纳米结构表面形貌成型机理及其对石墨烯拉曼光谱的影响

通过真空热蒸镀和高温退火法制备的金属纳米复结构SERS基底因其具有良好的灵敏度，稳定性和均匀性而广泛应用于各种检测领域。石墨烯具有优良的光学特性，化学惰性以及荧光猝灭效应，自被发现以后一直是光学微纳器件中的一大热门材料。石墨烯还可以有效分离探针分子与基底，优化拉曼光谱质量，因此广泛应用于SERS研究领域。同时石墨烯可以有效隔绝金属纳米结构与空气的直接接触防止金属纳米结构被氧化而失效，也可以催化氧化银的脱氧反应提升SERS基底的稳定性。在石墨烯/金属纳米复合结构SERS基底在制备过程中，受到金属膜的种类、厚度参数、气体种类、退火时间、温度和气压等因素的影响，制备的金属纳米结构形貌存在很大差异。石墨烯的拉曼光谱会因为应力和掺杂导致其拉曼特征峰出现不同程度的增强，移动以及展宽。（1）采用真空热蒸镀法和高温退火法制备石墨烯/银纳米复合结构SERS基底，建立了金属纳米颗粒成型机理的模型，从孔洞形成、孔洞生长、金属纳米岛形成三个阶段分析了金属纳米粒子的成型过程，实验沉积5，10，15以及20 nm的银薄膜，退火后银纳米结构的覆盖率分别为~35.1%，~24.4%，~30%以及~96.0%，在沉积银薄膜样品上使用湿法转移石墨烯，退火处理后发现石墨烯阻止了银纳米岛的形成过程；（2）理论分析了银薄膜厚度、石墨烯覆盖对复合结构的几何形貌、拉曼增强特性的影响，石墨烯由于其具有较高的杨氏模量和表面张力，可以有效抑制退火过程中银薄膜向纳米粒子转变的过程，从而实现对复合结构表面形貌的调控；（3）实验研究了银纳米粒结构形貌对石墨烯拉曼光谱的影响，并理论分析了蒸镀不同银薄膜厚度的样品对石墨烯的拉曼光谱增强，移动以及展宽影响的具体原因。

The Forming Mechanism of Surface Morphology of Nanostructures and Its Effect on Graphene Raman Spectra

All the time, SERS based metal nanoparticles structure prepared by vacuum thermal evaporation and high-temperature annealing has been widely used in various detection fields due to its good sensitivity, stability and uniformity. Because of its excellent optical properties, chemical inertness and fluorescence quenching effect, graphene has been a hot material in optical micro-nano devices since its discovery. Graphene can also effectively separate probe molecules and substrate to optimize Raman spectral quality, so it has been widely used in the SERS research field. Meanwhile, graphene can effectively isolate the direct contact between the metal nanostructure and the air to prevent the metal nanostructure from being oxidized and become ineffective. It can also catalyze the deoxidation reaction of silver oxide to improve the stability of SERS substrate. Affected by the types and thickness of the metal film, annealing time, temperature and pressure, and the type of gas during the preparation process of the graphene/metal nanostructure SERS substrate, the influence on metal nanostructure morphology is quite different. Besides, the Raman spectra of graphene will be enhanced, frequency-shifted and broaden because of the stress and doping characteristics of the Raman peak. (1) In this paper, the SERS substrate of graphene/silver nanocomposite structure was prepared by vacuum thermal evaporation and high-temperature annealing, the forming mechanism model of metal nanoparticles was established, and the forming process of metal nanoparticles was analyzed from the three stages of hole formation, hole growth and metal island formation. The silver films at 5, 10, 15 and 20 nm were deposited, and the coverage rates of silver nanoparticles after annealing were ~35.1%, ~24.4%, ~30% and ~96.0%, respectively. Graphene was transferred on the silver film samples, after annealing treatment, it was found that graphene prevented the formation of silver nanoislands. (2) The influence of the thickness of the silver film, the effect of covered graphene cover on the geometric morphology, and Raman enhancement characteristics of the composite structure was theoretically analyzed. Due to its high Young’s modulus and surface tension, graphene could effectively inhibit the transformation of the silver film to nanoparticles in the annealing process so as to realize the regulation of the surface morphology of the composite structure. (3)The effect of silver nanoparticle structure on Raman spectrum of graphene was studied experimentally, and the reasons for the effect of different silver film thickness on Raman spectrum enhancement, shift and broaden of graphene were analyzed theoretically.