Net-shaped pyramidal carbon-based ceramic materials designed for terahertz absorbers

Publication date: 15 April 2017
Source:Materials & Design, Volume 120
Author(s): Srisaran Venkatachalam, Guillaume Ducournau, Jean-François Lampin, Djamila Hourlier
This study on polymer-derived ceramic (PDC) materials is devoted to the fabrication of 3D structures with vertically aligned pyramids and their optical properties at terahertz frequencies. The materials have been prepared by thermal conversion of a crosslinked polydimethylsiloxane precursor. Pyrolysis of starting polymer in an inert atmosphere yields a ceramic nanocomposite constituted of excess carbon embedded into a Silicon oxycarbide matrix. The excess carbon, essentially composed of small stacked graphene layers, is beneficial to absorption of terahertz radiation. In the frequency domain 500–750GHz, a gradual variation in refractive index and absorption coefficient was obtained by the progressive thermal transition of the polymer. For samples heat-treated at 1500°C, a reflectivity of – 3dB was obtained for planar surfaces, whereas pyramidal surfaces exhibited a much lower value of – 22dB when measured at oblique incidence and receiving angle of 60°.For the first time, the proof-of-concept for PDC as the absorber element in microbolometers, specifically dedicated to the terahertz domain has been demonstrated. The microbolometer with 3D absorber element exhibited a responsivity of 0.76V/W at bias current of 1mA, time constant of 180ms, and noise equivalent power of 2nW/Hz.

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