Cluster als Bausteine neuer Nanomaterialien : Superhalogene und anorganische Fullerene

Abstract

The present work describes the development of an enhanced experimental setup for photoelectron spectroscopy on size selected clusters.Motivated by the idea to identify possible building blocks for new nano materials or compounds we investigated four different cluster systems.1.) The reaction of gold clusters with molecular and atomic oxygen is the first part of the present work. In contrast to former studies we found a surprisingly high number of different gold-oxygen clusters, which have been characterized by photoelectron spectroscopy. These results are quite interesting in the light of possible catalytic properties of these particle e.g. the carbon monoxide oxidation.2.) The expansion of this investigation to larger particles using a boron nitride cube inside the cluster source led to the interesting discovery of gold borate compounds. Species with an exceptionally high electron affinity were identified, the electron affinities were even above the one of chlorine. Corresponding theoretical calculations on the geometry and electronic structure of these clusters indicate a new class of extremely electronegative particles so called superhalogens. The term hyperhalogen was used to describe the electron affinity of Au(BO2)2 that exceeded 5.5eV. The discovery of these new compounds could allow the synthesis of salt-like cluster materials with remarkable properties.3.) Aluminum gold clusters were also investigated. Some geometrically and electronically magic clusters were identified.4.) The starting point for the last part of this work was the question for thermodynamically stable clusters formed from graphite-like layered materials MoS2 and WS2. Therefore particles with masses above 15000u were studied. The bimodal mass distribution as well as theoretical calculations suggests the presence of inorganic fullerenes. However, a consistent correlation of the mass spectra and corresponding TEM images was not possible. The interesting question if the identified clusters are the predicted true inorganic fullerenes could not be ultimately clarified.Two main improvements characterize the used experimental setup. First an increased mass resolution and a related expansion of the measurement range up to cluster masses of more than 50000u. Secondly a photon energy increase to 7.9eV without a pronounced decline of the signal-to-noise ratio. The combination of both improvements led to a unique experimental setup for extended analysis of the electronic structure of large clusters.