时间: 2014年4月23日 星期三 下午4:00

地点: 四川大学(望江校区)物理馆1楼103室

报告人: Dr. Han, Xiaoyu ; Dr. Morgan Stewart, Henry (英国伦敦大学学院)

报告题目：Some methods for opening graphene band gap

报告内容: Since the discovery of graphene, many efforts have ben made to tailor this 2D material of a Dirac-cone band gap structure without disturbing the high electron mobility. However, such efforts are still not conclusive. Here we propose two approaches on opening band gap by substrates and defects. The first propose is tuning the pristine graphene using single crystal diamond, which have more advantages than SiO2/Si base. The weakly van der Waals interaction dominated between the graphene and diamond surfaces, which highly reserved the graphene electron mobility. Compared with Diamond (111), diamond (100) have stronger electron overlapping with the graphene by graphene donated partly pi electron to the substrates. Consequently, the band gap reaches to 0.20 eV. Meanwhile, H termination of the surfaces plays a crucial role. Our simulation results give guides and prediction with our experimental work. The FET hall mobility is 222 cm2/Vc for G@H_D(100), while 137 cm2/Vs for G@H_D(111). Our 2K-RoomT electronic properties test also meets our simulation results, especial in low temperature range. The second one is presented a systematic study of nitrogen doping on defective graphene based on Density Functional Theory. Up to 6 adjacent carbon vacancies (Vc), nitrogen dopants (Nc) and defect complexes (nVc+mNc) were considered. In both pure vacancy defects and vacancy-doping complex scenarios, the geometries undergo a Jahn-Teller like distortion driven by the unterminated dangling bonds on carbon atoms. The pure nitrogen substitution defects have the lowest formation energy, particularly with one nitrogen substitution. When a vacancy defects exists, the nitrogen atoms prefer to substitute the positions around the vacancy. These defect complexes also have significant effect on its own electronic properties. In the 2Vc+4Nc defect configuration, the band gap can be opened to 0.25 eV. The Fermi velocity of this defective graphene is 0.48E-6 m/s, comparable to the pristine graphene. Such insight is very important for the design of electronic devices, grapheme-based catalysts and energy storage materials.

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