TAPPING MODE IMAGING WITH AN INTERFACIAL FORCE MICROSCOPE

In their present embodiment, sensors used in interfacial force microsc opy do not have the necessary mechanical bandwidth to be employed as f ree-running tapping mode devices. We describe an extremely stable meth od of obtaining tapping mode images using feedback on the sensor. Our method is immune to small de drifts in the force signal, and the prosp ect of diminishing the risk of damaging fragile samples is realized. T he feasibility of the technique is demonstrated by our imaging work on a Kevlar fiber-epoxy composite. We also present a model which account s for the frequency dependence of the sensor in air when operating und er closed loop control. A simplified force modulation model is investi gated to explore the effect of contact on the closed loop response of the sensor. (C) 1997 American Institute of Physics. [S0034-6748(97)040 11-2].