石墨烯掺杂设计与本征性质调控的第一性原理研究

发布时间：2018-03-17 20:30

  本文选题：第一性原理　切入点：石墨烯　出处：《哈尔滨工业大学》2017年博士论文　论文类型：学位论文

【摘要】：石墨烯自从出现便掀起了纳米科技领域的风暴,有关它的应用也日益增加。石墨烯独特而出色的特性让它成为了合成材料界的神奇焦点。虽然石墨烯被认为是21世纪的一种很有潜力的材料,但是它仍然具有一些缺陷,比如,零带隙、非磁性以及在可见光范围只有2%的吸收率。单层石墨烯的电子结构、磁学和光学特性可以通过在它的二维(2D)结构中掺杂其他原子或团簇来进行调控。为了克服以上提到的纯石墨烯的缺点并且调控其特性使其满足工程应用的需要,本文研究了在石墨烯晶格中引入其他的原子(比如,硼(B),氮(N),碱土金属(AEM)和5d过渡金属(TM))或团簇(比如,3d过渡金属三氧化物和四氧化物(TMO_3(4)))。通过运用基于密度泛函理论(DFT)的第一性原理计算,本文研究了石墨烯以及杂质原子或团簇掺杂的石墨烯材料的结构、电学、磁学和光学特性。纯石墨烯和杂质原子掺杂的石墨烯结构的光学性质是在随机相位近似(RPA)下进行计算的。计算中采用了温度为T=0 K下的参数。通过在石墨烯中掺入BN环,可以观察到,BN环掺杂的石墨烯结构表现为直接带隙,而且带隙宽度随着石墨烯中BN环数量的增加而增加,同时随着BN环数量的增加,吸收光谱呈现明显的红移趋势,14 e V处的吸收峰幅值减小。对于AEM原子(比如,Be、Mg、Ca、Sr和Ba)掺杂的石墨烯,计算结果表明,Be、Mg和Ca原子掺杂的石墨烯结构呈现半金属特性,并分别带有大小为0.00μB、1.86μB和4.00μB的磁矩。而Sr和Ba原子掺杂的石墨烯结构呈现间接带隙半导体特性,并分别带有大小为3.16μB和0.46μB的磁矩。通过研究电子态密度,我们发现掺杂石墨烯结构的磁矩是由杂质原子的sp轨道引起的。计算结果表明,AEM元素的掺杂可以增加0到3 e V的吸收,并且减小14 e V处的吸收峰。另外在7到11 e V之间出现了第三个较小的吸收峰值,此峰值在纯石墨烯吸收光谱中并未出现。可以明显观察出吸收光谱朝着可见光范围的红移趋势。同时可以发现AEM原子的掺杂引起了低能量区反射峰值的增加。同样地,在5d TM原子(比如,Hf,Ta,W,Os,Re,Ir和Pt)替换双空位的石墨烯中,Hf,Ta和W掺杂的石墨烯结构在高对称K点自旋向上和自旋向下的轨道处产生了带隙,并分别带有0.783μB、1.65μB和2.00μB的磁矩。Ir和Pt掺杂的结构表现出了间接带隙半导体性质。有趣的是,Os掺杂的石墨烯结构在自旋向上轨道处呈现直接带隙半导体特性,并带有1.5μB的磁矩。从态密度图我们可以推测掺杂石墨烯结构的磁性与5d TM原子的d轨道有关。所有杂质原子(比如,AEM和5d TM元素)都被石墨烯紧紧地束缚,具有较大的结合能,并且电荷转移的方向是从杂质原子到石墨烯。之后,本文研究了用两种不同的方法在石墨烯中嵌入3d TMO_3(TM=Ti、V、Cr、Fe、Co、Mn和Ni)。第一种是用TMO_3团簇直接替换了石墨烯中的四个碳(C)原子。在第二种方法中石墨烯环中的三个C原子被氧(O)原子替换而TM原子吸附在三个O原子的空位。在Cr、Fe、Co和Ni原子掺杂的情况下,费米能级向导带移动,从而引起狄拉克锥向价带移动,并且在高对称K点产生了带隙。在Ti O_3和VO_3掺杂的情况下,掺杂的结构表现出半导体性质。有趣的是,Ti O_3掺杂的结构表现出稀磁半导体(DMS)性质并带有2.0μB的磁矩。相应地,Co O_3、Cr O_3、Fe O_3和Mn O_3掺杂分别产生了1.015μB、2.347μB、2.084μB和3.584μB的磁矩。在第二种方法中O原子掺杂在石墨烯中,而TM原子吸附在空位,对于所有的掺杂结构费米能级向导带移动,狄拉克锥向价带移动。在Cr和Ni吸附的情况下,体系表现为间接带隙半导体,磁矩为0.0μB。Co吸附表现为DMS并产生了0.916μB的磁矩。Fe、Mn、Ti和V吸附在高对称K点产生了带隙,并分别产生了1.54μB、0.9909μB、1.912μB和0.98μB的磁矩。最后,我们分别用3d TMO_4替换石墨烯中的单空位和双空位,然后研究了它们的性质。计算结果表明,CrO_4和Mn O_4掺杂的单空位石墨烯结构在自旋向下轨道表现出稀磁半导体性质并分别具有2.15μB和3.51μB的磁矩。但是,Co O_4、Fe O_4、Ti O_4和Ni O_4掺杂的单空位石墨烯中,费米能级向导带移动,引起了狄拉克锥向价带移动,从而在高对称K点产生带隙。有趣的是,Co O_4、CrO_4,、Fe O_4和Mn O_4掺杂的双空位石墨烯结构在其自旋向上轨道表现出稀磁半导体性质,并分别具有1.74μB、3.27μB、3.09μB和1.99μB的磁矩。我们发现,对于所有的TMO_3(4)团簇掺杂,所有杂质原子都被石墨烯紧紧地束缚,具有较大的结合能,并且电荷转移的方向是从石墨烯到TMO_3(4)团簇。对TMO_3(4)团簇掺杂石墨烯结构态密度图的深入分析表明掺杂石墨烯的磁矩是由3d TM原子的d轨道引起的。本文进行的研究以及得到的结论可以促进纳米电子、自旋力学、能量存储以及光电设备等应用中以石墨烯为基础的器件的设计和优化。本文的研究还为未来本领域的研究指明了方向。同时对于本文提出的石墨烯掺杂结构还需要进行进一步的实验工作,从而和本文的理论预测结果进行对比。
