Chemical vapor deposition (CVD) has emerged as the most widely used method for producing high-quality, large-area graphene films suitable for industrial applications. The process involves the decomposition of hydrocarbon precursors on a catalytic metal substrate at elevated temperatures, followed by the formation of sp2-bonded carbon atoms into a hexagonal lattice. The growth dynamics, film quality, and scalability depend critically on process parameters, substrate choice, and post-growth handling.

The CVD process begins with the selection of a suitable metal substrate, which acts as both a catalyst and a template for graphene formation. Copper and nickel are the most commonly used substrates due to their distinct catalytic behaviors. Copper favors surface-mediated growth, where carbon atoms remain on the surface due to low carbon solubility, leading to monolayer graphene with relatively uniform coverage. Nickel, on the other hand, has high carbon solubility, resulting in carbon segregation upon cooling and often producing multilayer graphene. The choice between these substrates depends on the desired graphene thickness and application requirements. Other metals, such as ruthenium, platinum, and iridium, have also been explored but are less common due to cost and scalability limitations.

Process parameters such as temperature, pressure, and gas flow rates play a crucial role in determining graphene quality. Growth temperatures typically range between 900°C and 1050°C, as this range provides sufficient energy for precursor decomposition while minimizing excessive carbon diffusion that could lead to defects. The pressure regime is equally important; low-pressure CVD (LP-CVD) operates at pressures below 100 Pa and is known for producing uniform monolayer graphene with fewer defects. Atmospheric-pressure CVD (AP-CVD) is simpler in setup but often results in higher defect densities due to increased gas-phase reactions. The choice of precursor gas also influences growth dynamics. Methane is the most widely used precursor due to its stability and controllable decomposition rate, but other hydrocarbons such as ethylene and acetylene can be employed for faster growth at the cost of potential defect formation. Hydrogen is introduced as a carrier and etching gas to regulate graphene growth by passivating edges and removing amorphous carbon.

The nucleation and domain formation mechanisms in CVD-grown graphene are governed by the interplay between carbon supply, substrate surface energy, and growth conditions. On copper, graphene nucleation occurs at random surface sites, with domains expanding until they merge into a continuous film. The nucleation density is influenced by substrate pretreatment, surface roughness, and gas-phase carbon concentration. A higher nucleation density leads to smaller domains and more grain boundaries, which can degrade electrical and mechanical properties. To achieve large single-crystalline domains, researchers optimize growth conditions to reduce nucleation density while maintaining a steady carbon supply for lateral expansion. Techniques such as oxygen-assisted etching and controlled hydrogen flow have been shown to improve domain size by selectively removing defective nuclei.

Despite significant progress, several challenges remain in CVD graphene growth. Defect control is a major concern, as grain boundaries, vacancies, and adlayers can adversely affect performance in electronic applications. Grain boundaries introduce scattering centers that reduce carrier mobility, while multilayer patches disrupt uniformity. Strategies to mitigate defects include optimizing gas ratios, using ultra-smooth substrates, and post-growth annealing. Uniformity across large areas is another challenge, particularly for industrial-scale production. Variations in temperature and gas flow across the substrate can lead to thickness fluctuations and inhomogeneous strain. Scalability is further complicated by the need for high-temperature processing, which limits compatibility with certain substrates and increases production costs.

Post-growth transfer techniques are essential for integrating CVD graphene into functional devices, as the metal substrate is often incompatible with target applications. The most common transfer method involves spin-coating a polymer support layer, typically polymethyl methacrylate (PMMA), onto the graphene film. The metal substrate is then etched away using a chemical solution such as iron chloride or ammonium persulfate for copper, or hydrochloric acid for nickel. The polymer-supported graphene is rinsed and transferred to the desired substrate, after which the polymer is dissolved in acetone or another solvent. This process, however, can introduce wrinkles, cracks, and residual polymer contaminants that degrade performance. Alternative transfer methods, such as roll-to-roll techniques and sacrificial interlayers, have been developed to improve yield and minimize damage. Electrochemical delamination, where a voltage is applied to weaken the graphene-metal adhesion, has shown promise for cleaner transfers but requires precise control to avoid film rupture.

Efforts to improve CVD graphene growth continue to focus on achieving higher quality, larger area coverage, and better reproducibility. Advances in substrate engineering, such as the use of single-crystalline copper foils and alloy substrates, have led to improvements in domain size and defect density. In situ monitoring techniques, including optical microscopy and Raman spectroscopy, provide real-time feedback for process optimization. The development of low-temperature CVD processes compatible with flexible substrates could further expand the range of applications.

CVD-grown graphene has already found use in transparent conductive films, flexible electronics, and high-frequency transistors, but widespread adoption depends on overcoming the remaining challenges in growth and transfer. Future research will likely explore novel precursor chemistries, advanced reactor designs, and more robust transfer methods to meet the demands of next-generation technologies. The scalability and versatility of CVD make it a cornerstone of graphene production, with ongoing refinements pushing the boundaries of what is achievable in two-dimensional material synthesis.