Study Of Graphene Formation On Insulated Substrates And Its Mechanism

Graphene, also known as single layer graphite, is a two-dimensional crystal material with sp2carbon atoms packed into a honeycom lattice, with unique electrical, thermal and mechanical properties. Rearch results show that bilayer and few layer (<10layers) graphite sheet show different from graphite, while similar to graphene. Therefore, traditionally, it can be called as graphene for graphite film less than10layers.In2004, Geim and Novoselov, two scientists from the University of Manchester, UK, got the first piece of graphene samples via micro-mechanical exfoliation method, and observed series of unprecedented electrical properties. The finding attracted scientists’interest in graphene fabrication, thus, many preparation methods were developed, including silicon carbide epitaxial growth, oxidation-reduction method, chemical vapor deposition (CVD), etc. Wherein, CVD is an efficient method for controllable and large-scale graphene film. But, because of the destruction of the integrity of graphene and the impurity ion introducing during the transfer process, it can not match with the existing semiconductor technology. Accordingly, it is especially important to explore the direct growth of graphene on insulated substrates, for its application in electrical field.In this paper, we adopt the CVD method, using methane (CH4)(5%, in volum) as the carbon source, hydrogen gas (H2) as the reaction gas and argon (Ar) as the carrier gas, to study graphene growth on different insulated substrates under different growth conditions. The main work includes:1. Select sapphire (a-Al2O3(0001)) as the substrate for graphene grown, study the relationship between graphene CVD growth and influence factors. First, according to the initial experimental data, select an appropriate reference condition:gas flux and flux ratio of H2/CH4is50/80, the growth temperature is1100℃, the growth time is4hours; Secondly, further design comparative experiments, to study the influence of growth temperature, growth time, gas flux and flux ratio during graphene growth, explore the mechanism of graphene nucleation and growth, and give a more reasonable explanation about it. Finally, we obtain a uniform bilayer, large-scale graphene, under an optimal condition:the gas flux and flux ratio of H2/CH4is30/50, the growth temperature equal to 1100℃, growth time is4hours.2. On a silicon (Si), silicon dioxide (SiO2/Si) substrate, directly using CVD method to grow graphene.1) Under an atmospheric pressure, and the gas flux and flux ratio of H2/CH4is50/80, the growth time is4hours, we studied graphene growth on Si, SiO2/Si substrates under the growth temperature of1000℃,1050℃,1100℃and1150℃. According to the results of Raman spectroscopy, we conclused that the suitable temperature for graphene growth on SiO2/Si substrate is1100℃;2) Under the condition of the gas flux and flux ratio of H2/CH4is30/50, growth temperature is1100℃and growing for4hours, we compared the quality of graphene growth on Si and SiO2/Si substrates, and the results indicated that there exist differences between graphene growth on the two substrates;3) Try using low-pressure CVD to grow graphene on Si and SiO2/Si substrates. Under the low pressure of240Pa, there formed a bilayer graphene with grain size up to78.55nm. However, due to that the silicon wafer surface was oxidized forming an silicon dioxide nanowire powder, the binding between graphene and the substrate is not so strong, and easy to fall off. For SiO2/Si substrate, there was no formation of graphene. It was observed that no white powder adhered to the surface of SiO2/Si substrate, and the polishing layer was not destroyed, it should attribute to the exit of the300nm silicon dioxide layer, protecting the underlying silicon aginst oxidation.