Surface functionalization of graphene devices

Abstract

Graphene, a zero-gap semiconductor with massless charge carriers, is emerging as an amazing material for future electronics, due to its outstanding electrical and mechanical performances. However, the lack of a bandgap results in a high off-state current leakage and a nonsaturating drive current, both of which severely limit graphene's practical applications in electronic devices. Chemical functionalization on its surface promises a powerful tool to manipulate its electronic properties and modify its atomic structures. Graphene is a true two-dimensional material; every carbon atom in single layer graphene is exposed to its environment. Therefore, the surface functionalization in graphene can significantly change its physical and chemical properties, such as bandgap opening and piezoelectricity engineering, etc. Hydrogenation and fluorination have been experimentally demonstrated to be effective in changing the hybridization state of carbon atoms and opening a bandgap from 2.9 eV to 5.4 eV. However, both of these methods are destructive to graphene, and will degrade its carrier mobility. In this study, we fabricated graphene-based field effect transistors (FETs) and conducted surface functionalization via plasma reactions. We systematically investigated graphene chlorination and characterized the results with Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy (AFM) and transport measurement. A schematic picture of how the chlorine plasma interacts with graphene was also proposed. Hydrogenation and fluorination were also conducted and analyzed as comparison. We demonstrated that chlorination in graphene via plasma reactions is a very effective and controllable way to engineer its structural and electronic properties. The high mobility of the resulting structures is a very important advantage with respect to other functionalization approaches. Keywords: Graphene, functionalization, chlorination, plasma, bandgap, Fermi level, doping, mobility