The characterization of telephone cord buckling of compressed thin films on substrates

The topology of the telephone cord buckling of compressed diamond-like carbon (lms (DLC) on glass substrates has been characterized with atomic force microscopy (AFM) and with the focused ion beam (FIB) imaging system. The pro(les of the several buckles have been measured by AFM to establish the symmetry of each repeat unit, revealing similarity with a circular buckle pinned at its center. By making parallel cuts through the buckle in small, de(ned locations, straight-sided buckles have been created on the identical (lms, enabling the residual stress in the (lm to be determined from the pro(le. It has been shown that the telephone cord topology can be e;ectively modeled as a series of pinned circular buckles along its length, with an unpinned circular buckle at its front. The unit segment comprises a section of a full circular buckle, pinned to the substrate at its center. The model is validated by comparing radial pro(les measured for the telephone cord with those calculated for the pinned buckle, upon using the residual stress in the (lm, determined as above. Once validated, the model has been used to determine the energy release rate and mode mixity, G( ). The results for G( ) indicate that the telephone cord con(guration is preferred when the residual stress in the DLC is large, consistent with observations that straight-sided buckles are rarely observed, and, when they occur, are generally narrower than telephone cords. Telephone cords are observed in many systems, and can be regarded as the generic morphology. Nevertheless, they exist subject to a limited set of conditions, residing within the margin between complete adherence and complete delamination, provided that the interface has a mode II toughness low