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Special Issue "Metal Oxide Based Sensors"

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Chemical Sensors".

Deadline for manuscript submissions: closed (30 June 2020).

Special Issue Editor

Dr. Mikhael Bechelany
E-Mail Website
Guest Editor

Special Issue Information

Dear Colleagues,

Among the different types of sensors, semiconducting metal oxides (SMOx) have attracted attention due to their outstanding properties. The specific mechanisms of sensing involved in SMOx 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 SMOx 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? SMOx 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 (SMOx). It will deal with the design of different functional nanostructures (e.g., thin films, nanoparticles, nanowires, and nanofibers) based on different metal oxides (MOx) (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 MOx (MOx-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 MOx, HJ, and MOx-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 MOx-, HJ-, and MOx-C-based sensors with novel industrial microelectronic sensor platforms in low-cost manufacturing processes.

Dr. Mikhael Bechelany
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • semiconducting metal oxides (SMOx) 
  • thin film 
  • nanomaterial 
  • interface 
  • nanostructured materials 
  • porous materials 
  • energy
  • health
  • environment

Published Papers (4 papers)

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Research

Article
Detection of Organophosphorous Chemical Agents with CuO-Nanorod-Modified Microcantilevers
Sensors 2020, 20(4), 1061; https://doi.org/10.3390/s20041061 - 15 Feb 2020
Cited by 4 | Viewed by 962
Abstract
Microcantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper oxide (CuO) nanorods. The synthesis of the nanostructure consists of the oxidation of a copper layer deposited beforehand [...] Read more.
Microcantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper oxide (CuO) nanorods. The synthesis of the nanostructure consists of the oxidation of a copper layer deposited beforehand on the surface of the sample. The oxidation is performed in an alkaline solution containing a mixture of Na(OH) and (NH4)2S2O8. The synthesis procedure was first optimized on a silicon wafer, then transferred to optical cantilever-based sensors. This transfer requires specific synthesis modifications in order to cover all the cantilever with nanorods. A masking procedure was specially developed and the copper layer deposition was also optimized. These nanostructured cantilevers were engineered in order to detect vapors of organophosphorous chemical warfare agents (CWA). The nanostructured microcantilevers were exposed to various concentration of dimethyl methylphosphonate (DMMP) which is a well-known simulant of sarin (GB). The detection measurements showed that copper oxide is able to detect DMMP via hydrogen interactions. The results showed also that the increase of the microcantilever surface with the nanostructures improves the sensors efficiency. The evolution of the detection performances of the CuO nanostructured cantilevers with the DMMP concentration was also evaluated. Full article
(This article belongs to the Special Issue Metal Oxide Based Sensors)
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Article
Effect of Oxidization Temperatures and Aging on Performance of Carbonate Melt Oxidized Iridium Oxide pH Electrode
Sensors 2019, 19(21), 4756; https://doi.org/10.3390/s19214756 - 01 Nov 2019
Cited by 2 | Viewed by 989
Abstract
Iridium oxide pH electrodes employing the carbonate melt oxidation method were fabricated with oxidation temperatures of 750 °C, 800 °C and 850 °C, respectively. Scanning electron microscope (SEM) and atomic force microscope (AFM) images showed that the oxide film regularized with the increase [...] Read more.
Iridium oxide pH electrodes employing the carbonate melt oxidation method were fabricated with oxidation temperatures of 750 °C, 800 °C and 850 °C, respectively. Scanning electron microscope (SEM) and atomic force microscope (AFM) images showed that the oxide film regularized with the increase in oxidation temperatures. The pH response, response time and long-term stability of the electrodes indicated that the electrodes made at 850 °C had the best performance. X-ray photoelectron spectra (XPS) surveys investigated the change in the electrodes’ chemical composition and element oxidation states at 850 °C, and the results showed that the relative content of Ir3+ had increased by 23.9%, and the Ir4+ and Ir6+ had decreased by 10.9% and 13%, respectively, in the surface oxide layer after one month of aging. However, the relative contents of Ir3+, Ir4+ and Ir6+ were almost constant for the inner oxide layer. Meanwhile, the XPS result also indicated that the outer oxide layer of the electrode had a higher hydration degree than the inner oxide layer. Full article
(This article belongs to the Special Issue Metal Oxide Based Sensors)
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Article
ppb-Level Selective Hydrogen Gas Detection of Pd-Functionalized In2O3-Loaded ZnO Nanofiber Gas Sensors
Sensors 2019, 19(19), 4276; https://doi.org/10.3390/s19194276 - 02 Oct 2019
Cited by 13 | Viewed by 1412
Abstract
Pd nanoparticle-functionalized, xIn2O3 (x = 0.05, 0.1, and 0.15)-loaded ZnO nanofibers were synthesized by an electrospinning and ultraviolet (UV) irradiation method and assessed for their hydrogen gas sensing properties. Morphological and chemical analyses revealed the desired morphology and chemical composition [...] Read more.
Pd nanoparticle-functionalized, xIn2O3 (x = 0.05, 0.1, and 0.15)-loaded ZnO nanofibers were synthesized by an electrospinning and ultraviolet (UV) irradiation method and assessed for their hydrogen gas sensing properties. Morphological and chemical analyses revealed the desired morphology and chemical composition of the synthesized nanofibers. The optimal gas sensor namely Pd-functionalized, 0.1In2O3-loaded ZnO nanofibers showed a very strong response to 172–50 ppb hydrogen gas at 350 °C, which is regarded as the optimal sensing temperature. Furthermore, the gas sensors showed excellent selectivity to hydrogen gas due to the much lower response to CO and NO2 gases. The enhanced gas response was attributed to the excellent catalytic activity of Pd to hydrogen gas, and the formation of Pd/ZnO and In2O3/ZnO heterojunctions, ZnO–ZnO homojunction, as well as the formation of PdHx. Overall, highly sensitive and selective hydrogen gas sensors can be produced based on a simple methodology using a synergistic effect from Pd functionalization and In2O3 loading in ZnO nanofibers. Full article
(This article belongs to the Special Issue Metal Oxide Based Sensors)
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Article
The Enhanced H2 Selectivity of SnO2 Gas Sensors with the Deposited SiO2 Filters on Surface of the Sensors
Sensors 2019, 19(11), 2478; https://doi.org/10.3390/s19112478 - 30 May 2019
Cited by 15 | Viewed by 1375
Abstract
This paper reports a study on the enhanced H2 selectivity of SnO2 gas sensors with SiO2 on the surface of the sensors obtained via chemical vapor deposition using dirthoxydimethylsilane as the Si source. The gas sensors were tested for sensing [...] Read more.
This paper reports a study on the enhanced H2 selectivity of SnO2 gas sensors with SiO2 on the surface of the sensors obtained via chemical vapor deposition using dirthoxydimethylsilane as the Si source. The gas sensors were tested for sensing performance towards ethanol, acetone, benzene, and hydrogen at operating temperatures from 150 °C to 400 °C. Our experimental results show that higher selectivity and responses to hydrogen were achieved by the deposition of SiO2 on the surface of the sensors. The sensor with SiO2 deposited on its surface at 500 °C for 8 h exhibited the highest response (Ra/Rg = 144) to 1000 ppm hydrogen at 350 °C, and the sensor with SiO2 deposited on its surface at 600 °C for 4 h attained the maximum response variation coefficient (D = 69.4) to 1000 ppm hydrogen at 200 °C. The mechanism underlying the improvement in sensitivity and the higher responses to hydrogen in the sensors with SiO2 on their surface is also discussed. Full article
(This article belongs to the Special Issue Metal Oxide Based Sensors)
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