本文關(guān)鍵詞： 第一性原理 晶界 摻氮超納米金剛石 結(jié)構(gòu)特性 電學性質(zhì)　出處：《西南科技大學》2016年碩士論文　論文類型：學位論文

【摘要】：摻氮N型超納米金剛石薄膜因其低的電子親和勢,極低的表面吸附特性、化學惰性,高的熱導率和電導率等優(yōu)秀性能,已成為全新的冷陰極材料研究中的熱點。但目前,對于超納米金剛石薄膜的尺寸以及氮摻雜對于其結(jié)構(gòu)及電學性質(zhì)之間的關(guān)系還幾乎沒有了解。本文采用基于密度泛函的第一性原理研究,重點研究了晶界中無定形碳含量和摻雜氮原子對超納米金剛石的結(jié)構(gòu)與電學性質(zhì)的影響,該結(jié)果有望為實驗上制備出具有優(yōu)異電子發(fā)射性能的摻氮N型超納米金剛石薄膜陰極提供了一定的理論支撐。實驗結(jié)果表明:(1)對超納米金剛石結(jié)構(gòu)的研究發(fā)現(xiàn):晶界含量的增多會增加超納米金剛石結(jié)構(gòu)中C=C雙鍵的數(shù)量,并且結(jié)構(gòu)中sp2-C的含量增多,sp3-C的含量減少;(2)模擬超納米金剛石的能帶結(jié)構(gòu)的影響可以看出,晶界含量的增加會使超納米金剛石的帶隙減小,并且會在帶隙中引入與sp2-C相關(guān)的π*能級和與懸鍵相關(guān)的d.b.能級,減小電子從低能級往高能級躍遷的勢壘,增大導電性;(3)計算超納米金剛石的態(tài)密度發(fā)現(xiàn),晶界含量的增多會使超納米金剛石的態(tài)密度為零的區(qū)域逐漸減小,并且在π*能級和d.b.能級處的態(tài)密度值有所升高,增高電子在帶隙中占據(jù)的可能性,增強導電性;(4)模擬摻氮對超納米金剛石的結(jié)構(gòu)影響表明,摻雜氮原子會使超納米金剛石中晶界含量增多,增加超納米金剛石中未成鍵碳原子的含量和C=C含量,并且會使結(jié)構(gòu)中sp2-C含量增多,使金剛石晶粒減小;(5)研究摻氮超納米金剛石的能帶結(jié)構(gòu)發(fā)現(xiàn),摻雜氮原子會在超納米金剛石薄膜的帶隙中引入雜質(zhì)能級,減小電子躍遷勢壘,增強超納米金剛石的導電性;(6)進一步計算了摻氮對超納米金剛石態(tài)密度的影響,可以知道摻雜氮原子不僅僅是會在超納米金剛石的能帶結(jié)構(gòu)中引入雜質(zhì)能級,更重要的加深超納米金剛石自身的缺陷能級,使電子在帶隙中出現(xiàn)的概率增加,從而使超納米金剛石的導電性增加。
[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.
【學位授予單位】：西南科技大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TQ163;TB383.1
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本文編號：1459014