Two-dimensional control: quantum wells and solid-state superlattices
المؤلف:
Peter Atkins, Tina Overton, Jonathan Rourke, Mark Weller, and Fraser Armstrong
المصدر:
Shriver and Atkins Inorganic Chemistry ,5th E
الجزء والصفحة:
ص672-673
2025-10-14
306
in this section, we describe the design of so-called two-dimensional materials, which are materials that have macroscopic length scales in two dimensions and a nanoscale length scale along the third dimension. Thin-film processing methods permit the deposition of films only one atomic (or one unit cell) layer thick. By varying sequentially the types of atomic (or unit cell) layers being deposited, it is possible to control the material architecture along the growth direction at a sub-nanometre scale, thereby allowing the bottom-up development of artificially layered nanostructures. A quantum well (QW) is a thin layer of one material sandwiched between two thick layers of another material and is the two-dimensional equivalent of a zero-dimensional QD. In a superlattice, two (or more) materials alternate with an artificially induced periodicity along the growth direction. Superlattices often have repeat periods of about 1.5–20 nm or greater, and sublayer thicknesses that range from two-unit cells to many tens of unit cells. Artificial crystal structures usually have repeat distances similar to bulk crystals (about 0.3–2.0 nm) and have sublayer thicknesses that range from an atomic layer to two-unit cells (about 1 nm). These structures have found broad commercial application as key device elements in computer chip manufacturing, including hard disk read heads. To control a physical property such as absorption and emission, a quantum well can be used in a similar fashion to the QDs described earlier. The optical properties of quantum wells can be enhanced in quantum well superlattices (often called multiple quantum well structures), which are used in lasers. To control a physical property such as hardness, which is tied to dislocation formation and motion, it is known that many interfaces between dissimilar materials are required. Hardness can be increased substantially in such superlattices, as compared to monolithic films, ranking them among the hardest known materials and making them successful coatings in the tooling industry. To control a property such as ferroelectricity or superconductivity, which are intimately tied to the crystal structures, it is important to be able to engineer artificial crystal structures.
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