Atomic-level Microscopy 100 Times Faster

Cornell Professor Keith Schwab works on a low-temperature apparatus. 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 metres: a distance 30,000 times smaller than the diametre of an atom.

Measurements with the STM are slow. And the limiting factor is not in the signal itself - it's in the basic electronics involved in analyzing it. A theoretical STM could collect data as fast as electrons can tunnel - at a rate of one gigahertz, or 1 billion cycles per second of bandwidth.

But a typical STM is slowed down by the capacitance, or energy storage, in the cables that make up its readout circuitry - to about one kilohertz (1,000 cycles per second) or less.

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.; Source: Chronicle Online