A novel method and system for calibrating the spring constant of atomic force microscope cantilever based on electromagnetic actuation

Abstract

It is crucial to calibrate atomic force microscope (AFM) cantilevers for the development and further applications of AFM in precision engineering such as nanonewton force measurement. This paper presents a novel approach to calibrate the spring constant of AFM cantilever based on electromagnetic actuation and null position measurement. According to the method, a calibration system was designed. In order to optimize the static and dynamic characteristics of the calibration system, the analytical models for the electromagnetic force and the suspension mechanism stiffness have been developed. Finite Element Analysis (FEA) has been utilized to further investigate the precision of analytical modeling. The null position measurement method was utilized to monitor the deformation of the flexible beam, and then the deformation was compensated by the electromagnetic force. Experiments were carried out based on the developed prototype, and the results show that the electromagnetic force conversion rate is 40.08 μN/mA. Finally, a typical AFM cantilever was calibrated and the spring constant is (30.83 ± 0.24) N/m. The uncertainty of the proposed null position measurement method is better than 0.78%, which verifies the effectiveness and feasibility of the calibration method and system. I. INTRODUCTION With the rapid development of micro/nano manufacturing, more and more attention has been paid to the micro/nano newton force measurement. 1-3 Atomic force microscope (AFM) has been becoming more and more important for the measurement of the modulus of polymers, 4 the strength of chemical bonds, 5 and the intermolecular interaction force between single molecule. 6 The interaction force between the tip and the sample surface can be measured through the deflection of probe cantilever and the Hook's law. 7 Thus, the calibration of the spring constant of cantilever has become one of the major concerns, especially in the quantitative measurement of micro-scale force. 8 There are variety kinds of probes utilized with different shapes and functions. Unfortunately, the spring

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MEMS displacement generator for atomic force microscopy metrology

“…By careful engineering of the structure elasticity it is possible to apply force and induce structural deflection with high precision. A noticeable solution was proposed by Tian et al [20]. In this setup, a macroscopic electromagnetic actuator coupled with a capacitive sensor was applied to induce a calibrated force acting at the atomic force microscope cantilever's tip.…”

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“…The involved mechanical contact has been reported [ 36 ] to affect the dynamic behavior of CBs, deteriorating the representativeness of the measured response. This type of shortcoming exists also in other contact actuation methods such as electrostatic actuation [ 37 , 38 ] and magnetic actuation [ 39 , 40 ] methods, where the cantilever is attached to an electrode or magnetic film.…”