Researchers at the University of Illinois have literally made a pointed improvement in microscopic probe tips. Led by Joe Lyding, a professor of electrical and computer engineering, the investigators developed a new microscope probe-sharpening technique that can improve and retain the resolution of scanning tunneling atomic force microscopy and improve the workflow by cutting tip replacement downtime.
According to a UIUC news release, the idea came to Lyding while trying to sharpen a worn tip with an ion beam. He wondered what the effect would be from “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.”
Lyding reasoned, “You preserve the point and you sharpen what’s around it.”
With only an simple ion gun, his group found they could hone STM tips with a starting radius of 100 nanometers to a sharp 1-nanometer point.
But sharpening via what they dubbed Field-Directed Sputter Sharpening was only the first half of the problem. What about keeping a tip ultrasharp?
For this, Lyding recruited the assistance of chemistry professor Gregory Girolami and materials science and engineering professor John Abelson, both of whom had been involved with developing hard hafnium diboride coatings for silicon semiconductors.
The UIUC release says the expanded group applied the hafnium diboride coatings to the STM probes, “sputtered them further, and found that the resulting probes are stable, durable and excel in the types of microscopy and patterning applications for which such tips are used.”
“Nobody else makes probes with the combination of sharp, hard and metallic conduction,” says Lyding, who is working with the others and the university to commercialize their novel probes.
Lyding says the group’s system is being adapted the FDSS method to AFM probes, and the researchers have launched a company, Tiptek, to begin manufacture. Their work is also featured in a new paper in Nature Communications, “Field-directed Sputter Sharpening for Tailored Probe Materials and Atomic-Scale Lithography” (doi:10.1038/ncomms1907).