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Thin Film Gas Sensors
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Thin Film Gas Sensors

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

Deadline for manuscript submissions: closed (31 May 2023) | Viewed by 26946

Special Issue Editor

Dr. Emmanouil Gagaoudakis

E-Mail Website
Guest Editor
Transparent Conductive Materials and Devices Laboratory (TCMD Laboratory), Institute of Electronic Structure and Laser (IESL), Foundation of Research and Technology (FORTH), 70013 Heraklion, Greece
Interests: sputtering; thin films; materials characterization; gas sensors; thermochromic materials; hydrothermal synthesis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Gas sensors for toxic and hazardous gases such as NOx, SOx, H2, CH4, O3, volatile organic compounds (VOCs), etc. have been of great research interest for more than 50 years. Industries, automobiles, and hospitals are only a few of the sectors where there is a great demand for fast, accurate, and relatively inexpensive gas sensing devices. The explosive growth of advanced materials with superior properties over the last decade has enhanced the performance of gas sensors. Especially in the field of conductometric gas sensors, numerous new materials such as perovskites (inorganic and/or hybrid), in addition to the well-known metal oxide semiconductors, have been introduced and are currently investigated as gas sensing elements. Furthermore, a great number of techniques have been employed in order to deposit thin film gas sensors on various rigid and flexible substrates.

The scope of the present Special Issue is to focus on state-of-the-art recent advances regarding thin film gas sensors based on conductometric techniques. The topics that will be covered are

  • Novel metal oxide semiconductors for gas sensing applications;
  • Advanced materials as gas sensing elements and devices;
  • p-type materials as gas sensors;
  • Sensors for monitoring energy fuel gases (H2, CH4);
  • Sensors for monitoring indoor air quality.

Dr. Gagaoudakis Emmanouil
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 2600 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

  • metal oxide semiconductors
  • perovskites
  • thin films
  • gas sensors

Published Papers (7 papers)

