Structural and Electronic Transport Properties of Fluorographene Directly Grown on Silicates for Possible Biosensor Applications

Fluorographene (FG) ultrathin films are directly grown on flexible and nonflexible insulating silicate substrates and characterized in terms of their structural and electronic properties. FG is identified as an in-plane heterostructure consisting of sp(2) and sp(3) carbon domains. Solid-state F-19 NMR shows that fluorine is mainly localized in spaces adjacent to sp(2) carbon domains, which can be explained by a more uniform fluorine distribution in the boundaries between small sp(2) and sp(3) domains, rather than by an accumulation of fluorine in large sp(3) patches, and which is supported by Raman spectroscopy. The fluorine doping is further confirmed by spectroscopic ellipsometry studies, where it showed a band gap of 1.2 eV for thin-film FG, which is found to be consistent with density-functional-theory-based calculations for graphene layers doped with similar amounts of fluorine. Furthermore, this semiconducting FG layer grown with a large surface area has been identified as an ambipolar material from gate-controlled transport measurements, with holes being the majority of charge carriers. The transport properties of thin-film FG resemble those of reduced graphene oxide, another functionalized graphene derivative, with an Arrhenius-type temperature dependence of the resistance at high temperatures. This study opens up the possibilities of atomic-layer-based electronic circuitries and biosensors, where FG can be used as an active layer or dielectric support by tuning its fluorine content to the requisite level.