Separation of interactions by noncontact force microscopy

Quantitative measurements of frequency shift vs distance curves of ultrahig h-vacuum force microscopy in a noncontact mode are presented. Different con tributions from electrostatic, van der Waals, and chemical interactions are determined by a systematic procedure. First, long-range electrostatic inte ractions are eliminated by compensating for the contact potential differenc e between the probing tip and the sample. Second, the long-range van der Wa als contribution is determined by fitting the data for distances between 1 and 6 nm. Third, the van der Waals part is subtracted from the interaction curves. The remaining part corresponds to the shea-range chemical interacti on, and is found to decrease exponentially. A Morse potential is used to fi t these data. The determined parameters indicate that the interaction poten tial between single atoms can be measured by force microscopy in a nonconta ct mode.