Currents Smooth Thin-film Surface

Thin diamond films created by a rain of energetic carbon atoms onto a surface are amazingly smooth--a well-documented, but not well-understood, phenomenon. Now, Michael Moseler at the Fraunhofer Institute of Mechanics of Materials in Friedburg, Germany, and colleagues have modeled the process, showing that a carbon atom strikes the surface, burrowing in a few angstroms and pushing aside other atoms. This generates tiny particle currents that push and pull the atoms into valleys or dips, smoothing the surface (Science 2005, 309, 1545). "The induced currents point downhill simply because the displacement into the downhill direction requires smaller forces," Moseler says. Their predictions agree with atomic force microscopy measurements, and the authors say the effect can be generalized to other types of surfaces, such as amorphous silicon.