类石墨烯及纳米管的结构设计和性能预测

发布时间：2018-07-01 10:07

本文选题：第一性原理 + 类石墨烯　；参考：《山东大学》2017年博士论文

【摘要】：低维材料是当前凝聚态物理和材料科学领域的研究热点,石墨烯和碳纳米管的制备和性能研究推动了该领域的发展。石墨烯材料具有一系列独特的物理性质,例如:零带隙半导体,高载流子迁移率,最薄的晶体,超高的刚性和弹性,极高的电导率等优异的性能具有广泛的应用前景。碳纳米管可以看成由石墨烯卷曲而成的一维结构。根据手性、直径、堆叠方式的不同展现出规律可调的电学,热学和机械性质,例如比金刚石还要高的热导率,超强的机械性能,扶手椅状纳米管规律性变化的带隙等,碳纳米管被认为是下一代电子元器件的理想材料。石墨烯的应用还是会受到很多限制,例如其零带隙的半导体性质必须通过化学修饰等方式打开带隙,才能应用于逻辑电路等电子元器件中,石墨烯的自旋轨道耦合效应特别弱,无法在实验上实现量子自旋霍尔效应,石墨烯不存在自旋极化等等。碳纳米管在可控合成方面也面临很多困难。这些问题都限制了石墨烯和纳米管的实际应用范围。基于此,一种被称为"类石墨烯"的材料应运而生,这些类石墨烯及纳米管材料具有石墨烯的部分奇特性质,比如硅稀和锗烯是零带隙半导体的性质;某些特性甚至优于石墨烯,例如具有自旋极化零带隙半导体性质的氮化碳纳米材料。随着理论和实验工作的研究进展,类石墨烯纳米材料在未来的电子技术,通讯技术,机械制造,环境保护,能源动力等各个方面拥有广泛的应用前景。本论文通过基于密度泛函理论的第一性原理研究方法,设计研究了几种具有新奇特性的类石墨烯纳米材料。锗化硅(SiGe)纳米单层是具有零带隙半导体性质的类石墨烯单原子层化合物,二维氧化碳氮材料(g-C_2NO)的自旋极化零带隙半导体性质拓展了类石墨烯氮化碳材料的研究范围,新型超硬材料bct-C8来源于冷压T型石墨烯。一氧化碳(CO)纳米管束结构代表了固体一氧化碳低压下稳定的新结构,二氧化硅(SiO_2)纳米片层和纳米管在生物制药,催化剂载体等领域具有潜在的应用前景。上述材料的研究结果对于类石墨烯纳米材料的实验合成及应用提供了重要的理论依据。论文的第一章主要讨论研究背景和选题意义,第二章讨论基于密度泛函理论的第一性原理研究方法,结构设计方法以及在论文中所使用到的软件包,第三章至第六章详细的介绍了攻读博士学位期间的主要研究工作和研究成果。主要研究内容和结果如下所示:1)提出了由硅原子(Si)和锗原子(Ge)交替排列形成的稳定的锗化硅(SiGe)单层化合物,该材料是具有狄拉克锥能带的类石墨烯化合物。由于硅元素和锗元素的电负性相差很小,费米面附近锥带的来源是两种原子的pz轨道,自旋耦合效应很弱,但是区别于单质石墨烯,SiGe单层具有选择吸附性,能够首先在硅原子上完成氢化作用,合成具有自旋极化性质的半导体HSiGe。该半导体具有锗原子贡献的1μB每原胞的磁性,铁磁态最稳定,根据伊辛模型进行蒙特卡洛模拟证明在温度低于110K时HSiGe保持铁磁态性质。另外在能量上优于锗烯,因此更有利于实验合成。2)提出了由三嗪和碳氧环组成的类石墨烯氧化碳氮材料g-C_2NO,声子谱和分子动力学模拟均验证了该材料的稳定性。g-C_2NO具有自旋极化的零带隙半导体性质,每个原胞具有1μB的磁矩,在费米面上下,两条不同曲率的能带相切,使得电子和空穴两种载流子有效质量相差很大,有助于自旋注入和自旋过滤。与纯g-C_6N_6相比,氧原子的加入,使g-C_2NO费米面升高,g-C_6N_6中pz轨道贡献的导带,在g-C_2NO中成为费米面附近的两条相切能带,从而产生自旋极化的零带隙半导体性质。作为不含金属的有机二维材料,g-C_2NO具有环境友好的特点,在自旋电子器件领域具有应用潜力。3)在冷压T型石墨烯的基础上设计出一种新型的高对称性超硬材料bct-C8。在能量上,bct-C8比T型石墨烯更稳定,其声子谱没有虚频。尽管相对于其它超硬材料bct-C8有较大直径的8元碳环构成,但仍表现出较好的力学特性,在同密度材料中,它的硬度是最强的,在相同硬度的范围内,bct-C8的密度是最小的。能带结构显示,该材料为宽带隙半导体。作为碳元素家族的一个新成员,bct-C8的研究将对超硬材料的设计提供新的思路。4)研究了Ⅳ族硅(碳)氧化物的低维结构,提出了 Si02类石墨烯结构,即由Si-O六边形组成的双层结构,层间由Si-O-Si键连接。证明该类石墨烯结构比其它纳米结构更稳定。由该结构出发通过AB堆垛可以形成稳定的多层结构。由SiO_2准二维材料卷曲得到的纳米管最小直径约为12A。类石墨烯SiO_2纳米材料的结构孔径为5.23A,相较于仅有2.48A的石墨烯结构,类石墨烯SiO_2纳米材料在分子筛选,催化反应,缓释微胶囊等领域有着独特的发展潜力。另外,从理论上预言了一氧化碳(CO)一个新的低压相,纳米管束(bnudles)结构。焓变分析和声子谱分析均证明了该结构的稳定性。这种新结构为一氧化碳晶体结构的多样性及一氧化碳的贮存等提供了新思路。
[Abstract]:Low dimensional materials are the hot spots in the field of condensed matter physics and material science. The preparation and properties of graphene and carbon nanotubes have promoted the development of this field. The graphene materials have a series of unique physical properties, such as zero band gap semiconductors, high carrier mobility, the thinnest crystals, ultra high rigidity and elasticity. Excellent properties, such as conductivity, have wide application prospects. Carbon nanotubes can be seen as a one-dimensional structure made of graphene. According to the chirality, diameter, and stacking mode, the electrical, thermal and mechanical properties, such as the higher thermal conductivity, the super mechanical properties, the armchair nanotube gauge, are higher than the diamond. Carbon nanotubes are considered to be ideal materials for the next generation of electronic components. The application of graphene will be limited by many limitations. For example, its zero band gap semiconductor properties must be opened by chemical modification to be applied to the electronic components such as logical circuits, and