Transport properties of disordered CVD graphene in the strong localized regime

The Chemical Vapor Deposition (CVD) of graphene is nowadays one of the most promising methods for the production of large scale graphene films [1]. The growth is first initiated onto transition metal substrates (Cu, Pt.) before being transferred onto an insulating wafer. High quality and homogeneous graphene films can be obtained this way, displaying amazing electronic properties such as the anomalous Quantum Hall Effect at low temperature and high magnetic field [2]. On the other hand, achieving high quality graphene films requires states-of-the art techniques and when the ideal set of parameters is not fulfilled, one may end up with a variety of disordered graphene devices with interesting electronic properties. We investigated the extreme limit of a highly disrupted multi-layer graphene film showing high electrical resistance. We demonstrate that electronic conduction occurs through hopping between localized sites, provided the drain-source voltage remains higher than a temperature-dependent threshold value. An exhaustive data analysis concludes that the sample can be assimilated as an array of very tiny graphene dots (~6nm in diameter) weakly interacting each other. The presence of such few-layer graphene islands is confirmed thanks to Raman spectroscopy [3]. In the strongly localized regime, the magneto-conductance (MC) happened to be unusual, being first positive up to 6T and then negative by about 50% up to the maximum experimental magnetic field (55T).