Fabrication of Shape-Controlled Graphenes Based on Top-down and Bottom-up Approaches and Their Applications

Abstract

Graphene, typically composed of one-atom-thick layer of carbon in a 2D hexagonal lattice, is a basic building block for graphitic materials of all other dimensionalities. The graphene has attracted tremendous worldwide attention because of their fascinating properties different from those of the carbon-based graphitic materials (e.g., extremely high charge carrier mobility, large specific surface area, thermal/electrical conductivity, and chemical/mechanical stability). Up to date, various synthetic methods for preparing graphene have been developed. However, most previous synthetic methods suffer from the precise control of the size, shape, edge, layer of graphene sheets. Consequently, it is still challenging to produce graphene with tailored morphology and diameters for various applications. This dissertation describes the two different ways in the synthetic methodology of graphene will be presented in the viewpoint of top-down approach and bottom-up approach. As a top-down approach, the graphene sheets with well-defined shape are successfully fabricated using a simple oxidation and exfoliation process of high-crystalline carbon nanofibers (CNFs). Interestingly, the diameter and shape of the graphene sheets can be controlled by selectively designing the morphology of starting materials and optimizing the cutting method. As a bottom-up approach, graphene sheets are formed using layer-by-layer (LbL) self-assembly approach with a metallic dopant. The LbL approach is used to form poly(allylamine)(PAA)/poly(styrenesulfonate) (PSS) multilayer on a quartz substrate. During the carbonization process, the PSS layers can be transformed into graphene sheets due to its inherent aromatic and highly ordered structure. PAA layers served to protect the structural layers as well as prevent the agglomeration of graphene sheets. Most, importantly, these novel approaches can be used as an alternative tool for fabrication of various carbon-based nanomaterials with rational nanostructure design and may offer an opportunity for the further investigation of industrial applications, and might be expanded to allow the applications of graphene sheets in a wide range of areas (e.g., Transparent electrode, dipole antenna, acoustic actuator, nucleating agent, nano-filler, electro-responsive materials, and so on.).