Design and implementation of a large measurement-range AFM scanning system

Atomic force microscopy (AFM) opens a new window to the nano-world. It is a widely used tool in nano measurement techniques. However, a traditional AFM system suffers from the limitation of small scanning range, due to the short traveling range of piezoelectric positioners. In this paper, we propose a large measurement-range AFM scanning system which combines both fine positioners of piezoelectric and electromagnetic actuators. While the piezoelectric actuation positioner (PAP) provides high speed scanning with nanometer resolution in the z-axis, the precision electromagnetic positioner (PEP) is capable of 1 mm² large field positioning with 20 nm rms error in the xy axes. The overall design of the stage consists of 4 pairs of electromagnetic actuators, monolithic serial flexure guidance with compression springs, an eddy current damper, and a commercial z-axis PAP. Given that there are 1 DOF in PAP and 2 DOF in PEP, the scanning positioners can achieve a large field image scanning. Besides, a stationary compact disk/digital versatile disk pick-up-head (CD/DVD PUH) is used to measure the amplitude of the probe. Moreover, an adaptive sliding mode controller based on the analytical modeling is used to overcome the unmodeled system uncertainties, coupling motion and external noises, including the scanning disturbances. Finally, extensive experiments are conducted, demonstrating feasibility of the proposed system.