(Invited) Metrology of Solution Processable 2D Materials for Electronic Applications

Abstract

Two-dimensional materials have attracted intense interest due to their remarkable physical and electronic properties as well as their potential for a diverse range of applications. Many of these envisaged applications (i.e. printed/flexible electronics, energy storage, photovoltaics) require single or few layer flakes of a 2D material that can be dispersed in solution to facilitate deposition onto a substrate, formulation into an ink and/or mixing into a composite. A variety of powders and dispersions claiming to contain 2D materials such as graphene are now becoming available but the variable quality of these materials and lack of standardized protocols for their assessment is hampering the development of applications.Here we will describe ongoing work at the NRC aimed at developing characterization methods and standard protocols to characterize graphene and graphene oxide (GO) powders, dispersions and inks. We employ a variety of experimental techniques including scanned probe microscopies (AFM and STM), vibrational spectroscopy (Raman and FTIR), X-ray diffraction, X-ray photoelectron spectroscopy and dynamic light scattering in order to characterize the structure and chemical composition of in-house and commercially available materials. These methods allow us to measure key parameters to assess material quality such as flake thickness and lateral size, carbon to oxygen ratio and impurity content. Conductivity and work function of ultrathin films produced from various graphene and graphene oxide containing dispersions have been also measured. The performance of these films as transparent conductors can be characterized by a figure of merit based on the optical transmission and conductivity of the film. Performance of films made via reduction of GO will be compared with those based on graphene exfoliated without oxidation.Recently we have begun to extend this work to dispersions of other two-dimensional materials such as the transition metal dichalcogenides (TMDC). Initial characterization of commercially available TMDCs will be presented.