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Two-dimensional carbon nanowalls (CNWs) were prepared by microwave plasma-enhanced chemical-vapor deposition and scanning electron microscopy was used to observe their morphologies. The Raman observations of different sample orientations and polarizations show that CNWs are well crystallized. Micro-Raman scattering measurements were also carried out with different excitation laser lines (325, 488, 514, 532, and 633 nm). The D band shows a very strong shift of 46.19 cm-1/eV with excitation laser energy and this has been explained by the double resonance effect. The decreasing intensity ratios ID/IG and ID′/IG with increasing laser excitation energy were detected and discussed. [ABSTRACT FROM AUTHOR]

The role of sulphuric acid (H2SO4) in fabrication graphene oxide besides as intercalant has not been well addressed. In this work, Raman spectroscopy is used to monitor structural evolution in chemical vapor deposition (CVD) graphene chemically oxidized by dilute H2SO4. From the analysis of Raman spectra of oxidized graphene, we propose that oxidation first initiates at preexisting defects, and vacancy-like defects are formed. Following is the radial growth of the vacancy, and oxidation pits appear in graphene. This assumption is further confirmed by atomic force microscope measurement. It is also found that with increase of amounts of defects, G peak is blue shift, and this is explained by defect and hole doping effect. Hole doping in graphene is much stronger at hexagon regions near the oxidation pits. This work helps in understanding the role of H2SO4 in fabrication graphene oxide as oxidizer as well as helps in obtaining structure information of graphene oxide. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]