High-temperature degradation of one-dimensional metallodielectric (W/SiO₂) photonic crystal as selective thermal emitter for thermophotovoltaic system

In this paper, thermal stability of a one-dimensional metallodielectric photonic crystal (1D MDPhC) structure based on W and SiO₂ for thermophotovoltaic systems is reported. The thermal degradation mechanism of the structure, in its operating temperature range, is thoroughly investigated by using energy dispersive spectroscopy (EDS) with transmission electron microscope (TEM) and depth-profiling X-ray photoelectron spectroscopy (XPS). It is found that the structure is entirely destroyed under 1400 K by an inter-diffusion process forming a mixture of W and SiO₂ without measurable oxidization of W. But, long-term annealing results in oxidization of W layer even at a lower temperature of 1300 K. During the long-term annealing, oxygen atoms in outside atmosphere are believed to cause oxidation of the upper W layer below the top SiO₂ layer. Additionally, delaminated spots are observed over the surface. These thermal behaviors are potential clues to prevent or minimize thermal degradation of the multilayer structure under high temperature operation.