Effects of the substrate on the determination of hardness of thin films by the nanoscratch and nanoindentation techniques: A comparative study for the cases of soft film on hard substrate and hard film on soft substrate.
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ABSTRACTHardness values of Au/Fused Quartz and SiO2/Al systems, which correspond to the cases of soft film on hard substrate and hard film on soft substrate, were measured using both the nanoindentation and nanoscratch techniques. The effect of substrate interaction on the measurement of hardness using the nanoscratch technique is found to be much less pronounced compared to that of the nanoindentation technique. Such reduction in substrate effect is attributed to the features used in the nanoscratch analysis: (a) direct imaging of residual profile allows for the effect of pile-up/sink-in to be considered, (b) lower normal loads applied as compared to the nanoindentation, (c) effect of elastic recovery of the plastically deformed surfaces is included in the nanoscratch analysis, whereas the nanoindentation analysis is based solely on the load-displacement data. Moreover, experiments with residual scratch depths as shallow as 3 nm are used to estimate hardness of thin films; a promising indication for the use of such technique in the measurements of ultra-thin films.
