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N-doped Graphene: Beyond Single Substitution for Enhanced Molecular Sensing Experimental and simulated STM images of as- synthesized NG sheets. (a) Large-area STM image of the NG illustrating the presence of numerous N-dopants with a similar peapod-like configuration (highlighted by white arrows), The upper and lower squares are used to indicate the undoped region and N 2 AA dopants. (b) Highly resolved STM image of a N 2 AA dopant. (c) Ball- stick structural model of the N 2 AA dopant and simulated STM image obtained using first- principles calculations. The carbon and nitrogen atoms are illustrated using gray and cyan balls, respectively. (d) STM spectroscopy measured on N 2 AA dopants (red) and on undoped graphene region (blue). CNMS Staff Science Highlight Significance We describe the synthesis and imaging of large- area, highly-crystalline monolayer N-doped graphene (NG) sheets via atmospheric-pressure chemical vapor deposition, yielding a unique N- doping site composed of two quasi-adjacent substitutional nitrogen atoms within the same graphene sub-lattice (denoted N 2 AA ). R. Lv, Q. Li, A. R. Botello-Méndez, T. Hayashi, B. Wang, A. Berkdemir, Q. Hao, A. L. Elías1, R. Cruz-Silva, H. R. Gutiérrez, Y. A. Kim, H. Muramatsu, J. Zhu, M. Endo, H. Terrones, J. Charlier, M. Pan, M. Terrones, Nature Scientific Reports, 2,586(2012) Research Details • CNMS capability: Experiments were conducted with a CNMS-built variable temperature scanning tunneling microscope, whose operating temperature varies from 25 K to 300 K. • A simple but efficient method to synthesize large- area and highly-crystalline monolayer NG sheets is established. • As-synthesized NG sheets contain an abundant amount of N dopants within the same graphene sub- lattice (N 2 AA ) comprising 80% of all identified defects, as well as more complex configurations. • It was demonstrated for the first time that individual NG sheets could be used to efficiently identify organic molecules through a significant enhancement of the Raman signal. Scientific Achievement Substitutional doping of graphene with nitrogen results in the disruption of the ideal sp 2 hybridization, locally inducing significant changes in the electronic properties and chemical reactivity which has been exploited to enhance molecular sensing.
