Ordered mesoporous materials have great potential in the field of gas sensing. Today various template-assisted synthesis methods facilitate the preparation of silica (SiO2) as well as numerous metal oxides with well-defined, uniform and regular pore systems. The unique nanostructural properties of such materials are particularly useful for their application as active layers in gas sensors based on various operating principles, such as capacitive, resistive, or optical sensing. This review summarizes the basic aspects of materials synthesis, discusses some structural properties relevant in gas sensing, and gives an overview of the literature on ordered mesoporous gas sensors.
Mixed thin films of donor‐ and acceptor‐type molecular semiconductors were prepared by physical vapour deposition and studied by conduction measurements in the dark during film growth and under illumination at three distinct wavelengths across the visible range of the solar spectrum. The molecules were chosen to provide both, good spectral coverage of the solar spectrum and appropriate differences in the electronic energy levels to allow charge carrier separation. Photocurrents were observed that indicated the expected contributions to the net photoconduction but also anomal, negative contributions were found, leading to a decreased conduction under illumination, showing the presence of isolated clusters. Ripening of the mixed films in vacuum and conditioning the films at air were studied subsequently and consequences on conduction and photoconduction discussed. The applicability of such films in evaporated organic bulk heterojunctions as photoconductors or in photovoltaic cells is discussed.
Vacuum chamber for simultaneous evaporation of pure and mixed organic thin films equipped with in situ (photo)‐conduction measurements.
The performance of many chemical gas-phase reactions is strongly influenced by the interaction of reactants with interfaces. Nanoporous materials, which exhibit pore diameters up to 100 nm and high specific surface areas, can be utilized to reduce the amount of cost-intensive materials (e.g. noble metals). However, due to limitations in material transport and reaction kinetics detailed knowledge of the diffusion and the kinetics of a chemical reaction is necessary to improve the performance of chemical processes in industry and research. To experimentally study the diffusion and reaction kinetics of gaseous species inside such pores, the chemoresistive behavior of certain metal oxides such as InO can be utilized. In this work, we present a model system based on hierarchically porous monolithic indium oxide (InO) which allows the determination of kinetic effects by utilizing its gas transducing properties. The experimental data obtained by electrical measurements are compared to two diffusion and diffusion-reaction models. Using these methods, the rate constant of ozone decomposition in porous InO is estimated. The results are the basis for a suitable material design for semiconducting gas sensors, on the nano-, meso- and macroscale, which helps in understanding the underlying mechanisms of diffusion and reaction.
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