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Elektronische und geometrische Struktur von WS2 - und MoS2 - Clustern: Nanoplättchen und anorganische Fullerene

Subject Area Experimental Condensed Matter Physics
Term from 2005 to 2016
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 17526049
 
Final Report Year 2015

Final Report Abstract

Nanomatter has new properties. The most famous example is C60, a nano-soccerball consisting of 60 carbon atoms. The little sphere is highly stable and can be used as a building block for new materials with new physical and chemical properties. The new material is called "fullerite". It is pure carbon, but has properties very much different from the one of diamond and graphite, the two common forms of carbon. There might be many more materials, from which stable nanospheres can be synthesized, but so far carbon is the only material. The reason is the special structure of graphite. Graphite is a "layered structure" and consists of atom-thin sheets. A small particle of such a sheet is a nano-flake. The atoms at the edges have dangling bonds and this costs energy. To minimize the number of atoms at the edges, the flake bends into a nanosphere with no edge. Thus, the deeper reason why carbon forms nanospheres is the layered structure of bulk carbon. In the project nanoparticles of other layered materials have been synthesized. The hope was that more highly stable nanospheres are found, from which many new materials with advantageous properties can be made. Molybdenum sulfide has a layered structure similar to graphite. Similar to graphite, it is a lubricant, because the interaction between the sheets is week and they can easily be shifted against each other. As a result, graphite (soot) and molybdenum sulfide are very soft materials. Unfortunately, it turned out that nanoparticles of molybdenum sulfide have no fullerene-like structure. They are flat. There might be a simple reason for that. The energy-costly dangling bonds at the edges of the Molybdenum flakes are saturated by additional sulfur atoms. If it would be possible to control the amount of sulfur extremely accurately, this "passivation" of the edges could be avoided. However, in praxis it is almost impossible. There are always some sulfur atoms around and then the formation of a nano-sphere costs more energy than the formation of the flat flake with additional sulfur stabilizing its edges. So far, carbon is the only known material forming nanosoccerballs. Besides geometric and physical properties nano-matter also might have advantageous chemical properties. One important property is the ability to oxidize other materials. Toxic or even carcinogenic chemicals can be converted into harmless substances by oxidation. Oxidation does not necessarily mean the reaction with oxygen, i.e. in a burning process. In chemistry oxidation means the removal of electrons from the oxidized molecule. An oxidizer has a high affinity to electrons and tears out electrons from the toxic molecule. Some nano-objects have an extraordinary high electron affinity and might be better oxidizers than oxygen. During the research project, such a superoxidizer has been discovered by chance. Most oxidizers such as oxygen belong to the group of halogens. Improved oxidizers are the superhalogenes and they usually are molecules consisting of several halogenes. The newly discovered superoxydizer has been baptized a "hyperhalogen", because it is a molecule consisting of several superhalogenes. Only a very small amount of these new species has been synthesized so far, but it was enough to measure its extremely high electron affinity. If a method is invented to produce larger amounts of these new compounds at low cost, the "hyperhalogenes" might be important for several processes in chemical industry.

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