By varying the chemical composition in a semiconductor on a scale of nanometers, it is possible to confine some of the electron states to specific regions and create a variety of new quantum effects. The best known examples of this are epitaxially-grown quantum-well superlattices, in which the charge carriers are confined in one dimension to layers often only a few nanometers thick. Many useful devices are based on these materials, including semiconductor lasers, and optical receivers and modulators. Successes such as these as well as interest in fundamental phenomena have stimulated the development of materials in which the electrons are confined in all three dimensions. Such materials are known as quantum dots .

Quantum dot nanoparticles are molecular-sized semiconductor material that light up like LEDs and enable the detection and barcoding of biological materials from DNA to proteins. This powerful tool enables dramatic advances in genetic analysis, flow cytometry, high-throughput screening, fluorescence microscopy, drug discovery, and diagnostics.

The remarkable size-dependent optical properties of semiconductor nanocrystals, or quantum dots were discovered in the early 1980s by several research groups. Liquid phase methods for synthesizing supsensions of nanocrystals in solvents such as water and acetonitrile were developed. In the subsequent decade and a half, the synthesis of these particles has been refined to the point where a number of metal-semiconductor salts can be grown in suspensions. By tailoring the size and composition of these nanocrystals, it is possible to engineer fluorescent probes with new and specific properties, opening up all types of industrial and biological applications.

To explain it in other terms: A quantum dot is an artificial molecule. Standard semiconductors of the type used to create light behave differently when they are very, very tiny. That is because they then fall under the rules of quantum mechanics instead of classical physics. Large masses of stuff behave in a different way than individual bits of it.

In the case of quantum dots, by creating individual light-emitting molecules, the emission can be held at a single wavelength of light, and therefore all of the energy that you put into it comes out in the way you want it, making a bunch of quantum dots more efficient than a similar amount of bulk material. Also, each dot can be used individually as a light sources for optical transistors on a chip to create optical computers and cool stuff like that.

One of the ways to make quantum dots involves creating a layer of semiconductor on a substrate, like for a regular microchip. The way the process is different is that they use materials with different shrink rates, so that the top layer shrinks faster, causing the semiconductor to crack up and coalesce into individual molecule-sized bits.

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