Layer Dependence of Graphene for Oxidation Resistance of Cu Surface

We studied the oxidation resistance of graphene-coated Cu surface and its layer dependence by directly growing monolayer graphene with different multilayer structures coexisted, di- minishing the influence induced by residue and transfer technology. It is found that the Cu surface coated with the monolayer graphene demonstrate tremendous difference in oxidation pattern and oxidation rate, compared to that coated with the bilayer graphene, which is considered to be originated from the strain-induced linear oxidation channel in monolayer graphene and the intersection of easily-oxidized directions in each layer of bilayer graphene, respectively. We reveal that the defects on the graphene basal plane but not the boundaries are the main oxidation channel for Cu surface under graphene protection. Our finding indicates that compared to putting forth efforts to improve the quality of monolayer graphene by reducing defects, depositing multilayer graphene directly on metal is a simple and effective way to enhance the oxidation resistance of graphene-coated metals.

Film Thickness and Surface Plasmon Tune the Contribution of SFG Signals from Buried Interface and Air Surface

Sum frequency generation vibrational spectroscopy(SFG-VS)is a powerful technique for determining molecular structures at both buried interface and air surface.Distinguishing the contribution of SFG signals from buried interface and air surface is crucial to the applications in devices such as microelectronics and bio-tips.Here we demonstrate that the SFG spectra from buried interface and air surface can be differentiated by controlling the film thickness and employment of surface-plasmon enhancement.Using substrate-supported PMMA(poly(methyl methacrylate))films as a model,we have visualized the variations in the contribution of SFG signals from buried interface and air surface.By monitoring carbonyl and C-H stretching groups,we found that SFG signals are dominated by the moieties(-CH2,-CH3,-OCH3 and C=O)segregated at the PMMA/air surface for the thin films while they are mainly contributed by the groups(-OCH3 and C=O)at the substrate/PMMA buried interface for the thick films.At the buried interface,the tilt angle of C=O decreases from65°to 43°as the film preparation concentration increases;in contrast,the angles at the air surface fall in the range from 38°to 21°.Surface plasmon generated by gold nanorods can largely enhance SFG signals,particularly the signals from the buried interface.