Ferroelastic twin walls for nanotechnological applications

Ferroelastic twin structures may be tailored and used for chemical reaction s in the confined space of twin walls. As an example, superconducting twin walls are described in an isolating matrix of WO3. The crucial role of the wall energy and the wall thickness for compositional changes are discussed. Wall patterns include the bending of twin walls and the formation of needl e domains as steps in the construction of hierarchical wall structures. Emp hasis is given to the structural features at the intersection of twin walls with the sample surface.