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

Highlights: • For the first time, the refractive index and absorption coefficient were reported for polymer-derived ceramics at THz domain • The textured carbosiloxane ceramics exhibit lower reflectivity when compared to the planar surfaces • The performance of the designed micro-bolometer is in fair competition with the commercially available terahertz power meters 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 500–750 GHz, 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 – 3 dB was obtained for planar surfaces, whereas pyramidal surfaces exhibited a much lower value of – 22 dB 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 0.76 V/W at bias current of 1 mA, time constant of 180 ms, and noise equivalent power of 2 nW/$\sqrt{\mathrm{Hz}}$.