The materials

Graphene and its relatives: stacked and twisted graphene, oxidised graphene made in bulk by chemistry, and carbon networks that include triple bonds.

Hexagonal boron nitride, the flat insulator most high-quality 2D devices are built on, graphitic carbon nitride, a light-absorbing photocatalyst, MoSi₂N₄, a nitride monolayer that only exists because silicon caps it, and an electride whose interlayer space holds electrons instead of atoms.

A layer of metal atoms sandwiched between two layers of sulfur, selenium or tellurium. The family spans semiconductors that glow as monolayers, metals, superconductors and topological materials.

Layered sulfides, selenides and tellurides beyond the dichalcogenides, of main-group metals, iron, copper and other transition metals: fast semiconductors, thermoelectrics, ferroelectrics, topological insulators, Weyl and Dirac semimetals, iron-based superconductors, and chain compounds whose electrons move mostly in one direction.

Layered compounds of metals, semimetals and pnictogens – sometimes capped by a halogen skin – that cleave into thin flakes, along a van der Waals gap or a layer of alkali ions. Trigonal PtBi₂ is a Weyl semimetal whose surfaces superconduct while its bulk stays normal.

Single-element sheets beyond carbon: silicon, germanium, tin, lead, boron, phosphorus, antimony, bismuth and tellurium. Several exist only on the surface they were grown on.

Metallic carbides and nitrides made by etching one element out of a layered ceramic. They disperse in water and are already made in kilogram batches.

Crystals that stay magnetic down to one or a few atomic layers, first shown in 2017.

Layers built from two kinds of anion: a chalcogen and a halogen, oxygen and a halogen, oxygen and a heavier chalcogen, or nitrogen and a halogen. The mixed bonding breaks symmetries that simpler compounds keep, giving polar Janus semiconductors, giant spin splitting, ferroelectric layers, exceptionally strong nonlinear optics and layered photocatalysts.

Oxide and hydroxide nanosheets, including clays and catalysts, and one special case: the conducting layer that forms where two insulating oxide crystals meet.

Sheets of metal halide, either bare – as in PbI₂ and BiI₃, which stop X-rays and seed perovskite films – or separated by layers of organic molecules, which is how perovskite solar cells are made more stable.

Porous sheets assembled from organic molecules, with or without metal atoms, whose structure is designed before it is made – and dense hybrids in which inorganic sheets alternate with layers of organic ligands.