First-principle Calculations Of Nitrogen-doped N-type Ultrananocrystalline Diamond

Nitrogen-doped N-type ultrananocrystalline diamond films with low electron affinity; the extreme low surface adsorption characteristics and chemical inertness, high thermal and electrical conductivity, etc., have become a new hotspot of cold cathode materials research. But now, the relation between size, nitrogen atom of ultrananocrystalline diamond films and its structural, electrical properties have almost no understanding. This paper use a density-functional based first-principle theoretical simulation major calculated the content of grain boundary and doped nitrogen atom influence on ultrananocrystalline diamond's structural and electrical properties, which is expected to make a theoretical support for experimental preparation of nitrogen-doped N-type ultrananocrystalline diamond films with an excellent electron emission properties.Experimental results show that:(1) Study of ultrananocrystalline diamond's structure found that the number of C=C double bond and the content of UNCD sp2-C will increase when the content of grain boundary increases, while the content of sp3-C decreases.(2) Simulations of ultrananocrystalline diamond's band structure can be seen that band gap of UNCD will decrease when the content of grain boundary increases, and will introduce ?* level and d.b. level associated with sp2-C and dangling bond into band gap. This will reduce the electrons' transition barriers from low energy level to high energy level, increasing the conductivity(3) Calculations of ultrananocrystalline diamond's DOS found that value is zero's area will decrease when the content of grain boundary increases, while the DOS of ?* level and d.b. level increases. Thus the possibility of electron's occupation in band gap increased and also conductivity.(4) Simulations of doping nitrogen atom effects on ultrananocrystalline diamond's structure indicated that nitrogen atom will increase the content of grain boundary, unbonded carbon atom, C=C and sp2-C, while the size of diamond grain decreases.(5)Study on ultrananocrystalline diamond's band structure show that doping nitrogen atom will introduce impurity levels into the band gap of nitrogen-doped UNCD. This will reduce electron transition barrier and will enhance the conductivity of ultrananocrystalline diamond.(6) Further calculations of nitrogen-doped impact the UNCD's DOS can know that nitrogen atom will more than just introduce the impurity levels in band gap and the most important thing is to deepen ultrananocrystalline diamond's defect levels. Therefore, the probability of the electron band gap increases, so that the conductivity of ultrananocrystalline diamond.