For Immediate Release
Georgia Institute of Technology Researcher Seth Marder described the technique February 15 at the annual meeting of the American Association for the Advancement of Science (AAAS) in Seattle.
"We have developed a disruptive platform technology that we believe
will provide broad new capabilities," said Marder, a professor in
Georgia Tech's School of Chemistry
and Biochemistry. "We believe this technique provides a real
competitive advantage for making complicated three-dimensional microstructures."
The technique uses a family of organic dye molecules known as Bis-donor phenylene vinylenes that have a special ability to absorb two photons of light simultaneously. Once excited, the molecules transfer an electron to form a simple acid or a radical group that can initiate a chemical reaction - such as polymer cross-linking or ion reduction.
By adding small concentrations (0.1 percent) of the molecules to a resin
slab containing cross-linkable acrylate monomer, for example, researchers
can use a focused near-infrared laser beam to draw patterns and initiate
cross-linking reactions only in material exposed to the light. The reactions
can make that portion of the slab insoluble, allowing the remainder to
be washed away to leave a complex three-dimensional structure.
The researchers have demonstrated the ability to create both positive
and negative resists using two-photon activated reactions to alternatively
create soluble or insoluble 3D patterns. Beyond polymers, Marder and collaborator
have demonstrated the fabrication of tiny silver wires from patterns written
in materials containing silver nanoparticles and ions.
The molecules developed by Marder and Perry are hundreds of times more
efficient at absorbing two photons than previous photoactive materials.
That efficiency allows them to write 3D patterns in polymer slabs that
are typically 100 microns thick, at light intensities low enough to avoid
damaging the materials.
The laser writing process takes advantage of the fact that the chemical
reaction occurs only where molecules have absorbed two photons. Since
the rate of two-photon absorption drops off rapidly with distance from
the laser's focal point, only molecules at the focal point receive enough
light to absorb two photons.
"We can define with a very high degree of precision in the x, y
and z coordinates where we are getting excitation," Marder explained.
"Using 700-nanometer light, the patterning precision can be about
200 nm across by 800 nm in depth."
By scanning the laser in the sample while turning the laser off and on,
Perry's group has created a variety of structures, including objects with
moving parts like gears and chains. Three-dimensional structures produced
by the technique could be used as molds or templates for mass-producing
other structures through simple stamping processes. The technique could
also be used to create textured surfaces on which tissues can be grown,
or optical elements such as photonic band-gap structures used to manipulate
For producing 3D microstructures, the simple two-photon technique could
compete with complex multi-step fabrication processes that use lithography,
etching and layering technologies borrowed from the microelectronics industry.
However, the two-photon technique can produce only one structure at a
time, while the microelectronics-based processes simultaneously generate
hundreds or thousands of identical structures.
Right now, that makes the new system more suitable for adding specialized
3D structures to microsystems, prototypying new structures or making molds
than for producing entire systems, notes Perry, also a professor in Georgia
Tech's School of Chemistry and Biochemistry. Producing each structure
now requires about 25 seconds, but increases in speed could make mass-production
"We are working to integrate the technologies and develop a system
that should be able to operate at a thousand times the throughput of the
current system," he said. "A single 3D fabrication system should
be able to generate about a million individual device structures per day.
With a production facility using a number of fabrication systems, there
is potential for certain types of mass production."
The researchers envision tabletop fabrication machines that would use
a computer-generated design system to laser write the desired structures.
A cartridge containing the polymer film would then be removed for chemical
To move their technologies into the commercial world, Marder and Perry
have helped form a company known as Focal
Point Microsystems. The firm has licensed the technologies, which
were developed when the scientists worked at the California Institute
of Technology and the University of Arizona before joining Georgia Tech
In collaboration with researchers at Arizona and Cornell, Marder and
Perry have also been examining the fluorescent properties of the materials
for possible applications in biological imaging. The molecules also have
properties that are of interest for photodynamic therapy, which would
use light to destroy cancer cells.
For the future, Marder and Perry hope to continue improving their dyes,
increasing the resolution of the laser writing process, expanding their
family of materials - and better understanding the process. "The
scientific challenges are getting things smaller, writing faster and increasing
the number of materials in which you can write," Perry said.
The research has been supported by the National
Science Foundation, National Institutes
of Health, the Air Force Office
of Scientific Research, Office of Naval
Research and Defense Advanced Research
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WRITER: John Toon