Experimental identification of tilted bending formation of graphene monolayer with gap-plasmon

Abstract

Here, we study the out-of-plane phonon modes located at 300–700 cm⁻¹ region in addition to the strong radial breathing-like mode (RBLM) at 150 cm⁻¹ by employing an Au nanoparticle (NP)–graphene–Au thin film (TF) junction system. Three subsequent peaks from the lower-frequency, called transverse acoustic mode series (TA1, TA2, TA3), can be efficiently utilized as an indicator of subtly tilted out-of-plane phonon movement of graphene monolayer (GM) along with the z-axis. Peak position differences between TAs are carefully analyzed with regard to the degree of electron-phonon coupling (EPC) between Au nanostructure and GM by comparing the corresponding line width and peak position of RBLM signals. We find that the strong EPC additionally occurs between TA1 and TA3 peaks, which indicates that subtly tilted phonon is present along with the z-axis.