二维有机纳米硅片几何和电子结构性质的第一性原理研究

【作者】 宋健；

【导师】 肖传云； 阚二军；

【作者基本信息】 南京理工大学 ， 凝聚态物理， 2012， 硕士

【摘要】 石墨烯是只有一层原子的石墨片,具有完美的二维蜂窝状网格结构。伴随着其各种新颖的特性被发现,石墨烯也吸引了各国研究者越来越多的关注。由于在周期表中与碳同属一族,且具有许多相似的性质,因此,对于硅来说,是否具有石墨烯类似的结构就吸引了非常多的研究兴趣。虽然实验上还未能制备出类似石墨烯的纯硅材料,但是,科学家已于2010年成功制备出一种二维单层硅材料Si6H4Ph2。这种新材料的发现,也引出了很多有趣的科学问题,比如Si6H4Ph2的稳定性,Si6H4Ph2的电子性质有何特点等等。因此,相应的理论研究十分必要,在此基础上做出的理论解释也会进一步推动这类材料的发展和应用。得益于理论物理化学和计算技术的发展,利用基于密度泛函理论的第一性原理计算方法使得理论研究这类材料成为可能。在第一章中,我们首先对硅材料的研究进展做了一个简要综述,包括硅晶体材料、硅纳米团簇、硅纳米线和硅纳米管。然后着重介绍了二维类石墨烯结构的硅纳米单片材料的实验和相应的理论研究进展。第二章简要介绍了量子化学的历史及发展现状、密度泛函理论的理论框架和近年来的发展。Kohn建立了密度泛函理论基础,他证明了多粒子体系的任何基态性质,都可以表达为基态电子密度的泛函。通过将多体相互作用包含在交换关联能量中,使得多体问题化为有效单粒子问题。因此,密度泛函理论发展的主线,就是寻找合适的交换相关能量泛函。本章最后还简要介绍了本论文所使用的密度泛函计算软件包。在第三章中,我们研究了实验发现的二维单层硅材料Si6H4Ph2的稳定性及其电子结构。通过对纯硅纳米片Si6、加氢钝化的硅纳米片Si6H6以及添加苯基钝化的硅纳米片Si6H4Ph2进行对比研究,我们揭示了Si6H4Ph2的稳定性机理。此外,通过电子结构研究,我们发现Si6H4Ph2与Si6H6类似,显示间接带隙半导体性质,且拥有一个较大的能隙,不利于其实际应用。在第四章中,针对氢化和苯基钝化的硅纳米片均为间接能隙半导体且能隙较大的问题,我们试探性地对硅纳米片的能隙调控进行了初步研究。我们的研究显示,通过氟化硅纳米片,可以改变导带的成分,从而使硅基纳米片从原来的(氢化或苯基钝化)大能隙间接半导体转变成小能隙直接半导体,这将更有利于在光伏技术方面的应用。更多还原

【Abstract】 Graphene is a monolayer of graphite and has a perfect two-dimensional honeycomb structure. With the discovery of various novel properties, it has attracted more and more attention of researchers all over the world. Since silicon and carbon belong to the same group in the Periodic Table and they have many similar properties, it has aroused great interest whether there may exist graphene-like structure for silicon? Although pure silicon nanosheet of graphene-like structure has not yet been prepared in experiment up to date, it is reported in 2010 that a new two-dimensional organosilicon nanosheet Si6H4Ph2 was successfully synthesized. A number of interesting scientific questions are to be answered with respect to this new material, such as the stability, the nature of its electronic properties and so on. A theoretical research is thus highly expected, and a detailed theoretical understanding will forward the development and application of such kind of materials. Thanks to the progress in quantum physics and chemistry as well as computational techniques, it is now possible to perform theoretical study on such kind of materials by first-principles methods based on density functional theory.In Chapter 1, we first make a brief summary on the progress in the study of silicon materials, including bulk silicon, silicon clusters, silicon nanowires and nanotubes. Then, we focus on the experimental and theoretical research progress of two-dimensional graphene-like silicon nanosheets.In Chapter 2, we briefly review the historical development and current status of quantum chemistry and outline the framework of density functional theory and its recent progress. Kohn established the foundation of density functional theory, who proved that any properties of a many-particle system in the ground state can be expressed as a functional of the ground-state electron density. The many-particle is transformed into an effective single-particle problem by incorporating many-particle interactions into the exchange-correlation energy. Therefore, the major target of density functional theory is to look for reasonable exchange-correlation energy functional. The chapter ends with a brief introduction to the scientific computer codes of density functional methods used for studies in this thesis.In Chapter 3, we investigate the stability and electronic structure of Si6H4Ph2. By a comparative study of pure silicon nanosheet Si6, hydrogen-passivated silicon nanosheet Si6H6 and phenyl-passivated silicon nanosheet Si6H4Ph2, we elucidate the mechanism on the stability of Si6H4h2. In addition, by examining the electronic structures of Si6H6 and 2, we find they both behave like an indirect gap semiconductor with a quite large gap, which is unfavorable for practical applications.In Chapter 4, aiming at the problem that hydrogen-passivated and phenyl-passivated silicon nanosheets Si6H6 and Si6H4Ph2 are both indirect-gap semiconductors with a quite large band gap, we tentatively carried out a preliminary research to fine tune the band gap of silicon nanosheet. Our research shows that, by fluorine-passivating silicon nanosheet, we can change the conduction band character from indirect-gap semiconductors (hydrogen-passivated and phenyl-passivated) with a big gap into a direct-gap semiconductor with a small gap, which would be favorable for potential applications as photovoltaic materials.更多还原