Séminaire Oleg. V. Yazyev : Nonlocal disorder in graphene: From topological defects to amorphous state
Oleg. V. Yazyev, EPFL Lausanne
Le résumé :
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Grain boundaries and dislocations are intrinsic topological defects of polycrystalline materials, which inevitably affect their physical properties. I will discuss the structure of topological defects in graphene [1]. I will first introduce a general approach for constructing dislocations in graphene characterized by arbitrary Burgers vectors and grain boundaries covering the complete range of possible misorientation angles, making a connection to homotopy theory. First-principles calculations address the thermodynamic properties of grain boundaries, revealing energetically favorable large-angle configurations as well as dramatic stabilization of small-angle configurations via the out-of-plane deformation, a remarkable feature of graphene as a two-dimensional material [2]. Both the presence of stable large-angle grain-boundary motifs and the out-of-plane deformation of small-angle configurations have recently been observed by scanning tunneling microscopy [3].
Next, I will focus on the electronic transport properties of graphene in the presence of topological defects. Ballistic charge-carrier transmission across periodic grain boundaries is governed primarily by momentum conservation. Two distinct transport behaviors of such grain boundaries in graphene are predicted − either perfect reflection or high transparency with respect to low-energy charge carriers, depending on the grain boundary periodicity [4]. It is also shown that certain periodic line defect structures can be engineered and offer opportunities for generating valley-polarized charge carriers [5]. Beyond the momentum conservation picture, we find that the transmission of low-energy charge carriers can be dramatically suppressed in the small-angle limit [6].
Finally, I will present more recent results on monolayer amorphous carbon (MAC) [7], a system that can be viewed as polycrystalline graphene with a grain size of the order of the lattice constant. This highly disordered 2D material is very different from graphene, and many of its properties turn out to be interesting from the point of view of applications, e.g. in catalysis, as a battery material, etc. (see, e.g., Ref. [8]).
[1] O. V. Yazyev and Y. P. Chen, Nature Nanotechnol. 9, 755 (2014).
[2] O. V. Yazyev and S. G. Louie, Phys. Rev. B 81, 195420 (2010).
[3] Y. Tison et al., Nano Lett. 14, 6382 (2014).
[4] O. V. Yazyev and S. G. Louie, Nature Mater. 9, 806 (2010).
[5] J. H. Chen et al., Phys. Rev. B 89, 121407 (2014).
[6] F. Gargiulo and O. V. Yazyev, Nano Lett. 14, 250 (2014).
[7] C.T. Toh et al., Nature 577, 199 (2020).
[8] H. Zhang et al., Adv. Mater. 37, 2419112 (2025).
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