Experimental investigation of surface morphology of a chemical vapor deposition-grown graphene monolayer mediating with a gap-plasmonic system and the related ripple shape study

Abstract

We report a method to characterize z-directional surface roughness of chemical vapor deposition-grown graphene monolayers with the aid of surface-enhanced Raman scattering spectral signatures of “out-of-plane” phonon modes observed at Au nanoparticle (NP)–graphene–Au thin film junctions. This method reveals that intensities of the out-of-plane mode (Radial Breathing Like Mode) are strongly correlated with the Full Width at Half Maximum (FWHM) of the de-convoluted 2D peak. On the basis of our findings, in-plane 2D peak shape can be used as a straightforward, quantitative indicator in estimating surface roughness of graphene without loading Au NPs by calculating the FWHM [2D−]/FWHM [2D+] value. Furthermore, we examine the different ripple (RP) shapes on graphene by employing atomic force microscopy-correlated Raman microscopy to identify “threading” and “surrounded” RP types for further investigation on the relationship between spectral features and structural aspects. Electrostatic force microscopy (EFM)-based investigation further substantiates that threading-type RPs in graphene show higher EFM amplitude, indicating that the threading domains tend to be more neutral with a few more sp3 type defects than the surroundings.