A nanocrystal is a material particle having at least one dimension smaller than 100 nanometres, based on quantum dots[1] (a nanoparticle) and composed of atoms in either a single- or poly-crystalline arrangement.[2]
The size of nanocrystals distinguishes them from larger crystals. For example, silicon nanocrystals can provide efficient light emission while bulk silicon does not[3] and may be used for memory components.[4]
When embedded in solids, nanocrystals may exhibit much more complex melting behaviour than conventional solids[5] and may form the basis of a special class of solids.[6] They can behave as single-domain systems (a volume within the system having the same atomic or molecular arrangement throughout) that can help explain the behaviour of macroscopic samples of a similar material without the complicating presence of grain boundaries and other defects.[citation needed]
Semiconductor nanocrystals having dimensions smaller than 10 nm are also described as quantum dots.
Synthesis
The traditional method involves molecular precursors, which can include typical metal salts and a source of the anion. Most semiconducting nanomaterials feature chalcogenides (SS−, SeS−, TeS−) and pnicnides (P3−, As3−, Sb3−). Sources of these elements are the silylated derivatives such as bis(trimethylsilyl)sulfide (S(SiMe3)2 and tris(trimethylsilyl)phosphine (P(SiMe3)3).[7]
Some procedures use surfactants to solubilize the growing nanocrystals.[9] In some cases, nanocrystals can exchange their elements with reagents through atomic diffusion.[9]
Applications
Filter
Nanocrystals made with zeolite are used to filter crude oil into diesel fuel at an ExxonMobil oil refinery in Louisiana at a cost less than conventional methods.[10]
Wear resistance
Nanocrystals' level of hardness[11] is closer to the optimized molecular hardness[12] which attracts the wear resistance industry[13][14]