【作者】 吉璐；

【导师】 钟建新；

【作者基本信息】 湘潭大学 ， 凝聚态物理， 2010， 硕士

【摘要】 做为未来制备纳电子器件的目前最引人注意的新型纳米材料——单原子层石墨片(graphene),关于它的各类理论和实验的研究已经成为当今国际上凝聚态物理学领域一个新兴的热点问题。这一新型材料的各种可能的应用都要求人们对其制备技术的物理机制在微观尺度上有着更加准确和深刻的认识。本论文主要涉及的是6H-SiC热蒸发外延制备石墨片时,在生长初期石墨片生长机制的核心问题。到目前为止,由于实验方法,观测手段的限制,对graphene生长过程的微观机制中的很多问题都没有得到解决。已有的研究给出了多种生长模式,但却没能从原子尺度加以解释说明。本文中,我们采用基于密度泛函理论的第一性原理方法对6H-SiC的( 3×3)R30o重构面吸附碳原子生长石墨片缓冲层的微观过程从原子尺度进行了系统的理论研究。我们对6H-SiC- ( 3×3)R30o吸附graphene的情况进行了讨论。发现graphene下的Sia原子很难被脱附,却能通过两步置换的过程离开衬底。我们又分别对6H-SiC的( 3×3)R30o重构面进行了单个碳原子,单个硅原子,两个碳原子,三个碳原子的吸附性能进行了计算模拟。单个碳原子与单个硅原子的吸附性能的比对中,我们发现碳原子更易于吸附于6H-SiC- ( 3×3)R30o重构面。同时,我们还结合单个至三个碳原子时的吸附性能研究与相应结构下的置换构型研究,并进一步考察其电荷密度特性,发现Si a原子倾向于与外界C原子进行置换。本文找到可能的6H-SiC- ( 3×3)R30o重构面在graphene缓冲层生产过程中如何扮演着模版作用的微观解释。另外,针对实验上生长过程中所观测到的在SiC基底的不同区域出现不同生长速度的问题,本文对6H-SiC-(0001)面几种不同的晶体表面进行了比较研究。我们分别考察了它们的几何结构,表面能以及在不同晶面上的吸附作用。为它们对外延制备graphene时所产生的影响进行了分析。计算结果表明6H-SiC-(0001)的6个不同晶体表面S1、S2、S3、S1*、S2*、S3*在几何结构和表面能上存在差异。其中,S1与S1*,S2与S2*,S3与S3*的表面能分别相同。根据表面能的不同,这6类晶体表面可以被分为三组,按表面能由低到高的顺序排列为:S1(S*)<S2(S2*)<S3(S*)。同时,我们还发现,不同晶面在同一位置吸附原子时也存在着差别。实验上,也只观测到SiC外延生长过程中出现三类不同的生长速率区域,这与我们的结果相符合。因此,我们推测6H-SiC-(0001)面几种不同的晶体表面性质的差异是引起这一实验现象的原因之一。更多还原

【Abstract】 Nowadays, graphene as a novel two-dimensional crystal and one of the most promising candidates for the future nano-electronics has attracted intensive theoretical and experimental research attention. It has become a new research focus in the field of international condensed matter physics. Naturally, to realize fully controlled preparation of high quality graphene, as well as future relevant device fabrication, a more accurate and profound understanding of the epeitaxial growth procedure on the micro scale is an essential prerequisite.This thesis deals with the growth mechanism of epitaxial graphene on 6H-SiC-(0001) in the initial stage.So far, due to the limit of experimental methods and instruments, restrictions, there are still many problems on the micro-mechanism of graphene growth on 6H-SiC-(0001) which have not been resolved. Some previous studies have given a variety conjecture of the growth mechanism, however, there is not explanation based on atomic scale yet. In this paper, we studied the growth mechanism in the initial stage of epitaxial graphene growth on 6H-SiC-(0001)- ( 3×3)R30oreconstruction surface, employing density functional theory from the atomic scale. We discuss the situation of 6H-SiC- ( 3×3)R30o adsorbing graphene, and find that the Sia atomic is difficult to be desorbed, but able to leave the substrate through the two-step process of substitution, when under the graphene. On the 6H-SiC-(0001)- ( 3×3)R30o reconstruction surface, we find the most stable configuration after adsorption of one, two, and three C adatoms. We also compared the adsorption energy of carbon and silicon adatom. From the results, we find that carbon atom is more easily adsorbed on the reconstruction surface than Si atom. Based on the most stable configurations of C adsorbed reconstruction surface, we further investigated the substitution energy, desorption energy of Sia atom as well as analyzed their charge density difference. We find that Sia atoms are readily substituted by exotic C atoms. The results indicate that the 6H-SiC- ( 3×3)R30o reconstruction surface plays the role of template in the growth process of graphene buffer layer.Former experimental researches figure that there are three kinds of adjacent steps with different reaction speeds on the epitaxial graphene growth process. In order to figure out the mechanism of this issue, we study six possibilities of termination of 6H-SiC-(0001) referring as S1、S2、S3、S1*、S2*、S3*. Different nature of all these termination of SiC may determine the epitaxial growth of grapheme on each of them. We compare their geometric structure, electronic structure, surface energy and adsorption energy. We find that S1 and S1 *, S2 and S2*, S3 and S3* have the same surface energy, respectively. According to the different surface energy, these 6 types of crystal surface can be divided into three groups. According to the surface energy from low to high order is: S1 (S*) <S2 (S2*) <S3 (S*). This is consistent with experimental results showing three different regions with different growth rate. Therefore, we predicate that the experimental results derive form the different nature of the three groups of termination of 6H-SiC-(0001).更多还原