Effect of Si3N4 thickness on the optical characterization of grapheme.

Optical detection of graphene on a specific substrate is important for the analysis of the physical or chemical properties of graphene. Si3N4, an oxygen free substrate with high dielectric constant, is a good candidate to replace SiO2. In this letter, we report the optimization of the Si3N4 thickness for efficient optical characterization by means of the contrast, enhancement factor (F), and the Raman spectra of the graphene obtained on the selected Si3N4/Si substrate. The contrast (visibility) and enhancement factors (F, Raman intensity) of the graphene/Si3N4/Si structure were calculated as a function of the Si3N4 thickness and the wavelength of the excitation source. A suitable Si3N4 thickness generating high visibility and Raman intensities at the wavelength of the excitation source, 633 nm, was obtained.