Nanocrystalline materials: a way to solids with tunable electronic structures and properties?

It is the purpose of this paper to point out that nanometer-sized structures may open the way to modify the electronic structure (e.g. the charge carrier density) and the related properties of solids. The modification may be achieved by means of externally applied electric fields or by internal electric fields. These fields affect the charge carrier density in a surface region which in the case of nanostructured solids may attain a substantial fraction of the total volume. Tuning the charge carrier density by means of an externally applied electric field may be realized, for example, by immersing a chain (or a network of chains) of interconnected, nanometer-sized particles into an electrolyte. Similarly, the electronic structure of nanocomposites is proposed to deviate from the one of coarse-grained materials if a large volume fraction of the material consists of electronically modified regions at interphase boundaries. Experimental observations supporting these ideas are discussed.