Tungsten Oxide Photonic Crystals as Optical Transducer for Gas Sensing

Abstract

Some metal oxide semiconductors, such as tungsten trioxide or tin dioxide, are well-known as resistive transducers for gas sensing and offer high sensitivities down to the part per billion level. Electrical signal read-out, however, limits the information obtained on the electronic properties of metal oxides to a certain frequency range and its application because of the required electrical contacts. Therefore, a novel approach for building an optical transducer for gas reactions utilizing metal oxide photonic crystals is presented here. By the rational design of the structure and composition it is possible to synthesize a functional material which allows one to obtain insight into its electronic properties in the optical frequency range with simple experimental measures. The concept is demonstrated by tungsten trioxide inverse opal structure as optical transducer material for hydrogen sensing. The sensing behavior is analyzed in a temperature range from room temperature to 500 °C and in a wide hydrogen concentration range (3000 ppm to 10%). The sensing mechanism is mainly the refractive index change resulting from hydrogen intercalation in tungsten trioxide, but the back reaction has also impact on the optical properties of this system. Detailed chemical reaction studies provide suggestions for specific sensing conditions.

Improving the Performance of Gas Sensor Systems with Advanced Data Evaluation, Operation, and Calibration Methods

“…The optical output, however, allows true wireless transfer of the signal, e. g., from the inside of a vacuum chamber through a window to the outside. Systems are available with optical waveguides detecting changes in refraction index through evanescent waves just outside a fiber, as well as colorimetric sensors, e. g., for hydrogen (reversible) [25], [26] and formaldehyde (irreversible) [27]. The latter, based on a chemical reaction, currently reaches the best selectivity available on the market.…”

GS9.4 - Optical Hydrogen Sensing with Tungsten Oxide Photonic Crystals

“…Peak position of the reflectance peak of the tungsten oxide inverse opal depending on the hydrogen concentration in a log-log-plot. [4] The response to hydrogen is fast, e.g. t90=0.7 s for 5 % hydrogen at 200 °C.…”

Synthesis of Metal Oxide Inverse Opals from Metal Nitrates by PMMA Colloidal Crystal Templating

“…Metal oxide inverse opals are three‐dimensionally ordered macroporous materials that are interesting as catalysts, energy storage materials, and chemical or biological sensors , . The colloidal crystal templating approach is the most common synthetic method to produce metal oxide inverse opal structures .…”