Defects and localization in chemically-derived graphene

We have performed electron spin resonance (ESR) measurements on a large assembly of graphene oxide (GO) and reduced graphene oxide (RGO) flakes. In GO samples the Curie tail is coming from $1.4\times {10}^{18}$ cm${}^{-3}$ of localized spins. Although reduction of GO was expected to reestablish the pristine properties of graphene, no Pauli-like contribution was detected and only a low concentration of $1.2\times {10}^{16}$ cm${}^{-3}$ spin carrying defects were measured. Our study, completed by resistivity measurements, shows that the carrier transport in RGO samples is dominated by hopping. The incomplete reduction of GO leaves behind a large number of defects, presumably the majority of which are ESR silent, causing the Anderson localization of the electronic states. Slight doping with potassium indicates the appearance of a Pauli contribution in the spin susceptibility.

Figure 1

Electrical resistance of an assembly of GO flakes plotted as ln$\mathit{\text{R}}$ versus 1/$T$ pointing to the thermally activated behavior of conductivity. The room temperature resistance is $\sim {10}^{11}$ $\Omega$.

Figure 2

Electrical resistance of an assembly of RGO flakes plotted as $\ln$R versus $1/T$ showing a deviation from simple thermally activated behavior of the transport process. The room temperature resistance is $\sim 3\times {10}^4$ $\Omega$. The 3D variable-range hopping plot of the data is in the inset.

Figure 3

Spin susceptibility of GO sample versus temperature. The temperature independence of $\chi T$ in the inset reflects the Curie behavior of $\chi$.

Figure 4

Spin susceptibility of RGO sample versus temperature. The weak temperature dependence of $\chi T$ might originate from building up interactions between localized spins with decreasing temperature.

Figure 5

ESR linewidth (left scale) and $g$ factor (right scale) as the function of temperature for both GO and RGO samples.

Figure 6

Temperature dependence of $\chi T$ of the RGO sample reflects the Curie behavior of $\chi$, while the linear slope for the potassium-doped RGO sample indicates the appearance of a Pauli contribution.

Figure 7

ESR linewidth as a function of temperature of the RGO and potassium-doped RGO samples.