The Synthesis Of Graphene By Chemical-vapor-deposition (CVD) Method And Its Properties Research

As a two-dimensional atomically thick material, graphene has been attractingmuch attention in recent years since its outstanding electronic, thermal, optical,mechanical properties and the consequent application potentials in several fieldssuch as high-speed transistors, transparent conductive films, energy storage and soon. In variety methods for graphene preparation, chemical vapor deposition (CVD)is the most promising, affordable and readily accessible approach for deposition ofuniform large-area and high-quality graphene onto transition metal substrates suchas Ni, Pt, Fe or Cu. Currently, copper was the most wildly used substrates materialsbecause it is relatively inexpensive and can provide a single uniform layer grapheneover large areas. Synthesis of graphene on copper foil by CVD are discussed in thiswork, in particular, the pre-treatment of copper foil and the parameters dependencyof graphene growth.The specific content can be divided into the following chapters:The first chapter is a foreword, which given a brief introduction of graphene,including its structure and properties, the main preparation methods, applicationprospects, and finally presents the main contents of this paper.In chapter two, the experimental detail of this paper was explained firstly, andthen the mechanism of graphene synthesis by CVD is described; finally, severalmethods for graphene characterization were introduced.In the third chapter, we studied the effect of pretreatment of copper on thegraphene quality and found that, after annealing, there were many impurity particlesappeared on the surface of copper foil, and so the quality of the resulting graphene isdegraded. Several methods for copper pre-treatment were investigated, includingHCL etching, electrochemical polish and iron nitrate aqueous solutions etching. Theresults revealed that the surface quality of the copper substrate is improved bypre-etching in1M Fe(NO3)3aqueous solutions for90s before graphene growth. Theimpurity particles were eliminated after graphene growth when the as prepared copper foil was used, and the quality of the resulting graphene was improved. Theresults of graphene growth by different kinds of copper foils suggest that thismethod (Fe(NO3)3aqueous solutions pre-etched) has a good universality.Chapter four discussed the effects of the growth parameters for graphene growth,such as the temperature, carbon source concentration and so on. Found that:1) Nographene was yeild when the temperature lower than750℃and the quality ofgraphene was improved along with the temperature. Graphene with a very lowdefect density was got when the growth temperature reached1000℃.2) Lowerconcentration of hydrocarbon results in a lower density of graphene domain and abigger muti-layer area.3) Hydrogen played an important role in the growth processas it can etch the graphene in a particular way and assists the decompose of thehydrocarbon. Based on this, the exists of hydrogen can help to control the quality ofgraphene. In addition, we bestowed our method to solve the problems occuredduring the transfer stage, for example, the pre-treatment of the PMMA coatedsample before substrate etching. As to our experiments, the cleanness of thetransferred graphene was significantly improved when through an argon plasmaprocess for the backside. Finally, graphene samples we prepared were characterizedby several means, the results proved that it has a good quality and basically in linewith the requirements of optoelectronic applications.The concluding chapter summarizes the topics and prospects the future‘s work.