In materials science, the term single-layer materials or 2D materials refers to crystalline solids consisting of a single layer of atoms. More broadly, these materials also include structures in which individual monolayers are held together by interlayer van der Waals interactions. These materials are promising for some applications but remain the focus of research. Single-layer materials derived from single elements generally carry the -ene suffix in their names, e.g. graphene. Single-layer materials that are compounds of two or more elements have -ane or -ide suffixes. 2D materials can generally be categorized as either 2D allotropes of various elements or as compounds (consisting of two or more covalently bonding elements).

It is predicted that there are hundreds of stable single-layer materials. The atomic structure and calculated basic properties of these and many other potentially synthesisable single-layer materials, can be found in computational databases. 2D materials can be produced using mainly two approaches: top-down exfoliation and bottom-up synthesis. Exfoliation refers to the reduction of interlayer van der Waals interactions in bulk layered materials, leading to monolayer detach from the sample surface. The exfoliation methods include sonication, mechanical, hydrothermal, electrochemical, laser-assisted, and microwave-assisted exfoliation.

Graphene is a crystalline allotrope of carbon in the form of a nearly transparent (to visible light) one atom thick sheet. It is hundreds of times stronger than most steels by weight. It has the highest known thermal and electrical conductivity, displaying current densities 1,000,000 times that of copper. It was first produced in 2004.

Andre Geim and Konstantin Novoselov won the 2010 Nobel Prize in Physics "for groundbreaking experiments regarding the two-dimensional material graphene". They first produced it by lifting graphene flakes from bulk graphite with adhesive tape and then transferring them onto a silicon wafer.

Graphyne is another 2-dimensional carbon allotrope whose structure is similar to graphene's. It can be seen as a lattice of benzene rings connected by acetylene bonds. Depending on the content of the acetylene groups, graphyne can be considered a mixed hybridization, spⁿ, where 1 < n < 2, compared to graphene (pure sp²) and diamond (pure sp³).

The existence of graphyne was conjectured before 1960. In 2010, graphdiyne (graphyne with diacetylene groups) was synthesized on copper substrates. In 2022 a team claimed to have successfully used alkyne metathesis to synthesise graphyne though this claim is disputed. However, after an investigation the team's paper was retracted by the publication citing fabricated data. Later during 2022 synthesis of multi-layered γ‑graphyne was successfully performed through the polymerization of 1,3,5-tribromo-2,4,6-triethynylbenzene under Sonogashira coupling conditions. Recently, it has been claimed to be a competitor for graphene due to the potential of direction-dependent Dirac cones.

Borophene is a crystalline atomic monolayer of boron and is also known as boron sheet. First predicted by theory in the mid-1990s in a freestanding state, and then demonstrated as distinct monoatomic layers on substrates by Zhang et al., different borophene structures were experimentally confirmed in 2015. First-principle calculations predict that a bilayer Kagome-phase borophene is an anisotropic superconductor with strong electron-phonon coupling and a critical temperature on the order of 17-35K.

Germanene is a two-dimensional allotrope of germanium with a buckled honeycomb structure. Experimentally synthesized germanene exhibits a honeycomb structure. This honeycomb structure consists of two hexagonal sub-lattices that are vertically displaced by 0.2 A from each other. Experiments have demonstrated that germanene's quantum spin Hall edge states persist at room temperature and can be switched off by electrical field, indicating a robust and highly tunable topological phase.