Spiral scanning of atomic force microscope for faster imaging

An atomic force microscope (AFM) is an extremely versatile investigative tool in the field of nanotechnology, the performance of which is significantly influenced by its conventional zig-zag raster pattern scanning method. In this paper, we consider the use of a spiral scanning method with an improved model predictive control (MPC) scheme for its faster scanning. The proposed MPC controller reduces the phase error between the input and output sinusoids and provides better tracking of the reference signal. Also, a notch filter is designed and included in the feedback loop with the plant to suppress vibrations of the piezoelectric tube scanner (PTS) at the resonant frequency. Consequently, the proposed controller achieves a higher closed-loop bandwidth and significant damping of the resonant mode of the AFM's PTS. Experimental results show that, by using the proposed method, the AFM's scanning speed is significantly increased to up to 180 Hz and produces improved image quality.