掺氮N型超纳米金刚石的第一性原理研究

发布时间：2018-01-24 03:12

  本文关键词： 第一性原理 晶界 掺氮超纳米金刚石 结构特性 电学性质　出处：《西南科技大学》2016年硕士论文　论文类型：学位论文

【摘要】：掺氮N型超纳米金刚石薄膜因其低的电子亲和势,极低的表面吸附特性、化学惰性,高的热导率和电导率等优秀性能,已成为全新的冷阴极材料研究中的热点。但目前,对于超纳米金刚石薄膜的尺寸以及氮掺杂对于其结构及电学性质之间的关系还几乎没有了解。本文采用基于密度泛函的第一性原理研究,重点研究了晶界中无定形碳含量和掺杂氮原子对超纳米金刚石的结构与电学性质的影响,该结果有望为实验上制备出具有优异电子发射性能的掺氮N型超纳米金刚石薄膜阴极提供了一定的理论支撑。实验结果表明:(1)对超纳米金刚石结构的研究发现:晶界含量的增多会增加超纳米金刚石结构中C=C双键的数量,并且结构中sp2-C的含量增多,sp3-C的含量减少;(2)模拟超纳米金刚石的能带结构的影响可以看出,晶界含量的增加会使超纳米金刚石的带隙减小,并且会在带隙中引入与sp2-C相关的π*能级和与悬键相关的d.b.能级,减小电子从低能级往高能级跃迁的势垒,增大导电性;(3)计算超纳米金刚石的态密度发现,晶界含量的增多会使超纳米金刚石的态密度为零的区域逐渐减小,并且在π*能级和d.b.能级处的态密度值有所升高,增高电子在带隙中占据的可能性,增强导电性;(4)模拟掺氮对超纳米金刚石的结构影响表明,掺杂氮原子会使超纳米金刚石中晶界含量增多,增加超纳米金刚石中未成键碳原子的含量和C=C含量,并且会使结构中sp2-C含量增多,使金刚石晶粒减小;(5)研究掺氮超纳米金刚石的能带结构发现,掺杂氮原子会在超纳米金刚石薄膜的带隙中引入杂质能级,减小电子跃迁势垒,增强超纳米金刚石的导电性;(6)进一步计算了掺氮对超纳米金刚石态密度的影响,可以知道掺杂氮原子不仅仅是会在超纳米金刚石的能带结构中引入杂质能级,更重要的加深超纳米金刚石自身的缺陷能级,使电子在带隙中出现的概率增加,从而使超纳米金刚石的导电性增加。
[Abstract]:N-doped N-type ultrananocrystalline diamond films have excellent properties such as low electron affinity, very low surface adsorption, chemical inertia, high thermal conductivity and electrical conductivity. It has become a hot spot in the research of new cold cathode materials. There is little understanding of the relationship between the size of ultrananocrystalline diamond films and the relationship between nitrogen doping and their structure and electrical properties. The first principle study based on density functional is used in this paper. The effects of amorphous carbon content and doped nitrogen atoms in grain boundary on the structure and electrical properties of ultrananocrystalline diamond were studied. The results are expected to provide a theoretical support for the preparation of N-doped N-type nanocrystalline diamond film cathode with excellent electron emission properties. It is found that the increase of grain boundary content will increase the number of C / C double bonds in ultrananocrystalline diamond structure. And the content of sp2-C in the structure increased and the content of sp3-C decreased. 2) the influence of the energy band structure on the ultrananocrystalline diamond is simulated. It can be seen that the increase of grain boundary content will decrease the band gap of ultrananocrystalline diamond. The 蟺 * energy level related to sp2-C and the d.b. energy level related to hanging bond will be introduced in the band gap to reduce the barrier of electron transition from low energy level to high energy level and increase the conductivity. By calculating the density of states of nanocrystalline diamond, it is found that the increase of grain boundary content will decrease the region where the density of state of ultrananocrystalline diamond is zero. The density of states at the 蟺 * and d.b. energy levels increased, increasing the probability of electron occupation in the band gap and enhancing the conductivity. The simulated effects of nitrogen doping on the structure of nanocrystalline diamond show that the doping of nitrogen atom can increase the content of grain boundary and increase the content of unbonded carbon atom and C _ (C) in nanocrystalline diamond. The content of sp2-C in the structure will increase and the grain size of diamond will decrease. 5) the energy band structure of nitrogen-doped nanocrystalline diamond is studied. It is found that doped nitrogen atom can introduce impurity energy level into the band gap of ultrananocrystalline diamond film, reduce the barrier of electron transition, and enhance the conductivity of ultrananocrystalline diamond. The effect of nitrogen doping on the density of states of nanocrystalline diamond is further calculated. It can be seen that the doped nitrogen atoms not only introduce impurity energy levels into the energy band structure of nanocrystalline diamond. It is more important to deepen the defect energy levels of nanocrystalline diamond and increase the probability of electron appearing in the band gap, thus increasing the conductivity of ultrananocrystalline diamond.
【学位授予单位】：西南科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ163;TB383.1
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本文编号：1459014