CHARACTERIZATION OF SILICON OXYNITRIDE MULTILAYERED SYSTEMS FOR PASSIVE RADIATIVE COOLING APPLICATION

The realization of the so-called 'inverse greenhouse effect' requires the fabrication of devices that have a high emittance inside the atmospheric window, i.e. between 8 and '13 mu mm, and a high reflectance elsewhere. Among other materials, silicon oxynitrides are particularly well suited for this application, because the stretching vibrations of Si-N and Si-O species contribute to an intense absorption inside the desired wavelength range. From theoretical considerations, one can show that multilayered configurations using periodic repetition of oxynitride layers of various stoichiometries provide additional vibrational modes localized at the interfaces, which ideally contribute to filling the atmospheric window. Several devices have been realized by RF plasma sputtering of silicon oxynitrides on aluminum films. They were characterized by Rutherford backscattering and infrared and electron spectroscopies, and their radiative cooling efficiency could be evaluated.