Microscope probe-sharpening technique improves resolution, durability

A simple new improvement to an essential microscope component could greatly improve imaging for researchers who study the very small, from cells to computer chips.

Joseph Lyding, a professor of electrical and computer engineering at the University of Illinois, led a group that developed a new microscope probe-sharpening technique. The technique is described in research published this week in the journal Nature Communications.

Scanning probe microscopes provide images of tiny structures with high resolution at the atomic scale. The tip of the probe skims the surface of a sample to measure mechanical, electrical or chemical properties. Such microscopes are widely used among researchers who work with tiny structures in fields from nanotechnology to cellular biology.

Labs can spend hundreds of thousands of dollars on an elegant instrument – for example, a scanning tunnelling microscope (STM) or an atomic force microscope (AFM) – yet the quality of the data depends on the probe. Probes can degrade rapidly with use, wearing down and losing resolution. In such cases, the researcher then has to stop the scan and replace the tip.

''To put it in perspective, if you had an expensive racecar but you put bicycle tires on it, it wouldn't be a very good car,'' Lyding said.

To shape tips, researchers shoot a stream of ions at the tip. The material sputters off as the ions collide with the tip, whittling away the probe. One day in the lab, after yet another tip failure, Lyding had the simple, novel idea of applying a matching voltage to the tip to deflect the incoming ions. When a voltage is applied to a sharp object, the electrical field gets stronger as the point narrows. Therefore, ions approaching the sharpest part of the electrified tip are deflected the most.