With respect to this theme, the key word for describing the area in which the group's combined skills in physical chemistry and mechanics are ideally expressed is "adherence". The SIR group has built a solid reputation for determining the adherence energy of thin films deposited on various solid substrates or generated by their conversion. The aim is to determine adherence energy (energy of interface crack propagation) as quantitatively as possible by developing or improving appropriate micromechanical tests. The SIR group has established skills in metal-oxide adherence, directly connected with its research on oxidation, and in the durability of ceramic-metal systems (BaTiO3 condensers, thesis jointly supervised with Taipeh) or microsystems for use in electronics. Our participation in various groups or networks in the field was stepped up in 2007 (FLAMME project - FiLm Adhesion Multicouche Mince Environnement - FIRST network, metal-metal interface project: Rhône-Alpes MACODEV Cluster).
Of major interest here is the development of photo-electrochemical imaging owing to its extreme sensitivity to loss of cohesion at the interface. It is thus possible to produce genuine maps of contact loss at the interface between a substrate and a thin film, which are difficult to obtain using other techniques, except infrared thermography, which is equally effective but spatially less sensitive.
Adhesion measurements : Blister testing of a silver film on a BaTiO3 substrate a) Optical image b) phase image c) iso-altitude mapping d) 3D reconstruction
Finally, it is worth noting the increased interest in materials for the medical profession, where interfaces once again play a central role given that, in this type of application, it is often necessary to apply coatings (for reasons of biocompatibility or wear). In this field, our team is collaborating with Lausanne university hospital to study the adherence of surgical glues. This collaboration is on the point of culminating in an ambitious project involving other academic partners as well as manufacturers of medical equipment.
From the modelling standpoint, the thesis by Miss Kozlova has enabled us to test cohesive zone models. The method is not new, but is well suited to modelling interfaces and mastering it will enable us in particular to perform more detailed analyses of systems in which plasticity plays a significant role in the strength of the assembly, as is the case for example with copper/alumina interfaces.