Quantitative electrostatic force measurement in AFM

We describe a method for measuring forces in the atomic force microscope (A FM), in which a small amplitude oscillation(similar to 1 Angstrom(p-p)) is applied to a stiff(similar to 40 N/m) cantilever below its first resonant f requency, and the force gradient is measured directly as a function of sepa ration. We have used this instrument to measure electrostatic forces by app lying an ac voltage between the tip and the sample, and observed a variatio n in contact potential difference with separation. We also show how the ben efits of this instrument may be exploited to make meaningful capacitance me asurements, especially at small tip-surface separations, and demonstrate th e potential of this technique for quantitative dopant profiling in semicond uctors. (C) 2000 Elsevier Science B.V. All rights reserved.