2D Materials

2D materials are crystals just one or a few atoms thick — sheets whose width can span centimetres while their thickness is a single atomic layer. Confining electrons to a plane changes a material's behaviour profoundly, and this family has become one of the most active areas in condensed-matter physics, chemistry, and device engineering.

Discovery and the graphene revolution

The field began in 2004, when Andre Geim and Konstantin Novoselov isolated graphene — a single layer of carbon atoms — by repeatedly peeling graphite with adhesive tape. That a one-atom-thick crystal could be stable at room temperature overturned long-standing theoretical doubts, and the pair received the 2010 Nobel Prize in Physics. Graphene is a single hexagonal lattice of sp²-bonded carbon whose electrons move with a linear, relativistic-like (Dirac) energy–momentum relation, giving room-temperature charge-carrier mobilities above 200,000 cm² V⁻¹ s⁻¹ — far higher than silicon.

The main families

Graphene is one of several families. Other honeycomb semimetals — silicene, germanene, and stanene — share its geometry but add sizable spin–orbit coupling that opens small band gaps. Transition-metal dichalcogenides (TMDs) such as MoS₂, WS₂, and WSe₂ have the structure MX₂ (a metal layer between two chalcogen layers) and switch from an indirect to a direct band gap of about 1.8–2.0 eV when thinned to a monolayer, producing bright photoluminescence useful for optoelectronics. Hexagonal boron nitride (h-BN) is the insulating cousin, with a wide ~6 eV gap and an atomically flat, defect-free surface that makes it the standard substrate and encapsulant. Newer members include black phosphorus, the metallic MXenes, and borophene.

Properties and applications

Reduced dimensionality raises the surface-to-volume ratio and strengthens quantum confinement, reshaping how charge, heat, and light behave. In semiconducting TMDs the electron–hole pairs (excitons) bind so tightly — hundreds of meV — that they survive at room temperature, enabling LEDs, lasers, and photodetectors. Graphene's zero band gap allows ultrafast electronics and terahertz devices but prevents it from switching fully off, limiting its use in digital logic. Stacking different sheets into van der Waals heterostructures lets engineers combine properties layer by layer, and the large, tunable surface area makes 2D materials strong candidates for catalysis, batteries, supercapacitors, and chemical sensing.

Twisted bilayers and moiré physics

A landmark development came in 2018, when Pablo Jarillo-Herrero's group showed that stacking two graphene sheets and twisting them by a "magic angle" of about 1.1° produces a moiré superlattice in which electrons slow dramatically and the material becomes superconducting. This launched the field of "twistronics," where the twist angle between layers becomes a new experimental knob for engineering correlated and topological electronic states — one of the most active frontiers in modern materials physics.