Researchers measure force to move a single atom

LONDON — Researchers at the University of Regensburg in Germany and IBM's Almaden Research Labs in California have calculated for the first time exactly how much effort is needed to drag a single atom of cobalt across the surface of different metals.

They suggest the results could lead to major advances in nanotechnology, where it is important to know how stable an atom is on a surface before building structures on it. They add the fundamental measurement provides important information for designing future atomic-scale devices: semiconductors, and miniaturized storage devices.

The researchers used an atomic force microscope (AFM) equipped with a qPlus sensor and have come up with the answer that the force needed was 210 piconewtons.

An AFM works by scanning a surface with a tiny vibrating cantilever - similar to a miniature diving board - that has a sharp tip.

The teams placed a single atom of cobalt on a platinum surface and swept the tip of the AFM across the surface, moving it gradually nearer to the atom until it was close enough to flip the atom from one hollow on the surface to the next.

"This result provides fundamental information about atomic scale fabrication and could pave the way for new data storage and memory devices," said Andreas Heinrich, lead scientist in the scanning tunneling microscopy lab at the IBM Almaden Research Center. "Our mission is to create the foundation for what could someday be called the IBM nanoconstruction company."

The researchers also discovered that the force depends on the material used for the surface. The amount of force also changes greatly when a small molecule is used instead of a single atom.

The scientists published their findings in the latest edition of Science magazine.

To put their findings into perspective, the researchers noted that the force required to lift a copper penny that weighs just three grams is nearly 30 billion piconewtons - 2 billion times greater than the force to move a single cobalt atom over a copper surface.

IBM said the work builds on its long history in atomic force microscopy. The AFM was introduced by Nobel Laureate and IBM Fellow Gerd Binnig, IBM scientist Christoph Gerber and Stanford Professor Calvin Quate over 20 years ago.

"It is amazing to see how this tool, which at its heart uses the tuning fork of an everyday wrist watch, can be used to measure forces between individual atoms," said Professor Franz Giessibl of the University of Regensburg.