Using Metal-less Structures To Enhance the Raman Signals of Graphene by 100-fold while Maintaining the Band-to-Band Ratio and Peak Positions Precisely

Abstract

In this study, we developed a reliable method to analyze the interference-enhanced Raman scattering (IERS) effect on graphene by considering the surface electric field (E-field), which can be calculated precisely by measuring the optical admittance of the thin-film assembly. Through accurate tuning of the optical properties of one-dimensional photonic crystals (1D-PhCs), the strong and controllable interference effect allowed the surface E-field to be maximized and, thereby, to optimize the enhancement factors of the Raman scattering signals of graphene. Using this approach, we could enhance both the G and the 2D bands of graphene largely, uniformly, and equally, by about 180 times relative to those obtained on a silicon substrate. Under certain conditions, the Raman peak of graphene could even be enhanced by over 400 times. After transferring single-layer graphene (SLG) and few-layer graphene (FLG) onto various substrates, we found that the Raman spectra of both SLG and FLG on the 1D-PhCs substrate were enhanced without changing the band-to-band ratio or the peak positions of the main Raman bands of graphene. Without inducing any additional signal disturbance, this enhancement technique allowed us to maintain the accurate and precise informational features from the Raman spectra. The experimental enhancement factors in the coenhanced Raman spectra of graphene were higher than those previously obtained using the IERS effect. Moreover, the surface E-field of 1D-PhCs could be modulated by changing the incident angle of the excited light source, thereby allowing fine-tuning of the working wavelength. Thus, by controlling only the surface E-field, the Raman signals of graphene could be enhanced dramatically without any distortion on spectra. Accordingly, using 1D-PhCs and the optimized IERS effect is very helpful for fine structural characterization of graphene through conventional Raman spectroscopy