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Drawing the Atomic Line in Graphene

Drawing the Atomic Line in Graphene
Upper image shows TEM image of 5-5-8 line defect in suspended graphene, introduced in-situ inside the TEAM microscope via applied transport current and anisotropic strain field. The bottom image shows a schematic of a 5-5-8 defect, illustrating the alternating pentagons and octogons, in graphene.

Scientific Achievement
Alex Zettl’s sp2-Bonded Materials program developed method by which a favorable line defect can be grown in grapheme, when and where it is desired.

Significance and Impact
Special 5-5-8 line defect, which is a degenerate grain boundary consisting of alternating pentagons and octogons, in graphene facilitates “valleytronics” investigation and application: precise tailoring of graphene to enable unusual transport pathways and new nano-scale functional devices.

Atomically precise tailoring of graphene can enable unusual transport pathways and lead to new nanometer-scale functional devices. Such modification is extremely challenging. However, successful atomic manipulations could have dramatic impact on graphene’s properties, leading to novel functionalities exploitable in nanoscale devices. In this work, Zettl’s group developed an experimental technique by which to produce a line defect in graphene that until now has been observed in uncontrollable production.

An irregular structure called the “5-5-8” line defect had been observed in graphene grown uncontrollably on a nickel substrate, and theoretical studies suggested that this defect could aid valley-discriminating transmission of charge carriers. Zettl and team subjected a single layer of graphene to simultaneous electronic radiation and Joule heating inside atomic-resolution transmission electron microscope ‘TEAM’ to yield a desired line defect with selected orientation and length. Images showed individual steps of the 5-5-8 line defect formation process. Theoretical studies predicted a strong energy dependence of valley polarization of the charge carriers across the defect.

The ability to precisely engineer this defect in graphene may be exploitable in electrically switchable valleytronic devices such as filters and valves, due to the material’s valley-discriminating transport properties.

H.-H. Chen, G. Autès, N. Alem, F. Gargiulo, A. Gautam, M. Linck, C. Kisielowski, O. V. Yazyev, S. G. Louie and A. Zettl. Controlled growth of a line defect in graphene and implications for gate-tunable valley filtering. Phys. Rev. B. 89, 121407 1-5, (2014)