Deformation twins and phase interface are important planar defects and microstructures that
greatly influence the overall performance of a material system. In multi-layer thin-film heterostructures,
their effect is more manifest due to the small dimension of thin films and their influence on the
growth of multi-layer structures. This article reviews the recent progress in microstructure and defects
observed in thin film heterostructures, serving as a guideline for future research in this field. The multilayer
thin-film heterostructures studied here were grown by pulsed laser deposition technique. Microstructures
and defects were investigated by Transmission Electron Microscopy.