Chemical modification of graphene and its applications

Abstract

Graphene, a two-dimensional crystalline monolayer made of sp2-hybridized carbon atoms arranged in a honeycomb lattice, holds a set of remarkable electronic and physical properties, such as ballistic transport with low resistivity, high chemical stability, and high mechanical strength. By taking advantage of these, in recent years our research group has performed a series of studies for modifying the surfaces of graphene and tuning its properties. These studies can be mainly divided into two categories. First, we opened graphene's band gap to some extent through covalent and/or noncovalent chemical modifications, and installed sensing functions into graphene. In detail, we grafted nitrophenyl group onto graphene through an electrochemical method and methyl group onto graphene by plasma treatment to open its band gap. Also, we assembled lead sulfide or titanium dioxide onto graphene through electron beam evaporation to achieve optical or gas sensing. A rotaxane molecule with a bistable structure was also assembled onto graphene through π-π stacking to obtain optical switches with logic capability. On the other hand, we also fabricated graphene-based nanoelectrodes for making a new-generation molecular electronic devices with diverse functionalities. In detail, we cut graphene using electron beam lithography and reactive ion etching to obtain graphene electrodes. Poly(3-hexyl thiophene) or coppe phthalocyanine was spin-coated onto these electrodes to achieve field effect transistors with the high carrier mobility and photoresponsive property. We further developed graphene nanoelectrodes by dash-line lithography, and molecular bridges with different functions were connected between these nanoelectrodes. These single molecule devices can switch their conductance upon exposure to external stimuli, such as metal ion, pH and light. Looking into the future, graphene, as a representative of carbon-based nanomaterials, will continue to play an important role in the area of nano/molecular electronics.