Response Measurement Accuracy for Off-Resonance Excitation in Atomic Force Microscopy

Dynamic atomic force microscopy (AFM) is an invaluable tool for characterizing and interacting with micro- and nano-scale systems. Standard measurement methods use a laser beam and a segmented photodiode to monitor the probe’s response. The diode reading is proportional to the slope of the probe and the displacement is obtained indirectly. As most operation methods use excitation around the fundamental frequency, calibration methods for determining the conversion factor to calculate the probe’s displacement are strongly inspired by the first vibrational mode shape. Within this paper, the results of an analytical study to predict measurement accuracy under non-standard excitation conditions with this calibration are presented. The influence of the excitation frequency, damping level, and laser spot location on this accuracy is investigated. The measurement accuracy for excitation at 2.5 times the fundamental frequency is of particular interest to the authors. Based upon the results, the use of a correction factor or a frequency-specific calibration is recommended.