石墨烯纳米天线红外光谱增强机理研究

Infrared(IR) spectroscopy offers a powerful tool for analysis and characterization of a wide range of molecular species via their distinct vibrational and rotational absorption resonance, often referred to as molecular fingerprints. However, the wavelength of light at these infrared frequencies is significantly larger than the absorption crosssection of the molecules of interest, making absorption spectroscopy of thin layers or nanoscale volumes challenging. In this project, we propose a new idea that exciting local electromagnetic field mode through graphene nanoantenna to enhance the infrared absorption spectrum of the molecule under tests, based on the graphene surface plasmon's eigen mode in infrared waveband and tunable free electron desity. First principles and finite element method are utilized to research the graphene surface plasmon's coupling and modulating properties. Then nanoatenna local electromagnetic field coupling excitation model is established. We further analyze the nanoatenna structures and external electric fields on the effects of local electromagnetic field mode's energy distribution and spectrum properties. Also, we'll develop the broadband graphene nanoantenna design method and graphene nanoctrsuture patterning technique. To verify our idea, infrared spectrum measuring experiment beyond the diffraction limits and trace meolecule detecting experiment are conducted. The infrared spectrum enhancement method with graphene nanoantenna developed in our study provide a new method to overcome the high loss and narrow bandwidth bottleneck connecting the local electric field mode on the metal surface, which will solve the extremely weak interaction between the wide-bandwidth infrared light waves and molecules at nanoscale, paving the way to next generation highly sensitive infrared spectrun sensing technology.

面向痕量分子检测这一重大需求，针对红外光波与分子相互作用极其微弱这一难题，基于石墨烯支持红外波段表面等离子体本征模式和自由电子密度可调谐等特性，提出激发石墨烯纳米天线局域电磁场模式实现对被测分子红外吸收光谱增强的新方法。采用第一性原理及有限元数值计算方法，研究石墨烯表面等离子体局域及调控特性；建立纳米天线局域电磁场耦合激发的物理模型；分析天线结构和外加电场对局域电磁场模式的空间能量分布及光谱特征的影响；发展宽光谱波段石墨烯纳米天线的设计方法；研究石墨烯纳米图形化的加工工艺；构建突破衍射极限的红外光谱增强测试实验及痕量分子探测实验。本项目发展的石墨烯纳米天线红外光谱增强方法，为突破现有红外光谱增强技术中金属纳米结构存在高损耗及窄带限制的瓶颈提供了新思路，为实现下一代超高灵敏度的红外光谱传感技术奠定基础。

基于表面等离激元的表面增强红外光谱技术具有在亚波长尺度下突破红外波段光学衍射极限的独特优势，为发展下一代红外光谱技术具有极其重要的科学意义。本项目突破了传统金属表面等离子体局域电磁场模式在红外波段的带宽及损耗的限制，提出了一种基于石墨烯纳米天线表面等离激元效应，以实现痕量分子探测的新型红外光谱探测方法。紧密围绕石墨烯纳米天线红外光谱增强机理，石墨烯纳米天线关键加工工艺和性能表征，以及痕量分子红外光谱探测实验三个方面开展研究，取得了一些创新性的研究成果：.（1）建立了石墨烯表面等离子体耦合激发的三个基本物理模型（纳米光栅导模共振型、石墨烯纳米带天线型和共形石墨烯天线耦合激发型），研究了表面等离激元与分子的耦合关系，分析了纳米天线结构和外加电场对石墨烯表面等离激元局域模式的调控特性。在此基础上提出了有效提高光谱传感性能石墨烯纳米结构的设计方法。.（2）成功制备了二维/三维石墨烯纳米材料。从实验上发现了化学气相沉积过程中CH3-基团在限域空间的非平衡态，揭示了活性基团的空间分布均匀性对石墨烯成核与层数的影响规律。实现了大面积单层石墨烯薄膜生长，并成功地转移到二氧化硅基底上。研究了石墨烯的纳米图形化工艺，制备了石墨烯纳米天线红外光谱器件。.（3）完成了石墨烯表面等离激元红外光谱探测实验。观察到了石墨烯在红外波段的表面等离子体峰，并基于凝胶顶栅改变栅极电压，对石墨烯的费米能级进行调节，实现了石墨烯表面等离子体峰在8~10μm宽波段的动态调控。利用该器件对10nm厚PEO分子进行红外光谱探测实验研究，实现了PEO分子完整振动模式的宽波段红外光谱探测。.在本项目的资助下，发表与项目相关、已经标注本项目的学术论文15篇，其中SCI收录13篇，EI收录2篇，获中国微米纳米技术学会2016年学术年会优秀论文奖；培养研究生4名；发明专利4项，授权1项。本项目的研究成果为发展新型石墨烯表面等离激元红外光谱技术奠定了理论及实验基础。