Preparation And Application Of High-Quality Graphene

Graphene has excellent physical properties; including nanoscale thickness, high electron mobility at room temperature and good light transmission property that makes it have great application value in electronic devices and touch screens areas. Since graphene was firstly prepared by Geim’s group in 2004, it has aroused widespread concern in academia and industry. Then a variety of preparation methods have also developed. At present, chemical vapor deposition (CVD) used copper as the catalytic substrate is the most promising method for large-scale industrial production of high quality graphene film. Chemical vapor deposition method involves complex factors, including substrate quality, mixed-gas ratio, growth temperature, growth time, and growth pressure, understanding the role of these factors for the preparation of high-quality graphene film has very important significance.In this research, the factors influenced on the size and morphology of graphene domains in atmospheric and low pressure were systematically studied. Furthermore, the growth mechenisem of graphene in atmospheric and low pressurewas also studied. And the transistors based on low pressure graphene were fabricated on silicon and ferroelectric film substrates. Specific works summaried as follows:Atmospheric pressure:First, the influence of copper foil substrate was explored. Hexagonal graphene domains distributed evenly with higher quality in the mechanical and electrochemical polishing copper substrate. Second, different ratio of CH4 toH2 can change the shape of graphene domains. Hexagonal graphene domains were parepared in the ratio range of 1:75 to 1:100. Third, different graphene domains have different nucleation time. In the growth condition of 500ppm methane concentration,60min growth time and 1030℃ growth temperature, a hundred micron size graphene domains were successfully prepared. Raman spectroscopy showed that the quality of graphene domains is closed to the micromechanical peeling graphene, which indicated high quality.Low pressure:First, to study the effects of ratio of CH4 toH2, the smaller of the ratio value, the lower of the graphene domains nucleation density and the greater of the size of domains. Second, with the increase of growth temperature, the graphene domains have greater size, but the nucleation density first increase then decline. Third, as the prolonged of growth time, the morphology of graphene domains gradually changed from four-lobed to square. And the growth rate of the area graphene domains is greater than the growth rate of the size. Different positions of copper substrate have different nucleation density and coverage. In the positive of copper substrate, the nucleation density and coverage were 236/mm2and 69.1%, respectively. In the opposite position the values were only 86/mm2and 10.4%.At the low pressure, graphenel domains are mostly four-lobed and single-layer structure, which illustrate different growth kinetics compared to atmospheric pressure.The back gate graphene field effect transistor was fabricated based on 300nm SiO2, and the electrical performance tests showed that the carrier mobility reached 735cm2V-1s-1 at room temperature, indicating a good electrical conductivity. Furthermore, graphene field effect transistor based on BZT-0.5BCT ferroelectric thin film was prepared, transfer characteristic curve showing a graphene unique characteristics of bipolar.