Applied Physics

Darker Detectors

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Science  20 Aug 2010:
Vol. 329, Issue 5994, pp. 885
DOI: 10.1126/science.329.5994.885-a
CREDIT: LEHMAN ET AL., NANO LETT. 10, 10.1021/NL100582J (2010)

Infrared radiation is normally detected by its conversion to heat through absorption at surfaces. The darker the detector surface, the less incoming radiation is reflected away: Dark coatings are thus applied to materials that can convert heat into an electrical signal, such as lithium tantalate, a pyroelectric that generates a temporary change in voltage as its temperature changes. Carbon nanotubes grown as vertically aligned arrays have been reported to be the darkest of materials, but challenges remain in using them to create detectors. Lehman et al. grew multiwall carbon nanotubes on a lithium tantalate crystal surface. The catalytic growth conditions (temperatures of 750°C) were above the Curie temperature, so the surface had to be heated, repoled with an electric field, and then cooled to restore its full pyroelectricity. However, higher growth temperatures resulted in longer and more uniform nanotube coatings. Reported reflectances across the detector were less than 0.1% for wavelengths between 0.4 and 4 µm, and less than 1% in the mid-infrared region spanning 4 to 14 µm.

Nano Lett. 10, 10.1021/nl100582j (2010).

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