| Abstract Scope |
Graphene is a two-dimensional form of sp2 carbon in a honeycomb structure exhibits unusual electronic, optical and mechanical properties, being a promising candidate for nanoelectronics, advanced nanoelectromechanical systems (NEMS), etc. Because of graphene’s high optical absorption, transmission/reflection spectra are a convenient characterization tool, a challenge for ultrathin layers (<~2nm). The IR-transmission of EG on semi-insulating SiC was studied by Dawlaty et. al(2008)[1], Thickness in monolayers(N in ML), momentum scattering time(τ) and Fermi level position(Ef) were extracted on semi-insulating substrate only because conductive SiC absorbs strongly in the IR. EG-induced optical responses in reflection are larger than for transmission [2], yielding greater measurement precision. The presence of a phonon-induced singularity in the dielectric function in SiC’s restrahlen band predicts the formation of a polariton at the EG/SiC interface, leading to enhanced reflectivity. We present polariton-enhanced reflectivity of EG grown on N+ substrates for accurate extraction of N, τ and Ef. IR-reflectivity was measured in the 2.5-25μm range with an N+ SiC reference. Our developed mathematical model fitted to the experiment to extract N, τ and Ef. Increasing N gives higher conductivity, leading to enhanced interaction with the incoming light, increasing reflectivity similar to the Drude model [3]. Thickness measurements by FTIR were correlated with X-ray photoelectron spectroscopy (XPS) confirming the accuracy of our model. Raman spectra show the presence of G, D and 2D peaks, while D/G ratio <0.2, confirming the presence of EG. In reflectivity measurements, 2ML EG, reflectivity increases by 20% in the Restrahlen band, much higher than the ~2% observed outside the band. This behavior of the electromagnetic field at the SiC/EG interface constitutes the polariton. The model we used fit both Si-face EG and C-face EG equally well, As layer thickness increased from 2-38ML ’s, τ increased from 4-20fs, while IEFI decreased from 105meV to ~20meV, indicating that carrier scattering at the SiC/graphene interface is strong. By showing that τ ≈ 1/ √ ns, the carrier concentration/ML, we argue that scattering is likely dominated by short-range interactions [4]. Polariton formation finds application in near field optical plasmon-polariton devices such as an efficient plasmonic waveguide, near-field superlenses . This characteristic was also used as gas sensor where adsorption doping occurs, changing IEFI, resulting in a change of reflectivity. |