Calibration Technique Of The Normal Spring Constant Of AFM Microcantilever

Atomic force microscopy(AFM)is widely used in measurement of surface profile and force properties at micro/nanometer-scale. As the unit of AFM signal pickup or execution, microcantilevers play an important role in many fileds such as the application in micro/nano machining and measurement accuracy of the spring constant affects the final measurement results. A new calibration system based on bending method and the system was analyzed in this paper: the force and the deflection are measured by an ultra precision balance and the optical lever respectively, and then the normal spring constant can be calculated by Hooke’law. The paper mainly completed measuring and controlling circuit, installed and debugged optical path and the mechanical module of the system. Serevel types of cantilever were calibrated with this system and the relative standard deviations were less than 5%, which proved a high stability and reliability of this system. The major works in the paper are as following:1. Analyzed and compared existing calibration methods of AFM normal spring constants, completed the analysis of a new method based on precision balance and optical lever.2. The calibration system based on the requirements of deflection and bending has been demonstrated. The system inclueding tow-level position device, optical lever, precision balance and the monitoring CCD.3. The measuring and controlling circuit of the calibration system has been completed, including control of microcantilever positioning, acquisition and processing of optical lever based on MSP430F149. The sofeware of MCU has been designed.4. Completed experiment with this calibration system, several microcantilevers has been calibrated, and the results were compared with thermal noise method.