FORCE-BALANCING FORCE SENSOR WITH AN OPTICAL-LEVER

Scanning force microscopes (SFMs) are sometimes used to obtain a force curve, which shows the force variation as a function of tip-sample di stance. In the force curve measurement, if the spring constant of thr force detecting lever is small, the measured force curve has discontin uity and is different from the true force curve. In this paper, we pre sent a new type of farce balancing force sensor built in SFM. This for ce sensor employs an optical lever for detecting the rotation of the l ever and two electrostatic force actuators with transparent electrodes . This sensor has two operating modes; with and without feedback. In t he feedback mode, the farce detecting lever is balanced with the elect rostatic force. This system has the effect of enlarging the effective spring constant of the whole sensor. In the nonfeedback mode, this sen sor acts as an ordinary force sensor. By using this sensor in both mod es we will show the effectiveness of the force feedback in force curve measurements. (C) 1995 American Institute of Physics.