Graphene

• The manufacturing process of graphene

1. Mechanical stripping method (SCOTCH TAPE method)

Process: High oriented pyrolytic graphite (HOPG) is repeatedly peeled off with tape until a single layer of graphene is obtained.

characteristic: The highest purity (defect rate <0.1%) but very low yield (micron-sized fragments). Suitable for laboratory basic research (such as verification of quantum Hall effect).

2. Chemical vapor deposition (CVD)

flow path:

1. The metal substrate (copper/nickel) is annealed at high temperature (1000℃) to form a flat surface;

2. Methane (CH₄) and other carbon sources are introduced to catalyze the cracking of carbon atoms;

3. Carbon atoms self-assemble into graphene films;

4. Transfer to the target substrate (such as SIO₂/SI or flexible PET) by etching.

characteristic:

Continuous thin films can be prepared at wafer level (more than 30 inches);

Industrial-grade core processes, such as Samsung and Huawei, are used for flexible screens.

3. REDOX method

flow path:

1. Graphite is strongly oxidized by concentrated sulfuric acid/potassium permanganate to produce graphene oxide (GO);

2. GO ultrasonic dispersion into a single layer solution;

3. Chemical reduction (hydrazine hydrate, ascorbic acid) restores conductivity.

characteristic:

Low cost (<$50/G), suitable for mass production;

4. Liquid phase stripping method

Process: Graphite powder is dispersed in solvent (NMP, DMF), and then peeled into single layer graphene by ultrasonic or high pressure homogenizer.

characteristic:

Yield up to 80% (British HAYDALE technology);

Suitable for printed electronics (ink concentration up to 5 MG/ML).

• Material properties of graphene

1. Physical and chemical properties

| performance index            | Values/characteristics                       |Compare materials (such as silicon, copper)                                        | |carrier mobility       | 200,000 cm²/(V·s)(theoretical value)       | silicon：1,400 cm²/(V·s)

| heat conductivity         | 5,300 W/(m·K)(single layer)             | copper：400 W/(m·K)

| tensile strength        | 130 GPa                            | steel：0.4 GPa

|  light transmittance          | 97.7%（550 nmwavelength）               | ITO（Indium Tin Oxide）：~90%

| specific area       | 2,630 m²/g                        | acticarbon：1,000-3,000 m²/g

|  chemical stability      | Able to resist acid and alkali (except strong oxidizing acid)          | The metal is easily corroded

2. Unique quantum effect

Quantum Hall effect: at low temperature and strong magnetic field, the conductivity is quantized step (precision up to 10⁻⁹, used for resistance standard). Dirac cone band structure: zero mass fermion properties, supporting ultra-fast electron transport.

• Industry application and technical index advantages

1. Electronics and semiconductor devices

high frequency transistor:

Advantages: carrier mobility is 140 times that of silicon, and the operating frequency exceeds 300 GHZ (IBM 2023 prototype).

Technical indicators: Cut-off frequency (Fₜ) up to 700 GHZ, power density 1.5 W/MM (1.2 times that of GAN).

Flexible electronics:

Application: Foldable screen mobile phone (HuaweiMATE XS uses graphene heat dissipation film).

Advantages: Flexibility> 1 million times (resistance change <2%), transmittance> 97%.

2. Energy storage and conversion

Lithium-ion battery:

Graphene conductive agent: adding 1% graphene, the internal resistance of the battery is reduced by 20%, and the cycle life is increased by 30% (Ningde Times technology).

Silicon-based anode: capacity up to 2,000 MAH/G (traditional graphite anode 372 MAH/G).

Supercapacitors:

Technical indicators: energy density 30 WH/KG, power density 100 KW/KG (MAXWELL TECHNOLOGIES data).

3. Composite materials

aerospace:

Graphene reinforced aluminum matrix composites: 50% strength increase, 20% weight reduction (part of Boeing 787).

Thermal management materials: thermal conductivity increased to 400 W/ (M K) (traditional polymers <1 W/ (M K)).

Lightweight car: graphene/epoxy composite material improves impact resistance by 80% (Tesla battery case).

4. Biomedicine and sensors

biosensor:

Detection limit: 0.1 PG/ML (Novel Coronavirus antigen detection, 1000 times more sensitive than ELISA).

Response time: <5 seconds (glucose sensor).

Antibacterial dressings: The killing rate of Staphylococcus aureus by graphene oxide dressings was>99.9% (3 hours of contact).

5. Environmental engineering

Seawater desalination membrane:

Performance: water flux 200 L/ (M² H BAR), salt retention rate 99.9% (MIT 2022 annual experimental data).

Pollution adsorption: Graphene aerogel adsorbs crude oil at a weight ratio of 86 times (ExxonMobil’s offshore oil spill emergency plan).

• Technical Challenges and Future Directions

1. Scale production: CVD cost needs to be reduced to <$50/M² (currently ~$200/M²).

2. Number of layers control: the proportion of single layer graphene should be>95% (about 80% by CVD method at present).

3. Doping technology: precise control of nitrogen/boron doping concentration (target: carrier density 10¹³ CM⁻²).

4. Heterogeneous integration: interface engineering of graphene with GAN and SIC (interface resistance <1 Ω MM).

Graphene has achieved breakthroughs in semiconductors, new energy, biomedical and other fields with its ultra-high electrical conductivity, mechanical strength, light transmittance and chemical stability:

5G communication: graphene RF devices improve efficiency by 40% in the 28 GHZ band;

Space heat dissipation: the weight of satellite thermal control system is reduced by 30%, and the heat dissipation efficiency is increased by 50%;

Medical diagnosis: Ultra-sensitive sensors drive early cancer detection.

With the maturity of technologies such as roll-to-roll CVD and atomic layer deposition (ALD) doping, graphene is expected to make the leap from “lab miracle” to “industrial pillar material” by 2030.