Dopant Identification of Nitrogen-Doped Graphene on Pt (111) via Simultaneous Atomic Force Microscopy and Scanning Tunneling Microscopy

Nitrogen (N) doped graphene has been gained prominence as a candidate for catalysis, electronic devices or sensors by keeping the advantages of significant properties of graphene along with additional physical or chemical features. The atomic configurations of the dopant, however, show numerous variations with each doping type manifesting distinct properties and features. Hence, identifying and controlling the bonding arrangements is highly crucial for further applications. In this work, we present a schematic distinguishment on two specific nitrogen defects; Graphitic-N and pyridinic-N. N doped graphene was grown on a Pt (111) surface using pyridine precursors, followed by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS) for confirmation on graphene growth in a larger scale. Atomically resolved simultaneous scanning tunneling microscopy (STM) and atomic force microscopy (AFM) <i>via</i> qPlus sensor depicted complementary distinctions on the atomic and electronic structures between both defects. Electronic structure near graphitic-N site showed noticeable bulge with a vacancy-like morphology or a more distinctive protrusion in the center, while △f image showed little difference from pristine graphene. Pyridinic-N, despite of its carbon-vacancy-based structure, did not showed typical vacancy-like electronic topography, with a characteristic protrusive configuration in △f image. Corresponding theoretical calculations <i>via</i> density functional theory (DFT) further verified the experimental data. In addition to the discernment on the two defects, effects of Pt substrate and a plausible growth mechanism are suggested, through which the numerical proportions of the defects and dissociated pyridine precursors can be explained. This study will provide further in-depth understanding for application-driven research for graphene devices with controlled defects.