Schematic of coaxial probe for imaging a carbon nanotube (left) and chemical map of carbon nanotube with chemical and (right) topographical information at each pixel. Credit: Weber, et. Al
A pixel is worth a thousand words? Not exactly how the saying goes, but in
this case, it holds true: scientists at Berkeley Lab’s Molecular Foundry have
pioneered a new chemical mapping method that provides unprecedented insight
into materials at the nanoscale. Moving beyond traditional static imaging
techniques, which provide a snapshot in time, these new maps will guide
researchers in deciphering molecular chemistry and interactions at the
nanoscale—critical for artificial photosynthesis, biofuels production, and
light-harvesting applications such as solar cells.
“This new technique allows us to capture very high-resolution images of
nanomaterials with a huge amount of physical and chemical information at each
pixel,” says Alexander Weber-Bargioni, a postdoctoral scholar in the Imaging
and Manipulation of Nanostructures Facility at the Foundry. “Usually when you
take an image, you just get a picture of what this material looks like, but
nothing more. With our method, we can now gain information about the functionality
of a nanostructure with rich detail.”
The Molecular Foundry is a U.S. Department of Energy (DOE) Office of Science
nanoscience center and national user facility. With the Foundry’s
state-of-the-art focused ion beam tool at their disposal, Weber-Bargioni and
his team designed and fabricated a coaxial antenna capable of focusing light at
the nanoscale,—a harnessing of light akin to wielding a sharp knife in a
thunderstorm, Weber-Bargioni says.
Consisting of gold wrapped around a silicon nitride atomic force microscope
tip, this coaxial antenna serves as an optical probe for structures with
nanometer resolution for several hours at a time. What’s more, unlike other
scanning probe tips, it provides enough enhancement, or light intensity, to
report the chemical fingerprint at each pixel while collecting an image
(typically 256 x 256 pixels). This data is then used to generate multiple
composition-related “maps,” each with a wealth of chemical information at every
pixel, at a resolution of just twenty nanometers. The maps provide information
that is critical for examining nanomaterials, in which local surface chemistry
and interfaces dominate behavior.
Molecular Foundry postdoctoral scholar Alex Weber-Bargioni and colleagues have pioneered a new imaging capability for chemical mapping of nanoscale materials. Credit: Lawrence Berkeley National Laboratory
“Fabricating reproducible near-field optical microscopy probes has always
been a challenge,” says Frank Ogletree, acting Facility Director of the Imaging
and Manipulation of Nanostructures Facility at the Foundry. “We now have a
high-yield method to make engineered plasmonic probes for spectroscopy on a
variety of surfaces.”
To test out the capability of their new probe, the team examined carbon nanotubes.
Carbon nanotubes are ideal for this type of interactive investigation as their
unmatched electronic and structural properties are sensitive to localized
Users coming to the Molecular Foundry to seek information about
light-harvesting materials or any dynamic system should benefit from this
imaging system, Weber-Bargioni says.
Adds Jim Schuck, staff scientist in the Imaging and Manipulation of
Nanostructures Facility at the Foundry, “We’re very excited—this new
nano-optics capability enables us to explore previously inaccessible properties
within nanosystems. The work reflects a major strength of the Molecular Foundry,
where collaboration between scientists with complementary expertise leads to
real nanoscience breakthroughs.”
A paper reporting this research titled, “Hyperspectral nanoscale imaging on
dielectric substrates with coaxial optical antenna scan probes,” appears in Nano Letters. Co-authoring the paper
with Weber-Bargioni, Ogletree, and Schuck were Adam Schwartzberg, Matteo
Cornaglia, Ariel Ismach, Jeffrey Urban, Yuanjie Pang, Reuven Gordon, Jeffrey
Bokor, Miquel Salmeron, Paul Ashby, and Stefano Cabrini.
This work at the Molecular Foundry was supported by DOE’s Office of Science.