Ithaca (NY) and Boston (MA) - A physicist named Keith Schwab at Cornell University has given an old invention a new tweak. By modifying the scanning tunneling microscope (STM) to incorporate a simple radio transmitter, the researchers were able to measure the electrical resistance at the tip of the device. This new ability has yielded sampling rates close to 1 MHz, up from around 1 KHz previously. The STM’s new abilities can almost produce live video now, rather than just periodic still frames.

STMs can operate at extremely cold temperatures on the order of around 5 Kelvin, to super-elevated temperatures above 1,000 Kelvin. The device uses a type of ultra-fine probe which eventually tapers down to an emitter point of only 1 atom. Probes are made of platinum-iridium and, by measuring extremely small changes in current as the electrons tunnel between the sample and the probe, essentially penetrating, or tunneling through material barriers, a type of 3D surface map is created. The first STMs were developed back in the 1980s and there have been various improvements since then, some of them extremely complex. What makes Schwab’s solution stand out is its simplicity.

STMs are capable of looking at the smallest features, down to about 30,000x smaller than the diameter of an atom. They can even sense the temperature of individual atoms. This new device allows a much faster scan of a surface to be completed. Theoretically, the modifications made to the device would allow a maximum of 1 GHz scan rate. Today’s practical examples are only in the range of 100 KHz to 1 MHz, however.

The device works by sending a radio frequency (RF) through various portions of the STM via a transmitter network. By sending out these waves, they discovered an ability to determine the resistance at the tip of probe, based on the way the waves propagated. Using the derived data they could determine the distance between the tip and the sample’s surface. This allowed them to execute many more samples and scan significantly faster. The current model can scan up to 1,000x faster, and greater speeds are still possible.

Schwab said, "Our hope is that we can produce more or less video images, as opposed to a scan that takes forever ... Once you open up this new parameter [and] all this bandwidth, people will figure out ways to use it. I firmly believe 10 years from now there will be a lot of RF-STMs around, and people will do all kinds of great experiments with them."

Research funding for this project was provided by the National Science Foundation. The research was carried out at Cornell University by Schwab, as well as Boston University.