Study On CVD Synthesis And Hydrogen Etching Of Graphene

As a novel two-dimension carbon specy, graphene has attracted significant attention due to its unique physical properties such as crystallographic quality, electronic structure and high optical transparency, which have significant potential in optoelectronic devices, composite materials and energy storages. Compared with other graphene synthesis processes, graphene grown on transition metals via chemical vapor deposition (CVD) has the distinct advantage of providing extremely large-area graphene films transferable to other substrates. However, as limited by the growth and nucleation mechanism, it remains a challenge to control the quality and uniformity of CVD graphene, whose natural polycrystalline structure has greatly degraded its electrical performance. Since the preparation of materials is the premise and basis for the systematic study of its properties and applications, we study on the synthesis and characters of graphene grown on Mo and Cu substrate by chemical vapor deposition in this paper. The main results are summarized as follows:1. High quality graphene on single-crystal Mo (110) films has been successfully synthesized by a modified CVD equipment. The micro-Raman spectroscopy indicated that the thickness of Mo films, cooling rate and growing time play significant roles in the quality of as-grown graphene films. By optimizing the growth time (15min) and cooling rate (10℃/s), we achieved high quality graphene films with the small ratio IG/I2d≈0.26and the FWHM(2D)≈30.4cm-1on200nm-thick Mo films. Our experiments also suggested that graphene growth on Mo was a dissolution and segregation process.2. The morphology of copper surface such as roughness and grain boundary were found to be crucial roles for forming nucleation seeds of graphene domain. We reduced the nucleation seed density via polishing the Cu substrate by chemical mechanical method. Scanning electron microscope and optical microscope images indicated that it was preferential to form nucleation seeds along the Cu grain boundary and scratched area of the polished Cu substrate. We demonstrated that a very flat surface of Cu substrate was beneficial for growing hexagonal single-crystal graphene domain and could enhance the homogeneity and electronic transport properties of graphene films.3. Hexagonal single-crystal graphene domains were grown on copper (Cu) foil via chemical vapor deposition and were etched with hydrogen at950℃from7to60min at atmospheric pressure. Numerous trenches were observed on the initial graphene domains after etching, and the trench patterns were closely associated with the Cu crystal orientation. We proved that the etching trenches were caused by the hydrogenation of the wrinkles formed during the cooling down process. The etching process on the wrinkles was also examined and explained by SEM.