Transient absorption spectroscopy as a promising optical tool for the quality evaluation of graphene layers deposited by microwave plasma

Abstract

The qualified analysis of structure, morphology and defects in graphene is crucial for graphene layers evaluation and development of various electro-optical applications. In this work, we present the detailed analysis of properties of planar graphene and vertical graphene nanosheets (VGNs) prepared by means of microwave plasma enhanced chemical vapour deposition method (PECVD), employing common analysis methods (scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Raman scattering spectroscopy), as well as ultrafast transient absorption spectroscopy (TAS) technique with different excitation wavelengths (at 350, 400 and 700 nm) to analyze excited state relaxation dynamics in different types of graphene. By measuring relaxation duration (or hot electrons cooling dynamics that originates from electron-phonon interactions, leading to phonon-phonon interactions) we showed that TAS provides with the information about phonons and defects in graphene. The complex analysis of graphene layers, in parallel to the TAS measurements, demonstrates that TAS analysis of the excited state dynamics in graphene might lead to the creation of effective methodology of control of quality of graphene in terms of effective defect analysis.