| AVS 58th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing Division | Wednesday Sessions |
| Session EM-WeA |
| Session: | Defects in Electronic Materials |
| Presenter: | Yevgeniy Puzyrev, Vanderbilt University |
| Authors: | Y.S. Puzyrev, Vanderbilt University B. Wang, Vanderbilt University S.T. Pantelides, Vanderbilt University and ORNL |
| Correspondent: | Click to Email |
The properties of polycrystalline graphene largely depend on the properties of the grain boundaries (GB) [1,2]. Classical molecular dynamics simulations coupled with density functional calculations of vacancies and self-interstitials at grain boundaries show that lower formation energies are induced by the local strain near the GB. The vacancies interact with each other as well as the interstitials. Vacancies and interstitials [3] can diffuse in graphene due to their low migration barrier. We investigated the time scale of vacancy and interstitial dynamics in pristine graphene and at grain boundaries at the distances where defect-defect and defect-GB interactions are found to be significant. GB-558 consists of pentagon and octagon pairs, whereas GB-575 is formed by repeated pentagon-heptagon pairs. We show that recombination of vacancies and interstitials can occur at grain boundaries resulting in efficient annealing of defects. The compression (stretch) for GB-558 is up to 3%, while in GB-575, the stretch reaches 9% at the C-C bonds between pentagon and heptagon or between hexagon and heptagon. We find that single vacancies can diffuse towards a grain boundary, attach to a pentagon, then merge into the grain boundary to release the compressive strain and cause local reconstruction. Molecular dynamics simulations show that if a single vacancy exits at 1nm from the grain boundary GB-558, it diffuses towards the grain boundary and attaches at the pentagon ring after 160 ps at 3000 K. It takes another 40 ps to merge into the grain boundary. Similar phenomena occur in GB-575. Stretched C-C bonds at the heptagon, on the other hand, accumulate interstitials. An interstitial that was initially positioned 7 Å above the graphene sheet, was adsorbed on the grain boundary. Once the vacancy coalesces into the grain boundary, the carbon adatom fills the reconstructed vacancy and recovers the original grain boundary structure. This recombination takes only ~ 0.5 ns at 2000 K. The results suggest a new mechanism of defect annealing with a two-step procedure, i.e. point defects (single vacancies and interstitials) diffuse and recombine locally at grain boundaries. This work was supported by DTRA Grant No. HDTRA1-10-1-0016, the US Department of Energy, Basic energy Sciences, and the William A. and Nancy F. McMinn Endowment at Vanderbilt University. The calculations were performed at ORNL's Center for Computational Sciences and the Air Force Research Laboratory DoD Supercomputing Resource Center
[1] P. Y. Huang et. al, Nature 469, 389-393, 2011.
[2] Q. X. Pei, Y. Z. Zhang, V. B. Shenoy, Carbon 48, 898-904, 2010.
[3] A. Hashimoto, et. al, Nature 430, 870-873, 2004.