  Strain engineering is the art of inducing controlled lattice distortions in a
material to modify specific physicochemical properties. Strain engineering is
applied for basic fundamental studies of physics and chemistry of solids but
also for device fabrication through the development of materials with new
functionalities. Thin films are one of the most important tools for strain
engineering. Thin films can in fact develop large strain due to the crystalline
constrains at the interface with the substrate and/or as the result of specific
morphological features that can be selected by an appropriate tuning of the
deposition parameters. Within this context, the in situ measurement of the
substrate curvature is a powerful diagnostic tool allowing a real time
monitoring of the stress state of the growing film. This manuscript reviews a
few recent applications of this technique and presents new measurements that
point out the great potentials of the substrate curvature measurement in strain
engineering. Our study also shows how, due to the high sensitivity of the
technique, the correct interpretation of the results can be in certain cases
not trivial and require complementary characterizations and an accurate
knowledge of the physicochemical properties of the materials under
investigation.
