Shape-memory Ni-Ti films on corrugated Si substrates

Shape memory Ni-Ti films deposited on corrugated Si substrates (bimorphs) w ere studied. It is shown that the corrugation leads to the concentration of stresses in the film and results in the selection of preferred martensitic variants. The deflection of the bimorph with a corrugated film/substrate i nterface depends on the orientation of the corrugation with respect to the plane of martensitic displacement. If the corrugation is normal with respec t to this plane, its effect on martensitic transformation is maximal. The s election of martensitic variants due to the corrugation results in an aniso tropic dimensional change of the film. The maximal dimensional change occur s across the corrugation and the minimal dimensional change occurs along th e corrugation. Experimental data on the dependence of martensite induced di splacements of NiTi/Si bimorphs with corrugated and flat film/substrate int erfaces agree with this theoretical prediction.