Development, analysis and control of a high-speed laser-free atomic force microscope

This paper presents the development and control of a laser-free atomic force microscopy (AFM) system for high-speed imaging of micro- and nanostructured materials. The setup uses a self-sensing piezoresistive microcantilever with nanometer accuracy to abolish the need for a bulky and expensive laser measurement system. A basic model for the interaction dynamics of AFM tip and sample in the high-speed open-loop imaging mode is proposed, accounting for their possible separation. The effects of microcantilever and sample stiffness and damping coefficients on the accuracy of imaging are studied through a set of frequency-domain simulations. To improve the speed of operation, a Lyapunov-based robust adaptive control law is used for the AFM XY scanning stage. It is shown that the proposed controller overcomes the frequency limits of the PID (Proportional-Integral-Derivative) controllers typically used in AFM. Finally, the paper presents a set of experiments on a standard calibration sample with 200 nm stepped topography, indicating accurate imaging up to the scanning frequency of 30 Hz.