基于平面等离子共振效应的电子转移研究

发布时间：2018-03-08 15:40

本文选题：硫化镉光催化　切入点：表面等离子　出处：《南京大学》2017年硕士论文　论文类型：学位论文

【摘要】：提高光致电子-空穴分离效率有助于实现太阳能转换效率的提高,对于发展高效的光催化剂和光电转换器件具有至关重要的意义。半导体器件是研究电子和空穴分离效率的传统方式,而基于表面等离子激元的能量转换则是一种具有较大潜力的提高的电子-空穴分离效率的新颖方法。本论文研究了这两种能量转换方式,提出了一种在单纳米粒子水平上对电子转移过程进行实时成像研究的新技术,对电子和空穴的分离机理进行深入的探讨,以期有助于新型高效光催化剂和光电转换器件的研制。本论文构建了单个硫化镉纳米粒子和金膜的肖特基结,利用表面等离子共振显微成像技术实时、原位地观察硫化镉纳米粒子电子转移过程中伴随的光学图像变化,进而探究了单颗粒界面的双向电子转移规律。利用静电吸附法将硫化镉纳米粒子以极低的密度(100×100平方微米的区域内均匀分布数十个纳米粒子)修饰在金膜上,置于以0.05 mM的硫化钠溶液中。当蓝光(λ540nm)照射该金膜-溶液界面时,硫化镉纳米粒子对蓝光光子的吸收会导致光生电子和价带空穴的产生;由于硫化镉纳米粒子与金膜接触形成了肖特基结,产生肖特基势垒(电子陷阱),光生电子可以顺利的转移至金膜。光生电子的转移,有利于硫化镉纳米粒子的光生电子和价带空穴的分离,使硫化镉纳米粒子表面富集空穴。富集的空穴能够氧化溶液中的硫离子,生成单质硫沉积在硫化镉纳米粒子表面。单质硫的沉积改变了硫化镉纳米粒子的等效折射率,使硫化镉纳米粒子的成像对比度增强。而当另一种660 nm的红光对金膜光照时,在合适的激发角度下金膜内的自由电子与入射光发生共振,产生电子集体震荡(平面表面等离子共振效应)。这些具有较高动能的热电子又重新注入到表面价带空穴富集的硫化镉纳米粒子上,导致硫化镉纳米粒子表面沉积的单质硫被还原,使硫化镉纳米粒子的成像对比度减弱,从而实现了该肖特基结上电子双向转移的可视化。本论文利用了平面表面等离子共振成像技术成功地监测了单个硫化镉纳米粒子表面单质硫的沉积和溶解过程,从而实现了硫化镉纳米粒子/金膜构建的肖特基结之间的双向电子转移动力学的可视化研究。与金、银纳米粒子的局域表面等离子共振效应相比,金膜的平面表面等离子共振效应能够很容易地通过调整光学和几何参数实现热电子激发效率的调节。同时,半导体纳米材料个体的形貌和化学组成可以被全面地表征,有利于肖特基结中电子转移规律的系统研究。这些优势将有助于对金属-半导体界面的电子转移机制的深入理解,并对于光催化、光伏器件和光电化学传感的相关应用研究具有很大的促进作用。
[Abstract]:Increasing the efficiency of photoinduced electron-hole separation can improve the conversion efficiency of solar energy. Semiconductor devices are the traditional way to study the efficiency of electron and hole separation. The energy conversion based on surface plasmon is a novel method to improve the efficiency of electron-hole separation with great potential. A new technique for real-time imaging of electron transfer process at the level of single nanoparticles is proposed. The separation mechanism of electron and hole is discussed. In this paper, a Schottky junction of single cadmium sulfide nanoparticles and gold film was constructed, and real time surface plasmon resonance microscopy (SPR) technique was used to construct the Schottky junction. In situ observation of the changes of optical images associated with electron transfer of cadmium sulfide nanoparticles, Furthermore, the bidirectional electron transfer law of single particle interface was investigated. The cadmium sulfide nanoparticles were modified on the gold film by electrostatic adsorption with dozens of nanoparticles uniformly distributed in a region of 100 脳 100 square microns of extremely low density. When the gold film is irradiated by blue light (位 540nm), the absorption of blue photons by cadmium sulfide nanoparticles will lead to the generation of photogenerated electrons and valence band holes. Due to the contact of cadmium sulfide nanoparticles with gold film, Schottky junction is formed, which produces Schottky barrier (electron trap, photogenerated electrons can be transferred to gold film smoothly. In favor of the separation of photogenerated electrons and valence band holes of cadmium sulfide nanoparticles, the surface of cadmium sulfide nanoparticles is enriched with holes which can oxidize sulfur ions in solution. Formation of elemental sulfur deposition on the surface of cadmium sulfide nanoparticles. The deposition of elemental sulfur changes the equivalent refractive index of cadmium sulfide nanoparticles and enhances the imaging contrast of cadmium sulfide nanoparticles. When another kind of 660 nm red light illuminates the gold film, At a suitable excitation angle, the free electron in the gold film resonates with the incident light. The generation of collective electron oscillations (planar surface plasmon resonance effects). These hot electrons with higher kinetic energy are re-injected into cadmium sulfide nanoparticles enriched with holes in the valence band on the surface, The elemental sulfur deposited on the surface of the cadmium sulfide nanoparticles is reduced, which weakens the imaging contrast of the cadmium sulfide nanoparticles. Thus the visualization of electron bidirectional transfer on the Schottky junction is realized. The deposition and dissolution of sulfur on the surface of single cadmium sulfide nanoparticles are successfully monitored by planar surface plasmon resonance imaging. Thus, the visualization of electron transfer kinetics between Schottky junctions constructed by cadmium sulfide nanoparticles / gold films has been realized. Compared with the local surface plasmon resonance effect of gold and silver nanoparticles, The planar surface plasmon resonance effect of gold film can easily adjust the thermal electron excitation efficiency by adjusting optical and geometric parameters. At the same time, the morphology and chemical composition of semiconductor nanomaterials can be fully characterized. These advantages will contribute to an in-depth understanding of the electron transfer mechanism at the metal-semiconductor interface and for photocatalysis, which is beneficial to the systematic study of electron transfer laws in Schottky junctions. The research on photovoltaic devices and photochemical sensors has a great role in promoting the application of photovoltaic devices and photochemical sensors.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN304;TB383.1

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