A study on the graphene-based materials for high-performance device applications

Abstract

Carbon based materials such as graphite, graphene oxide and reduced graphene oxides have appreciable attention as a next generation electronic materials because of its distinctive electrical and chemical properties including high electron mobility, chemical stability, and hydrophobicity at nanometer scale. In Chapter 1, we introduce various materials derived from graphite and fabrication methods such as graphene oxide and reduced graphene oxides. Graphene oxide could be fabricated by oxidation of graphite powder and it has oxidation sites on each graphite layer. There are several methods to synthesize graphene oxide sheets. Reduced graphene oxide is made with reducing the graphene oxide. We can reduce the graphene oxide sheets by using various method such solution dipping, plasma, and heating. In this thesis we use diethanolamine and hydrazine to fabricate uniform reduced graphene oxide. Reduced graphene oxide has high surface area and conductivity. In Chapter 2, we report that AgNPs/rGO hybrid materials could be applied for the conductive electrodes with biocompatible electrolyte in energy storage devices due to the large surface area and chemical stability of rGO and high conductivity of AgNPs. There are two types of supercapacitor, where one is electric double-layer capacitors which does not involve chemical reaction between charge carrier and electrode. The other is pseudocapacitor which include faradaic reaction between charge carrier and electrode. In terms of retention, capacitors without chemical reaction have an advantage in long-term stability. Therefore, we designed EDLCs with AgNPs/rGO hybrid elctrodes. In Chapter 3, three terminal devices with rGO channel is reported for neuromorphic applications. Artificial synaptic devices have been actively researched with two terminal devices, such as Ag2S atom switch, WOx memristor, HfOx-based resistive switching and Ge2Sb2Te5-based phase change switch. On the contrary, artificial synaptic devices with three terminal structure have not yet been studied when compared to two terminal devices. Here we suggest three terminal neuromorphic devices which occupy reduced graphene oxide as channel materials and Li-doped polyethylene oxide (PEO) as gate oxide materials. The device shows typical synaptic behavior such as EPSC and PPF. Therefore, we demonstrate that graphite-based materials could be applied for various electronic and energy storage devices.