the spin orbit coupling effect of graphene. It should be especially weak, the quantum spin Holzer effect can not be realized in the experiment, the spin polarization does not exist in graphene and so on. The carbon nanotubes are also faced with many difficulties in the controllable synthesis. These problems restrict the practical application of graphene and nanotubes. Based on this, a kind of material called "graphene like" has come into being, these kinds of graphite. Alkene and nanotube materials have some peculiar properties of graphene, such as silicon thin and germanium are zero band gap semiconductors; some properties are even better than graphene, such as carbon nitride nanomaterials with spin polarized zero band gap semiconductors. With the progress of theoretical and experimental research, the future electricity of graphene nano materials is in the future Sub technology, communication technology, mechanical manufacturing, environmental protection, energy power and other aspects have wide application prospects. In this paper, several novel graphene like nanomaterials with novel properties are designed and studied by the first principle research method based on density functional theory. The SiGe nano monolayer is with zero band gap semiconductor properties. A qualitative graphene like single atomic layer compound, the spin polarized zero band gap semiconductor properties of two dimensional carbon and nitrogen oxides (g-C_2NO) expand the scope of the study of graphene carbon nitride materials. The new superhard material bct-C8 is derived from the cold pressed T type graphene. The carbon monoxide (CO) nanotube structure represents the new stability of the solid carbon monoxide under low pressure. Structure, silica (SiO_2) nanoscale and nanotube have potential applications in the fields of biopharmaceuticals, catalyst carriers and other fields. The research results of these materials provide important theoretical basis for the experimental synthesis and application of graphene like nanomaterials. The first chapter of the paper mainly discusses the research background and the significance of the topic, second chapters The first principle research method based on density functional theory, structure design method and software package used in the paper, third chapters to sixth chapters are introduced in detail to introduce the main research work and research results during the period of studying the doctorate. The main research contents and results are as follows: 1) the silicon atoms (Si) and germanium are proposed. A stable single layer of germanium (SiGe) compound formed by the alternating arrangement of Ge. The material is a graphene like compound with a Dirac cone. Because the electronegativity of the silicon and germanium elements is very small, the source of the cone in the vicinity of the Fermi surface is the PZ orbit of the two atoms. The self spin coupling effect is very weak, but it is distinguished from the single graphene, SiGe The monolayer has the choice of adsorbability. It can first complete the hydrogenation of the silicon atom and synthesize the semiconductor HSiGe. with spin polarization properties. The semiconductor has 1 u B of germanium atom contribution, and the ferromagnetic