[Abstract]:Since the emergence of graphene nano science and technology has set off a storm, the application is also increasing. The unique and outstanding characteristics of graphene makes it a focus of magical materials. Although the synthesis of graphene is believed to be a potential material in twenty-first Century, but it still has some defects, for example. The zero band gap, nonmagnetic and in the visible light absorption rate of only 2%. The electronic structure of graphene, magnetic and optical properties through its two-dimensional (2D) structure doped with other atoms or clusters to carry out regulation. In order to overcome the above mentioned pure graphene defects and control because of its characteristics to meet the needs of engineering application, the other atoms in the graphene lattice (for example, boron (B), nitrogen (N), alkaline earth metal and transition metal (AEM) 5D (TM)) or clusters (e.g., transition metal oxides and 3D three Four oxide (TMO_3 (4))). By using the density functional theory (DFT) based on the first principle calculation is studied in this paper, electrical and structure of graphene, graphene materials doped with impurity atoms or clusters, magnetic and optical properties. The optical properties of pure and impurity atoms of graphene doped graphene the structure is in the random phase approximation (RPA) was calculated. In the calculation of temperature parameters T=0 and K. The graphene doped BN ring can be observed, the graphene structure of BN doped ring for direct band gap and the band gap width increases with the increase of graphite by BN ring number at the same time, with the increase of BN ring number, the absorption spectra showed obvious red shift, 14 e V peak amplitude for AEM atoms (e.g., Be, Mg, Ca, Sr and Ba) doped graphene, the calculation results show that Be, Mg and graphene Ca doped The structure presents half metallic properties, and respectively provided with a size of 0 B, the magnetic moment of 1.86 B and 4 B. The graphene structure of Sr and Ba atoms present indirect bandgap semiconductor properties, and respectively provided with a magnetic moment size of 3.16 B and 0.46 B. Through the research on the electronic density of States, we that moment doped graphene structure is caused by impurity atoms SP orbit. The calculation results show that the AEM doping can be increased by 0 to 3 E V absorption, and reduce the 14 e absorption peak at V. In addition, between 7 to 11 e V the absorption peak appeared third smaller, the peak the values in the pure graphene absorption does not appear in the spectrum. It can be observed that the absorption spectra in the range of visible light. The red shift can be found at the same time the doping of the AEM atom caused an increase in the low energy region of the reflection peak. Similarly, in the 5D (for example, Hf, TM atoms Ta, W, Os, Re, Ir replace and Pt) 鍙岀┖浣嶇殑鐭冲ⅷ鐑�涓�,Hf,Ta鍜學鎺烘潅鐨勭煶澧ㄧ儻缁撴瀯鍦ㄩ珮瀵圭ОK鐐硅嚜鏃嬪悜涓婂拰鑷�鏃嬪悜涓嬬殑杞ㄩ亾澶勪骇鐢熶簡甯﹂殻�

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