Nanopartikel aus der Gasphase : Depositionsmechanismen und strukturierte Anordnung auf glatten Substratoberflächen
The increasing knowledge about the properties of nanostructured materials is a source of ideas for the improvement of existing and the development of new electronic or opto-electronic devices. One approach is the implementation of nanoparticles as building blocks. Among other synthesis routes, different kinds of gas phase synthesis have been developed which open the possibility to produce nanoparticles with defined properties like chemical composition, crystal structure, shape and size distribution. In order to make use of these properties, the particles have to be transferred from the three dimensional distribution in the gas phase to a two dimensional arrangement on a carrier material, for instance a substrate surface. The first goal of the investiagtion is to describe the microscopic aspects of the deposition process of nanoparticles in the size range between 5 nm and 100 nm at ambient pressure and temperature, under the condition that the particle density (which is the number of particles per unit area)on the substrate surface is below one monolayer. For this purpose, a computer simulation program has been developed, which calculates the particle trajectory that results from the balance of forces on the particle. It takes into account the interaction of incoming individual particles with the substrate surface as well as the interactions with already deposited particles. A parameter study has been carried out in order to point out how the particle arrangement on the substrate depends on the deposition parameters. The results obtained by the computer simulations are compared with experimental results. The parameters varied were the particle diameter, the particle charge, the number of particles per unit area, the substrate properties and the electric field strength. The second goal of the investigation is the structured deposition of nanoparticles from the gas on oxidized silicon substrates by direct deposition from the gas phase of an aerosol. The particles are attracted onto charge patterns created on the plane surface by contact charging. The basic principle of which is that charges cross the interface between an insulator and a metal brought into contact. After the metal is removed, charges retain on the insulator. The charge patterns can either be transferred by a sharp metal tip which is allowed to slide over the substrate surface or by a metal stamp which is pressed on the substrate surface. In the second case even complex structures may be transferred. The resolution of the patterns obtained with these methods is in the order of below 100 nm.