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Researchers Develop Darkest
Manmade Material
Other topics:
Nanocoatings
Newswise
January 22, 2008
Researchers at Rensselaer Polytechnic Institute and Rice
University have created the darkest material ever made by
man.
The material, a thin coating comprised of low-density arrays
of loosely vertically-aligned carbon nanotubes, absorbs more
than 99.9 percent of light and one day could be used to
boost the effectiveness and efficiency of solar energy
conversion, infrared sensors, and other devices. The
researchers who developed the material have applied for a
Guinness World Record for their efforts.
“It is a fascinating technology, and this discovery will
allow us to increase the absorption efficiency of light as
well as the overall radiation-to-electricity efficiency of
solar energy conservation,” said Shawn-Yu Lin, professor of
physics at Rensselaer and a member of the university’s
Future Chips Constellation, who led the research project.
“The key to this discovery was finding how to create a long,
extremely porous vertically-aligned carbon nanotube array
with certain surface randomness, therefore minimizing
reflection and maximizing absorption simultaneously.” |
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The
research results were published in the journal Nano Letters.
All materials, from paper to water, air, or plastic, reflect
some amount of light. Scientists have long envisioned an
ideal black material that absorbs all the colors of light
while reflecting no light. So far they have been
unsuccessful in engineering a material with a total
reflectance of zero.
The total reflectance of conventional black paint, for
example, is between 5 and 10 percent. The darkest manmade
material, prior to the discovery by Lin’s group, boasted a
total reflectance of 0.16 percent to 0.18 percent.
Lin’s team created a coating of low-density, vertically
aligned carbon nanotube arrays that are engineered to have
an extremely low index of refraction and the appropriate
surface randomness, further reducing its reflectivity. The
end result was a material with a total reflective index of
0.045 percent – more than three times darker than the
previous record, which used a film deposition of
nickel-phosphorous alloy.
“The loosely-packed forest of carbon nanotubes, which is
full of nanoscale gaps and holes to collect and trap light,
is what gives this material its unique properties,” Lin
said. “Such a nanotube array not only reflects light weakly,
but also absorbs light strongly. These combined features
make it an ideal candidate for one day realizing a super
black object.”
“The low-density aligned nanotube sample makes an ideal
candidate for creating such a super dark material because it
allows one to engineer the optical properties by controlling
the dimensions and periodicities of the nanotubes,” said
Pulickel Ajayan, the Anderson Professor of Engineering at
Rice University in Houston, who worked on the project when
he was a member of the Rensselaer faculty.
The research team tested the array over a broad range of
visible wavelengths of light, and showed that the nanotube
array’s total reflectance remains constant.
“It’s also interesting to note that the reflectance of our
nanotube array is two orders of magnitude lower than that of
the glassy carbon, which is remarkable because both samples
are made up of the same element – carbon,” said Lin.
This discovery could lead to applications in areas such as
solar energy conversion, thermalphotovoltaic electricity
generation, infrared detection, and astronomical
observation.
Other researchers contributing to this project and listed
authors of the paper include Rensselaer physics graduate
student Zu-Po Yang; Rice postdoctoral research associate
Lijie Ci; and Rensselaer senior research scientist James
Bur.
The project was funded by the U.S. Department of Energy’s
Office of Basic Energy Sciences and the Focus Center New
York for Interconnects.
Lin’s research was conducted as part of the Future Chips
Constellation at Rensselaer, which focuses on innovations in
materials and devices, in solid state and smart lighting,
and applications such as sensing, communications, and
biotechnology. A new concept in academia, Rensselaer
constellations are led by outstanding faculty in fields of
strategic importance. Each constellation is focused on a
specific research area and comprises a multidisciplinary mix
of senior and junior faculty, as well as postdoctoral
researchers and graduate students.
About Rensselaer
Rensselaer Polytechnic Institute, founded in 1824, is the
nation’s oldest technological university. The university
offers bachelor’s, master’s, and doctoral degrees in
engineering, the sciences, information technology,
architecture, management, and the humanities and social
sciences. Institute programs serve undergraduates, graduate
students, and working professionals around the world.
Rensselaer faculty are known for pre-eminence in research
conducted in a wide range of fields, with particular
emphasis in biotechnology, nanotechnology, information
technology, and the media arts and technology. The Institute
is well known for its success in the transfer of technology
from the laboratory to the marketplace so that new
discoveries and inventions benefit human life, protect the
environment, and strengthen economic development. |
