COPPER-GRAPHENE BASED SYSTEMS FOR FIELD EMISSION APPLICATION

Abstract

This research is focused on the synthesis and application of graphene-based hybrid structures for field emission. Goal of this doctoral research work was to enhance the field emission properties of graphene by supporting/depositing it on 1-D nanostructures. Graphene and its derivatives such as graphene oxide (GO), reduced graphene oxide (rGO) are the potential candidates for high-performance field emission devices owing to their unique geometry and electrical properties. However, flat surface of graphene results in lower field emission efficiency due to emission of electrons only from sharp edges of graphene sheets. In the present study, graphene was deposited on 1-D nanostructures to enable maximum field emission current density at low applied field. The basic idea behind supporting graphene on 1-D nanostructures was to create sharp protrusions in graphene sheets to achieve enhanced field emission properties. Local field enhancement at the apex of sharp protrusions allowed tunnelling and hence emission of electrons from tips at considerable lower voltage. In order to reach to the objective effectively, the research work was divided into three sections. The first section was focused on synthesis and optimization of process parameters of 1-D nanostructures to achieve enhanced field emission. CuO nanorods, Cu nanorods and carbon nanotubes (CNTs) were used as 1-D nanostructures in the present work. The second section was concentrated on the synthesis of reduced graphene based (rGO) based hybrids for field emission application. Though rGO is less conductive than graphene, but rGO is solutionprocessable and can be deposited on any desired substrate by very simple techniques such as dip coating and spin coating. In present work, graphene oxide (GO) was deposited on 1-D nanostructures. rGO based hybrids were prepared by the thermal reduction of graphene oxide (GO) deposited 1-D nanostructured samples. Last section was focused on the synthesis of CVD-graphene based hybrids for field emission application. For CVD-graphene synthesis,the greatest potential for synthesis of high quality graphene due to same symmetry (hexagonal) of (111) surface of FCC material and honeycomb structure of graphene. In present work, CVD-graphene was grown on Cu rich Cu-Ni alloys (FCC) of various compositions. Cu- Ni alloy substrates were rolled and annealed to achieve high volume fraction of (111) texture just before the graphene growth during the graphene synthesis recipe. CVD graphene based hybrids for field emission were prepared by transfer of CVD-graphene on 1-D nanostructures. Details of this doctoral thesis have been described in five different chapters separately. First chapter entitled “Introduction” provides the background for presented research and gives an introduction of the study. It briefs about advantages of graphene and its synthesis methods. Importantly, this chapter establishes the motivations for selecting graphene for field emission application. It also provides the aim of research and objectives of the thesis presented. Second chapter entitled “Literature Review” describes the basics of field emission process and discusses the literature available on copper oxide, copper, carbon nanotubes and graphenebased field emitters. Third chapter entitled “Materials and Methods” gives details of materials used for synthesis and different synthesis schemes adopted for synthesis of copper oxide, copper, carbon nanotubes and graphene-based cathodes for field emitters. Fourth chapter entitled “Field Emission Response of Bare 1-D Nanostructures” presents a detailed analysis of results obtained from synthesis of 1-D nanostructures (copper oxide, copper, carbon nanotubes) and from their application as field emitters. Fifth chapter entitled “Graphene on 1-D Nanostructures for Field Emission” gives the results obtained for the field emission application of synthesized rGO based hybrids and CVD-graphene based hybrids. Chapter sixth summarizes the results of this research. Seventh chapter gives an overview of future scope of the research work presented. Findings of this thesis indicate the potential of graphene based hybrids for field emission application. FCC metals with (111) orientations are preferred because the (111) surface of FCC metals has