A FASCINATING NEW FIELD IN COLLOID SCIENCE - SMALL LIGAND-STABILIZED METAL-CLUSTERS AND POSSIBLE APPLICATION IN MICROELECTRONICS .1. STATE-OF-THE-ART

Small metal clusters, like Au55(PPh3)12Cl6, which fall in the size regime of 1-2 nm are colloidal nanoparticles with quantum properties in the transitional range between metals and semiconductors. These chemically tailored quantum dots show regarding the Quantum Size Effect (QSE) a level splitting between 20 and 100 meV, increasing from small particle sizes to the molecular state. The organic ligand shell surrounding the cluster acts like a dielectric ''spacer'' generating capacitances between neighboring clusters down to 10(-18) F. Therefore, charging effects superposed by level spacing effects can be observed. The ligand-stabilized colloidal quantum dots in condensed state can be described as a novel kind of artificial solid with extremely narrow mini or hopping bands depending on the chemically adjustable thickness of the ligand shell and its properties. Since its discovery, the Single Electron Tunneling (SET) effect has been recognized to be the fundamental concept for ultimate miniaturization in microelectronics. The controlled transport of charge carriers in arrangements of ligand-stabilized clusters has been observed already at room temperature through Impedance Spectroscopy (IS) and Scanning Tunneling Spectroscopy (STS). This reveals future directions with new concepts for the realization of simple devices for Single Electron Logic (SEL). Part I presents the fundamental aspects of small ligand-stabilized metal clusters as well as their physical properties, emphasizing their electronic and optical properties with respect to dielectric response at ambient temperatures.