Pure graphene has limited practical applications due to its low carrier density, zero band gap, and chemical inertness. Local structures of graphene can be modified to obtain useful properties and applications such as semiconductor nanodevices, batteries, and chemical separation. Chemical treatment is one of the practical methods to functionalize graphene and to study mechanisms of their interaction with environment. The single-atom thickness nature of graphene makes it an ideal medium for revealing its own defect structure, bonding and dynamics on the atomic level. The ability to directly observe reactions on the atomic level, which has long been expected in many areas of science and technology, can significantly advance our understanding on the physical and chemical mechanisms controlling the formation of functional structures based on graphene.
In this talk, we will present direct atomic-level observations and density functional analyses on the atomic dynamics, incorporation of single Si atoms, electronic structures at topological defects in monolayer graphene. We monitored dynamic atomic processes during the formation of a rotary Si trimer in monolayer graphene using an aberration-corrected scanning-transmission electron microscope. An incoming Si atom competed with and replaced a metastable C dimer next to a pair of Si substitutional atoms at a topological defect in graphene, producing a Si trimer. Other atomic events including removal of single C atoms, incorporation and relocation a C dimer, reversible C-C bond rotation, and vibration of Si atoms occurred before the final formation of the Si trimer. Theoretical calculations indicate that it requires 2.0 eV to rotate the Si trimer. Density functional calculations showed that the heights of Si atoms did not change during the rotation of the Si trimer. The observed rotation of the Si trimer embedded in graphene is quite similar to the behavior of atomic/molecular rotors driven by current or light. Our real-time results provide insight with atomic precision for reaction dynamics during chemical doping at defects in graphene, which have implications for defect nanoengineering of graphene.
Institute of Metal Research, Chinese Academy of Science, Oak Ridge National Laboratory
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