state is the most stable. According to the isin model, the Monte Carlo simulation shows that HSiGe maintains the ferromagnetic properties when the temperature is below 110K. In addition, the energy is superior to germanium, so it is more beneficial to the experimental synthesis of.2). A graphene like carbon and nitrogen oxide material composed of three azinazine and carbon oxygen ring is proposed. G-C_2NO, phonon spectrum and molecular dynamics simulation all verify that the stability of the material has the properties of spin polarized zero band gap half conductor, and the magnetic moment of each primary cell with 1 mu B, at the expense of.G-C_2NO. In the upper and lower sides of the rice, two bands of different curvature of the energy are tangent, which makes the two carrier mass of the electron and hole very different, and helps to spin and spin. Compared with the pure g-C_6N_6, the oxygen atom is added, the g-C_2NO Fermi surface is raised, the guide band of the PZ orbit in g-C_6N_6 is the two tangent energy near the Fermi surface in g-C_2NO. Band, thus producing spin polarized zero band gap semiconductor properties. As a non metallic organic two-dimensional material, g-C_2NO has environmental friendly characteristics and has potential application potential in the field of spintronic devices. A new type of high symmetry superhard material, bct-C8., is designed on the basis of cold pressed T graphene, bct-C8. in energy, bct-C8 than T stone. It is more stable and its phonon spectrum has no imaginary frequency. Although it is made up of 8 yuan carbon ring with larger diameter than other superhard material bct-C8, it still exhibits better mechanical properties. In the same density material, its hardness is the strongest and the density of bct-C8 is the smallest in the range of same hardness. The band structure shows that the material is half gap half. Conductor. As a new member of the family of carbon elements, the research of bct-C8 will provide a new idea for the design of super hard materials (.4). The low dimensional structure of Si (carbon) oxide is studied. The structure of Si02 class graphene is proposed, which is a double layer structure composed of Si-O hexagons and the interlayer is connected by the Si-O-Si bond. It is proved that the structure of this kind of graphene is more than the others. The structure is more stable. A stable multilayer structure can be formed by the structure of the AB stacking. The minimum diameter of the nanotube obtained by the SiO_2 quasi two-dimensional material is about 5.23A of the structure of the 12A. class graphene SiO_2 nanomaterials. Compared with the graphene structure with only 2.48A, the graphene SiO_2 nanomaterials are screened and catalyzed by molecules. In addition, a new low pressure phase, nano tube bundle (bnudles) structure of carbon monoxide (CO) was predicted theoretically. Both enthalpy and phonon spectrum analysis proved the stability of the structure. This new structure is the diversity of the crystalline structure of the mono oxygenated carbon and the storage of carbon monoxide. A new way of thinking is provided.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O613.71;TB383.1

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