The effect of thermal reduction on the photoluminescence and electronic structures of graphene oxides.
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 sp(2) 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.
Department of Physics, Tamkang University, Tamsui 251, Taiwan.
C-H
CH
Chuang
Department of Physics, Tamkang University, Tamsui 251, Taiwan.
Y-F
YF
Wang
Department of Physics, Tamkang University, Tamsui 251, Taiwan.
Y-C
YC
Shao
Department of Material Science and Engineering, National Taiwan University, Taipei 106, Taiwan.
Y-C
YC
Yeh
Department of Material Science and Engineering, National Taiwan University, Taipei 106, Taiwan.
D-Y
DY
Wang
Department of Material Science and Engineering, National Taiwan University, Taipei 106, Taiwan.
C-W
CW
Chen
Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan.
J W
JW
Chiou
Department of Physics, College of Science, Engineering and Technology, University of South Africa, Private Bag X6, Florida, 1710, Science Campus, Christiaan de Wet and Pioneer Avenue, Florida Park, Johannesburg, South Africa.
Sekhar C
SC
Ray
Department of Physics, Tamkang University, Tamsui 251, Taiwan.
W F
WF
Pong
National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei230029, China.
L
L
Zhang
National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei230029, China.
J F
JF
Zhu
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
J H
JH
Guo