As the development of the nanotechnology, the demands of accurate manipulation are becoming more and more urgent. For example, graphene can be cut into different shapes for electronic applications. The traditional method of graphene-cutting includes strong oxidation and energetic plasma. Therefore, scientists need to create milder environment to achieve perfect edges.

A desirable craft uses mental nanoparticles as the catalyst. The traditional explanation of the craft reaction is the unzipping mechanism. In this theory, C-C bonds are broken by single cutting atoms. If the unzipping mechanism is true, the nanoparticle size can’t influence catalytic rate, and it is against the experimental data. To understand the underlying atomic mechanisms of the progress, a research team led by Pro. LI Zhenyu from Hefei national laboratory for physical sciences at the microscale put forward a new hypothesis: the “Pac-Man” Mechanism.

In reactive molecular dynamics simulation, the interaction between Ni and C weakened the bond in graphene. The resulting dangling C atoms then were eaten by nanoparticle, just like Pacman. The dissolved C atoms diffused into the surface of Ni, where dissociative hydrogen adsorbed, and then turned into hydrocarbon species. C etching prefers to proceed at flexible armchair edge sites which results in the zigzag edge of the production. By using a multiscale simulation approach, researchers identified the breaking of the interfacial carbon bond as the rate-limiting step. Once the bond of zigzag edge sites was broken, the remaining formed an active armchair fragment, which would be etched rapidly.

High-level DFT calculations also showed the unzipping mechanism required higher energetic barrier. In kMC simulations, it has been proved that the reactive rate is linearly dependent on R2 value. As a result, larger the nanoparticles were, longer the graphene-metal interface was, and faster the etching become. What’s more, C atoms at kink sites were more likely to be removed. Researchers explained that wide interface contained more zigzag sites, which increased the possibility of activation and shortened the waiting time.

The research on the mechanism of graphene-cutting helps scientists better control the fabrication of planar nanodevices. It also provides a new insight into other aspects, such as discrete dynamics of nanoparticle channeling. The work was published on Angew. Chem. Int. Ed with title The Nanoparticle Size Effect in Graphene Cutting: A “Pac-Man” Mechanism.

The research was supported by the National Natural Science Foundation of China (NSFC), Ministry of Science and Technology (MOST), CAS, Ministry of Education and etc.