Effect of out-of-plane directional intra-layer coupling from graphene monolayer on sp³ type defect with gap-plasmonic structures

The author investigates an intra-layer coupling effect through transverse acoustic (TA) phonon modes along the z -direction at Au nanoparticle (NP)–graphene monolayer (GM)–Au thin film (TF) plasmonic junctions in regard with sp³ type defect effect. The oxidation and resulting disorder of GM with breaking of six-fold symmetry have been explored. Because a Raman-forbidden D peak can be activated due to unwanted single-phonon inter-valley and intra-valley scattering processes, the quantitative estimation of the sp³ type defect is being performed by the intensity ratio between G and D peaks. By exploring the difference of the maximum peak position (TA3-TA1) and the intensity ratio, (TA1/TA3) the author can reveal that a lower z -protruded GM accompanied with weak intra-coupling and a weaker RBLM intensity show relatively high D/G. It means that larger surface area of a GM to be functionalized by oxidization can secure more easily than the higher z -protruded. This investigation presents the importance of controlling the degree of z -protrusion of GM surface in terms of not only the presence of high D/G but also its related and detailed nano-structural surface shape, leading to the enhancement of electrical properties such as a carrier mobility and sheet resistance value. The out-of-plane phonon modes will be considered as a key factor in further exploring nano-physical deformation of 2D materials in sync with its electrical performance. (letter)