Design and control of atomic force microscopes

Models for two atomic force microscope (AFM) designs were presented, namely, cantilever-on-scanner and sample-on-scanner design. It was found that coupling between scanner's bending and extension motion is present in both designs, making the scanner bending mode observable from the output. As a result, the ultimate feedback bandwidth is limited by the lower frequency bending mode in contrast to being ideally by the extension mode. Simulation and experimental data provided insight into pole-zero flipping and changes in the system dynamics as a function of force set point and input amplitude. Closed loop performance under integral and PID control were compared. It was found that PID control offers lower bandwidth over integral control if high-frequency roll-off and step response overshoot constraints were to be met. In addition, integral controller has a single gain compared 3 for PID, which makes it easier for parameter tuning by AFM users.