Evaluation of mechanical properties of porous OSG films by PFQNM AFM and benchmarking with traditional instrumentation

Characterization of mechanical properties of thin porous films with nanoscale resolution remains a challenge for instrumentation science. In this work, atomic force microscopy (AFM) in the PeakForce quantitative nanomechanical mapping (PFQNM) mode is used for Young's modulus measurements of porous organosilicate glass films. The test samples were prepared by sol-gel techniques using silicon alkoxide and methyl-modified silicon alkoxide to prepare films with different CH3/Si ratios. The film porosity was engineered by using a Brij 30 template and the evaporation-induced self-assembly technique. The chemical composition, pore structure, and modification during air storage and thermal annealing were studied using FTIR spectroscopy and ellipsometric porosimetry (EP). Since PFQNM AFM was first used for evaluation of Young's modulus of thin porous films, the obtained results are benchmarked using nanoindentation (NI), surface acoustic wave (SAW) spectroscopy, and EP. The results have good agreement with each other, but PFQNM and NI give slightly larger values than SAW and EP. The difference is in agreement with previously reported data and reflects the different physical meaning of the obtained values. It is shown that the presence of physically adsorbed water strongly influences the results generated by PFQNM AFM, and therefore, reliable water removal from the studied materials is necessary.