Analysis of Single Crystal Graphene Growth Model and Single Phase Rotation Angle

Graphene of Introduction

Graphene, also known as single-layer graphite, carbon atoms form a two-dimensional hexagonal honeycomb structure with sp2 bonding. Single layer graphene (SLG) has only one carbon atom with a thickness of 0.34 nm. The special structure makes it have many excellent characteristics, such as fast carrier mobility and high specific surface area, very good mechanical strength and extremely high light transmittance. Single-layer graphene only absorbs 2.3% of visible light. Because there is no energy gap, there is no strong absorption in the ultraviolet (Ultraviolet, UV) band, and the conductive mechanism is different from general transparent conductive films (TCFs). Therefore, it is almost completely transparent to the infrared (Infrared, IR) band; the room temperature download mobility is up to 2×105 cm2/Vs, the resistivity is about 10-6 Ω·cm; elastic constant (spring constants) is about 1~5 N/m, and Young's modulus is about 0.5 Tpa. Combining its optical, electrical and elastic properties, it is very suitable as a flexible transparent conductive film. The purpose of this study is to derive the growth model of graphene and use Fourier transform to prove that copper (111) has a single rotation angle for graphene.

Experimental Design of Graphene

Place the copper foil (1cm2) in a high-temperature furnace tube, pass in argon (Ar) and hydrogen (H2), heat to 1050 °C and maintain this state for annealing for 180 minutes. Argon gas is used as a dilute safety gas. Hydrogen can reduce the copper oxide on the copper surface, prevent copper foil oxidation and act as a catalytic gas. High temperature annealing can increase the crystallinity and flatness of the copper foil. We introduce a hydrogen flow rate of 30sccm and let in 0.5sccm of methane (CH4) to grows graphene. Methane will degrade into hydrocarbons (CHx) or C deposited on the surface of the copper foil under the catalysis of hydrogen and copper. Finally, we remove the copper foil from the high temperature area to quickly cool down. Avoid cooling too slowly, causing carbon atoms to continue to move on the copper surface will result in inconsistent quality. In order to obtain unidirectional copper (111), we sputtered a 1μm copper film on the sapphire (c-plane) substrate, then used electrochemical plating to increase the thickness, and then peeled off the copper foil with mechanical force. After annealing, the copper foil with the surface of copper (111) is obtained; we grow single-crystal graphene on the surface of copper (111) and polycrystalline copper at a high temperature of 1000 degrees, methane and hydrogen flow at 0.4 sccm and 24 sccm parameters, and use Fourier transformation. We use a scanning electron microscope (SEM) to photograph the morphology of single crystal graphene and derive the growth model of single crystal graphene, and use the Fourier transform to prove that graphene grows on a copper (111) surface with a single rotation.

Conclusion of Graphene Experimental

In this study, a chemical vapor deposition system was used to grow graphene films on copper metal. The growth model of graphene was first derived. It can be found that the deposition of carbon atoms on the copper surface is an acceleration growth, which is a quadratic equation of one element. The experimental results and the equation find that the fitting curve is consistent, we can use this equation to accurately predict the film formation time required for the graphene film and the sheet resistance and optical transmittance are 310Ω/ and 97.7 at a temperature of 1050 degrees, hydrogen 30sccm and methane 0.5sccm. We fabricated a unidirectional copper (111) substrate and used copper (111) to have a small lattice constant gap with graphene to grow graphene grains with a single rotation direction. Finally, it can be calculated by Fourier transform the angle difference is about 2~3 degrees, which is different from the previous method of observing through a transmission electron microscope.

Remarks Quoted from  Associate Professor/ ChienCheng Kuo of the Department of Optics and Photonics of National Central University, Professor of the  Department of Optics and Photonics, National Central University/Cheng-Chung Lee.