纳米尺度下有机分子吸附对石墨烯光电学性质调控规律的研究

How to change and control the density of free charge of graphene in order to achieve manipulation of the band gap and Fermi level of graphene is the most important physical issue in the modification of the optical and electronic properties of graphene. Conventional doping methods have the drawbacks of deteriorating the extraordinary high free carrier mobility. Nobel Laureates professor Geim’s pioneering researches on “molecular doping” have demonstrated that charge transfer occurs during the adsorption of molecules on graphene. More importantly, certain adsorption molecules significantly alter the band structure of graphene without deteriorating the high carrier mobility, which provides a new direction for the graphene modification.. This project proposes to employ scattering-Scan Near-field Optical Microscope (sSNOM) to study the graphene surface plasmon behavior before and after organic molecule adsorption on graphene, and deduce the change of band structure of graphene on nanoscale. Based on the previous researches this project has selected four representative organic molecules to carry out the study of the manipulation effect of molecular absorption on the charge transfer and band structure of graphene, and also the influence of nanoscale features of the graphene surface on the manipulation. The project will reveal the general rules of “molecular doping” and support the modification and applications of graphene fundamentally.

如何改变和控制石墨烯的载流子浓度，从而达到调控石墨烯的能带间隙以及费米能级是石墨烯改性所需要解决的最核心的物理问题。常规掺杂方法往往会大幅减小石墨烯的超高载流子迁移率。诺贝尔奖获得者Andre Geim教授团队的研究表明分子吸附石墨烯过程中电荷会发生转移，更值得注意的是某些分子的吸附在不剧烈影响石墨烯载流子迁移率的前提下，依然能够明显改变石墨烯的能带结构，为石墨烯改性提供了新的契机。. 本项目拟运用散射型扫描近场光学显微镜在纳米尺度下研究石墨烯表面吸附分子前后等离激元的行为变化，从而推知石墨烯微观载流子浓度以及费米能级的改变。本项目拟在前人研究的基础上选择四种有代表性的有机分子，研究其与不同类型，不同微观结构石墨烯的吸附对石墨烯能带结构的影响，同时在纳米尺度上揭示出微观细节对有机分子和石墨烯之间电荷转移的影响，为更精确的调节和控制石墨烯能带结构提供坚实的基础。

石墨烯表面等离激元为解决传统光学系统的衍射极限问题提供了新的技术途径。其在中红外波段的优良特性使得石墨烯表面等离激元在生物传感、光子调控、以及光探测等方面具有很大潜在应用价值。石墨烯表面等离激元传播过程的微观探测以及决定表面等离激元行为的石墨烯载流子浓度和费米能级的调控机理的研究在近年来成为研究的热点。按照原研究计划，本项目通过机械剥离的方法制备得到了大面积高质量的单层石墨烯样品，并通过拉曼光谱对分子化学掺杂后石墨烯费米能级变化规律进行了研究。后期根据实际情况对研究计划进行了调整和扩展之后，本项目对石墨烯手性边界的能带和表面等离激元微观行为进行了深入的研究。研究结合实验和数值模拟重构了石墨烯的光电导分布，表明由于精细的电子能带子带结构，石墨烯 zigzag 边界具有比 armchair 边界更高的光电导。与体光电导相比，zigzag 和 armchair 边界光电导具有不同的增强倍数，分别为 7.2 和 1.8。近场光学实验表明石墨烯 zigzag 边界态的有效宽度可以通过入射光波长和费米能级进行调控，局域因子高达 1/188，比常规光学极限高了两个量级。与此同时，最后，手性边界处等离激元传播动力学过程的实验测量表明 zigzag 边界处等离激元具有更长的寿命。本工作实现了石墨烯边界态的近场光学测量及其调控，为材料电子能带结构的表征提供了一种新的思路，并且具备空间分辨率高、普适性等优势。