Abstract
We demonstrate the possibility to tune the electronic transport properties of graphene mono-layers and multi-layers by functionalisation with fluorine. For mono-layer samples, with increasing the fluorine content, we observe a transition from electronic transport through Mott variable range hopping (VRH) in two dimensions to Efros-Shklovskii VRH. Multi-layer fluorinated graphene with high concentration of fluorine show two-dimensional Mott VRH transport, whereas CF0.28 multi-layer flakes exhibit thermally activated transport through near neighbour hopping. Our experimental findings demonstrate that the ability to control the degree of functionalisation of graphene is instrumental to engineer different electronic properties in graphene materials.
Highlights
Graphene, a mono-layer of sp2 bonded carbon atoms arranged in a honeycomb pattern (Figure 1a), is a twodimensional semi-metal where the valence and conduction bands touch in two independent points at the border of the Brillouin zone, named K and K’ valleys [1,2,3,4,5]
We show that the electronic transport properties of fluorinated graphene can be tuned by adjusting the fluorine content, so that different transport regimes can be accessed, like Mott variable range hopping (VRH) in two dimensions [47,48], Efros-Shklovskii VRH [49] and nearest neighbour hopping (NNH) transport
We find that the measured r(T) for the samples produced from CF0.07 and CF0.24 graphite is described well by the two-dimensional Mott variable range hopping (2D-VRH) model
Summary
A mono-layer of sp bonded carbon atoms arranged in a honeycomb pattern (Figure 1a), is a twodimensional semi-metal where the valence and conduction bands touch in two independent points at the border of the Brillouin zone, named K and K’ valleys [1,2,3,4,5]. For this sample, characterised by the largest disorder LD ~1.5 nm, the experimental data cannot be described by thermally activated law nor Mott VRH. To the fluorinated mono-layer graphene, the resistivity dependence on temperature is fitted well by VRH with the value of T0 = 20000 K This confirms that the previously found activation energy of 25 meV is not the activation energy Δε that separates the localised states from extended states at the mobility edge, but is an activation energy δε of hopping between localised states within the mobility gap, see Figure 4d. The electrons involved in the covalent C-F bonds in F-GIC are slightly delocalised by this hyperconjugation, which may result in a smaller transport gap
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