Observation of domain-selective defect effects from a CVD-grown graphene monolayer sandwiched at individual nanoparticle-on-mirror plasmonic junctions

초록

The author examines the different defect effects of chemical vapor deposition graphene monolayer (CVD-GM) relying on domain position at an individual nanoparticle-on-mirror (NPoM) plasmonic junction. The NPoM, composed of Au nanoparticle (NP)/CVD-GM/Au thin film (TF), could previously show the mode-selective Raman enhancement, in which the center domain exhibited the highest Raman enhancement of both radial breathing like mode (RBLM) and D mode considering the local z-directional electromagnetic (EM) field enhancement effect in the NPoM. Meanwhile, the outer domain of the NPoM also displays the near-two symmetrical deep pits via atomic force microscope (AFM) with the accompanying lower I[D]/I[D*], higher FWHM[RBLM], I[RBLM], and relatively red-shifted (tensile strained) Max [RBLM] from surface-enhanced Raman scattering (SERS) information than the central case. With these observations, the physical loading of Au NP on CVD-GM/Au TF may induce the threading effect on the most outer position of CVD-GM at the NPoM, leading to sp(2) defect-rich domains. In contrast, the central domains, where the sp(3) defects are rich, exhibit the opposite SERS spectral phenomena, indicating that the near-flat surface shape of Au NP bottom has a higher probability to exert a strong charge transfer along the z-direction, resulting in higher I[RBLM] and I[D]/I[D*] than the most outer domain. As such, the author anticipates various chemical sensing using subtle changes in CVD-GM morphology at both the most outer and center positions in the NPoM with the comparison of each SERS spectral signature.

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