Effect of doping on the properties of graphene electrodes

Abstract

Graphene is a promising material for application as electrodes in electronic sensing and energy storage devices To increase the intrinsic charge carrier concentration imparted by its unique band structure doping with charge donators or acceptors has to be carried out This thesis investigates the interaction of charges with graphene to identify the limitations and applications of doped graphene electrodes First the study of the charge transfer between dopants and graphene reveals a limited charge transfer efficiency as low as 5% of the expected values This issue was found to originate from the low geometrical capacitance of small dopant clusters and a combination of treatment steps was developed to increase the dopant cluster size and eometrical capacitance Increased surface energy was demonstrated to increase the charge transfer efficiency to 70% and yield ultra-transparent electrodes that showed resistances of 106 Ω/sq at 97% transmittance which represents the highest reported performance for doped single layer graphene and is on par with commercially available transparent conductors However the increase in dopant cluster size was found to negatively impact the carrier transport in graphene Using in-situ spectroscopic and Hall effect characterization we demonstrate that at high dopant coverage percolative transport occurs that decreases the carrier mobility without increasing the carrier concentration resulting in an increasing resistance which represents the first observation of a window for useful doping Finally we show that the application of graphene to electrochemical electrodes is affected by the presence and character of dopants Employing micro-electrode arrays within one sheet of graphene we find large variations in the heterogeneous charge transfer rate (HCT) that correlates with the spatially varying doping level Electrostatic doping can exploit this phenomenon and dynamically tune the electrochemical reactivity of graphene over an order of magnitude This novel property was applied to enhance the sensitivity of Electrochemical Impedance Spectroscopy

Date of Award	2019
Original language	English
Supervisor	Yen-Hsun Su (Supervisor)