The conversion of epoxy to carbonyl group in graphene oxide (GO) thin films has been carried out via oxygen plasma treatment, and the effects of this conversion on structural and optical properties were investigated. Hydrophilicity of the prepared GO solution allows it to be uniformly deposited onto substrates in the form of thin films. Highresolution transmission electron microscopy and electron diffraction analysis confirmed 4−5 layers of the graphene oxide layers which are polycrystalline in structure, and the oxygen plasma treatment results in short-range order crystallization in graphene oxide films with an increase in interplanar spacing which can be attributed to the presence of oxygen functional groups on the graphene oxide layers. Electron energy loss spectroscopy (EELS) and Raman spectroscopy confirm the presence of the sp 2 and sp 3 hybridization due to the disordered crystal structures of the carbon atoms results from oxidation, and XPS analysis shows that epoxy pairs convert to more stable CO and O−CO groups with oxygen plasma treatment. The broad energy level distribution resulting from the broad size distribution of the sp 2 clusters produces excitation-dependent photoluminescent (PL) emission in a broad wavelength range from 400 to 650 nm. Our results suggest that as oxygen pressure increases, there is a change from epoxide to carbonyl linkages which also resulted in variation in PL emission.

Present state-of-the-art graphene-based electrodes for supercapacitors remain far from commercial requirements in terms of high energy density. The realization of high energy supercapacitor electrodes remains challenging, because graphene-based electrode materials are synthesized by the chemical modification of graphene. The modified graphene electrodes have lower electrical conductivity than ideal graphene, and limited electrochemically active surface areas due to restacking, which hinders the access of electrolyte ions, resulting in a low energy density. In order to solve the issue of restacking and low electrical conductivity, we introduce thiol-functionalized, nitrogen-doped, reduced graphene oxide scrolls as the electrode materials for an electric double-layer supercapacitor. The fabricated supercapacitor exhibits a very high energy/power density of 206 Wh/kg (59.74 Wh/L)/496 W/kg at a current density of 0.25 A/g, and a high power/energy density of 32 kW/kg (9.8 kW/L)/9.58 Wh/kg at a current density of 50 A/g; it also operates in a voltage range of 0~4 V with excellent cyclic stability of more than 20,000 cycles. By suitably combining the scroll-based electrode and electrolyte material, this study presents a strategy for electrode design for next-generation energy storage devices with high energy density without compromising the power density.

A resistive random access memory (RRAM) device with self-rectifying I-V characteristics was fabricated by inserting a silicon nitride (SiN) layer between the bottom electrode and solution-processed active material of an iron oxide-graphene oxide (FeO-GO) hybrid. The fabricated Au/Ni/FeO-GO/SiN/n-Si memory device exhibited an excellent resistive switching ratio and a rectification ratio higher than 10. In the Au/Ni/FeO-GO/SiN/n-Si device, resistive switching occurs in both the FeO-GO and SiN layers separately, resulting in a highly uniform and stable switching performance. The resistive switching from a high resistance state to a low resistance state in the Au/Ni/FeO-GO/SiN/n-Si device occurs through a trap-assisted tunneling process in the SiN layer, enabled by the FeO-GO layer which prevents diffusion of the migrating Ni metal into the switching nitride layer. The intrinsic self-rectifying characteristics of our memory devices arise from the asymmetric barriers for electrons tunneling into the traps of the SiN layer which is sandwiched between the top and bottom electrodes having dissimilar work functions. Our study confirmed that integrating a suitable dielectric layer into the conventional RRAM cell is an innovative strategy to simplify the architecture and fabrication process to realize self-rectifying crossbar arrays.

The low volumetric energy density of reduced graphene oxide (rGO)-based electrodes limits its application in commercial electrochemical energy storage devices that require high-performance energy storage capacities in small volumes. The volumetric energy density of rGO-based electrode materials is very low due to their low packing density. A supercapacitor with enhanced packing density and high volumetric energy density is fabricated using doped rGO scrolls (GFNSs) as the electrode material. The restacking of rGO sheets is successfully controlled through synthesizing the doped scroll structures while increasing the packing density. The fabricated cell exhibits an ultrahigh volumetric energy density of 49.66 Wh/L with excellent cycling stability (>10 000 cycles). This unique design strategy for the electrode material has significant potential for the future supercapacitors with high volumetric energy densities.

Graphene oxide (GO) thin films on various substrates show surprising variations of their structural and optical properties. These variations were also studied by depositing GO via introducing a gold nanoparticles buffer layer on quartz substrate. The effect of the substrate as well as buffer layer results in short range order crystallization in deposited GO films with an increase in inter-planar spacing. XPS analysis shows that GO undergoes reduction when spin coated on ITO/glass substrate. The deposited GO films exhibit luminescence emission, and the introduction of gold buffer layer results in a blue shift of the photoluminescent emission spectra. The GO on gold buffer layer shows almost constant optical absorption in the whole visible spectral region like graphene. The present study indicates that buffer layer effects and the interaction between different substrates and GO is strong enough to affect the oxygen linkages in GO which in turn changes its structural and optical properties, which may find potential application in graphene based optoelectronic device fabrication.