The mechanical behaviour of thin metal films on substrate under stress and particularly the analysis of the first stage of buckling have been characterized. Nickel/polycarbonate samples have been studied using a specific atomic force microscopy which allows the observation in situ of the sample surface during deformation. Straight wrinkle-like shapes are induced in the Ni thin film above a critical stress perpendicular to the compression axis. Undulations of very low amplitude appear also on these debonded regions. The dependence on stress of the shape of the straight wrinkles and of the undulations is discussed. It is shown that theses experiments may be thought of as an alternative method to estimate the localised internal stress sigma(i) and the adhesion energy Gamma between the film and substrate.