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Reaction kinetics of bond rotation in graphene

Chuvilin, Andrey (CIC nanoGUNE Consolider, Donostia -San Sebastian, ESP); Skowron, Stephen (School of Chemistry, University of Nottingham, Nottingham, GBR); Koroteev, Victor (Nikolaev Institute of Inorganic Chemistry, SB RAS, Novosibirsk, RUS); Baldoni, Matteo (School of Chemistry, University of Nottingham, Nottingham, GBR); Lopatin, Sergei (King Abdulla University of Science & Technology, Thuwal, Makkah, SAU); Zurutuza, Amaia (Graphenea S.A., Donostia -San Sebastian, ESP); Besley, Elena (School of Chemistry, University of Nottingham, Nottingham, GBR)

The raise of nanoscience and nanotechnology and necessity to characterize the structure of individual objects consisting of countable number of atoms determined the shift of structure characterization paradigm from bulk methods like X-ray diffractometry to local high resolution methods like electron microscopy. The similar shift in paradigm is urging now in chemistry - chemical processes defining structure and properties of nanoscale and low dimensional objects often constitute a negligible part of the total volume of the material, and thus their assessment by bulk chemical methods if often impossible. The new concept is provided by the time resolved electron microscopy allowing for direct observation of atomic rearrangements. We have adopted the methodology of macroscopic chemical kinetics for evaluation of atomic rearrangements observed by HRTEM and applied this approach for extracting kinetic characteristics of bond rotation in graphene - the fundamental process defining the mobility of defects. Observation of statistically significant number of events at variable experimental conditions allowed decoupling of radiation induced and thermal reaction pathways and obtaining independent estimations of crosssections and activation energies for direct and backwards rotations. The crosssections of direct rotation were found to be in a decent agreement with theoretical estimations. Interestingly the backwards rotation is characterized by very high crosssection exceeding theoretical values by 3-4 orders of magnitude. Moreover the threshold energy determined assuming the knock-on induced process appeared to be smaller than the activation energy for thermally induced pathway, which rules out electron-nucleus collision as the main mechanism of energy transfer from electron beam to the sample. We speculate that the energy is transferred through electronelectron interactions via strong coupling of excited electron states with the phonon modes localised around the defect.

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