Atomic force microscopy of work functions on the nanometer scale

The Kelvin probe force microscope, introduced some years ago, has opened up several avenues of investigation. In this letter, we demonstrate that the technique is capable of distinguishing constituents of a metal alloy through their work-function differences. The intermetallics in the alloy are clearly resolved. We discuss the basic principles of the measurement technique and present our results on aluminum/copper surfaces. The limits of the technique are also discussed.