High-temperature stable indium oxide photonic crystals: transducer material for optical and resistive gas sensing

Abstract. Indium oxide (In₂O₃) inverse opal is a promising new transducer material for resistive and optical gas sensors. The periodically ordered and highly accessible pores of the inverse opal allow the design of resistive sensors with characteristics independent of structure limitations, such as diffusion effects or limited conductivity due to constricted crosslinking. Additionally the photonic properties caused by the inverse opal structure can be utilized to read out the sensors' electronical state by optical methods. Typically semiconducting sensors are operated at high temperatures (> 300 °C). To maintain a good thermal stability of the transducer material during operation is a minimum requirement. We present results on the synthesis and investigation of the structural stability of the In₂O₃ inverse opal structure up to a temperature of 550 °C (limit of substrate material). As will be shown, their optical properties are maintained with only slight shifts of the photonic band gaps which can be explained by the results from the structural characterization using X-ray diffraction and electron microscopy combined with optical simulations.