The voltage response of thermoelectrically coupled nanoantennas (TECNA) to infrared light (IR) is greatly enhanced by suspending them above quasi-spherical cavities. The cavities behave as optical elements that focus the IR radiation onto the nanoantennas. The wavelength response of a cavity depends on its geometrical profile, for which the resonant cavity mode must match the resonant wavelength of the antenna. In this work, TECNAs were designed to detect four different wavelengths in the mid- and long-wave IR and fabricated in a single chip, requiring different cavity profiles. Cavities were fabricated by isotopically etching Si using xenon difluoride (XeF2). XeF2 gas etches the Si substrate through circular windows patterned in resist. The antenna is patterned before the cavity is formed to avoid difficulties in filling and planarizing the supporting layer for antenna patterning and is left suspended over the cavity after etching. The different cavity profiles were formed in a single etch, since subsequent resist patterning and etching of unfilled cavities would destroy previous antennas. This work compares cavity profiles etched using both pulsed and continuous-flow XeF2 etch methods using different etch window sizes to produce variously sized and shaped cavities in a single etch. The cavity profiles were characterized using a laser-scanning confocal microscope. Piecewise equations made up of a torus, a cone, and a cylinder were fitted to the profiles and used in COMSOL simulations of electromagnetic standing-wave patterns within the cavity. Antennas were then chosen to have peak responses at wavelengths that match a simulated cavity’s peak response.
Thermoelectrically coupled nanoantennas (TECNAs) are a new class of infrared detectors based on the resonant absorption of freely propagating electromagnetic waves. When IR light illuminates the devices, radiation-induced antenna current heats the nanothermocouples. The temperature difference with respect to the cold junction at the substrate is converted to electrical signals by the Seebeck effect. The physical size of the nanoantenna determines the spectral response of the device. In this work, we show experimentally obtained spectral responses of TECNAs using Fourier-transform infrared spectroscopy (FTIR) and compare the results to simulations.
Thermoelectrically coupled nanoantennas (TECNAs) are fast thermal sensors for the mid- to far-IR regime. TECNAs resonantly absorb EM radiation using a nanoantenna and nanothermocouple, and can be made directionally sensitive using a reflecting cavity. We present TECNAs located above a cavity etched into a substrate to determine angle of incidence of laser beams. The position of the antennas relative to the cavity center provides beam steering capability. We show in simulations that radiation and receiving characteristics of TECNAs are strongly dependent on position above the cavity. Positioning multiple antennas above a cavity provides angle-of-incidence resolution capability in the thermal infrared.
Polarization information regarding solar radiation is not readily available in the mid- to far-infrared regimes. Conventional thermal IR detectors capture intensity with a loss of specific spectral and polarization information. Thermoelectrically coupled nanoantennas (TECNAs) capture infrared radiation by using an antenna that provides the capability for spectral, polarization, and angle-of-incidence selectivity. The nanoantenna resonantly absorbs the incident IR radiation and heats the hot junction of a nanothermocouple, which provides an output voltage that is proportional to the intensity. This is accomplished with minimal thermal mass, and provides μs response times. Here we present TECNAs with log-spiral antennas that are capable of distinguishing left- and right-handed circular polarization (LHCP/RHCP) in the long-waveinfrared. The log-spiral TECNAs are suspended above quasi-hemispherical cavities etched into a Si substrate. The cavity thermally isolates the nanoantenna from the substrate and focuses the incident radiation onto it. Simulations show electromagnetic (EM) fields and resulting thermal distributions along the antennas for different polarizations. When the handedness of the EM polarization matches that of the antenna, the EM field is concentrated at the center of the antenna, while for opposite polarization it is concentrated toward the antenna leads. As a result, the temperature increase at the center of the nanoantenna for the two polarization directions is different. This provides an extinction ratio VRHCP/VLHCP ~ 4.
Thermoelectrically coupled nanoantennas (TECNAs) for mid- to far-infrared radiation are developed to study the Sun. TECNAs are resonantly absorbing the IR radiation using a nanoantenna that provides wavelength and polarization selectivity, as well as providing uncooled, and fast detection. This technology will enable transient solar measurements in the mid- to far- and wavelength ranges.
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