CVD graphene film generally refers to single-layer graphene prepared by CVD method. Because it is a single layer, its strength, conductivity and transparency are relatively good. Graphene is one of the materials known to be very strong, and it also has good toughness and can be bent. The theoretical Young's modulus of graphene is 1.0tpa, and the intrinsic tensile strength is 130gpa. The reduced graphene modified by hydrogen plasma also has good strength, and the average modulus can be greater than 0.25tpa. So, what are the common problems in the CVD graphene growth process?

1. There is a problem with the vacuum degree of the equipment. The specific manifestation is that the vacuum of the body is too high or the pressure rise rate is too high after the vacuum valve is closed. Since the graphite structure is relatively easy to oxidize, it is easy to understand that when there is a problem with the vacuum of the equipment and the oxygen content is too high, it will be difficult for graphene to completely cover the surface of the substrate, or even completely unable to grow so that the metal substrate is oxidized .

The cause of the problem can be many common ones including the following:

1. The sealing rubber ring is aging or damaged;

2. Fatigue or corrosion perforation of bellows;

3. The vacuum pump is faulty;

4. Improper installation of the flange, uneven force on the sealing ring leads to deflection to one side;

5. The contact surface between the quartz tube and the sealing rubber ring is damaged.

2. Obtain amorphous carbon film or multilayer graphene with many defects

Common reasons are the following:

1. The partial pressure of methane is too high. The partial pressure of methane is equal to the volume fraction of methane in the entire process gas (approximately an ideal gas so it is also the mass fraction and volume flow fraction) multiplied by the total pressure of the process gas. When the partial pressure of methane is too high, the concentration of active carbon-containing groups generated by decomposition at high temperature will increase greatly, which will increase the nucleation density of graphene on the surface of copper foil (the supersaturation increases and the nucleation barrier decreases), which intensifies The tendency of graphene to grow into multiple layers leads to an increase in defects such as grain boundaries. Even collisional nucleation in the gas phase leads to the formation of amorphous carbon.

2. The vacuum pump oil is aging or inappropriate pump oil or even inferior pump oil is used. Under the above conditions, the saturated vapor pressure of the pump oil will increase, and a considerable amount of hydrocarbon gas will be emitted when the vacuum pump is running. will become an additional carbon source gas, causing a situation similar to that of methane partial pressure being too high.

 3. The copper foil melts or even evaporates completely

Common reasons are the following:

1. The thermocouple is short-circuited, deteriorated, the contact between the thermocouple and the compensation wire is poor, and the compensation wire of the thermocouple is reversed. These conditions will cause the thermoelectric potential measured by the temperature control instrument to be smaller than the actual thermoelectric potential, that is to say, the temperature measured by the instrument will be lower than the actual temperature, because the temperature control instrument will adjust the heating power of the furnace body according to the set temperature to make the measured temperature close to the set temperature. Therefore, the actual temperature of the furnace body will eventually exceed the set temperature. Since the common process temperature for CVD growth of graphene on the surface of copper foil is 1000 to 1050 °C and the melting point of copper is 1083 °C, the difference is small, so the copper foil will melt or even evaporate completely.

2. The thermocouple type bound by the temperature control instrument does not match the actual thermocouple type; the thermocouple does not match the compensation wire 4. A large number of white spots (usually oxides containing silicon and aluminum) are found in the grown graphene under SEM The dots often lead to multilayer nucleation of graphene, adding additional nucleation density and defects.

 Common reasons are the following:

1. Improper use of vacuum silicone grease or silicone rubber sealing ring. Under high temperature and hydrogen atmosphere, such silicone materials will release small molecular weight siloxanes, resulting in silicon contamination;

2. The surface of the copper foil itself contains impurities and lacks proper cleaning;

3. The purity of the quartz products used is not enough or it is polluted by magazines containing alkali metals or alkaline earth metals. Impurities in the quartz products at high temperatures will cause the quartz to precipitate silicon oxide particles;

4. The wrong use of pipe plugs such as mullite fiber pipe plugs that are prone to dust particles.