A FASCINATING NEW FIELD IN COLLOID SCIENCE - SMALL LIGAND STABILIZED METAL-CLUSTERS AND THEIR POSSIBLE APPLICATION IN MICROELECTRONICS .2. FUTURE-DIRECTIONS

Small metal clusters, like Au-55(PPh(3))(12)Cl-6, which fall in the si ze regime of 1 - 2 nm are colloidal nanoparticles with quantum propert ies in the transitional range between metals and semiconductors. These chemically tailored quantum dots show by the Quantum Size Effect (QSE ) a level splitting between 20 and 100 meV, increasing from small part icle sizes to the molecular state. The organic ligand shell surroundin g the cluster acts like a dielectric ''spacer'' generating capacitance s between neighboring clusters down to 10(-18) F. Therefore, charging effects superposed by level spacing effects can be observed. The ligan d-stabilized colloidal quantum dots in condensed state can be describe d as a novel kind of artificial solid with extremely narrow mini or ho pping bands depending on the chemically adjustable thickness of the li gand shell and its properties. Since its discovery, the Single Electro n Tunneling (SET) effect has been recognized to be the fundamental con cept for ultimate miniaturization in microelectronics. The controlled transport of charge carriers in arrangements of ligand-stabilized clus ters has been observed already at room temperature through Impedance S pectroscopy (IS) and Scanning Tunneling Spectroscopy (STS). This revea ls future directions with new concepts for the realization of simple d evices for Single Electron Logic (SEL). Part II presents models and co nnections between microscopic and macroscopic level, regardless of whe ther there already exist suitable nanoscale metal cluster compounds, a nd is aimed at the ultimate properties for a possible application in m icroelectronics.