First invented by American astronomer Samuel Langley in 1878, bolometers are extremely sensitive instruments that help measure heat or electromagnetic radiation. Modern devices use absorbent elements made out of superconductors or semiconductors that can detect changes in temperature as little as 0.0001°C.
Below is the Abstract from ‘A fast and sensitive room-temperature graphene nanomechanical bolometer’ published October 17 2019 in Nature Communications volume 10, Article number: 4726 (2019)
Bolometers are a powerful means of detecting light. Emerging applications demand that bolometers work at room temperature, while maintaining high speed and sensitivity, properties which are inherently limited by the heat capacity of the detector. To this end, graphene has generated interest, because it has the lowest mass per unit area of any material, while also possessing extreme thermal stability and an unmatched spectral absorbance. Yet, due to its weakly temperature-dependent electrical resistivity, graphene has failed to challenge the state-of-the-art at room temperature. Here, in a departure from conventional bolometry, we use a graphene nanoelectromechanical system to detect light via resonant sensing. In our approach, absorbed light heats and thermally tensions a suspended graphene resonator, thereby shifting its resonant frequency. Using the resonant frequency as a readout for photodetection, we achieve a room-temperature noise-equivalent power (2 pW Hz−1/2) and bandwidth (from 10 kHz up to 1.3 MHz), challenging the state-of-the-art.
Findings and Additional Information
University of Oregon. "Physicists develop fast and sensitive mechanical tool to measure light." ScienceDaily. www.sciencedaily.com/releases/2019/10/191017111718.htm (accessed October 17, 2019)
A team of University of Oregon physicists has developed a fast, sensitive bolometer that can measure light at and far above room-temperature. The technology out of the Alemán Lab, known as a "graphene nanomechanical bolometer," leverages a new method and an ultrathin material, and could have wide-spread use in everything from astronomy and medicine to fire fighting.
"This tool is the fastest and most sensitive in its class," said Benjamín Alemán, a professor of physics at the University of Oregon and a member of the UO's Center for Optical, Molecular, and Quantum Science and an associate of the Phil and Penny Knight Campus for Accelerating Scientific Impact.
The device, which consists of a trampoline-shaped piece of graphene suspended over a hole, offers an alternative to conventional electronic light detectors, like those found in a smartphone's camera. Instead, the Alemán Lab uses a mechanical method to relate absorbed light to small changes in the mechanical resonance frequency of the graphene trampoline.
The way the technology works is similar to the effect of banging a drum on a hot day. As the instrument heats up under the piping sun, the drumhead membrane will expand and its pitch changes - emitting a different tone than it would at cooler temperatures.
The waves of light do the same thing to a mechanical bolometer. As light hits the device's drumhead, the membrane heats up, expands and the vibrational pitch changes. The physicists can track these pitch changes to measure how much light hit the device.
"This is a very new way of detecting light," said David Miller, a doctoral student in the Alemán Lab. "We're using a purely mechanical method to turn light into sound. This has the advantage of being able to see a much broader range of light."
Conventional detectors are very reliable at reading high energy light, like visible light or X-rays, but less adept at measuring the longer wavelengths on the electromagnetic spectrum, including infrared and radio waves, Miller said. This mechanical device fills that void and allows the detection of light of nearly any wavelength -- which could be especially useful in astronomical observations, thermal and medical body imaging and seeing deep into the infrared.
The team constructed the device by first stretching a thin sheet of atoms over a hole etched into a piece of silicon. Then, using a focused ion beam technique, developed previously in the lab, they cut the sheet to resemble a trampoline. The device is just one-tenth the width of a human hair, while the material used for the trampoline is even smaller -- a single atom thick, about a million times thinner than that same strand of hair.
"This system uses graphene, which is just a single layer of atoms. It's as small as it can be." said Andrew Blaikie, another doctoral student in the Alemán Lab and lead author on the paper, which was published in Nature Communications this week.
Graphene, a material discovered in 2004 is the key ingredient for the technology's success. Although it's the thinnest possible material, graphene is 200 times stronger than steel. It won the 2010 Nobel Prize in Physics for its potential to revolutionize physics and engineering.
Graphene's mechanical properties allow the material to respond to temperature changes incredibly fast, enabling it to measure light at equally speedy rates, Blaikie said.
"Graphene offered a tantalizing prospect for ultrasensitive and ultrafast light detection," Blaikie said. "It also possesses an unmatched ability to measure nearly any wavelength of light and can withstand much higher temperatures than conventional detectors."
The team of physicists was able to harness the powers of graphene through a mechanical approach to measuring light. The material has performed poorly through the traditional methods of using electrical resistance to measure light -- mainly due to its temperature-dependent electrical resistivity and need to be chilled to ultralow temperatures to be useful in conventional detectors.
When the researchers realized they could turn light into sound through their mechanical method, they were able to unlock the prospects of graphene and create the ultrafast, ultrasensitive device that excels at and far above room temperature.
Its ability to perform at such a wide range of temperatures is one of the device's most advantageous qualities when it comes to measuring light, Blaikie said. It can operate at room temperature, which allows for critical portability, and it can perform under high heat, which is a benefit that traditional light detectors don't offer. Many detectors fail with the "sunburn effect," when they begin to breakdown as temperatures spike.
"Graphene is a thermally stable material that can withstand temperatures over 2,000 degrees Celsius, so that our detector, unlike electronic detectors, could possibly take pictures on hot planets like Venus or Mercury" Blaikie said.
Its versatility and ultrasensitive nature potentially make the nanomechanical bolometer a useful tool in many arenas across science, medicine, industrial manufacturing and astronomy. The Alemán Lab has a patent pending for the technology with the U.S. Patent and Trademark Office.
"We hope this device will help scientists crack the mysteries of our sun and other stars, improve medical diagnostics through safer thermal X-ray imaging, and help firefighters see better in fires to save more lives," Alemán said.
The National Science Foundation supported the research.