Functionalization and Characterization of Chemical Vapor Deposited Graphene Sheets Towards Application in Chemical Vapor Sensing

Chemical/biological sensors serve many purposes in protecting machinery, the environment, and human life/wellness. Graphene, a two-dimensional (2-D) material made up of carbon atoms in a honeycomb-like lattice, is promising for applications to chemical/biological sensing due to its unique properties. Functionalization of graphene by surface decorating with nanoparticles and increasing interior adsorption sites can tailor its catalytic activity and electrical properties, and hence, important for detecting and distinguishing trace hazardous gases. This research introduces two different approaches to functionalize graphene towards enhanced sensitivity and selectivity of graphene-based sensors. The morphologies, structures, and electrical properties of the functionalized graphene are systematically characterized. The first approach is to decorate graphene surface with gold and platinum nanoparticles using air-spraying technique. It is determined that the sheet resistance nearly linearly increased as the nanoparticle concentration on graphene increased. Both metals resulted in the increase in sheet resistance due to reduction of charge carriers. The resulted difference in electrical properties can be utilized to tune graphene sensing capabilities. The second approach is to modify graphene via oxygen doping or partial oxidation under oxygen plasma or thermal treatment. Evolution of structure and changes of electrical properties at microwave frequencies were qualitatively analyzed. The width of electrically inactive layer near micro-pattered graphene resulting from oxygen plasma etching is determined with the help Raman spectroscopy and scanning microwave microscopy (SMM.) The effects of annealing temperature on structural and electrical parameters are also analyzed. It is found that graphene annealed at and above 350°C shows distinct structural and electrical changes, which is not suitable for sensor recovery. These two insightful observations will provide critical guidance for processing optimization and recovery control of graphene-based sensors