Mediator atoms drive structural evolution of defects in graphene
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. The mediator-atom mechanism nicely reproduced the experimental miMediator atoms drive croscope images and showed energy structural evolution of defects in graphene barriers lower than 2.0 eV (mostly below 1.0 eV). These energy barriers are much smaller than those predicted by n a recent article in Science Advances the Stone–Thrower–Wales mechanism (doi:10.1126/sciadv.aba4942), Gun-Do commonly accepted for explaining the Lee of Seoul National University and coevolution of graphene defects. workers reported the first direct observa Boris I. Yakobson, a materials physicist tions of under-coordinated carbon atoms at Rice University, says, “An impressive in mediating the structural evolution of mix of state-of-the-art, high-resolution midefects in graphene. Their work provides croscopy and atomistic simulations shows, valuable data for understanding defect in real-time, the transient morphology evotransformation and growth in graphene lution of defects mediated by extra atoms. and more broadly in two-dimensional My group has theorized about such ‘radinanomaterials. cal-dislocations’ mobility in MoS2, so I am Previously, it was revealed that undercoordinated atoms in graphene catalyze particularly intrigued seeing it for the first the breaking and formation of C–C bonds time. I almost want to say ‘in vivo,’ as if in graphene. The temporal and spatial stiff graphene is alive at these conditions— resolution of conventional electron miwarm and under the beam.” Yakobson was croscopy, however, has impeded elucidanot involved in this study. tion of the precise role of these catalytic Lee says that the concept of the mediatoms during the structural change. Lee ator-induced structural evolution applies and co-workers tackled this challenge by to other two-dimensional materials, for using an advanced transmission electron example, MoS2 and WS2, as well as microscope (TEM) equipped with an abthree-dimensional (3D) materials. For 3D erration corrector and a double Wien filter compounds, “it is difficult to observe the mediating phenomenon because point defects such as under-coordinated atoms can overlap with other atoms along the observation direction,” Lee says. Lee also envisions that “future studies of structural transformation by mediator atoms will become more vigorous both experimentally and theoretically.” A mediator atom (red) alters five-membered (yellow) and seven-membered (pink) rings into six-membered (light blue) Tianyu Liu and eight-membered rings (dark blue) in a graphene network. Credit: Gun-Do Lee.
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