This thesis reports the investigation of thin ferroelectric films of lead zirconium titanate (Pb(Zr048Ti052)O3 : PZT) by means of scanning force microscopy under additionally applied mechanical stress. The film thickness ranged from 100 nm to 120 nm. The rst part of this work describes the set-up of a homemade atomic force microscope which is able to perform contact mode as well as non-contact mode measurements. A bending stage was available for stress creation. In the second part, local ferroelectric hysteresis loops are reported which were obtained for dierent tensile stresses using piezoresponse force microscopy. The analyzed coercive fields reveal an increase with rising tensile stress which is explained by the occurrence of ferroelastoelectric switching and changes in the domain structure. Furthermore, the variation of the coercive fields between dissimilar grains was studied. By changing the cantilever coating from platinum to gold, the infuence of the top-electrode material was investigated. A displacement of approximately 50 kV/cm in positive direction along the electric-field axis is predicted for the hysteresis curves assuming a Schottky contact between electrode and PZT, and could be partly confirmed.