November 12, 2007 — Using an existing technique in a novel way, Cornell physicist Keith Schwab and colleagues at Cornell and Boston University have made the scanning tunneling microscope (STM) — which can image individual atoms on a surface — at least 100 times faster.
The simple adaptation, based on a method of measurement currently used in nano-electronics, could also give STMs significant new capabilities — including the ability to sense temperatures in spots as small as a single atom, and to detect changes in position as tiny as 0.00000000000001 meters: a distance 30,000 times smaller than the diameter of an atom.
The finding is described in the Nov. 1 issue of the journal Nature.
The STM uses quantum tunneling, or the ability of electrons to “tunnel” across a barrier, to detect changes in the distance between a needlelike probe and a conducting surface.) By measuring changes in current as electrons tunnel between the sample and the probe, scientists can construct a map of the surface topology.
By adding an external source of radio frequency (RF) waves and sending a wave into the STM through a simple network, the researchers showed that it’s possible to detect the resistance at the tunneling junction — and hence the distance between the probe and sample surface — based on the characteristics of the wave that reflects back to the source.
The technique, called reflectometry, uses the standard cables as paths for high-frequency waves, which aren’t slowed down by the cables’ capacitance.