碳化硅表面石墨烯脱附行为与去耦机制的理论研究

发布时间：2018-06-04 06:02

本文选题：碳化硅 + 插层　；参考：《湘潭大学》2017年硕士论文

【摘要】：石墨烯作为一种单原子层二维材料,由于它具有很多优异的性能,被称为是21世纪最具影响力的材料,未来将在诸多领域有非常重要的应用。碳化硅热分解外延生长石墨烯被认为是最有希望制备大面积石墨烯的方法。然而,缓冲层与碳化硅衬底之间存在大量的共价键连接,从而导致石墨烯的性能受到严重的影响。因此,如何使缓冲层从碳化硅衬底上脱附,转变成独立的石墨烯层成为人们所关注的重要问题之一。最近的实验研究发现,在水和氧气环境中,碳化硅衬底上生长的石墨烯能够大面积的去耦。然而,氢和氧进入缓冲层和碳化硅界面内,并使石墨烯脱附的机制并不十分清楚。因此,本文采用密度泛函的第一性原理方法,从原子尺度上对石墨烯如何从碳化硅衬底上脱附的过程与机制进行了研究。首先,我们对分子在碳化硅表面的分解和扩散行为进行了研究。研究发现氢分子、氧分子、水分子能够在6H-Si C(0001)表面自发地分解。由于碳化硅表面具有很强的催化作用,氨气分子和单分子在一定的温度条件下,能够完全分解成原子吸附在表面。同时,研究还发现,氧原子在碳化硅表面容易扩散,而氢原子和氮原子在碳化硅表面相对难以扩散。其次,我们研究了氢原子进入石墨烯/碳化硅界面的过程与机制。研究发现,氢钝化石墨烯边缘和碳化硅衬底,是石墨烯去耦的关键因素。钝化石墨烯边缘能够弱化石墨烯边缘与碳化硅衬底之间的相互作用,并降低氢原子进入界面的能量势垒。随着氢原子进入界面并饱和界面内硅原子的悬挂键,石墨烯将会从衬底上完全脱附。最后,我们研究了氧原子从石墨烯边缘进入界面并在界面扩散的过程。我们发现氧原子难以打破边缘的共价键,从氧化石墨烯边缘进入到界面内,并且在界面内也难以扩散。在水环境中,石墨烯边缘可能被氢化。氧原子容易从氢化石墨烯边缘进入界面,并且氢原子也容易在界面内扩散,在两者的相互协同作用,使得缓冲层从碳化硅衬底上脱附。
[Abstract]:Graphene, as a kind of single atomic layer two-dimensional material, is regarded as the most influential material in the 21st century because of its many excellent properties. It will be used in many fields in the future. The epitaxial growth of graphene by thermal decomposition of silicon carbide is considered to be the most promising method for the preparation of large area graphene. However, there are a large number of covalent bond connections between the buffer layer and the silicon carbide substrate, which results in a serious impact on the performance of graphene. Therefore, how to desorption buffer layer from silicon carbide substrate to independent graphene layer has become one of the most important issues. Recent experimental studies have shown that graphene grown on silicon carbide substrates can decouple in large areas in water and oxygen environments. However, the mechanism of hydrogen and oxygen entering buffer layer and silicon carbide interface and desorption of graphene is not very clear. Therefore, the first principle method of density functional is used to study the desorption process and mechanism of graphene from silicon carbide substrate at atomic scale. First, we studied the decomposition and diffusion behavior of the molecules on the surface of silicon carbide. It is found that hydrogen molecule, oxygen molecule and water molecule can decompose spontaneously on 6H-Si C0001) surface. Due to the strong catalytic action on the surface of silicon carbide, ammonia molecules and monolayers can be completely decomposed into atoms and adsorbed on the surface at a certain temperature. At the same time, it is found that oxygen diffuses easily on the surface of silicon carbide, while hydrogen and nitrogen atoms are relatively difficult to diffuse on the surface of silicon carbide. Secondly, we studied the process and mechanism of hydrogen atom entering graphene / silicon carbide interface. It is found that the edge of hydrogenated graphene and silicon carbide substrate are the key factors for the decoupling of graphene. The passivation of graphene edge can weaken the interaction between graphene edge and silicon carbide substrate and reduce the energy barrier for hydrogen atoms to enter the interface. With the hydrogen atom entering the interface and saturated the hanging bond of the silicon atom in the interface, graphene will be completely desorbed from the substrate. Finally, we study the diffusion of oxygen atoms from the edge of graphene to the interface. It is found that oxygen atoms are difficult to break the covalent bond at the edge, enter into the interface from the edge of graphene oxide, and it is difficult to diffuse in the interface. In water environment, the edge of graphene may be hydrogenated. Oxygen atoms easily enter the interface from the edge of hydrogenated graphene, and hydrogen atoms also diffuse easily in the interface, which makes the buffer layer desorption from silicon carbide substrate.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O613.71

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