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
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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