C. Coupeau

Atomic force microscopy of in situ deformed nickel thin films

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 s i and the adhesion energy G between the film and substrate. q 1999 Elsevier Science S.A. All rights reserved.

Atomic force microscopy study of the morphological shape of thin film buckling

Thin films elaborated by sputtering methods often develop very high internal compressive stresses and are then susceptible to delamination and buckling. The various buckling patterns have been investigated by atomic force microscopy and are reviewed and discussed in the frame of elastic theory.

Worm-like delamination patterns of thin stainless steel films on polycarbonate substrates

Abstract Thin films of type 304L stainless steel on polycarbonate substrates have been deformed under uniaxial compression up to 1.9% to generate straight-sided wrinkles perpendicular to the compression axis. On release of the external stress, these buckling patterns evolve to telephone cords. The elastic energy variation associated with the buckling of the film, after the decohesion of the film from the substrate, has been determined and the different stages of delamination discussed.

Characterization of thin film elastic properties using X-ray diffraction and mechanical methods: application to polycrystalline stainless steel

The Youngs modulus and Poissons ratio of reduced thickness layers are generally unknown whereas simulation of mechanical behavior of thin film/substrate systems or stress determination by X-ray diffraction cannot be done in an accurate way without the knowledge of these values. In this paper, we present three types of experiments which are used in our laboratory for determining elastic constants in polycrystalline thin films elaborated by ion beam sputtering: A vibrating reed device, X-ray tensile testing and AFM buckling geometry analysis. Results obtained for metallic 304L stainless steel thin films are given.

Delamination of metal thin films on polymer substrates: From straight-sided blisters to varicose structures

Abstract Uniaxial compression has been generated in thin films of nickel deposited on a polycarbonate substrate. Atomic force microscopy investigations have emphasized the formation of straight-sided blisters which have been observed to evolve to periodic distributions of droplets. The energy variation associated with the formation of the droplets has been computed and the morphological change of the film has been discussed as a function of the residual stress.

Statistical analysis of in-situ slip lines by atomic force microscopy observations

Abstract Atomic force microscopy images have been performed in situ during deformation of MC2 Nickel-based alloy phase γ and LiF single crystals at room temperature. The appearance of slip lines was continuously observed. We propose methods to determine the statistic average step height and terrace width of this pattern. For the two crystals, hierarchical organization of slip lines is deduced.

Atomic force microscopy investigation of buckling patterns of nickel thin films on polycarbonate substrates

The evolution of buckling patterns of nickel thin films have been studied in situ by atomic force microscopy during cyclic tests composed of uniaxial compression followed by release of the external applied stress. After the first strain cycling, buckling structures evolve from straight-sided wrinkles to varicose patterns characterized by a debuckling of some parts of the film. Further cycling tests reveal that rebonding of the film on its substrate does not occur once decohesion has taken place.

ATOMIC FORCE MICROSCOPY OF DISLOCATION LOCKING EFFECTS AT GOLD FILM LiF SUBSTRATE INTERFACE

Laboratoire de Me´tallurgie Physique, UMR 6630, SP2MI Bld P. & M. Curie 86962, FuturoscopeCedex, France(Received March 14, 2000)(Accepted in revised form March 21, 2000)Keywords: Dislocations; Coating; Atomic force microscopy; Plastic; Slip linesIntroductionThin films and coatings are commonly used either to protect bulk materials subjected to an aggressiveenvironment (thermal, tribologic, optical), or to improve and confer particular properties to a substrate(refractory, hardness, corrosion). For instance, recent works have shown that thin films stronglyimprove the fatigue life of 316L stainless steel crystal [1,2].The capability of dislocations to shear or not a thin film has been extensively studied as a functionof the nature of the interface [3,4], but only few experimental observations on iron on MgO substrates[5] and on GaAs/GaAlAs heterostructure [6] have been carried out to characterise the efficiency of suchcomposite materials.The aim of this paper is to study quantitatively the influence of gold thin films on the emergenceprocess of dislocations nucleated in LiF substrates. Plastic deformation in pure LiF single crystals ishomogeneous with slip line structure of very low step height [7]. The topographical changes of thecoated surface under a compression of the substrate have been followed by an atomic force microscope(AFM) and compared to the reference structure. The total number of dislocations emerging at the coatedand uncoated surfaces has been determined as a function of strain, to investigate the locking phenom-enon of dislocations at the film/substrate interface and to characterise the efficiency of such protectivethin films.Experimental ProcedureGold thin films were deposited on LiF cleaved surfaces using an argon ion beam sputtering techniquedescribed elsewhere [8]. The deposition conditions are as follows: the starting pressure is 2.10

In-situ atomic force microscopy and transmission electron microscopy observations of the deformation of MC2 nickel-based superalloy γ phase

Pile-up interactions in the γ phase of MC2 nickel-based superalloy have been studied by both atomic force microscopy and transmission electron microscopy. The examinations of surface slip-line patterns and the fine structure of dislocation pile-ups enable a minimum distance between pile-up slip planes to be derived. The behaviour of two pile-ups gliding in opposite directions has been simulated. The critical applied stress required for these pile-ups to cross over in the bulk crystal has been determined in good agreement with the microscopy observations.