When you want to see something small, you use an optical microscope; when you want to see something really small, you can use some form of electron microscope; when you want to "see" individual atoms or molecules, you break out the scanning probe microscopes. Scanning probe microscopes work by running a very sharp tip over a surface and forming the image of the surface from a signal read from the tip—akin to a record player reading the grooves on a record in order to play sound. The first of these microscopy techniques, scanning tunneling microscopy (STM), was developed by IBM researchers in 1981 and resulted in its inventors receiving the Nobel Prize in physics a short five years later. STM relies on quantum mechanical tunneling effects; as the microscope's tip is scanned over a surface, electrons tunnel from the tip into the surface, the tunneling current is measured and can be transformed into an image.

STMs are capable of imaging particles as small across as 1 angstrom and can measure changes in height as small as 0.1 angstroms. The image to the right is an STM image of a gold surface; the individual gold atoms are clearly visible. One of the biggest drawbacks of STM is speed: while the current between the tip and surface can change in a nanosecond, it takes considerably longer to image properly—typical speeds are on the order of 10 kilohertz. New research, reported in last week's edition of Nature, from groups at Boston University and Cornell University have devised a simple modification that is capable of greatly speeding up the operation of a STM.

The researchers found that by adding an external radio frequency (RF) source to the setup that they could measure the resistance at the tunneling junction. This measurement is carried out by examining the characteristics of the wave that gets reflected back to the RF source. With knowledge of the junction resistance, the researchers can easily deduce the distance between the tip and the surface. This method allowed for 100 to 1000 fold increase in measurement speeds. The researchers who developed this technique have dubbed their modified method as RF-STM, they believe that this technique will be applicable to a number of scientific and technological problems. Since the technique is so simple, the researchers list three reasons that this will be an attractive method: only minor modifications are needed to an STM, the needed RF components are easy to obtain, and finally the added RF circuit can work under a wide variety of conditions.

In addition to developing the novel method, the researchers discuss some of the more incredible applications that this technique could make possible. The researchers discuss how this setup can be used for atomic scale thermometry—measuring the temperature of just a few atoms. This would allow a scientist or engineer to easily study the nanoscale heat flow in an advanced semiconductor chip. Since heat flow is the limiting factor in clock speeds and densities, such rapid scale thermal imaging would provide a useful analysis tool. In the closing paragraph of the article the authors state that "electron tunneling is expected to enable quantum mechanically-limited position detection." Basically the device could be used to measure distances at the edge of measurability according to the Heisenberg uncertainty principle. "This STM will be used for a lot of good physics experiments," said article author K.C. Schwab. "Once you open up this new parameter, 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."

Nature, 2007. DOI:10.1038/nature06238