**Definition of quantum dots**: If all the three dimensions of a material are reduced to nano range, then the nanomaterial or the structure is called the quantum dot.

**Preparation of quantum dots:**

Quantum dots are in between in size to that of single atoms and solids. The size of quantum dot should be in the range of 4nm < L < 20 nm, where L is the length of a quantum dot. The quantum dots should be uniform in shape and size. These dots include the self forming nano sized semi conductor clusters. These are formed by direct method and by imposing geometrical restriction on the electrons in two additional directionals on quantum wells. These dots are made from a two dimensional hetero structure by using colloidal synthesis or an electron etching method. Quantum dots of 10nm can be prepared by lithography.

A quantum dot is a zero dimensional quantum confinement, therefore there are no free moving carriers in quantum dots. It may contain thousands of atoms, therefore it contain a number of allowed states that are separate from one another and can be counted. Therefore the energy level of a quantum dot in nanotechnology is intermediate to a single atom and a solid and it contains discrete energy levels.

**Use or applications of quantum dots:**

- Quantum dots are used in the preparation of quantum dot lasers.
- Quantum dots can be used as the building blocks of quantum computers because they can emit photons one by one on demand.
- Quantum dots in nanotechnology are used in fabrication of infra red detectors.

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