ABSTRACT
Throughout most of the twentieth century, the size of a solid has been an uninteresting parameter in the developing areas of solid-state physics and chemistry. Millimetre-thick gold wires have the same colour, conductivity and melting point as gold coins; even in state-of-the-art microelectronics, where structural features with sub-micrometre sizes have become typical, semiconductors and metals have the same behaviour as measured in their macroscopic counterparts. These facts are not surprising, as most material properties, such as conduction and colour, emerge from interactions between, at most, hundreds of unit cells, each less than a nanometre in size. Thus size is not an important factor in understanding and controlling crystalline solids unless the length of solid shrinks to the nanometre length scale. Of course, this is the relevant size range for the next generation of microelectronics, and is evidently an important length scale for many biological systems. These factors have spurred the development of the field of nanoscience, which is the study of the influence of size on the properties of solids. Innumerable studies of the properties of nanocrystalline materials have amply demonstrated that size really does matter; it can be a powerful parameter in the systematic study of bulk behaviour, as well as in the design of new materials with unique and special properties.
