New depth for nano-scale cameras
Engineers at MIT have created a new atomic force microscope (AFM) that can create near real-time videos of nano-scale processes.
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.
Scanning these images has been a meticulous, time-consuming process, so they are usually limited to capturing static samples.
But now, research engineers have designed an AFM that can scan images 2,000 times faster than existing commercial models.
With their new high-speed instrument, the MIT team has captured exciting moving images of chemical processes taking place at the nanoscale.
In one demonstration, the researchers scanned a 70-by-70-micron sample of calcite as it was first immersed in deionised water and then exposed to sulphuric acid.
The team 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.
Kamal Youcef-Toumi, a professor of mechanical engineering at MIT, says; “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.”
“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.”
Before now, atomic force microscopes have scanned samples using an ultrafine probe, or needle, that skims along the surface of a sample, tracing its topography, similar to the way that a blind person reads Braille.
But this approach can take several minutes to build up a single image, and so is only useful for static samples that do not change over time.
The main innovation in the new device is a multiactuated scanner and its control: A sample platform that incorporates a smaller, speedier scanner as well as a larger, slower scanner for every direction, which work together as one system to scan a wide 3-D region at high speed.
“Our controller can move the little scanner in a way that it doesn’t excite the big scanner, because we know what sort of motion triggers this scanner, and vice versa,” MIT’s Iman Soltani Bozchalooi says.
“In the end, they’re working in synchrony, so from the perspective of the scientist, this scanner looks like a single, high-speed, large-range scanner that does not add any complexity to the operation of the instrument.”
After optimising other components on the microscope, such as the optics, instrumentation, and data acquisition systems, the team found that the instrument was able to scan a sample of calcite forward and backward, without any damage to the probe or sample.
The microscope scans a sample faster than 2,000 hertz, or 4,000 lines per second — 2,000 times faster than existing commercial AFMs. This translates to about eight to 10 frames per second.
“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.”
Their latest paper has been published in the journal Ultramicroscopy, and footage from the AFM can be seen below.