Force calibration of a dual-probe nanotweezer using a mechanical lever

This paper presents a noncontact force calibration method in applications of the dual-probe nanotweezer. A 2 DOF mechanical lever has been developed to directly calibrate both the normal and lateral sensitivities of two optical levers used to independently measure normal and lateral forces applied on the nanotweezer. The mechanical lever is designed with a configuration of two mutually perpendicular levers, each consists of two flexible hinges, sharing a same rotational center, Each lever can convert the translation into a nanoscale rotation angle that provides an accurate conversion between the photodiode voltage output and deflective angle of a cantilever. During the calibration, a cantilever is mounted on the mechanical lever and attached on the rotational center of the flexible hinges. By making use of its nanomotion on the Z-axis and using an external motion on the barrier, this device can complete the local and full-range sensitivity calibrations of the optical levers without modifying the actual AFM or the cantilevers. Nonlinearities on both normal and lateral of the optical levers have been accurately compensated.