The study and use of layered materials whose structure involves the stacking of individual platelets has a very long history. Among these materials, graphite, an allotrope of carbon, is perhaps the best-known example. It was already used by Neolithic Danubians around 4,000 BC as paint for pottery . Its chemical composition was determined by Carl Wilhelm Scheelein 1779 , with details of its atomic structure in 1924 , and electronic structure calculations in the 1950s [4, 5]. Other important families of layered materials include the transition metal dichalcogenides (e.g., MoS2, MoSe2), certain metal halides (e.g., PbI2 and MgBr2), and oxides (e.g., MnO2, MoO3), perovskites (general form ABO3), layered III-VIs (e.g., GaS, InSe), and V-VIs (e.g., InSe, GaS) materials and layered silicates (clays, micas). The insulating hexagonal boron nitride (h-BN) system is another important layered material, one isostructural with graphite, but exhibiting very different properties. Currently, around 500 different layered materials have been identified [6, 7]. Until relatively recently, research and applications of layered materials involved their bulk solids. It was the mechanical exfoliation of a single graphene layer from graphite in 2004 by Geim, Novoselov, and co-workers  that focused the attention of the scientific community on the study of single or few layers of these materials. A considerable variety of other layered 2D materials has now also been mechanically exfoliated using adhesive tape . Chemical exfoliation in liquid dispersions is another widely used technique. Ancient Mayas applied such an approach with clays for use as pigments, while in the 1960s Boehm  isolated thin graphite films in this fashion, and Frindt  exfoliated metal dichalcogenides thin films. Typically, chemical exfoliation involves dispersion of the material in high-surface tension solvents, oxidation, or intercalation by a variety of agents that lead to exfoliation . Chemical techniques can produce large quantities of 2D layers in a solvent, appropriate for depositing films that can be used in industry. Increasingly, for electronics and more high-end applications, 2D layers are directly synthesized using catalytic chemical vapor deposition (CVD) or van der Waals epitaxy techniques . Heterostructures involving atomic layers of different materials can also be produced, by either sequential transfers or direct growth.
|Original language||English (US)|
|Title of host publication||2D Materials|
|Subtitle of host publication||Properties and Devices|
|Publisher||Cambridge University Press|
|Number of pages||4|
|State||Published - Jan 1 2017|