Propiedades electrodinámicas de grafeno dopado con plasma de nitrógeno en el terahertz

In this study, we present a detailed examination of the influence of nitrogen-plasma induced defects on the electrodynamic properties of few-layer graphene using terahertz (THz) time-domain spectroscopy. Initially, few-layer graphene was obtained using the chemical vapor deposition technique. Then, it was repeatedly treated with sub-3 kV nitrogen plasma that results in the creation of multiple lattice defects and insertion of nitrogen observed by means of Raman and Xray photoelectron spectroscopy (XPS). According to obtained spectra, the lattice of graphene transferred to a quartz substrate successfully withstands up to 600 sec of plasma treatment. However, the number of defects increases with treatment time: even 10 sec treatment of initial graphene considerably reflects in Raman spectra. At the same time, 600 sec of plasma treatment leads to the insertion of up to ~ 9 at. % nitrogen, predominantly in pyridinic and pyrrolic/pyrazolic forms. Notably, the ratio between pyridinic, pyrrolic/pyrazolic and graphitic forms of nitrogen insertion in graphene remains constant independently on the treatment time. The described structural changes lead to the increase of THz transmittance with treatment time observed using THz time-domain spectroscopy. According to the proposed theoretical explanation based on the Kubo formalism, such dependence of THz spectra on an extension of treatment time indicates the decrease in total conductivity of graphene corresponding to the sufficient increase in electron collisional broadening and the decrease in chemical potential caused by plasma treatment. Therefore, nitrogen plasma treatment is proven as an effective, robust and scalable method for adjusting the conductivity and transport properties of the graphene widening its applicability for THz electronics and photonics.