Microwave plasma-assisted growth of 2D and 3D graphene

Abstract

Graphene is now considered as the most promising next-generation semiconductor material to substitute the now widely used silicon because of its highest reported carrier mobilities (200 000 cm2/Vs) and extremely high thermal conductivity (~ 3080 W/mK). The synthesis procedure determines the quality of graphene. An advance method, microwave plasma-assisted chemical vapour deposition (MWCVD), was employed to synthesize 2D (dimensional) and 3D graphene. The graphene layers were successfully grown on two different substrates, nickel (Ni) and copper (Cu) foils through MWCVD. Methane was used as a gaseous carbon source to synthesize graphene on Ni substrate. Poly(methyl methacrylate) (PMMA) was the solid carbon source to synthesize graphene on Cu foil. The utilization of plasma facilitates the decomposition of CH4/ methyl methacrylate more efficiently so as to provide carbon species, which results in synthesizing graphene under low temperature. In addition, other growing condition such as cooling rate, time, and power was investigated. The obtained graphene was characterized under Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM). Furthermore, the electrical measurement of the obtained graphene was also tested. The Raman spectroscopy helps to identify the existence of grown graphene on the substrates. The existence of two main peaks in Raman Spectra, G peak and 2D peak, verified the graphene were successfully grown in both substrates. From the ratio of I2D/ IG, the numbers of layers of the graphene were determined. Monolayer and multi-layer graphene were fabricated respectively. The cooling rates 25°C/min and 25°C/10mins were compared. The lower cooling rate shows the crystillinity of graphene is better and the defects decreased dramatically. TEM shows the flexibility and transparency of the graphene. The atomic structure was also examined under HRTEM. The morphology of the graphene was studied by the SEM. The growing times of 1min and 5 mins were investigated through SEM. It reveals carbon species cannot be released within short period of time. In addition, the microwave power is another predominant factor which affects the growing graphene. Different powers of 400W, 800W and 1200W were taken into the experiments. The power was found to be an important condition for decomposition of the carbon source. The electrical measurement of the graphene was carried out in FET device. The synthesized graphene from Cu foil was transferred to SiO2/Si substrate. The electrical properties such as mobility and conductivity can be obtained. The I-V characterization can be acquired from the FET device. The mobility and conductivity were found to be 1001cm2/Vs and 13262.6 S/m respectively.