Darkest material-world record set by Rensselaer
Polytechnic Institute and Rice University [Jan
28]Troy, N.Y. — Researchers at Rensselaer
Polytechnic Institute and Rice University have created the
darkest material ever made by man.
Photo: The vertically aligned carbon nanotube
samples were mounted in the center of a integrating sphere, which
measured the material's reflectivity.Photo Credit: Rensselaer
(enlarge
photo)
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.
“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.”
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.
