Microscopy, Scanning Tunneling

A Sideshow Becomes the Main Event

The STM arose from a multimillion-dollar IBM project to develop a supercomputer based on superconducting (rather than semiconducting) logic elements. Researchers on the project had trouble making thin oxide films and asked a colleague at the IBM Zurich laboratory, Heinrich Rohrer, to investigate. Rohrer put a newly hired physicist, Gerd Binnig onto the task. Together, they decided to develop a new kind of instrument based on electron tunneling, rather than try to understand the problem using existing instruments. Their “tunneling [Page 425]microscope” consisted of a sharp metal or semiconductor probe, which approached a metal or semiconductor sample to within a few angstroms (0.1 nanometer or 1 × 10−10 meters), at which point electrons would “tunnel” between probe and sample. Tunneling is a quantum phenomenon in which there is a finite probability that a particle's waveform will collapse in one region and re-form in another region without having to surmount the energy barrier between those regions (like moving through a wall without having to break the bricks).

A Community Forms

This instrument became a microscope when Binnig and Rohrer moved the tip back and forth, recording the strength of the tunneling current as it passed over a matrix of points on the sample. By the time they accomplished this, though, the supercomputer project was winding down. So they consulted IBM colleagues to see what other samples to look at. Some surface scientists suggested the silicon (111) 7 × 7, an intriguing surface in which the silicon atoms arrange in a then-unknown pattern. When Binnig and Rohrer published images of single atoms of the 7 × 7 in 1983, the STM quickly catapulted to the wider scientific community's attention. Though they did not solve the mystery of the 7 × 7 themselves, their work on it won Binnig and Rohrer the 1986 Nobel Prize in physics, and spurred many surface scientists and others to build their own STMs.

...