Modeling and control of atomic force microscope for imaging using high order harmonic modes

This research assesses the imaging of specimen surface features using higher flexural modes associated with the oscillation of the atomic force microscope (AFM) cantilever. A computer simulation based on the Euler-Bernoulli Beam Equation is designed to measure variations in the oscillation amplitude due to variations in the specimen surface. The results are then compared to those of an experiment employing a real AFM and lock-in amplifier. Both simulation and experimental results demonstrate that examining higher modes yields more accurate information about a specimen surface property---particularly elasticity and topography---which is consistent with previous studies. More importantly, this research achieves improved sensitivity to surface information in lower modes when exciting the cantilever at a higher resonance frequency. The latter finding eliminates the need to extract and enhance the amplitude of higher modes, which are magnitudes smaller and consequently more difficult to measure and analyze.