Orientation and interface control of various two-dimensional materials and its electrochemical applications

Abstract

Two-dimensional (2D) materials are very attractive in practical electrochemical devices due to their low cost, large scale production, ultrahigh surface area, and tunable electrical properties. Optimized performances of various 2D materials have shown performances comparable to the best performing materials such as noble metals. Despite their outstanding estimated properties, the performance of 2D materials is much lower than that of conventional materials used in electrochemical applications. Previous researches have shown that the orientation of individual 2D sheets plays an important role in determining the overall electrochemical activity. Therefore, it is highly desirable to fabricate structures to enhance and optimize the properties of 2D materials for future practical applications. In this thesis, the influence of the interface on the structure and orientation of various 2D materials is investigated, and controlled for enhanced performance in electrochemical applications. First, the domain orientation of multilayer graphene grown by chemical vapor deposition (CVD) on Ni was investigated by liquid crystal observation method. By observing domain structures at various growth conditions, we were able to figure out the critical factors of the Ni substrate that determines the graphene domain structure. Second, a novel buckled $MoS_2$ structure was demonstrated for the first time. Buckled $MoS_2$ was fabricated over a large area by simply introducing a single layer of graphene below the Mo film prior to $MoS_2$ film growth via CVD. In a more in-depth investigation, $MoS_2$ buckling was tuned by manipulating the interfacial adhesion energy of the underlying graphene substrate where computational calculations were performed to support the experimental results. This study is anticipated to provide an insight for the precise control of various 2D structures for optimal performance in electrochemical applications.