Simulations of the Frequency Modulated - Atomic Force Microscope (FM-AFM) Nonlinear Control System

The Frequency Modulated Atomic Force Microscope (FM-AFM) is a powerful tool to perform surface investigation with true atomic resolution. The control system of the FM-AFM must keep constant both the frequency and amplitude of oscillation of the microcantilever during the scanning process of the sample. However, tip and sample interaction forces cause modulations in the microcantilever motion. A Phase-Locked Loop (PLL) is used as a demodulator and to generate feedback signal to the FM-AFM control system. The PLL performance is vital to the FM-AFM performace since the image information is in the modulated microcantilever motion. Nevertheless, little attention is drawn to PLL performance in the FM-AFM literature. Here, the FM-AFM control system is simulated, comparing the performance for different PLL designs.