Fig. 4 | Nature Communications

Fig. 4

From: Raman enhancement on ultra-clean graphene quantum dots produced by quasi-equilibrium plasma-enhanced chemical vapor deposition

Fig. 4The alternative text for this image may have been generated using AI.

The proposed enhancement mechanism and the size-dependent Raman enhancement for R6G. a–c The ground state charge transfer between R6G and graphene, GQDs (2.2 nm), or GQDs (6.2 nm). The electron states in the R6G/graphene (or GQD) system, which have the possibility to contribute to the surface-enhanced Raman spectroscopy (SERS), are marked by red shadows. d–f The calculated density of state (DOS) and g–i the calculated molecular orbital (at the HOMO level of R6G) densities of R6G/graphene, R6G/GQDs (2.2 nm), and R6G/GQDs (6.2 nm), respectively. (g–i) The atomic models used in the density functional theory (DFT) calculations and the calculated charge transfer integrals (I). j The calculated DOS of a graphene and GQDs with different diameters near Fermi level. k Raman spectra of thermally evaporated R6G on P-GQDs with different sizes. l Relative intensity of the characteristic peaks of R6G on P-GQDs with different sizes, normalized to the signals on SiO2/Si. The largest enhancement of R6G signal occurs on P-GQD-2

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