Typically the surface characteristics of conventional materials cannot be changed without disturbing materials' intrinsic properties. For example, chemical treatments are used to alter the surface characteristics of semiconductors, and a continuous flow of electrical currents is used to change the surface characteristics of metals. In contrast, the surface characteristics of graphene, a material which consists of a single atomic layer of hexagonally bonded carbon atoms, can be dynamically tuned while preserving the superb properties of graphene. This is due to the atomically-thin nature and unique properties of graphene. This project studies tunable surface characteristics of graphene to enable a novel and multi-functional coating material. The capacity to dynamically tune the surface characteristics of graphene can be used to advance corrosion and oxidation resistant coating, sensing, condensation heat transfer, battery and supercapacitator efficiency, and microfluidics. These improvements increase productivity and reduce costs in the energy, manufacturing, and health sectors. In addition, the new knowledge and broader implications realized in this project offer an excellent educational opportunity to enhance community engagement and outreach in the exciting and growing field of nanotechnology. Specific avenues for dissemination include online learning platforms, summer research experiences for students, and field trips and summer science camps for high-school students.
Graphene, which consists of fully saturated and chemically inert sp2-hybridized carbon atoms, senses and interacts with external molecules in close vicinity via delocalized pi electrons. Unlike conventional bulk materials, external molecules can modulate the doping levels of graphene by interacting with these delocalized, massless Dirac fermions. Likewise, the modulation of doping levels can in turn affect the way graphene reacts with external molecules. The objective of this project is to establish a fundamental understanding of electrical doping-induced tunable surface energy and reactivity of graphene to address the knowledge gap concerning the coupling between graphene's electronic states and its surface energy/reactivity. The principal investigators' hypothesis is that the modulation of graphene's electron state by doping contributes to the tunable electrostatic force which graphene exerts on external molecules, and in turn impacts the tunable surface energy and reactivity of graphene. The research combines in situ experimental investigations with quantum and atomistic theoretical modeling. In situ microscopy, such as atomic force microscopy and electron microscopy, as well as spectroscopic characterizations, including Raman spectroscopy and X-ray photoelectron spectroscopy, are performed to experimentally investigate how doping influences the surface energy and reactivity of graphene. Furthermore, theoretical investigations, including detailed quantum, atomistic and reactive molecular dynamics calculations, are performed to complement and explain experimental finding of doping-induced surface energy/reactivity, while the experimentally obtained parameters are used to develop a comprehensive theory for the prediction and development of new surface phenomena. This project advances the scientific knowledge of how modulation of doping levels affect graphene's reaction to external molecules as well as improves the technical capability of tunable surface characteristics of graphene.
