Graphene The Hot Bolometer?


Graphite-Graphene-News-208CA bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley. The name comes from the Greek word bole (????), for something thrown, as with a ray of light
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Another day and yet another use for graphene announced, albeit a highly technical one. Graphene is apparently ideal for making hot-electron bolometers, and comes with the future promise of getting tweaked to operate at room temperature. That last, if it eventually happens, would be quite some feat. Most existing bolometers operate at close to absolute zero, requiring extensive expensive cooling.

While bolometers will always be a minor use for graphene, the real point here is the extensive research going on into graphene and its amazing properties, and the fact that almost weekly now, we get new uses for graphene announced that involve new areas of research with great potential. While this decade won’t be the “graphene decade,” the next decade, the second of the 21st century probably will be.

Graphene holds promise for hot-electron bolometers
Jun Yan, Myoung-Hwan Kim, H. Dennis Drew and Michael S. Fuhrer
The superior capability of graphene to limit electronic energy from being dissipated within the lattice makes it a fast photon detector with unprecedented sensitivity.
24 August 2012,

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A bolometer is an electronic device that converts light into heat, which can then be detected by a thermometer. The thermal resistance, Rh, provides the coefficient linking incident power P and change in temperature ?T, such that ?T = PRh. An important consideration in designing a bolometer is the time taken for it to recover, given by ? = RhC, where C is the heat capacity. This has influenced the design of bolometers, which often used thin metal films with low C as absorbers that were suspended in vacuum with a spiderweb of fine nylon or Kevlar fibers to minimize thermal leak to the environment.

In contrast, a hot-electron bolometer uses a simpler approach. At low temperature, the electron gas in a material becomes increasingly decoupled from the phonons or lattice vibrations, leading to a large Rh, while C of the electrons becomes small and proportional to T. Currently, the most sensitive hot-electron bolometers are transition edge sensors (TES), which make use of a metal near its superconducting phase transition as both the absorber and thermometer, with the sharpness of the superconducting transition providing excellent sensitivity.

—- However, Fong and Schwab12 successfully used an impedance-matching scheme and noise thermometry to measure a graphene bolometer at 1.2GHz with an 80MHz bandwidth. We therefore see no insurmountable barriers to the adoption of graphene-based bolometry for ultra-sensitive detection of sub-millimeter wave photons. Future work will include efforts to demonstrate the ultrahigh sensitivity of graphene bolometers at lower temperatures. Other mechanisms, such as plasmons in graphene, may also be explored to make the graphene detector work at room temperature.
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