Contact resonance force microscopy with higher-eigenmode for nanoscale viscoelasticity measurements

Nanoscale viscoelastic properties are essential for polymeric materials in their wide applications in nanotechnology. Here we proposed a contact resonance force microscopy (CRFM) method for viscoelasticity measurements by utilizing a cantilever's higher-eigenmode (n > 3). Numerical analysis results show that, compared to its lower eigenmodes, a cantilever's higher eigenmode is more sensitive to contact damping and less affected by contact stiffness variations. This tendency is then verified by nanoscale viscoelasticity mapping on a polystyrene (PS)/polymethyl methacrylate (PMMA) copolymer thin film using a compliant cantilever's different eigenmodes. Results show that higher-eigenmode CRFM can provide better imaging contrast and is thus suggested for viscoelasticity measurements.