Artificial Inverse Opal Structures for Sensing Applications

摘要

Optical sensing using photonic crystals (PhCs) as transducing materials is an emerging field in the gas and liquid sensor research. There is a wide range of properties of the PhCs that can be utilized to gain information about the pore fluid (gas/liquid). Identifying new sensing mechanisms is therefore one major topic in current research. Concepts are based on detection of e.g. refractive index changes in the pore fluid, structural changes in the PhC or optical changes caused by electronic interaction of the material with the target species. Therefore, irrespective of the details of the mechanism, elaborate material design is required. In this regard artificial inverse opal films synthesized by nano-casting methods are especially interesting because of their ease of fabrication and the variety of possible materials that can be structured. As an example WO_3 inverse opal films fabricated by a simple nano-casting process and its application as sensing material in refractive index sensor for fluid detection are presented. A combination of theoretical considerations and experimental investigations leading to some general recommendations for the design of this type of sensor are given. For the presented fluid sensor, limit of detection of 0.001 refractive index unit (RIU) can be achieved. Also the thermal stability of the WO_3 films will also be addressed briefly since it is crucial for potential high temperature (> 500 °C) applications.