One of the cornerstones of the U.S. National Nanotechnology Initiative was the establishment of nanotechnology research facilities that would be available to outside users.
One of the five user facilities operated by the U.S. Department of
Energy (DOE) is located at Berkeley National Lab and is known as The Molecular Foundry.
In a visit to The Molecular Foundry, we had the opportunity to discuss the state of nanofabrication with Stefano Cabrini,
who is the director of its nanofabrication facility. “The mission of
The Molecular Foundry is dedicated to nanoscience in general, but it is a
user facility,” Cabrini told IEEE Spectrum. “So we are hosting
here people from all over the world, from companies and from academia,
from Europe, from Asia, from everywhere. They come here to work with us,
to use or our instruments and facilities, but also to have access to
The goal of the research facility is to split the research 50-50
between outside users and the resident experts at the lab. However,
Cabrini acknowledges that the boundaries quickly become blurry,
especially when pursuing the best science.
While nanofabrication is Cabrini’s main bailiwick, much of his work
of late has been focused on nanophotonics, especially in the emerging
Plasmonics exploits the waves of electrons (plasmons) that are
created on the surface of a metal when it is struck by photons.
Metamaterials are artificially structured materials fabricated by
assembling different objects in place of the atoms and molecules that
make up a conventional material. The resulting material has very
different electromagnetic properties than those found in naturally
occurring or chemically synthesized materials. Both plasmonics and
metamaterials are often used in antenna technologies for essentially
squeezing down the size of light waves.
Back in 2012, Cabrini and his colleagues described, in the journal Science, a
device that operates like a transducer for far-field light to
near-field light. The near-field light overcomes the diffraction limit
of light and provides a much higher resolution than far-field light in
Prior to this work, electron microscopy was the way to collect
information about nanomaterials, but the data it collects about the
nanomaterials is only at the sub-atomic level. But information about the
nanomaterial’s chemical makeup requires analysis at the larger
molecular level. While optical or vibrational spectroscopy typically
provides chemical information on materials on the macroscale, the
problem with these light-based techniques is that the light comes up
against its diffraction limit when it tries to focus in on the
nanoscale. You simply cannot focus a light down to a spot smaller than
half its wavelength.
By using plasmonics, the researchers were able to exploit the surface
plasmons that are created on a metal surface when light hits it. When
the plasmons on two surfaces are separated by a small gap, it’s possible
to collect and amplify the optical field in the gap, making a stronger
signal for scientists to measure.
“We saw that with plasmonics it was possible to focus light onto a
very small spot—a few nanometers—and normally you can’t squeeze the
light in that small a dimension,” said Cabrini.
When the light is squeezed down to these very small spots, it begins
to interact with the matter it is focused on. Once you have collected
the photons that are either scattered or emitted because of this
interaction with the near-field light and the material, it is possible
to turn it back into far-field light.
The key to making all this work was the design and fabrication of the
near-field probe. Cabrini and his colleagues were able to fabricate a
tapered, four-sided tip on the end of an optical fiber. The researchers
dubbed the resulting tip “campanile” after the tower that resembles a
church campinile on the UC Berkeley campus. Two of the campanile's
gold-coated sides are separated by just a few nanometers at the tip. The
three-dimensional taper enables the device to channel light of all
wavelengths down into an enhanced field at the tip. The size of the gap
determines the resolution.
Research has continued at the Foundry with this device and has been led by Keiko Munechika, the manager for nanofabrication at aBeam Technologies, a small company that is working on next-generation nanofabrication.
In the latest research, described in the journal Scientific Reports,
Munechika and her colleagues have developed a simplified and robust
method for fabricating the campanile near-field probe. The
nanoimprinting technique operates much like a stamp used on sealing wax.
There is a mold with the desired shape that is pressed down into a
polymer that sits on the optical fiber. Once the polymer cools, the tip
of the optical fiber is in the shape of the near field probe .
“The original version of the campanile was made one-by-one, by
curving out an optical fiber into a campanile structure consisting of
micro and nanometer features using a focused ion beam,” explained
Munechika, in an email interview with IEEE Spectrum. “It
requires both time and expertise (and a lot of patience). The throughput
was only a few campanile probes per month. Many researchers have been
interested in using the probes but there was no way to scale up the
fabrication. So, we developed a new way to fabricate campanile probes
using nanoimprint lithography. Now it’s possible to make several probes
The probes will be used for nano-spectroscopic imaging of various
materials including new-generation photovoltaic materials to learn
optoelectronic processes at the nanometer scale resolution. “We are
hoping that many new discoveries will be made, now that these probes
will be more accessible to researchers,” said Munechika.
This latest research highlights what Cabrini believes is one of the
foundations of The Molecular Foundry’s mission: that technologies be
developed for widespread use.
Cabrini adds: “Our aim here is not just to make the smallest things
while maintaining the same quality, but to transfer these devices to the
widest spectrum of applications so that everyone can use them.”