A new high-speed
microscope produces images of chemical processes taking place at the
nanoscale, at a
rate that is close to real-time video. This closeup shot of the microscope
shows transparent
tubes used to inject various liquids into the imaging environment.
This liquid can be
water, acid, buffer solution for live bacteria, cells, or electrolytes in an
electrochemical process.
Researchers use one as an inlet and the other as an outlet to
circulate and
refresh the solutions throughout an experiment.
(December 14, 2015) Instrument
scans images 2,000 times faster than commercial models.
State-of-the-art atomic force microscopes (AFMs) are
designed to capture images of structures as small as a fraction of a nanometer
— 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 single
strands of DNA to individual hydrogen bonds between molecules.
But scanning these images is a meticulous, time-consuming
process. AFMs therefore have been used mostly to image 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.
(Left to right)
Fangzhou Xia, a new lab member who was not involved in the study;
professor Kamal
Youcef-Toumi; and postdoc Iman Soltani Bozchalooi.
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 deionized water and later exposed to sulfuric acid. The team
observed the acid eating away at the calcite, expanding 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, over a
period of several seconds.
Kamal Youcef-Toumi, a professor of mechanical engineering at
MIT, says the instrument’s sensitivity and speed will enable scientists to
watch atomic-sized processes play out as high-resolution “movies.”
Bozchalooi came up
with a design to enable high-speed scanning over both large and small
ranges. The main
innovation centers on a multiactuated scanner: A sample platform 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.
“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,” Youcef-Toumi 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 group’s design and images, which are based on the PhD
work of Iman Soltani Bozchalooi, now a postdoc in the Department of Mechanical
Engineering, are published in the journal Ultramicroscopy.
Watch and learn
more about how the researchers were able to capture near real-time
video of chemical
processes at the nanoscale.
Video: Melanie
Gonick/MIT (AFM videos courtesy of the researchers)
The big picture
Atomic force microscopes typically scan samples using an
ultrafine probe, or needle, that skims along the surface of a sample, tracing
its topography, similarly to how a blind person reads Braille. Samples sit on a
movable platform, or scanner, that moves the sample laterally and vertically
beneath the probe. Because AFMs scan incredibly small structures, the
instruments have to work slowly, line by line, to avoid any sudden movements
that could alter the sample or blur the image. Such conventional microscopes
typically scan about one to two lines per second.
“If the sample is static, it’s ok to take eight to 10
minutes to get a picture,” Youcef-Toumi says. “But if it’s something that’s
changing, then imagine if you start scanning from the top very slowly. By the
time you get to the bottom, the sample has changed, and so the information in
the image is not correct, since it has been stretched over time.”