ABSTRACT
Materials at the nanoscale have been the subject of intensive study owing to their unusual electrical, magnetic, and optical properties [1-9]. e combination of new synthesis techniques o ers unprecedented opportunities to tailor systems without resort to changing their chemical makeup. In particular, the physical properties of the material can be modi ed by con nement. If we con ne a material in three, two, or one dimensions, we create a nanocrystal, a nanowire, or a nano lm, respectively. Such con ned systems o en possess dramatically di erent properties than their macroscopic counterparts. As an example, consider the optical properties of the semiconductor cadmium selenide. By creating nanocrystals of di erent sizes, typically ∼5 nm in diameter, the entire optical spectrum can be spanned. Likewise, silicon can be changed from an optically inactive material at the macroscopic scale to an optically active nanocrystal.
