Comparing the Young's Modulus of Near-Frictionless Carbon Films Obtained From Different Methods
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ABSTRACTThe near-frictionless carbon (NFC) thin films grown at Argonne National Lab are excellent candidates for mitigating friction and wear issues in rotating and sliding MEMS applications. In this study, NFC films with Si/Si3N4 substrates were tested with static and CSM (continuous stiffness measurement) nanoindentation methods. Furthermore, the same NFC films with 900 nm thickness were fabricated into freestanding structures for the membrane deflection experiment (MDE). The Young's modulus obtained from these three methods were compared and contrasted. The E values obtained from the nanoindentation methods were nearly constant when the indent depth was less than 100 nm (1/10 of the film thickness). Both the static and CSM indentation data indicated a clear increasing trend of the Young's modulus with the indent depth until the elastic response from the substrate started to dominate the values (depth larger than 800 nm). The average modulus obtained from static and CSM nanoindentations were 49.5 4.3 GPa and 50.2 1.8 GPa for as-deposited films, respectively. The values changed to 46.9 5.4 GPa and 46.8 2.9 GPa after microfabrication processing. The larger standard deviation values indicated the affect of the increased surface roughness to the indentation tests. The E value determined from MDE tests was 35.1 2.3 GPa, which was measurably smaller those from the indentation tests. As the AFM analysis showed little/no pile-up during indentation, the difference might come from the residual stress relief, which influences the measurement, when the NFC membranes were released from the substrate.
