 10~(11) s~(-1) based on the average lifetime measured for CdSe with and without TiO2. This very high rate of electron injection is attributed to the large interfacial area and strong coupling between the two materials in CdSe/TiO2 composite-nanorods. Such strongly coupled semiconductor—metal oxide heterostructures are desired for applications in solar energy conversion.
机译：使用飞秒瞬态吸收 （TA） 光谱研究了由CdSe或CdSe/TiO2组成的排列的多晶纳米棒阵列的超快激子动力学，这些阵列使用斜角沉积/编码沉积在导电玻璃基板上生长。扫描电子显微镜图像显示，两个样品的形貌在高度、宽度和倾斜角度上相当。X射线衍射和拉曼光谱表明，沉积的CdSe纳米棒阵列处于六方相，而TiO2是非晶态的。在 TA 研究中，使用 580 nm 的泵浦波长来确定两个样品中 CdSe 的激子寿命。在 695 nm 处探测的瞬态漂白动力学可以拟合三重指数函数，CdSe 纳米棒的寿命为 7 ps、84 ps 和 ~1.0 ns，而 CdSe/TiO2 复合纳米棒的寿命为 0.5 ps、3 ps 和 24 ps。这些寿命与泵浦功率无关，表明不涉及非线性过程。对于CdSe纳米棒，两次快速衰变主要是由于非辐射电子-空穴复合或由陷阱态介导的激子弛豫。CdSe/TiO2纳米棒的整体衰变速度要快得多，这是由于电子从CdSe的导带转移到TiO2的导带。根据含和不含TiO2的CdSe的平均寿命，计算出CdSe向TiO2的电子注入速率为1,7 X 10~（11） s~（-1）。这种非常高的电子注入速率归因于CdSe/TiO2复合纳米棒中两种材料之间的大界面面积和强耦合。这种强耦合的半导体-金属氧化物异质结构是太阳能转换应用的理想选择。

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