Underlying Mechanisms on Tunable Electronic Structures of Graphene Quantum Dots Doped with Nitrogen and Sulfur Heteroatoms

Doping heteroatoms into graphene quantum dots (GQDs) is an efficient way to tune electronic structures. Herein, electronic mechanism of GQDs doped with N and S is studied by density functional theory (DFT). The formation energies, electronic structures, and electrostatic potentials of pristine and co-doped GQDs are calculated to reveal effects of different doping types on electronic properties. It is found that the introduction of sulfur-containing groups can enhance positive area around N and increase atomic charge density of C atoms connected to N, which indicates that heteroatom co-doped GQDs have improved electron transports. The introduction of S and oxidized S into graphitic and pyridine N structures influences energy difference between the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO). Therefore, this work will provide valuable information on understanding electronic properties of N/S co-doped GQDs for the applications in nanoelectronic devices.