Observation of Different Charge Transport Processes and Origin of Magnetism in rGO and rGO-ZnSe Composite

The effect of nanoparticle incorporation inside reduced graphene oxide (rGO) layers on the electrical transport properties has been investigated by temperature-dependent resistivity measurements on rGO and rGO-zinc selenide (rGO-ZnSe) thin films in a wide temperature range of 84-473 K. The fraction of ZnSe in rGO-ZnSe composite has been varied from 26 to 98%. Resistance curve derivative analysis reveals a conduction mechanism consistent with Mott two-dimensional (2D) variable range hopping (VRH) in rGO films, whereas different rGO-ZnSe samples exhibit threedimensional (3D) VRH at lower temperatures (84-280 K). At higher temperatures (290-473 K), Arrhenius-like transport was observed for all of the samples. A model where ZnSe nanoparticles are incorporated inside wrinkled rGO layers to facilitate interlayer connections, thus 3D charge transport, has been proposed. Room-temperature carrier mobility values, calculated using trap-free space charge limited current conduction model in the dark, reach a maximum at 54 wt % ZnSe content. Vibrating sample magnetometer and electron paramagnetic resonance measurements reveal paramagnetic nature of the composites, in contrast to the diamagnetic behavior of pure rGO and ZnSe at room temperature. Evidences from X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy suggest that the unreduced carbonyl groups present at the edge of rGO sheets could be held responsible for observed paramagnetism in rGO-ZnSe composites.