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 distance. In the force curve measurement, if the spring constant of the force detecting lever is small, the measured force curve has discontinuity and is different from the true force curve. In this paper, we present a new type of force balancing force sensor built in SFM. This force sensor employs an optical lever for detecting the rotation of the lever and two electrostatic force actuators with transparent electrodes. This sensor has two operating modes; with and without feedback. In the feedback mode, the force detecting lever is balanced with the electrostatic force. This system has the effect of enlarging the effective spring constant of the whole sensor. In the nonfeedback mode, this sensor acts as an ordinary force sensor. By using this sensor in both modes we will show the effectiveness of the force feedback in force curve measurements.