基底介电环境对石墨烯等离激元寿命的调制研究

Graphene plasmons have unique electrical tunability, ultra-strong field confinement and very low intrinsic damping, making them a significant candidate for nano-photonics such as electro-optical modulation, strong light-matter interactions, and quantum plasmonics. However, it is difficult to achieve the theoretically predicted long lifetime in substrate-supported graphene devices due to the strong substrate scattering from impurity charges and substrate phonons, which restrict the development of practical plasmonic devices. Here, we focus on how to improve the graphene plasmon lifetime and study the effect of dielectric environment of substrate on the damping rate of plasmons and related fundamental mechanics. By using experimental techniques such as scanning near-field optical microscopy, far-field spectrum and theoretical simulations, we will analyze the influences of three kinds of physical processes: scattering of surface charge and surface optical phonon, leaky radiation induced from asymmetric dielectric environment, and strong plasmon-phonon coupling. On this basis, the physical mechanism of graphene plasmon damping in complex dielectric environment will be introduced and heterostructures with selected materials and structures will be designed to increase graphene plasmon lifetimes. This proposal presents a fundamental investigation of graphene plasmons for practical devices, providing theoretical and experimental basis in the field of nano-photonics and photonic integration circuits.

石墨烯等离激元具有高局域场增强、电学动态可调和低本征损耗等优异特性，为实现纳米尺度光调控提供了重要技术手段,已在超材料、单光子非线性、电光调制等领域取得一系列进展。但因为支撑基底的影响，目前报道的石墨烯等离激元寿命（仅飞秒量级）远低于理论预测值（皮、纳秒量级），成为构筑实用化器件所面临的挑战。围绕如何实现长寿命石墨烯等离激元这一关键科学问题，本项目拟系统研究基底介电环境对其的影响及相关物理机制。通过使用远场、近场光学探测等实验方法并结合数值模拟，分别从杂质电荷的散射、石墨烯等离激元-声子的强耦合、电介质对称性破缺导致的等离激元溢出损耗这三个方面的影响进行深入分析，建立复杂介电环境中石墨烯等离激元衰减的物理模型。在此基础上，通过优化设计基底介电环境如构筑范德华异质结构等实现长寿命等离激元。本项目是发展高性能石墨烯等离激元器件的基础，将为其在纳米光子学以及光电集成的应用提供理论和实验依据。

石墨烯等离激元具有极低的本征损,但是实际器件中石墨烯等离激元的寿命却远低于理论值。其中，基底介电环境是一个重要的影响因素。本项目采用理论结合实验的方式系统研究不同基底对石墨烯等离激元寿命的影响，主要有以下四方面的进展：（1）完善了石墨烯等离激元寿命的物理模型和影响机制，石墨烯等离激元的寿命与其载流子迁移率密切相关，基底对石墨烯中载流子迁移率的影响超过介电损耗的影响；等离激元-声子强耦合产生杂化激元，改变等离激元的基本性质包括模式分布和模式寿命等。（2）高性能基底设计：i.设计并制备了无声子干扰且能高效电学调控基底，具体是将氟化钙纳米薄膜蒸镀在低掺杂导电硅上。实现了高增强且高效调节的石墨烯等离激元，并基于此实现了高灵敏的红外信号探测。ii.制备出大面积悬空石墨烯，为研究无基底干扰的石墨烯等离激元提供基础。iii.基于氟晶云母的原子级平整柔性基底，制备了柔性等离激元器件，石墨烯等离体激元的谐振频率、强度、品质因子、电学可调性和寿命等性质均不受基底弯曲的影响。(3)构筑了多功能石墨烯范德华异质结二硫化钼/石墨烯异质结，该异质结不仅保持了石墨烯等离激元的寿命及其他主要特征，还实现了与单层半导体接触的电学可调的石墨烯等离激元。(4)构建了石墨烯等离激元与金光栅的超材料结构，该结构将金反射面和金光栅与石墨烯等离子激元结构相结合，分别引入干涉效应和避雷针效应，从而极大增强了光与石墨烯等离激元的耦合，使得在低迁移率石墨烯（高衰减）中实现完美吸收。经过该项目的研究，我们建立了基底介电环境对石墨烯等离激元寿命的调制机理，设计和制备了多种石墨烯等离激元基底，并实现了高灵敏红外传感和柔性石墨烯离激元等多种光电功能器件，为实现纳米光子学器件提供了基础。