Nat. Nanotech. 12, 969–973 (2017)

Devices designed for continuous monitoring of light typically need to remain ‘on’ and consume electrical power. However, for some applications, such as remote battery-powered sensors for detecting infrequent events like fires or earthquakes, it would be useful to conserve power, and only switch on the detector when a relevant event is occurring. Now, Zhenyun Qian and a team at Northeastern University in the USA have done just that and demonstrated an infrared digitizing sensor that becomes active only when light of a particular wavelength impinges on the device.

The detector system makes use of plasmonics to actuate a micromechanical switch, with the incoming light ‘powering’ a micromechanical relay and activating the system. The structure relies on microcantilevers with thermally sensitive bimaterial legs that actuate on heating. Heating is generated by the incident light, via the generation of plasmons on a metallic array whose intrinsic absorption losses result in a change of temperature and mechanical displacement enabling the relay switch. For the scheme to work, absorption and losses are deliberately maximized in the structure with 50-nm-thick Au patches, a 100-nm-thick SiO2 spacer layer and a 100-nm-thick Pt metal reflector. The set-up is naturally wavelength-selective and different regions of the spectrum can be targeted by adjusting the structural geometry of the absorber. The digitized output from the device is produced at mid-infrared frequencies when incident power is above ∼500 nW.