Thermal stability of micro-structured selective tungsten emitters

摘要

The microstructuring of a tungsten emitter allows a remarkable increase of the emittance in a defined spectral range with low mid IR emission at the same time. The optical properties of the selective emitter are determined by the grating period and the shape of the grating. Furthermore for the spectral angle dependency the structure depth plays a significant role. As theoretical investigations using Rigorous Coupled Wave Analysis (RCWA) have shown the spectral angle dependency decreases in case of deep or high spatial-frequency structures. At usual TPV emitter temperatures (typically above HOOK) microstructured selective tungsten emitters show both surface diffusion and the so-called recrystallisation effect. In some cases a modification and destruction of the surface structure due to this phenomena have been observed. At first, the technique of producing selective tungsten emitters is described. In addition, the result of our investigations concerning thermal stability of both shallow and deep gratings is presented and some attempts to handle thermal deterioration are discussed.