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 reg ime of 1-2 nm are colloidal nanoparticles with quantum properties in t he transitional range between metals and semiconductors. These chemica lly tailored quantum dots show regarding the Quantum Size Effect (QSE) a level splitting between 20 and 100 meV, increasing from small parti cle 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 e ffects 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 hop ping bands depending on the chemically adjustable thickness of the lig and shell and its properties. Since its discovery, the Single Electron Tunneling (SET) effect has been recognized to be the fundamental conc ept for ultimate miniaturization in microelectronics. The controlled t ransport of charge carriers in arrangements of ligand-stabilized clust ers has been observed already at room temperature through Impedance Sp ectroscopy (IS) and Scanning Tunneling Spectroscopy (STS). This reveal s future directions with new concepts for the realization of simple de vices for Single Electron Logic (SEL). Part I presents the fundamental aspects of small ligand-stabilized metal clusters as well as their ph ysical properties, emphasizing their electronic and optical properties with respect to dielectric response at ambient temperatures.