Reaction kinetics of bond rotations in graphene

Abstract

The formation and healing processes of the fundamental topological defect in graphitic materials, the Stone-Wales (SW) defect, are brought into a chemical context by considering the rotation of a carbon-carbon bond as chemical reaction. We investigate the rates and mechanisms of these SW transformations in graphene at the atomic scale using transmission electron microscopy. We develop a statistical atomic kinetics formalism, using direct observations obtained under different conditions to determine key kinetic parameters of the reactions. Based on the obtained statistics we quantify thermally and irradiation induced routes, identifying a thermal process of healing with an activation energy consistent with predicted adatom catalysed mechanisms. We discover exceptionally high rates for irradiation induced SW healing, incompatible with the previously assumed mechanism of direct knockon damage and indicating the presence of an efficient nonadiabatic coupling healing mechanism involving beam induced electronic excitations of the SW defect.

The Stone–Wales transformation: from fullerenes to graphite, from radiation damage to heat capacity

“…In the case of the electron beams below the displacement threshold, the annihilation barrier should be in the region of 7 eV [13]. This would make the destruction rate negligible and the concentration stable, but the observation is that this is not the case for graphene, and an unspecified electronic mechanism has been invoked [34]. Above the displacement threshold, it is already known that the adatom on graphene will catalyse removal: it is a highly mobile species even at room temperature and is attracted to, binds with and annihilates the Dienes defect [13,30].…”

“…It is striking how the understanding of graphene in the electron microscope has evolved from simple evidence of existence, to the beginnings of quantitative understanding of defect motion and lifetimes [34]. So far, it appears that the catalytic mechanisms of Dienes defect destruction in the electron microscope are not sufficient to explain their unexpectedly low lifetime, and furthermore, it is enigmatic that their creation at accelerating voltages below the displacement threshold (60 keV) appears little different from that at the threshold (80 keV).…”

“…So far, it appears that the catalytic mechanisms of Dienes defect destruction in the electron microscope are not sufficient to explain their unexpectedly low lifetime, and furthermore, it is enigmatic that their creation at accelerating voltages below the displacement threshold (60 keV) appears little different from that at the threshold (80 keV). For both of these, electronic excitation mechanisms have been suggested [34].…”

Probing Chemical Kinetics in Two Dimensional Materials Using Atomic Resolution Imaging.

“…Focussing on specific examples of atomic-scale defect dynamics in graphene, our first study [1], involving the Stone-Wales defects, exemplifies this principle. Two surprising results emerged concerning the healing of these defects: the thermal route was accessible at room temperature, with comparisons to barrier calculations suggesting that a previously hypothesized catalytic route is active.…”

Single-molecule imaging and kinetic analysis of intermolecular polyoxometalate reactions

“…Unlike the optical microscopy methods discussed above TEM is still in its infancy in this regard, with very recent progress in the development of fast direct electron detectors 26 and machine learning techniques 27 only just starting to enable the kinds of high throughput experiments and large datasets required to build up meaningful statistics at the singlemolecule level (as distinct from class-averaging techniques used in cryo-EM 28 and elsewhere 29 ). Hence, there have been relatively few quantitative studies of single-molecule (or entity) kinetics using TEM; [30][31][32][33] a notable exception is the work of Isaacson et al in the Crewe lab in the 1970's shortly following the development of the scanning TEM, 34,35 whichakin to Rotman's 1961 study for optical single-molecule kinetics 36 may come to be seen as being decades ahead of its time.…”