使用散射型扫描近场光学显微镜研究石墨烯等离激元增强红外光谱的物理机制

Owing to its tunable plasmon resonance in the mid-infrared frequency range, graphene is an ideal material for infrared-enhancing substrate. The strong infrared plasmonic fields confined in deep sub-wavelength dimensions (i.e., infrared hot spots) make graphene plasmons enhanced infrared spectroscopy (GPEIRS) promising in promoting the sensitivity of the infrared spectroscopy drastically, thus pave the way to the ultimate sensitivity of single molecule infrared detection. However, due to the poor spatial resolution of the far-field research means such as Fourier transform infrared spectrometry (FTIR), the physical mechanisms of GPEIRS have not been fully uncovered yet, the graphene-based infrared-enhancing substrate thus cannot be rationally designed to its optimized form, and the latent high sensitivity of GPEIRS cannot be fully exploited. To break this deadlock, in this project, we propose to research the physical mechanisms of GPEIRS thoroughly by taking advantage of the nanoscale spatial resolution of the scattering-type scanning near-field optical microscope (s-SNOM), aiming to acquire the distribution law of the infrared hot spots at the surface of graphene-based infrared-enhancing substrate and the evolution rule of the enhanced molecular infrared spectrum with the varying coupling strength between the probed molecules and the graphene plasmons. Acquisitions of the aforementioned law and rule would deepen our understanding of the physical mechanisms of GPEIRS, and make the great sensitivity potential of GPEIRS fully fulfilled by enabling optimized design of the graphene-based infrared-enhancing substrate.

因其等离激元共振频率位于中红外波段且电学可调谐，石墨烯是一种理想的红外吸收光谱增强基底材料，以其作为增强基底的石墨烯等离激元增强红外光谱技术有望大幅提高红外光谱技术的检测灵敏度，甚至实现单分子红外检测。然而，受目前采用的远场研究手段空间分辨率的限制，石墨烯等离激元增强红外光谱具体的物理机制还未被完整地揭示，石墨烯红外增强基底的优化设计因而无法实现，石墨烯等离激元增强红外光谱技术潜在的巨大灵敏度优势无法得到发挥。为打破这一僵局，本项目拟利用散射型扫描近场光学显微镜纳米级的空间分辨率深入研究石墨烯等离激元增强红外光谱的物理机制，揭示石墨烯红外增强基底表面红外热点的分布规律及分子的红外增强光谱随其与石墨烯等离激元耦合强度变化的演变规律。这两大规律的获取将使我们更加深刻完整地理解石墨烯等离激元增强红外光谱的物理机制，进而通过对石墨烯红外增强基底的优化设计使这一红外增强技术的潜力得到充分发挥。

因其等离激元共振频率位于中红外波段且电学可调谐，石墨烯是一种理想的红外吸收光谱增强基底材料，以其作为增强基底的石墨烯等离激元增强红外光谱技术有望大幅提高红外光谱技术的检测灵敏度，甚至实现单分子红外检测。然而，受此前采用的远场研究手段空间分辨率的限制，石墨烯等离激元增强红外光谱具体的物理机制还未被完整地揭示，石墨烯红外增强基底的优化设计因而无法实现，这一技术潜在的巨大灵敏度优势无法得到发挥。为了使石墨烯等离激元红外增强技术的潜力得到充分发挥，本项目利用散射型扫描近场光学显微镜纳米级的空间分辨率深入研究了其物理机制，揭示了石墨烯红外增强基底表面红外热点的分布规律及分子的红外增强光谱随其与石墨烯等离激元耦合强度变化的演变规律，取得了一系列研究成果：（1）设计制备了柔性石墨烯红外增强基底；（2）设计制备了石墨烯等离激元气体传感器；（3）实现了大面积悬空石墨烯的制备；（4）解释了不同类型激元模式在石墨烯/氮化硼面内异质结处的耦合现象；（5）发展了复杂纳米结构近场图像的仿真方法；（6）实现了石墨烯等离激元的超快光调控；（7）发现了各向异性范德华晶体中波导模式双折射的可调谐特性；（8）系统总结了近场光学技术在纳米材料表征领域的应用。上述成果的取得有助于石墨烯等离激元增强红外光谱技术的进一步发展，推动其成为与表面增强拉曼光谱比肩的表面敏感技术。