报告题目：Synthesis of Nitrogen-Doped Graphene on Metals from Azafullerene
报告人：Li Gao (Department of Physics and Astronomy, California State University Northridge)
Substitutional doping of graphene with heteroatoms is one of the most fascinating strategies for tailoring various properties of graphene and hence expanding the practical applications of this wonder material. The synthesis of nitrogen-doped graphene from nitrogen-containing sole precursors has recently demonstrated its feasibility with several different sole precursors. In this talk, I will present our recent studies on the synthesis of nitrogen-doped graphene on metals by using a nitrogen-containing sole precursor azafullerene. The synthesis process and doping properties are investigated by combining scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) measurements. Three different metal substrates have been used, including the Ru(0001), Cu(111), and Ir(111) surfaces. For the synthesis experiments performed on the Ru(0001) surface, we found that the concentration of nitrogen-related defects in the graphene layer can be tuned by adjusting the dosage of sole precursor azafullerene and the number of growth cycles. The spatial homogeneity of nitrogen-related defects is high and improves with increasing doping concentration. The predominant doping configuration is pyridinic nitrogen, while some nitrogen atoms are in an anionic state due to their bonding with the ruthenium surface. The pyridinic nitrogen doping configuration is correlated to single-atom vacancies in the graphene layer, as suggested by STM and XPS measurements. For the synthesis experiments performed on the Cu(111) surface, we observed that within graphene islands almost all nitrogen dopants are in the form of graphitic nitrogen and they tend to arrange into rings after multiple growth cycles. XPS measurements indicate that the predominant doping configuration on the sample surface is pyridinic nitrogen, which suggests that most nitrogen atoms on the sample surface are bonded to the edges of graphene islands in the form of pyridinic nitrogen. The influence of nitrogen doping on local work function of graphene has also been investigated. In addition, some results for the synthesis experiments performed on the Ir(111) surface will also be presented. Our studies indicate that azafullerene is an effective nitrogen-containing sole precursor for the controlled synthesis of nitrogen-doped graphene, and the growth substrates strongly influence the synthesis process and doping properties. The work is supported by the U.S. Department of Defense and National Science Foundation.
Prof. Li Gao received his PhD in Condensed Matter Physics at the Institute of Physics, Chinese Academy of Sciences in 2006. After that, he worked at University of California Los Angeles and Argonne National Laboratory as a postdoctoral researcher. In 2012, he joined California State University Northridge as an Assistant Professor in the department of Physics and astronomy, and was promoted to Associate Professor in 2018. He has been working on the preparation and characterization of low-dimensional materials. His primary research interest is to gain atomic-scale insights into the growth and properties of low dimensional materials by using STM.