Closed-buckling structures have been opened by a focus ion beam process. Atomic force microscopy investigations prior to and after the opening have evidenced a significant increase of the maximum deflection of the buckling structures. These experimental results have been discussed in the framework of the Foppl-Von Karman theory of thin plates and are interpreted in terms of the existence of vacuum between the delaminated film and the substrate. The critical stress for buckling to occur is consequently modified taking into account this pressure mismatch. (C) 2010 Elsevier B.V. All rights reserved.