New microscope is 2,000 times faster

A new atomic force microscope developed by MIT can scan images 2,000 times faster than existing commercial models. This allows it to capture near-real-time video of nanoscale processes.

State-of-the-art atomic force microscopes (AFMs) are designed to capture images of structures as small as a fraction of a nanometre – a million times smaller than the width of a human hair. In recent years, AFMs have produced desktop-worthy close-ups of atom-sized structures, from DNA strands to individual bonds changing between molecules. But scanning these images is a meticulous, time-consuming process. AFMs have therefore been used mostly for static samples as they are too slow to capture active, changing environments.

Now engineers at MIT have designed an atomic force microscope that scans images 2,000 times faster than existing commercial models. With this new high-speed instrument, the team produced images of chemical processes taking place at the nanoscale, at a rate that is close to real-time video.

In one demonstration of the instrument’s capabilities, the researchers scanned a 70- by-70-micron sample of calcite as it was first immersed in deionised water and later exposed to sulphuric acid. Zooming into an area of interest, they observed the acid eating away at the calcite, expanding existing nanometre-sized pits in the material that quickly merged and led to a layer-by-layer removal of calcite along the material’s crystal pattern, over a period of several seconds.

Calcite immersed in deionised water.

Sulphuric acid creating pits in the calcite.

Professor of Mechanical Engineering at MIT, Kamal Youcef-Toumi, says the instrument’s sensitivity and speed will enable scientists to watch atomic-sized processes play out as high-resolution “movies.”

“People can see, for example, condensation, nucleation, dissolution, or deposition of material, and how these happen in real-time – things that people have never seen before,” he says. “This is fantastic to see these details emerging. And it will open great opportunities to explore all of this world that is at the nanoscale.”

The MIT researchers' achievement was made possible through an innovative new technique. This involved controlling the movement of the needle over the sample surface with two actuators (a small, fast scanner and a larger, slower one) in combination with a set of algorithms to ensure they never interfered with each other. At present, this method provides scans at eight to 10 frames per second, but further research is underway to increase this.

“We want to go to real video, which is at least 30 frames per second,” Youcef-Toumi says. “Hopefully we can work on improving the instrument and controls so that we can do video-rate imaging while maintaining its large range and keeping it user-friendly. That would be something great to see.”

The team's design and images, which are based on the PhD work of Iman Bozchalooi – now a postdoc in the Department of Mechanical Engineering – appear in the journal Ultramicroscopy.