Development of a High-Speed Laser-Free Atomic Force Microscopy

To reduce the cost and improve the speed of Atomic Force Microscopy (AFM) in molecular scale imaging of materials, we propose a laser-free AFM scheme augmented with an accurate control strategy for its scanning axes. It employs a piezoresistive sensing device with a high level of accuracy to avoid using the bulky and expensive laser interferometer. Change in the resistance of piezoelectric layer due to the deflection of microcantilever caused by the variation of surface topography is monitored through a Wheatstone bridge. Hence, it captures the surface topography without the use of laser and with nanometer scale accuracy. To improve the speed of imaging, however, a Lyapunov-based robust adaptive control strategy is implemented in the 2-DOF scanning stage. It has been demonstrated in an earlier publication that this control framework has superior performance over the conventional PID controllers typically used in commercial AFMs. The paper, then, demonstrates a set of experiments on a standard AFM calibration sample with 200 nm stepped topography. Results indicate accurate imaging of the sample up to the frequency of 30 Hz, for a 16μm×16μm scanning area, proving the feasibility of less costly and high speed AFM-based metrology.