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

Abstract

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 three-dimensional (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.

Electrical transport properties and ultrafast optical nonlinearity of rGO–metal chalcogenide ensembles

“…31 The detailed synthesis procedures of rGO, rGO-ZnSe, and rGO-ZnTe samples with different ZnSe and ZnTe contents are described in our previous reports. 14,32 The ZnSe contents in the rGO-ZnSe composite have been varied as 26, 38, 54, 72, and 81 wt% and labelled them samples A1, B1, C1, D1, and E1, respectively. 32 Similarly, ZnTe fractions in the rGO-ZnTe composites are 16, 36, 50, 69, and 75 wt% and marked as samples A2, B2, C2, D2, and E2, respectively.…”

“…14 For electrical measurements, samples were prepared in top-bottom and top electrode conguration for SCLC and photoresponse measurements, respectively, as described previously. 16,32 The powder X-ray diffraction (XRD) patterns of the samples were recorded using a Rigaku-Miniex II spectrometer with Cu-K a radiation (l ¼ 1.5418Å) operated at 10 mA and 30 kV. X-ray photoelectron spectroscopy (XPS) measurements were performed with a ULVAC-PHI 5000 Versa Probe II spectrometer using Al-K a monochromatic radiation (energy 1486.6 eV) operated at 25 watt and 15 kV.…”

Charge Transfer and Ultrafast Nonlinear Optical Properties above Percolation Threshold in Graphene-Induced ZnTTBPc

“…Figure S3 in the Supprting Information shows that the resistances of sample G vary almost linearly with the separation between two electrodes which indicates that contact resistance has minimal effect on charge transport process. 6 The current−voltage (I−V) characteristics of ZnTTBPc−RGO show linear behavior throughout the whole applied voltage range (±10 V) as shown in Figure S4 in the Supporting Information. For the sample configuration (inset of Figure 2b), the I−V responses show significant increase in photocurrent (I ph = I illumination − I dark ) for all the compositions (Figure S4).…”

“…There are many reports on VRH behavior of charge transport for RGO and RGO-based composites. 6,9,15,17 In general, the primary charge transport mechanism for RGO is Mott 2D-VRH, 17,18 whereas RGO-based hybrid composites follow Mott 3D-VRH behavior. 6,9 On the other hand, RGO− organic semiconductor blends exhibit the ES-VRH mechanism of charge transport.…”

“…For all electrical measurements, samples were prepared in a side-by-side top electrode configuration on glass substrate as described in our previous report. 6,9 The typical sample dimension was 2 mm × 2 mm.…”