激光减薄及图案化石墨烯研究

发布时间：2018-11-22 08:51

【摘要】：石墨烯作为一种以sp2杂化的碳原子组成的单原子层二维材料,自2004年首次在实验中被制备以来,受到了广泛的关注和研究。石墨烯独特的电学、热学和光学等特性,使其在微电子、储能、透明导电电极以及复合材料等领域有着广阔的应用前景。石墨烯在许多领域的应用对其电子结构、电导率以及透光率等性能有着严格的要求,而这些性能与石墨烯的层数紧密相关。因此,精确的控制石墨烯的层数成为十分重要的研究内容。虽然现有报道提出了一些得到确定层数石墨烯的方法,快速可控得到精确层数石墨烯仍然是现阶段石墨烯应用的一大瓶颈。同时,制备图案化石墨烯也是石墨烯应用中亟需解决的问题。另外,石墨烯零带隙半导体的特性导致了本征石墨烯难以直接应用到半导体器件中,所以石墨烯电学性能的调控成为了研究热点之一。结合以上在石墨烯应用领域的研究热点,本论文提出了一种通过激光辐照的方式对石墨烯进行精确的层数控制、图案化和性能调控的新方法。由于具有加工过程简单、非接触式加工、环境友好、加工效率高以及加工过程柔性等优势,本方法在石墨烯电子器件领域有着广阔的应用前景。采用连续CO2激光在真空环境下对石墨烯进行辐照,通过功率密度和辐照时间的调控,将原始多层石墨烯均匀减薄至2层。采用拉曼光谱、透射电子显微镜以及透过率等手段表征了实验的结果。提出了一种采用皮秒激光精确减薄石墨烯的新方法。通过皮秒激光扫描的方法实现多层石墨烯的减薄。研究了激光能量密度和扫描速度对石墨烯减薄的影响,得出了将石墨烯减薄至不同层数的能量阈值。精确减薄的结果通过拉曼光谱、扫描电镜、透过率等手段进行表征。根据超快激光与石墨烯的相互作用机制,提出了一种石墨烯减薄的剥离机理。本方法加工过程简单,加工环境友好,加工速度快,单次加工即可得到所需层数的石墨烯,与现有方法相比具有很大的优势。通过图案化的石墨烯减薄和切割实现了任意层数任意形状石墨烯的制备。通过能量密度和扫描速度的调控,得出飞秒激光切割单层和多层石墨烯的能量阈值。与现有图案化方法相比,具有非接触式加工、加工效率高、柔性加工等优点。采用低功率皮秒激光对石墨烯进行掺杂,通过拉曼光谱和XPS分析了掺杂效果和掺杂机理。并采用掺杂后的石墨烯搭建了单层石墨烯-硅太阳能电池,将其转换效率提高至6.4%。
[Abstract]:Graphene, as a two-dimensional monatomic layer material composed of sp2 hybrid carbon atoms, has been widely studied since it was first prepared in the experiment in 2004. Because of its unique electrical, thermal and optical properties, graphene has a broad application prospect in the fields of microelectronics, energy storage, transparent conductive electrodes and composites. The applications of graphene in many fields have strict requirements for its electronic structure, conductivity and transmittance, which are closely related to the number of layers of graphene. Therefore, it is very important to control the layer number of graphene accurately. Although some methods for determining the layer number of graphene have been put forward in the present reports, rapid and controllable obtaining of accurate layer number of graphene is still a major bottleneck in the application of graphene at present. At the same time, the preparation of patterned graphene is an urgent problem in the application of graphene. In addition, because of the characteristics of graphene zero-band gap semiconductor, the intrinsic graphene is difficult to be directly used in semiconductor devices, so the regulation of graphene electrical properties has become one of the hot research topics. In this paper, a new method for controlling the number of layers, patterning and performance of graphene by laser irradiation is proposed. Due to the advantages of simple process, non-contact processing, environmental friendliness, high processing efficiency and flexible processing process, this method has a broad application prospect in the field of graphene electronic devices. Graphene was irradiated by continuous CO2 laser in vacuum environment. The original multilayer graphene was evenly thinned to 2 layers by the control of power density and irradiation time. The experimental results were characterized by Raman spectroscopy, transmission electron microscopy and transmittance. A new method for accurately thinning graphene by picosecond laser is proposed. The multilayer graphene is thinned by picosecond laser scanning. The effects of laser energy density and scanning speed on graphene thinning are studied and the energy threshold of reducing graphene to different layers is obtained. The exact thinning results were characterized by Raman spectroscopy, scanning electron microscopy and transmittance. According to the interaction mechanism between ultrafast laser and graphene, a mechanism of graphene thinning is proposed. The method is simple in processing, friendly in processing environment, fast in processing speed, and can obtain the required layers of graphene in a single process, which has a great advantage compared with the existing methods. The preparation of graphene with any number of layers and shapes was realized by thinning and cutting graphene with pattern. The energy threshold of femtosecond laser cutting monolayer and multilayer graphene was obtained by adjusting the energy density and scanning speed. Compared with the existing patterning methods, it has the advantages of non-contact machining, high processing efficiency and flexible machining. Graphene was doped by low power picosecond laser. The doping effect and doping mechanism were analyzed by Raman spectroscopy and XPS. A monolayer graphene silicon solar cell was built with doped graphene, and its conversion efficiency was improved to 6.4.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ127.11

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