Metal Oxide Based Sensors

Dear Colleagues,

Among the different types of sensors, semiconducting metal oxides (SMO_x) have attracted attention due to their outstanding properties. The specific mechanisms of sensing involved in SMO_x are complex and not fully understood (e.g., adsorption and chemisorption steps, charge transfers, oxygen migration). The sensor’s functional material surface properties such as the (nano)structure, morphology, and crystallinity are crucial for its final performances. The main SMO_x sensors’ parameters are the sensitivity (measured variation of the signal as a function of a variation of molecule concentration), the selectivity (capacity to measure individual molecules within a mixture), the time interval needed for measurement (and of recovery), and the stability of characteristics over time.

Three challenges drive the very active research on the topic:

• How to improve the sensor sensitivity? For example, the research carried out on this topic includes the synthesis of highly porous or nanostructured materials to maximize the effective surface and therefore the number of adsorption sites.
• How to obtain the required selectivity? SMO_x sensor sensitivity is intrinsically poor; therefore, a great deal of effort has been devoted to compose “sensor arrays” with different functional properties whose responses are treated comparatively.
• How to miniaturize the sensors? One crucial aim is to reduce the energy consumption of the sensors in order to include them in small batteries. A promising route to achieve this purpose is to replace the usual thermal activation by UV irradiation, which would also enable the measurement of explosive materials. Another objective related to miniaturization is to make them more easily transportable, so as to integrate new functionalities in devices such as smartphones.

The aim of this Special Issue is to assemble high-quality contribution on the synthesis, modification, characterization, and the application of semiconducting metal oxides (SMO_x). It will deal with the design of different functional nanostructures (e.g., thin films, nanoparticles, nanowires, and nanofibers) based on different metal oxides (MO_x) (e.g., SnO₂, TiO₂, Al₂O₃, NiO, WO₃, CuO, ZnO, LiNbO₃, etc.) with controlled chemical composition (e.g., doping and mixed multilayers (nano-laminates)) and carbon-based MO_x (MO_x-C using carbon nanotubes (CNTs) and graphene), and to functionalize/modify the surfaces with noble metal particles or other nanostructures and to fabricate p–n hetero-junctions (HJs). The relation between these parameters and the structural, electrical, and optical properties of the MO_x, HJ, and MO_x-C nanostructures, as well as their sensing capabilities, will be explored.

All new concepts targeting the optimization of sensor parameters by tailoring the structural properties and surface chemistry of the nanostructures in order to achieve (i) increased sensitivity, (ii) higher selectivity, (iii) lower operation temperature, and (iv) enhanced stability over time will be investigated. The final target is to provide new concepts allowing for the integration of MO_x-, HJ-, and MO_x-C-based sensors with novel industrial microelectronic sensor platforms in low-cost manufacturing processes.

Dr. Mikhael Bechelany
Guest Editor

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