石墨烯和石墨炔纳米结构的量子等离子激发

Collective electron oscillations in nanostructures form the surface plasmon resonance (SPR) upon interaction with light. This resonance can confine electromagnetic energy down to deep sub-wavelength regions (truly nano-meter scales) and, consequently, enhance the intensity of an incident light wave by several orders of magnitude. Therefore, it is finding promising applications of a wide range, such as nonlinear optics, single-molecule sensing, and optical harvesting of nanometer-sized objects. The SPR in metal particles larger than 10nm can be explained as a collective oscillation of free electrons responding to the electromagnetic perturbation. However, for systems consisting of only hundreds of atoms and of a size bridging the atomic and condensed phase scales (quantum regime) they feature some extraordinary properties which are neither the same as the Mie plasmon in a classical metal sphere nor like the compressional bulk plasmon. The difference is related to the existence of discrete energy levels in small nanostructures, in contrast to the continuous energy bands present in solids. For traditional noble metal plasmon, its frequency is diffcult to tune since the electron density cannot be altered. Additionally, the plasmon scattering time in metals is usually very short and thus the plasmons decay quickly. These drawbacks limit the performance of metamaterials and transformation optical devices and greatly motivate people to explore plasmons in newly available materials, for instance, graphene. Very recently, graphene plasmons are found experimentally to have big advantages over noble metal plasmons, such as high tunability and low loss. However, for graphene nanostructures smaller than 10nm, little is known about the nature of their plasmons or even whether a regular plasmonic behavior exists, despite their potential applications. For the newly found graphynes with Dirac cones in their band structures, the same questions exist. In this project, we will study systematically the quantum plasmon excitations in 2-dimensional graphene and graphyne nanostructures by performing full quantum mechanical simulations. We will focus on the quantum nature of the plasmons and the difference from the classical behavior. The effects from the size, shape, atomic structure, and chemical doping will be investigated systematically. The structures with a regular plasmonic behavior will be found. The results will not only provide a theoretical basis for the future applications of these nanostructures in plasmonics, but also provide an extension to the classical plasmonics.

光场下纳米结构中载流子的集体震荡形成表面等离子共振（SPR），它能把电磁场能量约束在小于光波长的纳米尺度，使其强度增大几个数量级，因而在非线性光学、单分子检测、纳米尺度光俘获等领域有着广泛的应用前景。10nm以上体系的SPR一般可用经典电动力学描述，但在10nm以下，由于分立能级和量子效应的浮现，SPR需要全量子力学的描述。最近石墨烯二维等离子被发现具有比贵金属等离子更好的特性，如高度的可调性、低的损耗、大的振子强度。但进入10nm以下的量子区域，人们对其等离子特性还知之甚少，甚至不清楚其是否具有规则的等离子行为。对于最近发现的具有Dirac锥的石墨炔，也可以提出同样的问题。本项目将采用全量子力学模拟，系统地研究石墨烯和石墨炔纳米结构中的量子等离子激发，得出其物理特性及与经典行为的差异，分析其受尺寸、形状、原子构形、和化学掺杂的影响，得出具有规则激发行为的结构，为以后的应用提供理论基础。

在低维纳米结构中，光场下的载流子的集体震荡形成表面等离子共振（SPR），它能把电磁场能量约束在小于光波长的纳米尺度，使其强度增大几个数量级，因而在非线性光学、单分子检测、纳米尺度光俘获等领域有着广泛的应用前景。10nm 以上体系的SPR 一般可用经典电动力学描述，但在10nm 以下，由于分立能级和量子效应的浮现，SPR 需要全量子力学的描述。最近石墨烯二维等离子被发现具有比贵金属等离子更好的特性，如高度的可调性、低的损耗、大的振子强度。但进入10nm 以下的量子区域，人们对其等离子特性还知之甚少，甚至不清楚其是否具有规则的等离子行为。另外，受石墨烯发现的推动，近年来，人们也发现了各种碳基和非碳基的二维类石墨烯纳米结构，对于这些二维纳米结构，人们也可以提出同样的问题。本项目采用全量子力学模拟，系统地研究了石墨烯和二维类石墨烯纳米结构的电子性质及量子等离子激发，得出了其物理特性及与经典行为的差异，分析了其受尺寸、形状、原子构形、静电掺杂、和化学掺杂的影响，为以后的器件研发和应用提供了理论基础。研究的主要内容和结果包括：（1）不同大小、形状、掺杂、和激发方向的石墨烯纳米带片段的量子等离激子激发。发现其具有规则的SPR行为，并在0-1.5eV能量窗口存在一个SPR共振峰，当体系的宽度大于~1.5 nm时，频率随着宽度的变化近似满足于经典的静电标度律，而当尺寸小于~1.5 nm时，则显示出完全不同的量子行为。结果也揭示出石墨烯纳米带片段中的plasmon 是近自由电子的 plasmon，而不是Dirac plasmon；（2）石墨烯对双金纳米颗粒的等离激发行为及其耦合的调制。得出了不同激发方向以及不同间距下的调制效应；（3）发现了一种新的更稳定的二维类石墨烯结构lipentoctahexatite，并对不同大小、形状、掺杂、激发方向的纳米结构的等离子激发进行了研究，发现了其与石墨烯纳米结构完全不同的行为；（4）对其他数种二维非碳基类石墨烯结构的电子性质和电子激发进行了计算研究，发现了它们在不同方面的可能应用。