Evolution of millimetric-range electrostatic forces between an AFM cantilever and a charged dielectric via suspended force curves

The evolution of millimetric-range electrostatic force between a silicon cantilever and a negatively charged dielectric sample was studied by recording “suspended” force curves at a fixed distance on an atomic force microscope (AFM). Results show that the long-range force increases sharply at first with time, then increases moderately until reaching a global maximum, and at last decreases slightly and exponentially. The sharp increase was attributed to carrier drift at a high velocity. Moreover, a repelling electric field due to accumulated charges leads to the moderate increasing trend. In addition, the exponential decrease was attributed to charge decay on the sample surface. With the absence of the sample for a while (absent time) and presence again, the force increases sharply again with a lower value. The longer the absent time, the larger the decreasing rate. This was attributed to carrier diffusion due to the concentration difference. The proposed method can be used to measure millimetric-range electrostatic forces at a fixed distance, and investigate its evolution with time, and study the effect of some factors on the charge dissipation. Furthermore, the outcomes may suggest that charge carriers inside an AFM silicon cantilever play a part in the electrostatic force contribution.