Dielectric properties and potential applications of nanocrystal networks

In 1930, Pfund produced nanocrystal networks ("blacks") by evaporating bismuth in an imperfect vacuum where the particles nucleate from supercooled vapor. Modern nanotechnology revived interest in a refined version of Pfund's technique using noble background gas to yield nanoparticles under high-purity conditions. Their exotic properties (e.g. "xerofluids", "quantum alloys", "skeleton metals", "fractal structures", "soft matter") make nanocrystal networks promising candidates for fundamental research and technical applications. Their easy-to-change low filling factor f allows us to control dielectric and thermal properties in a wide range. The quantum dot contacts between neighboring particles determine the properties of metal nanocrystal networks as was demonstrated by comparing the dielectric function epsilon Of percolating structures with that of matrix-isolated particles. The dependence of epsilon on f, measuring frequency omega, and temperature T reveals networks as an intermediate state between metal and non-metal ("Anderson dielectric"). In an in situ setup combining the noble-gas technique with tunneling microscopy, the quantum contacts of single particles deposited and manipulated on a smooth surface and their current/voltage characteristics were investigated. Nanocrystal networks, especially mixtures of chemically different components or gradient materials, may turn out to be absorbers, sensors, detectors, or converters, designed for a variety of specific purposes with high sensitivity and flexibility.