3D fabrication technique uses light-activated molecules to create complex
Georgia Institute of Technology Professors Seth Marder (left) and Joe
Perry pose with laser equipment they use to write complex 3D structures in
polymers and other materials.
A three-dimensional microfabrication technique that uses a unique class of
light-activated molecules to selectively initiate chemical reactions within
polymers and other materials could provide an efficient way to produce
complex structures with sub-micron features.
Known as "two-photon 3D lithography," the technique could compete with
existing processes for fabricating microfluidic devices, photonic bandgap
structures, optical storage devices, photonic switches and couplers,
sensors, actuators, micromachines -- and even scaffolds for growing living
Georgia Institute of Technology Researchers Seth Marder and Joseph Perry
will describe the technique February 15 at the annual meeting of the
American Association for the Advancement of Science (AAAS).
"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
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, Perry and Marder
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 light.
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 last summer.
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 Projects Agency.
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