High-speed molecular imaging microscope
26 February 2006
Researchers at the Georgia Institute of Technology have created a highly
sensitive atomic force microscope (AFM) capable of high-speed imaging 100
times faster than current microscopes. The research, funded by the National
Science Foundation and the National Institutes of Health, appears in the
February issue of Review of Scientific Instruments.
The technology could prove invaluable for many types of nanotechnology
research, in particular for measuring microelectronic devices and observing
fast biological interactions on the molecular scale, even translating into
movies of molecular interactions in real time.
|The FIRAT probe is smaller than the head of a
The new technology, called FIRAT (force sensing integrated readout and
active tip) is much faster than AFM (the current workhorse of nanotech), and
it can capture other measurements never before possible with AFM, including
material property imaging and parallel molecular assays for drug screening
and discovery. FIRAT could also speed up semiconductor metrology and even
enable fabrication of smaller devices. It can be added with little effort to
existing AFM systems for certain applications.
“I think this technology will eventually replace the current AFM,” said
Dr. Levent Degertekin, head of the project and an asscoiate professor in the
Woodruff School of Mechanical Engineering at Georgia Tech. “We’ve multiplied
each of the old capabilities by at least 10, and it has lots of new
FIRAT solves two of AFM’s chief disadvantages as a tool for examining
nanostructures — AFM doesn’t record movies and it can’t reveal information
on the physical characteristics of a surface, said Dr. Calvin Quate, one of
the inventors of AFM and a professor at Stanford University. “It is possible
that this device provides us with the ‘ubiquitous’ tool for examining
nanostructures,” Quate added.
FIRAT works a bit like a cross between a pogo stick and a microphone. In
one version of the probe, the membrane with a sharp tip moves toward the
sample and just before it touches, it is pulled by attractive forces. Much
like a microphone diaphragm picks up sound vibrations, the FIRAT membrane
starts taking sensory readings well before it touches the sample.
And when the tip hits the surface, the elasticity and stiffness of the
surface determines how hard the material pushes back against the tip. So
rather than just capturing a topography scan of the sample, FIRAT can pick
up a wide variety of other material properties.
“From just one scan, we can get topography, adhesion, stiffness,
elasticity, viscosity — pretty much everything,” Degertekin said.
For a regular AFM to detect the features of the object, the actuator must
be large enough to move the cantilever up and down. The inertia of this
large actuator limits the scanning speed of the current AFM. But FIRAT
solves this problem by combining the actuator and the probe in a structure
smaller than the size of a head of a pin. With this improvement, FIRAT can
move over sample topography in a fraction of the time it takes AFM to scan
the same area.
|"FIRAT simultaneously captures a variety of
material properties from just one touch including (from upper
left to right) topography, adhesion energy, contact time and
Georgia Tech researchers have been able to use FIRAT with a commercial
AFM system to produce clear scans of nanoscale features at speeds as
high as 60 Hertz (or 60 lines per second). The same system was used to
image the topography as well as elastic and adhesive properties of
carbon nanotubes simultaneously, which is another first.
FIRAT’s new speed and added features may open up many new applications
for AFM. For instance, FIRAT is capable of scanning integrated circuits for
mechanical and material defects. And in biomolecular measurement
applications, FIRAT can scan the surface quickly enough for a researcher to
observe molecular interactions in real time.
“The potential is huge. AFM started as a topography tool and has exploded
to many more uses since. I'm sure people will find all sorts of uses for
FIRAT that I haven’t imagined,” Degertekin said.