Prof. Peter Schaaf
Group of Materials for Electrical Engineering and Electronics
Phone: +49 3677 69-3611
Self-advancing reactions in metallic multilayers, especially those based on Ni/Al, have been extensively investigated in recent years. The focus has been on nanofoils and sputtered layer systems. The exploitation of these reactions for joining electronic chips or micromechanical components (MEMS) offers the advantage of a locally limited heat load. Unfortunately, the chain reaction triggered by local ignition is difficult to control and the reaction products often exhibit high stresses. It is known that nanoscale radii of curvature influence the surface and interfacial energy. This can be exploited to specifically influence the free enthalpy of a multilayer sequence and thus to influence acceleration and speed of the reaction propagation. An additional factor is the changed multilayer morphology due to the nanostructure, which also influences the progress of the reaction. Nanostructures of silicon and silicon oxide are produced here with a variety of geometries. Both materials differ in their thermal conductivity and are therefore suitable for the investigation of different scenarios. The proposed project aims at identifying essential features of nanostructured surfaces that influence the progression of chain raclination and the resulting stress in the resulting alloy and compound. The geometry of nanostructured samples will be varied systematically on the basis of an experimental design. The quantitative determination of essential geometry parameters, e.g. tip radius, angle of inclination, height and structure density provides a guideline for the design of the multi-layer architecture, which takes into account both the surface shape and the layer structure. Their influence on the phase transformation is investigated by tempering.