RESUMEN
This paper reports the experimental, analytical, and numerical study of resistive-nanoindentation tests performed on gold samples (bulk and thin film). First, the relevant contributions to electrical contact resistance are discussed and analytically described. A brief comparison of tests performed on gold and on natively oxidized metals highlights the high reproducibility and the voltage-independence of experiments on gold (thanks to its oxide-free surface). Then, the evolution of contact resistance during nanoindentation is fully explained in terms of electronic transport regimes: starting from tunneling, electronic transport is then driven by ballistic conduction before ending with pure diffusive conduction. The corresponding analytical expressions, as well as their validity domains, are determined and compared with experimental data, showing excellent agreement. From there, focus is made on the diffusive regime. Resistive-nanoindentation outputs are fully described by analytical and finite-element modeling. The developed numerical framework allows a better understanding of the main parameters: it first assesses the technique capabilities (validity domains, sensitivity to tip defect, sensitivity to rheology, effect of an oxide layer, and so on), but it also validates the different assumptions made on current line distribution. Finally, it is shown that a simple calibration procedure allows a well-resolved monitoring of the contact area during resistive-nanoindentation performed on samples with complex rheologies (ductile thin film on an elastic substrate). Comparison to analytical and numerical approaches highlights the strength of resistive-nanoindentation for continuous area monitoring.
RESUMEN
A combinatorial approach has served as a high-throughput strategy to identify compositional windows with optimized desired properties. Here, ZrCuAg thin-film metallic glasses were deposited by DC magnetron sputtering. For the purpose of using these coatings as biomedical surfaces, their durability in terms of mechanical and physicochemical properties as well as antibacterial properties were characterized. The effect of the chemical composition of thin films was studied. In particular, two key parameters were highlighted: the atomic ratio of Zr/Cu (with three values of 65/35, 50/50, and 35/65) and the silver content (from 1 to 16 at. %). All thin films are XRD amorphous and exhibit a typical veinlike pattern, which is characteristic of metallic glasses. They also show a dense and smooth surface and a hydrophobic behavior. Mechanical properties are found to be deeply influenced by the Zr/Cu ratio and the atomic structure. Although a low Zr/Cu ratio and/or a high silver content is detrimental to corrosion behavior, it favors the bactericidal effect of thin films. For all Zr/Cu ratios, ZrCuAg thin-film metallic glasses with silver contents higher than 12 at % are fully bactericidal. For lower silver contents, the bactericidal effect progressively decreases, which paves the way for a biostatic behavior of these surfaces.
