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Molecular scale resolution achieved in polymer nanoimprinting technique - dimensions smaller than the wavelength of light.

Molecular scale resolution achieved in polymer nanoimprinting technique - dimensions smaller than the wavelength of light. - Physics Forum

Molecular scale resolution achieved in polymer nanoimprinting technique - dimensions smaller than the wavelength of light. - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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Old 01-22-2005, 09:17 PM
Ken Kubos
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Default Molecular scale resolution achieved in polymer nanoimprinting technique - dimensions smaller than the wavelength of light.



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Molecular scale resolution achieved in polymer nanoimprinting technique

January 21, 2005

Scientists using molds derived from carbon nanotubes have approached
the ultimate resolution - defined by molecular scale dimensions - in a
widely used polymer nanoimprinting technique. By accurately replicating
features with nanometer dimensions, the technique could play future roles in
fabricating structures in fields as diverse as microelectronics,
nanofluidics and biotechnology.
Polymer nanoimprint lithography works by pressing a mold with embossed
relief structures against a thin polymer film. Little is known, however, of
the basic physics and chemistry that operate between the two surfaces at the
molecular level, let alone how these interactions relate to resolution.

"A better understanding of the basic physics and resolution limits of
nanoimprint lithography will allow us to develop design criteria for better
polymer materials for molds and films that would improve the performance,"
said John Rogers, a professor of materials science and engineering at the
University of Illinois at Urbana-Champaign and a researcher at the Beckman
Institute for Advanced Science and Technology.

In a paper published in the December issue of the journal Nano Letters,
Rogers and colleagues at Illinois and Dow Corning Corp. explored the
fundamental resolution limits of polymer nanoimprint lithography. The work
involved a broad interdisciplinary collaboration between experts in several
fields, including nanoimprint lithography, carbon nanotubes, nanoscale
imaging techniques for polymers, and polymer chemistry.

The researchers began by growing single-walled carbon nanotubes on a silicon
wafer. Then they prepared a mold of the nanotubes by pouring a
thermal-setting polymer over the wafer.

After curing the mold, they gently pressed it against a thin layer of
photocurable polyurethane. Passing light through the transparent mold caused
the material to cross-link and harden. The researchers then used atomic
force microscopy to measure the heights of the resulting relief structures
and transmission electron microscopy to determine their widths.

"Our approach allowed us to reach a critical size regime never explored
before," Rogers said. "From a detailed analysis of the microscope images, we
were able to demonstrate reliable patterning at the 2 nanometer scale, and
even some capability down to 1 nanometer. These dimensions are comparable to
the sizes of individual macromolecules."

To obtain features with a resolution of 2 nanometers, both the average
distance between polymer cross-links (approximately 1 nanometer) and the
lengths of individual chemical bonds (approximately 0.2 nanometers) become
important in the molding process.

"We normally wouldn't be concerned with the molecular structure of the
polymer," Rogers said, "but at these dimensions we have feature sizes that
are only a few times larger than the length of individual bonds in the
polymer. In addition, we have a countable number of polymer bond lengths
that are available to replicate the relief structure."

By varying the density of cross-links in the polymer, the researchers also
established a connection between resolution limit and molecular structure of
the polymer. "The ultimate resolution is correlated to the ability of the
prepolymer to conform to the surface and the ability of the cross-linked
polymer to retain the molded shape," Rogers said.

The ability to mold nano-scale features can benefit many fields, from
semiconductor device manufacturing to emerging areas of biotechnology. For
example, polymer nanoimprint lithography could help the electronics industry
achieve the resolution requirements needed for next-generation devices. By
structuring materials with dimensions smaller than the wavelength of light,
the technique also could create photonic devices whose optical properties
are defined by the geometry of the relief structures embossed on them.

In other applications, polymer molds with molecular scale channels could
prove useful in nanofluidics, where the tiny tunnels would transport fluids
or separate materials based on size, Rogers said. And, by allowing for the
nanoimprinting of individual macromolecules, the technique might open new
paths to molecular recognition, drug discovery and catalysis.

Source: University of Illinois at Urbana-Champaign (by James E. Kloeppel)
--
Ken

"Buddhism elucidates why we are sentient."



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