Small scale contact behavior in metallic films: Indentation and adhesion experimental studies

In this study, various experimental techniques were used to investigate the contact behavior of metallic films at micron- to nano-levels. Specifically, multi-scale indentation experiments were performed in face centered cubic single crystal materials with different orientation. After the detail description of the experiments, the related experimental phenomena such as dislocation bursts and pile-up profiles were discussed. The observed indentation size effects were analyzed within a strain gradient plasticity framework, and the microstructure material length scales were extrapolated for the materials tested. The indentation size effect between the micron- and nano-scales is well characterized by a bi-linear indentation behavior, which is attributed to a transition from source-limited behavior at the nano/sub-micron scales to established dislocation substructures at the micron-scale.; Adhesion energy measurements were performed for the nano- and micron-scale contacts of Au microswitch. For micron-scale contact, the detachment length is measured for adhered Au microcantilever structure, energy balance model is used to calculate the adhesion energy for Au-Au interface. For nano-scale contact, AFM pull-off force measurements were performed between the Au-coated AFM tips and the Au-coated silicon substrates. These were used to simulate a single asperity contact. The modified Maugis-Dugdale model was adopted to compute the adhesion energy. The results show that the adhesion energies measured at the two scales are comparable, after correcting for asperity shielding estimated from fracture mechanics models.; Finally, as an industrial application of the experimental techniques, the AFM pull-off force measurement techniques were used to quantify the adhesion force between/within the layers of drug eluting stent. Shear assay experiments were used to investigate the adhesion strength of endothelial cells cultured on the same bio-compatible materials used in the drug-eluting-stent device. An experimental framework was presented using AFM pull-off force measurements to rank the interfacial robustness of the layers in the drug eluting stent.