Investigation on Formation of Metals and Metal Oxides on Two-Dimensional Carbon Materials

Abstract

Department of Materials Science and EngineeringDiscovery of low dimensional materials is attracting various interest in research filed. As a feature, surface properties and quantum size effects are dominated due to two-dimensional (2D) space constraints. These features lead to excellent electronic, optical, thermal, mechanical, and chemical properties that can be used in a wide range of nanotechnology. Particularly, graphene leads the study of 2D materials with the discovery of a method for manufacturing materials in the late 2000s. Nowadays, a lot of new 2D materials such as hexagonal boron nitride, transition metal dichalcogenide, black phosphorene, and 2D metal oxide are found and widely studied. With advancement of nanotechnology and the integration of technology, importance of research on combination of 2D materials and conventional materials is emerging. Based on this issue, this work mainly focuses on formation of thin metals and metal oxides on 2D carbon materials including graphene, graphene oxide and nanocrystalline graphene (nc-G). From study for metal formation on pristine monolayer graphene and nc-G, effect of surface structure of graphene and adsorbate on the surface on the formation of metallic materials on graphene is investigated. It is observed that the influence of the graphene surface structure on formation of metal materials is insignificant but in situ heating experiments shows behavior of deposited metals are different with substrate. By analyzing the adsorbate on graphene, I reveal that metal oxide can be formed at interface between metal and graphene, and crystallinity of the formed metal thin film is affected by amount of the adsorbates. Study of metal on graphene oxide reveals possibility of graphene oxide as solid oxygen source and substrate, simultaneously. I report the atomic-scale investigation of a novel self-formation of a ZnO monolayer from Zn metal on a graphene oxide substrate. The spontaneous oxidation of ultra-thin Zn metal occurs by reaction with oxygen supplied from the graphene oxide substrate and graphene oxide is deoxygenated by a transfer of oxygen from O-containing functional groups to zinc metal. Finally, atomically thin aluminum oxide is analyzed by deposition on graphene through atomic layer deposition. The aluminum oxide formed on graphene is in an amorphous state, but crystallization of aluminum oxide under electron beam and in situ heating experiment are observed by atomic-resolution transmission electron microscopy analysis. These studies allow us to reveal a structural, chemical changes of metal and metal oxide formation on 2D carbon materials from atomic-scale to micro-scale.clos