Researchers at MIT have produced a new sensitive atomic force microscope (AFM) that can scan images 2,000 times faster than any current commercial models, as well as produce high-resolution videos of atomic-sized processes in near real time.

Although the new generation of atomic force microscopes (AFMs) can capture high-resolution close-up images of structures down to only a fraction of a nanometer, the scanning process is very time-consuming, and they are better used for imaging static samples as they are not quick enough to capture active and varying environments. However, as reported in the journal Ultramicroscopy [Bozchalooi et al. Ultramicroscopy (2016) DOI: 10.1016/j.ultramic.2015.10.016], this new high-speed instrument can take images of chemical processes occurring at the nanoscale at a rate close to that of real-time video.

AFMs usually scan with an ultrafine probe that moves slowly along the surface of a sample, line by line, to trace its topography, with the sample placed on a movable platform or scanner that moves it laterally and vertically under the probe. To speed up the scanning process, other studies have attempted to develop smaller, quicker platforms that scan more quickly but over a smaller area, but they don’t allow for zooming out to get a wider view or assess larger features.

"This is fantastic to see these details emerging... it will open great opportunities to explore all of this world that is at the nanoscale."Kamal Youcef-Toumi

This new design achieves high-speed scanning over large and small ranges using a multi-actuated scanner controlled through a sample platform incorporating a smaller, quicker scanner and a larger, slower scanner for each direction, combining to form a single system. For the first time, the instrument allows viewing of details of events such as condensation, nucleation, dissolution and deposition of material in real time. The team demonstrated the instrument’s capabilities by scanning a 70 by 70-micron sample of calcite that was immersed in deionized water and then exposed to sulfuric acid, observing the acid eroding the calcite, increasing the size of existing nanometer-sized pits in the material that quickly merged and led to a layer-by-layer removal of calcite along the material’s crystal pattern.

Previous multi-actuated scanners have been unsuccessful, usually because of scanner interactions that can alter their precision and motion, and which are difficult to control separately. To resolve these issues, Bozchalooi produced control algorithms that account for the effect of each scanner on the other. On optimizing the microscope’s other components, the instrument could scan the calcite sample forward and backward without any damage to the probe or sample.

The team claim there is no limit to the instrument’s imaging range, and that it can optimally scan across hundreds of microns and image features of only several microns in height, and are now looking to expand its functionality and its controls to improve video-rate imaging.