Dissertations

Magnetic nanoparticles (MNP) have attracted considerable interest in many fields of research and applied science due to their impressive properties. In the past, especially biomedical problems have promoted the development of MNPs. For technical applications e.g. wastewater treatment and absorption of electromagnetic waves, the existing synthesis approaches are too expensive and/or the producible quantities are too low. In this work we present a method for simple preparation of size-controlled magnetic iron oxide nanoparticles by electroerosion dispersion (EED) of carbon steel in water. We describe the synthesis method, the laboratory installation and discuss the structural, chemical and electromagnetic properties of the synthetized EED powders as well as their applicability for microwave absorption compared to other available ferrite powders.

The fracture behavior of multilayers in the nanometer thickness range has attracted an increased attention due to microelectronics and high-speed technologies. In this work, Al/Si3N4 multilayers fabricated by magnetron sputtering on the silicon substrate were subjected to three-point bend testing. It was investigated that the fracture behavior of Al/Si3N4 multilayers with different individual layer thickness (50, 100, 250 nm) but with the same total thickness (1.0 [my]m). There is a significant layer thickness effect on the fracture behavior of the whole multilayer-substrate system: when the individual layer thickness is large (250 nm), the failure of the whole system was dominated by the fracture of the substrate, while the failure of the whole system was dominated by the fracture of the multilayer with smaller individual layer thickness (50 nm). This effect is clearly obvious, although the total thickness of the multilayer is very small compared with that of the substrate. As the individual layer thickness decreased from 250 nm to 50 nm, the fracture strain on the Al/Si3N4 multilayer decreased from 0.073% to 0.026%.