Metal Clusters and Colloids

The properties of solid matter are determined by the “infinite” three-dimensional arrangement of its building blocks. These can consist of single ions, covalently organized units such as “SiO2” in quartz, or individual molecules in a molecular lattice, e.g., I2 in iodine crystals. What does “infinite” mean? How small can a piece of a distinct material become and still be the same material? The optical properties of quartz, the brilliance of diamond, the conductivity of graphite, or the melting point of gold will all change at some point if the number of specific building blocks becomes small enough. In the last decade there has been important progress towards answering these questions and it has been shown that the nature of materials can dramatically change if the borderline of what we call the “solid state” is reached. Nanometer-sized “cutouts” of various solid materials have been made and their properties studied. In all cases the chemical and physical properties deviate considerably from those of the bulk: the rules of classical mechanics are replaced by those of quantum mechanics. A few examples are presented to elucidate this. Fullerenes as well as carbon nanotubes are considered as nature’s fascinating answer to what happens if the size of an element is reduced to the