Tuning to G(O) flat: Photoluminescence in graphene oxide (GO) suspensions can be tuned from red to blue emission (see scheme) by gradually changing the amounts of sp2‐ and sp3‐bonded carbon atoms through reduction of the surface oxide groups. Electron–hole recombination from two different types of excited states is proposed to explain the luminescence in GO at varying degrees of reduction.

This paper presents an innovative approach to fabricating controllable n-type doping graphene transistors with extended air stability by using self-encapsulated doping layers of titanium suboxide (TiOx) thin films, which are an amorphous phase of crystalline TiO(2) and can be solution processed. The nonstoichiometry TiOx thin films consisting of a large number of oxygen vacancies exhibit several unique functions simultaneously in the n-type doping of graphene as an efficient electron-donating agent, an effective dielectric screening medium, and also an encapsulated layer. A novel device structure consisting of both top and bottom coverage of TiOx thin layers on a graphene transistor exhibited strong n-type transport characteristics with its Dirac point shifted up to -80 V and an enhanced electron mobility with doping. Most interestingly, an extended stability of the device without rapid degradation after doping was observed when it was exposed to ambient air for several days, which is not usually observed in other n-type doping methods in graphene. Density functional theory calculations were also employed to explain the observed unique n-type doping characteristics of graphene using TiOx thin films. The technique of using an "active" encapsulated layer with controllable and substantial electron doping on graphene provides a new route to modulate electronic transport behavior of graphene and has considerable potential for the future development of air-stable and large-area graphene-based nanoelectronics.

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120–180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp2 bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG.

This study investigates the strong photoluminescence (PL) and X-ray excited optical luminescence observed in nitrogen-functionalized 2D graphene nanoflakes (GNFs:N), which arise from the significantly enhanced density of states in the region of π states and the gap between π and π* states. The increase in the number of the sp 2 clusters in the form of pyridine-like N−C, graphite-N-like, and the CO bonding and the resonant energy transfer from the N and O atoms to the sp 2 clusters were found to be responsible for the blue shift and the enhancement of the main PL emission feature. The enhanced PL is strongly related to the induced changes of the electronic structures and bonding properties, which were revealed by the X-ray absorption near-edge structure, X-ray emission spectroscopy, and resonance inelastic X-ray scattering. The study demonstrates that PL emission can be tailored through appropriate tuning of the nitrogen and oxygen contents in GNFs and pave the way for new optoelectronic devices.

No abstract