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Rensselaer Polytechnic Institute Professor Shan-Yu Lin has developed a new nanotechnology-based “microlens” that uses gold to boost the strength of infrared imaging and could lead to a new generation of ultra-powerful satellite cameras and night-vision devices. The device, pictured, leverages the unique properties of nanoscale gold to “squeeze” light into the tiny holes in its surface.
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Researchers
from Rensselaer Polytechnic Institute have developed a new nanotechnology-based
“microlens” that uses gold to boost the strength of infrared imaging and could
lead to a new generation of ultra-powerful satellite cameras and night-vision devices.
By
leveraging the unique properties of nanoscale gold to “squeeze” light into tiny
holes in the surface of the device, the researchers have doubled the
detectivity of a quantum dot-based infrared detector. With some refinements,
the researchers expect this new technology should be able to enhance
detectivity by up to 20 times.
This
study is the first in more than a decade to demonstrate success in enhancing
the signal of an infrared detector without also increasing the noise, said
project leader Shawn-Yu Lin,
professor of physics at Rensselaer and a member of the university’s Future Chips Constellation
and Smart Lighting Engineering Research
Center.
“Infrared
detection is a big priority right now, as more effective infrared satellite
imaging technology holds the potential to benefit everything from homeland
security to monitoring climate change and deforestation,” said Lin, who in 2008
created the world’s
darkest material as well as a coating for solar panels
that absorbs 99.9 percent of light from nearly all angles.
“We
have shown that you can use nanoscopic gold to focus the light entering an
infrared detector, which in turn enhances the absorption of photons and also
enhances the capacity of the embedded quantum dots to convert those photons
into electrons. This kind of behavior has never been seen before,” he said.
Results
of the study, titled “A Surface Plasmon Enhanced Infrared Photodetector Based
on InAs Quantum Dots,” were published
online recently by the journal Nano
Letters. The paper also will appear in a forthcoming issue of the
journal’s print edition. The U.S. Air Force Office of Scientific Research
funded this study. The paper is available online at: http://pubs.acs.org/doi/abs/10.1021/nl100081j
The
detectivity of an infrared photodetector is determined by how much signal it
receives, divided by the noise it receives. The current state-of-the art in
photodetectors is based on mercury-cadmium-telluride (MCT) technology, which
has a strong signal but faces several challenges including long exposure times
for low-signal imaging. Lin said his new study creates a roadmap for developing
quantum dot infrared photodetectors (QDIP) that can outperform MCTs, and bridge
the innovation gap that has stunted the progress of infrared technology over
the past decade.
The
surface plasmon QDIPs are long, flat structures with countless tiny holes on
the surface. The solid surface of the structure that Lin built is covered with
about 50 nanometers—or 50 billionths of a meter—of gold. Each hole is about 1.6
microns—or 1.6 millionths of a meter—in diameter, and 1 micron deep. The holes
are filled with quantum dots, which are nanoscale crystals with unique optical
and semiconductor properties.
The
interesting properties of the QDIP’s gold surface help to focus incoming light
directly into the microscale holes and effectively concentrate that light in
the pool of quantum dots. This concentration strengthens the interaction
between the trapped light and the quantum dots, and in turn strengthens the
dots’ ability to convert those photons into electrons. The end result is that
Lin’s device creates an electric field up to 400 percent stronger than the raw
energy that enters the QDIP.
The
effect is similar to what would result from covering each tiny hole on the QDIP
with a lens, but without the extra weight, and minus the hassle and cost of
installing and calibrating millions of microscopic lenses, Lin said.
Lin’s
team also demonstrated in the journal paper that the nanoscale layer of gold on
the QDIP does not add any noise or negatively impact the device’s response
time. Lin plans to continue honing this new technology and use gold to boost
the QDIP’s detectivity, by both widening the diameter of the surface holes and
more effective placement of the quantum dots.
“I
think that, within a few years, we will be able to create a gold-based QDIP
device with a 20-fold enhancement in signal from what we have today,” Lin said.
“It’s a very reasonable goal, and could open up a whole new range of
applications from better night-vision goggles for soldiers to more accurate
medical imaging devices.”
Co-authors of the paper are Rensselaer
Senior Research Scientist James Bur, graduate student Chun-Chieh Chang, and
Research Associate Yong-Sung Kim; Yagya D. Sharma, Rajeev V. Shenoi, and Sanjay
Krishna of the Center for High Technology Materials at the University of New
Mexico, Albuquerque; and Danhong Huang of the Space Vehicles Directorate at the
Air Force Research Laboratory, Kirtland Air Force Base.
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