利用近场光学显微镜研究二维材料的光学特性

发布时间：2018-09-03 10:35

【摘要】：石墨烯等离子体因其相当低的损耗、极高的空间局域性、非凡的可调性以及宽波段激发等特点受到了广泛的关注,在诸多领域显示出巨大的应用潜力。继石墨烯之后,二硫化钼(MoS_2)是研究最多的二维层状材料,其光学性质与层数密切相关,对于光伏,光电探测器和光发射器等器件的搭建极具意义。本文采用散射式近场光学显微镜(Scattering-Type Scanning Near-Field Optical Microscope,s-SNOM)研究具有不同纳米结构的石墨烯和MoS_2晶体在中红外光的激发下所具有的光学特性。研究内容如下:1.利用s-SNOM研究化学气相沉积(Chemical Vapor Deposition,CVD)法制备的石墨烯纳米结构的表面等离子体特性,发现纳米图案上的等离子体局域模式与激发波长和结构的尺寸密切相关,且能够在宽为25 nm的间隙中发生共振增强。此外,不同手性石墨烯边缘的测试结果表明,之字边处的等离子体会出现额外的展宽。并且,在近场光学图像中,多晶石墨烯薄膜上的晶界清晰可见,该光学表征结果是定性分析局部电荷浓度和化学成分的重要依据。2.利用s-SNOM对其他方法制备的石墨烯纳米结构的表面等离子体特性进行研究,发现金属纳米粒子裁剪的沟道越浅,宽度越小,产生的近场振幅强度就越强。此外,纳米石墨烯的等离子体特性与其尺寸和激发波长密切相关,随着尺寸的增大,等离子体共振增强由样品边缘向中心位置移动。一定尺寸的纳米石墨烯的近场振幅强度随激发光波长的增大而增大。3.利用s-SNOM对MoS_2晶体进行近场光学表征,发现单层MoS_2晶体的晶界在原子力显微镜的相貌图中可分辨,而在光学振幅图图中不可见。而且,相较于单层MoS_2,多层MoS_2的近场信号出现明显增强,意味着对光的散射性显著增强。
[Abstract]:Graphene plasma has attracted wide attention due to its low loss, extremely high spatial localization, special tunability and wide band excitation, and has shown great application potential in many fields. After graphene, molybdenum disulfide (MoS_2) is the most studied two-dimensional layered material, whose optical properties are closely related to the number of layers. In this paper, the optical properties of graphene and MoS_2 crystals with different nanostructures under the excitation of medium infrared light have been studied by means of scattering near-field optical microscope (Scattering-Type Scanning Near-Field Optical Microscope,s-SNOM). The research is as follows: 1. The surface plasma characteristics of graphene nanostructures prepared by chemical vapor deposition (Chemical Vapor Deposition,CVD) method were investigated by s-SNOM. It was found that the local plasma modes on the nanostructures were closely related to the excitation wavelength and the size of the structures. Resonance enhancement can occur in a gap of 25 nm wide. In addition, the results of different chiral graphene edge measurements show that the plasma at the edge of the zigzag will exhibit additional broadening. Moreover, the grain boundaries on polycrystalline graphene thin films are clearly visible in near-field optical images, which is an important basis for qualitative analysis of local charge concentration and chemical composition. The surface plasma characteristics of graphene nanostructures prepared by other methods were studied by s-SNOM. It was found that the shallower the channel and the smaller the width of the metal nanoparticles, the stronger the near field amplitude intensity. In addition, the plasma characteristics of nano-graphene are closely related to its size and excitation wavelength. With the increase of the size, the enhancement of plasmon resonance shifts from the edge of the sample to the center position. The near field amplitude strength of nano-graphene increases with the increase of excitation wavelength. The near field optical characterization of MoS_2 crystals by s-SNOM shows that the grain boundaries of monolayer MoS_2 crystals can be distinguished in the atomic force microscope (AFM) images, but not in the optical amplitude diagrams. In addition, the near field signal of monolayer MoS_2, multilayer MoS_2 is obviously enhanced, which means that the scattering of light is enhanced significantly.
【学位授予单位】：苏州大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O613.71;O53

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