Reference

Graphene Glossary

A comprehensive glossary of graphene terminology — from production methods and material types to characterization techniques and industry standards.

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Bilayer Graphene: Two stacked layers of graphene, which can be arranged in AB (Bernal) or twisted configurations. Bilayer graphene can develop a tunable electronic bandgap when an electric field is applied perpendicular to the layers, unlike monolayer graphene which remains gapless.

Chemical Vapor Deposition (CVD): A scalable production method in which a carbon-containing gas (typically methane) is decomposed at high temperature (900-1050 °C) on a catalytic metal substrate — usually copper or nickel — to grow large-area, high-quality graphene films. See also: How graphene is made

Dirac Fermion: Charge carriers in graphene that behave as massless relativistic particles, obeying the Dirac equation rather than the Schrödinger equation. This gives graphene its exceptionally high electron mobility, exceeding 200,000 cm²/V·s in suspended samples.

Exfoliation: The process of separating individual graphene sheets from bulk graphite by overcoming the van der Waals forces between layers. Exfoliation can be performed mechanically (e.g., tape method), in liquid media, or through chemical intercalation and oxidation. See also: Exfoliation methods

Few-Layer Graphene (FLG): Graphene material consisting of 2 to approximately 10 stacked layers. FLG retains many of graphene's enhanced properties while being easier and cheaper to produce at scale than monolayer graphene, making it the most common form in commercial applications.

Graphene: A single atomic layer of carbon atoms arranged in a two-dimensional hexagonal (honeycomb) lattice. Graphene exhibits extraordinary electrical conductivity, thermal conductivity (~5,000 W/m·K), mechanical strength (~130 GPa tensile strength), and optical transparency (~97.7%). See also: What is graphene?
Graphene Nanoplatelet (GNP): Short stacks of graphene sheets (typically 1-15 nm thick, up to 25 μm in lateral dimension) produced by exfoliation of graphite. GNPs are among the most commercially available graphene materials and are widely used as fillers in polymer composites, coatings, and energy storage devices.
Graphene Oxide (GO): A chemically modified form of graphene with oxygen-containing functional groups (hydroxyl, epoxide, carboxyl) attached to the basal plane and edges. GO is hydrophilic and dispersible in water, making it useful as a precursor for solution-processed graphene films, but its electrical conductivity is significantly reduced compared to pristine graphene.

Hummers Method: The most widely used chemical process for producing graphene oxide, involving the oxidation of graphite using a mixture of sulfuric acid, sodium nitrate, and potassium permanganate. Modified versions of this 1958 method remain the industrial standard for large-scale GO production.

Liquid-Phase Exfoliation (LPE): A scalable technique that uses ultrasonic energy or high-shear mixing to separate graphene layers from graphite dispersed in a solvent. LPE typically produces few-layer graphene flakes and avoids the chemical damage associated with oxidation routes, though flake sizes are generally smaller (sub-micron to a few microns). See also: Graphene manufacturing

Monolayer Graphene: A single, one-atom-thick sheet of sp²-bonded carbon — the strictest definition of graphene per ISO/TS 80004-13. Monolayer graphene exhibits the material's theoretical maximum properties and is typically produced by CVD on metal catalysts or by mechanical exfoliation of highly oriented pyrolytic graphite.

PECVD: Plasma-Enhanced Chemical Vapor Deposition — a variant of CVD that uses plasma energy to decompose precursor gases at lower substrate temperatures (300-700 °C instead of ~1000 °C). PECVD enables direct graphene growth on non-catalytic substrates such as glass and polymers, potentially eliminating the need for a transfer step.

Raman Spectroscopy: The primary analytical technique for characterizing graphene, using inelastic scattering of laser light to identify the material's vibrational modes. The G peak (~1580 cm⁻¹), 2D peak (~2700 cm⁻¹), and D peak (~1350 cm⁻¹) reveal layer count, defect density, and stacking order, making Raman the standard quality-control tool in graphene production. See also: Standards & testing
Reduced Graphene Oxide (rGO): Graphene oxide that has been chemically, thermally, or electrochemically treated to remove most oxygen-containing groups and partially restore the sp² carbon network. rGO recovers significant electrical conductivity but retains residual defects and functional groups, resulting in properties between GO and pristine graphene.
Roll-to-Roll: A continuous, high-throughput manufacturing process in which CVD graphene is grown on a metal foil fed through a furnace on rollers, then transferred to a target substrate in a continuous operation. Roll-to-roll processing is critical for scaling graphene production to industrial volumes for applications such as transparent conductive films and flexible electronics. See also: Scaling production

Sheet Resistance: A measure of a thin film's electrical resistance independent of its thickness, expressed in ohms per square (Ω/sq). High-quality monolayer CVD graphene typically achieves sheet resistance of 125-500 Ω/sq, compared to 10-100 Ω/sq for indium tin oxide (ITO), making it a key metric for transparent conductor applications.
sp² Bonding: The hybridization state of carbon atoms in graphene, in which each carbon forms three sigma bonds with neighboring atoms in a trigonal planar arrangement, with one remaining p-orbital electron contributing to a delocalized π-electron system. This bonding geometry gives graphene its planar hexagonal structure and enables its exceptional electrical and thermal conductivity.

Technology Readiness Level (TRL): A standardized scale from 1 (basic research) to 9 (proven in operational environment) used to assess the maturity of a technology. In the graphene industry, most composite and coating applications have reached TRL 7-9, while semiconductor and biomedical applications are typically at TRL 3-5. See also: Market readiness
Transfer (CVD graphene): The process of detaching a CVD-grown graphene film from its metal catalyst substrate and placing it onto a target substrate (e.g., SiO₂/Si, polymer, glass). Common methods include PMMA-assisted wet transfer and direct dry lamination; the transfer step remains a major source of defects, wrinkles, and contamination in CVD graphene production.

Van der Waals Forces: Weak, distance-dependent intermolecular forces arising from transient dipole interactions between atoms. In graphite, van der Waals forces hold the graphene layers together with an interlayer binding energy of approximately 2 eV/nm², which is strong enough to maintain the layered structure yet weak enough to allow mechanical exfoliation into individual sheets. See also: Graphene fundamentals