Written by Sophia Chen
Franz Giessibl is the 2023 recipient of the Innovation in Materials Characterization Award. Over more than three decades, the physicist at University of Regensberg in Germany has worked to develop and popularize the technology known as the atomic force microscope (AFM), which has allowed materials scientists to characterize subatomic such as the shape of electron clouds. “As far as I know, it [has] the best spatial resolution of any microscopy,” Giessibl says.
But it took just about Giessibl’s entire career so far for the field to achieve subatomic resolution. He delivered a virtual presentation tracing the evolution of the technology. Giessibl began working on AFM as a graduate student at ETH Zürich under Nobel laureate Gerd Binnig, who won the prize for co-inventing the scanning tunneling microscope. (Giessibl chose atomic force microscopy over Binnig’s other two suggested research topics, gravitational waves or sequencing DNA using the scanning tunneling microscope. “What project would you have chosen?” he asked the audience.)
Binnig had co-invented the AFM in 1986, just prior to Giessibl joining his team. The microscope images a material by scanning the surface with an extremely fine tip on the end of a cantilever. Early models of the microscope used silicon as a cantilever material and could not achieve atomic resolution, Giessibl said. It also used a piezoresistive material that required significant electric current, and thus produced heat, to sense motion in the tip. This presented a technical challenge, as researchers were interested in studying materials in a cryogenic setting.
The field grew in the 1990s, with Seizo Morita of University of Osaka starting the International Conference on Non-contact Atomic Force Microscopy, which is still held today. Still, Giessibl noted that atomic force microscopes didn’t sell, with only about 80 sold worldwide at the time. During that time, he pivoted to management consulting at McKinsey in Germany to try to understand the business aspects.
During his time at McKinsey, Giessibl began to develop what is now the QPlus sensor, a new type of force sensor for the AFM. Instead of a silicon cantilever, the QPlus uses a quartz one. Instead of piezoresistive material, they use piezoelectric material, which doesn’t heat up as prior models. In addition, the QPlus sensor converts the surface of the material into a vibration.
In the early 2000s, more groups began to develop this new type of microscope with a stiffer probe. Giessibl noted that it was easier to convince scientists from the scanning electron microscopy field than from atomic force microscopy. In 2008, Giessibl and his colleagues measured the force it took to push a single atom. In 2009, Leo Gross of IBM and his team discovered that adding a carbon monoxide molecule of the tip improved the resolution.
At the end of the talk, Giessibl showed the progression in the AFM’s imaging capability with a series of photos from 1995 to 2015. There are now more than 400 atomic force microscopes with QPlus sensors worldwide, he said. He noted that the field has finally demonstrated subatomic imaging in 2015 and 2019, and that he is now working on achieving ultrafast time resolution with atomic force microscopy.
The Innovation in Materials Characterization Award has been endowed by Gwo-Ching Wang and Toh-Ming Lu.