When the size or dimension of a material is continuously reduced from a large or macroscopic size, such as a meter or a centimetre, to a very small size, the properties remain the same at first, and then small changes start to occur, until finally when the size drops below 100 nm, where dramatic changes in properties can occur. If one dimension is reduced to the nanorange while the other two dimensions remain large, then we get a structure called a quantum well. If two dimensions are so reduced and one remains large, the resulting structure is referred to as a quantum wire. The extreme case where all the three dimensions reach the low nanometer range, the resulting structure is termed to as a quantum dot. These structures are illustrated in the diagrams below:
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Related Resource: Quantum Physics For Dummies
