Strain Engineering of Adsorbate Self-Assembly on Graphene for Band Gap Tuning

Abstract

Recent interest in functionalised graphene has been motivated by the prospect of creating a two-dimensional semiconductor with a tuneable band gap. Various approaches to band gap engineering have been made over the last decade, one of which is chemical functionalisation. In this work, a predictive physical model of the self-assembly of halogenated carbene layers on graphene is suggested. Self-assembly of the adsorbed layer is found to be governed by a combination of the curvature of the graphene sheet, local distortions, as introduced by molecular adsorption, and short-range intermolecular repulsion. The thermodynamics of bidental covalent molecular adsorption and the resultant electronic structure are computed using density functional theory. It is predicted that a direct band gap is opened that is tuneable by varying coverages and is dependent on the ripple amplitude. This provides a mechanism for the controlled engineering of graphene's electronic structure and thus its use in semiconductor technologies.

Ripples in isotropically compressed graphene

“…The difference in energy between both Γ -K (zigzag) and Γ -M (armchair) directions is small enough that in a chemical environment, a combination of both ripple orientations is more likely for the compressive strains reported in this work. This has also shown to be true in our previous work on the chemisorption of halogenated carbenes, which suggests the likely formation of an eggboxtype (containing both armchair and zigzag ripple formations) structure [16]. However, in accordance with the results of reference [44], we expect a more significant difference in ripple formation energy and thus an increased anisotropy between the Γ -K (zigzag) and Γ -M (armchair) directions at strains of > 5% [44].…”

“…Chemical functionalisation of graphene for real world applications has been a strong area of interest in academic and industrial research since the discovery of two-dimensional materials [1,2,3,4,5,6,7,8,9,10,11]. The addition of certain molecules on the surface of graphene can induce a change in its electronic characteristics, such as its band gap [1,2,12,13,14,15,16,17,18,19] its electron mobility [1,2,3] and its electrical resistance [1,2,3,8,9,10] . Moreover, any molecule that covalently binds onto the surface of graphene will undoubtedly alter its physical structure by disturbing its sp2 -backbone [12,13,14,15,16].…”

“…The addition of certain molecules on the surface of graphene can induce a change in its electronic characteristics, such as its band gap [1,2,12,13,14,15,16,17,18,19] its electron mobility [1,2,3] and its electrical resistance [1,2,3,8,9,10] . Moreover, any molecule that covalently binds onto the surface of graphene will undoubtedly alter its physical structure by disturbing its sp2 -backbone [12,13,14,15,16]. We have suggested in previous theoretical studies that such molecular patterns with long range order can tune the electronic band gap, magnetic coupling and transport properties of graphene [17,18].…”

“…Depending on the nature of the bonding, chemi-or physisorbed molecules will bind to convex/concave regions in the rippled graphene [19,20,21,22,23,24,25,26,27,28,29,30,31]. In our previous work on the chemisorption of halogenated carbenes on graphene, we suggested a simple model that exploits the rippling behaviour of the graphene sheet in order to obtain, for that specific case, well-ordered and controllable molecular pattern formations [16]. In that instance, the rippling is generated spontaneously by adsorption induced strain.…”

Density Functional Theory Investigation of Graphene Functionalization with Activated Carbenes and Its Application in the Sensing of Heavy Metallic Cations

“…These values are in good agreement with previous literature values. 6,12,19 Again, in the case of adsorbate 2c, the reaction energy is the weakest probably due to the presence of the sodium cation in the adsorbate.…”