Near-field scanning optical microscopy SECM

Adapted from the technology implemented in scanning near field optical microscopy, SECM with shear-force detection involves vibrating the SECM tip with a piezoelectric acmator and recording variations in resonance frequency when the tip is within a few hundred nanometers from the sample surface [124,125]. This is a fast method when operated in real time during the scan, but it is tricky to implement in practice. The tip must be long and narrow to be appropriately flexible but, more importantly, the control loop parameters need to be frequently adjusted as the resonance and shear force properties vary with the tip dimensions, solution viscosity, and sometimes with the elasticity of the sample surface. Moreover, the parameters need to be readjusted if the tip is removed for polishing. 

---