STUDIES ON ATOM CLUSTERS BY ULTRA-HIGH VOLTAGE ELECTRON-MICROSCOPY

When the number of constitutive atoms decreases to 10(3) approximately 10(5), depending on the bonding mode and binding strength, the materials show different behavior from bulk ones as if they are new materials. These ultra-fine blocks are named ''atom clusters'' whose behavior is closely related to the many body effect of constitutive atoms. Recently, an ultra-high voltage electron microscope ''micro-laboratory'' has been developed, in which the material behavior can be widely changed in-situ and the identification and characterization of materials in the atomic scale can be done. Various studies on the atom clusters have been carried out by this method. In the present report, the anomalous behavior of these atom clusters is shown from the experimental results, and is discussed in terms of the formation of hybrid orbitals of valence electrons. Furthermore, the relationship between the so called ''magic number'' of micro-clusters and ''magic size'' of atom clusters is discussed.