Preparation And Properties Of Graphene Materials By CVD Process

Nowadays, with the rapid development of microelectronics and integrated circuit technology, graphene has become the most ideal semiconductor material. It is expected to have the ability of replacing silicon material. It has unique hexagonal structure, unique semiconductor characteristics and many good excellent performances, such as perfect mechanical properties, high thermal conductivity, and good light transmission. Besides, it has abundant reserves, so it be paid more attention since it appears. At the beginning, the graphene material was prepared by chemical deposition method with copper foil as the substrate, then it was transferred and characterized in various ways. The contents and results of this paper as follows:The graphene material was prepared by CVD method on a copper foil, the results showed that it was a single layer and it had the typical characteristics of graphene sheets.Then the effect of growth parameters on the experimental results was studied. We took the control of variables, sequentially changed methane and hydrogen partial pressure ratio(7 : 1, 8 : 1, 9 : 1, 10 : 1) and the growth time(10 min, 20 min, 30 min, 40 min) during the growth process. The results showed that the thickness and number of layers of graphene can be controlled by changing the methane and hydrogen partial pressure ratio in growth process, and the coverage of graphene on the substrate can be controlled by varying the time. Growing 30 min under the partial pressure of 7 : 1 ratio most likely to be the optimal experimental parameters.Meanwhile, the influence of U-fold placement of copper foil on thickness uniformity of graphene was studied, and the horizontal copper sheet, U-shaped copper with space of 5 mm, U-shaped copper with space of 10 mm were chose as the growing substrates. Then we explained the aerodynamic behavior during the growth process from two perspectives, and finally the experimental results were expected: the graphene growed on U-folded copper with a smaller space had the best thickness uniformity.The transfer method of graphene was studied, the graphene sheets structure was more clear after transfer process. Then the morphology of graphene on silicon dioxide was characterized by atomic force microscopy, the results showed that the surface of material was flat and it had uniform thickness. Finally the influence of the annealing step after the transfer process on the morphology and properties of graphene was studied, results indicated that annealing step for reducing the surface roughness and removing the impurities such as PMMA played a significant role.Finally, the optical and electrical properties of graphene were characterized by IV tester and spectrophotometer. The light transmittance and electrical properties of graphene were tested, the results showed that the light transmittance almost of all bands was over 80%, and it showed the conductivity of the material. Then the Graphene-AZO heterojunction was prepared, the results indicated that IV curve did not show rectification characteristics and there was no barrier, thus further research was needed for graphene doped.