Fluorination of Isotopically Labeled Turbostratic and Bernal Stacked Bilayer Graphene

Abstract

Fluorination of graphene opens up a bandgap, which creates opportunities for optoelectronics, and also paves the way for the creation of extremely thin insulating layers, which can be important for applications in devices. However, in spite of many interesting features offered by, for example, unequally doped layers in multilayered systems, most of the work has concerned the fluorination of graphene monolayers. Here, the fluorination process of graphene bilayers is investigated through high-resolution Raman mapping followed by analysis of more than 10,000 spectra of bilayer graphene. Isotopically labeled bilayers are used, allowing each individual layer in bilayer graphene to be addressed unambiguously. The fluorinated graphene is prepared through exposure to XeF2. Monolayer graphene is found to be significantly more sensitive to fluorination than bilayer graphene. Through comparison of the D/G area ratio and the position of the G band for turbostratic and Bernal stacked (AB) bilayers, it is found that the fluorination process is more effective for turbostratic than for AB-stacked bilayer graphene. The fluorination changes the electronic structure similarly for the top and bottom layers in turbostratic bilayers. However, the top layer is more sensitive than the bottom layer in AB-stacked bilayers.

Decomposition of Fluorinated Graphene under Heat Treatment

“…This is for example demonstrated by the higher reactivity of a graphene monolayer compared with the lower reactivity of graphene bilayer . The bilayer can be considered as a monolayer on the graphene substrate . Interpretation of higher graphene reactivity towards fluorine usually invokes several factors.…”

“…The graphene was grown on polycrystalline copper foil using CVD. The samples were cut from the same lot of graphene kept on the Cu growth substrate and subsequently they were fluorinated simultaneously at room temperature in a homebuilt chamber using XeF 2 . After fluorination, samples were immediately inserted into separate vacuum chambers of XPS and TPD apparatus.…”

Two‐Dimensional Fluorinated Graphene: Synthesis, Structures, Properties and Applications

“…Fluorination mainly include direct gas‐fluorination,[[qv: 4a]],[[qv: 12a]],[[qv: 13b]],[[qv: 21a]],22 plasma fluorination,23 hydrothermal fluorination,24 and photochemical/electrochemical synthesis 25. Exfoliation methods includes sonochemical exfoliation,[[qv: 9a]],26 modified Hummer's exfoliation,20,[[qv: 21b]] and thermal exfoliation 27.…”

Raman signature of defected twisted bilayer graphene

“…This yields a self-consistent standard to quantify defect density in TBG, independent of a monolayer reference, and may be more representative under certain experimental conditions. For example, under chemical modification, monolayer and bilayer graphene exhibit different reactivity [28,41,42], such that one cannot assume a comparable defect density on the monolayer, thus necessitating a TBGbased metric. For pristine TBG films, the coupling factor is $2.4, and falls to $1 in highly defected samples.…”

“…As a result, an improved understanding of the Raman spectra of defective TBG is necessary to facilitate the study of defective or chemically-modified TBG and to extend earlier studies of ion irradiated graphene [19,25] and carbon nanotubes [26,27]. Already, the chemical-modification of TBG has been explored and modeled [28,29]. DFT simulations have elucidated the influence of structural defects on the electronic structure of TBG films.…”