Magazine article Science News

Friction Reveals Chemical Composition

Magazine article Science News

Friction Reveals Chemical Composition

Article excerpt

A new type of atomic force micro-scope now lets scientists tell in molecular detail not only what a surface looks like, but also the distribution of its chemical components.

The technique, which takes advantage of differences in the friction forces exerted by various materials, may prove useful for chemical analysis, characterization of mixtures of molecules, and studies of wettability and friction, says Jane Frommer, a chemist with the IBM Almaden Research Center in San Jose, Calif.

Typically, scientists monitor the vertical shifting of the very fine tip of an atomic force microscope (AFM) to image the surface of a sample. Then in 1987, IBM researchers discovered that the sideways deflection of the tip was indicative of friction between the tip and the surface, and they modified an AFM to make a "friction force" microscope, Frommer says.

Now, working with physicist Hans-Jorg Guntherodt and his colleagues at the University of Basel in Switzerland, Frommer has demonstrated that this microscope can distinguish materials based on the friction forces exerted by clusters of molecules. "We use the lateral response [of the tip] to differentiate between species in surfaces with more than one compound," she says.

To explore this potential, the Swiss group obtained special films from Masamichi Fujihira, a chemist at the Tokyo Institute of Technology. Fujihira's group makes these films by dipping a silicon plate into a solution of hydrocarbon and fluorocarbon molecules. The resulting film consists of discrete islands of hydrocarbon in a sea of fluorocarbon, Frommer notes. …

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