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Research

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12 pages, 4879 KiB  
Article
Room-Temperature Nitric Oxide Gas Sensors Based on NiO/SnO2 Heterostructures
by Emmanouil Gagaoudakis, Apostolos Tsakirakis, Marilena Moschogiannaki, Angeliki Sfakianou and Vassilios Binas
Sensors 2023, 23(20), 8583; https://0-doi-org.brum.beds.ac.uk/10.3390/s23208583 - 19 Oct 2023
Cited by 1 | Viewed by 1127
Abstract
Nitric oxide (NO) is a very well-known indoor pollutant, and high concentrations of it in the atmosphere lead to acid rain. Thus, there is great demand for NO sensors that have the ability to work at room temperature. In this work, NiO/SnO2 [...] Read more.
Nitric oxide (NO) is a very well-known indoor pollutant, and high concentrations of it in the atmosphere lead to acid rain. Thus, there is great demand for NO sensors that have the ability to work at room temperature. In this work, NiO/SnO2 heterostructures have been prepared via the polyol process and were tested against different concentrations of NO gas at room temperature. The structural and morphological characteristics of the heterostructures were examined using X-ray diffraction and scanning electron microscopy, respectively, while the ratio of NiO to SnO2 was determined through the use of energy-dispersive spectrometry. The effects of both pH and thermal annealing on the morphological, structural and gas-sensing properties of the heterostructure were investigated. It was found that the morphology of the heterostructures consisted of rod-like particles with different sizes, depending on the temperature of thermal annealing. Moreover, NiO/SnO2 heterostructures synthesized with pH = 8 and annealed at 900 °C showed a response of 1.8% towards 2.5 ppm NO at room temperature. The effects of humidity as well as of stability on the gas sensing performance were also investigated. Full article
(This article belongs to the Special Issue Thin Film Gas Sensors)
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15 pages, 5827 KiB  
Communication
Recent Progress in the Topologies of the Surface Acoustic Wave Sensors and the Corresponding Electronic Processing Circuits
by Mariya Aleksandrova and Dimiter Badarov
Sensors 2022, 22(13), 4917; https://0-doi-org.brum.beds.ac.uk/10.3390/s22134917 - 29 Jun 2022
Cited by 6 | Viewed by 2174
Abstract
In this paper, we present an overview of the latest achievements in surface acoustic wave (SAW) sensors for gas or liquid fluid, with a focus on the electrodes’ topology and signal processing, as related to the application of the sensing device. Although the [...] Read more.
In this paper, we present an overview of the latest achievements in surface acoustic wave (SAW) sensors for gas or liquid fluid, with a focus on the electrodes’ topology and signal processing, as related to the application of the sensing device. Although the progress in this field is mainly due to advances in the materials science and the sensing coatings, the interdigital (IDT) electrodes’ organization is also an important tool for setting the acoustic-wave-distribution mode, and, thus, for improvement of the SAW performance. The signal-conditioning system is of practical interest, as the implementation of the SAW, as a compact and mobile system is dependent on this electronic circuit. The precision of the detection of the SAW platform is related not only to the IDT electrodes’ geometry but also to their location around the sensing layer. The most commonly used architectures are shown in the present paper. Finally, we identify the needs for the future improvement of these prospective sensors. Full article
(This article belongs to the Special Issue Thin Film Gas Sensors)
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18 pages, 5867 KiB  
Article
Classification of Two Volatiles Using an eNose Composed by an Array of 16 Single-Type Miniature Micro-Machined Metal-Oxide Gas Sensors
by Jordi Palacín, Elena Rubies, Eduard Clotet and David Martínez
Sensors 2022, 22(3), 1120; https://0-doi-org.brum.beds.ac.uk/10.3390/s22031120 - 01 Feb 2022
Cited by 9 | Viewed by 2694
Abstract
The artificial replication of an olfactory system is currently an open problem. The development of a portable and low-cost artificial olfactory system, also called electronic nose or eNose, is usually based on the use of an array of different gas sensors types, sensitive [...] Read more.
The artificial replication of an olfactory system is currently an open problem. The development of a portable and low-cost artificial olfactory system, also called electronic nose or eNose, is usually based on the use of an array of different gas sensors types, sensitive to different target gases. Low-cost Metal-Oxide semiconductor (MOX) gas sensors are widely used in such arrays. MOX sensors are based on a thin layer of silicon oxide with embedded heaters that can operate at different temperature set points, which usually have the disadvantages of different volatile sensitivity in each individual sensor unit and also different crossed sensitivity to different volatiles (unspecificity). This paper presents and eNose composed by an array of 16 low-cost BME680 digital miniature sensors embedding a miniature MOX gas sensor proposed to unspecifically evaluate air quality. In this paper, the inherent variability and unspecificity that must be expected from the 16 embedded MOX gas sensors, combined with signal processing, are exploited to classify two target volatiles: ethanol and acetone. The proposed eNose reads the resistance of the sensing layer of the 16 embedded MOX gas sensors, applies PCA for dimensional reduction and k-NN for classification. The validation results have shown an instantaneous classification success higher than 94% two days after the calibration and higher than 70% two weeks after, so the majority classification of a sequence of measures has been always successful in laboratory conditions. These first validation results and the low-power consumption of the eNose (0.9 W) enables its future improvement and its use in portable and battery-operated applications. Full article
(This article belongs to the Special Issue Thin Film Gas Sensors)
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20 pages, 9694 KiB  
Article
P-type Inversion at the Surface of β-Ga2O3 Epitaxial Layer Modified with Au Nanoparticles
by Maciej Krawczyk, Ryszard Korbutowicz, Rafał Szukiewicz, Patrycja Suchorska-Woźniak, Maciej Kuchowicz and Helena Teterycz
Sensors 2022, 22(3), 932; https://0-doi-org.brum.beds.ac.uk/10.3390/s22030932 - 25 Jan 2022
Cited by 4 | Viewed by 2543
Abstract
The electric properties and chemical and thermal stability of gallium oxide β-Ga2O3 make it a promising material for a wide variety of electronic devices, including chemiresistive gas sensors. However, p-type doping of β-Ga2O3 still remains a challenge. [...] Read more.
The electric properties and chemical and thermal stability of gallium oxide β-Ga2O3 make it a promising material for a wide variety of electronic devices, including chemiresistive gas sensors. However, p-type doping of β-Ga2O3 still remains a challenge. A β-Ga2O3 epitaxial layer with a highly developed surface was synthesized on gold electrodes on a Al2O3 substrate via a Halide Vapor Phase Epitaxy (HVPE) method. The epitaxial layer was impregnated with an aqueous colloidal solution of gold nanoparticles with an average diameter of Au nanoparticle less than 5 nm. Electrical impedance of the layer was measured before and after modification with the Au nanoparticles in an ambient atmosphere, in dry nitrogen, and in air containing dimethyl sulfide C2H6S (DMS). After the impregnation of the β-Ga2O3 epitaxial layer with Au nanoparticles, its conductance increased, and its electric response to air containing DMS had been inversed. The introduction of Au nanoparticles at the surface of the metal oxide was responsible for the formation of an internal depleted region and p-type conductivity at the surface. Full article
(This article belongs to the Special Issue Thin Film Gas Sensors)
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17 pages, 9973 KiB  
Article
The Heterostructures of CuO and SnOx for NO2 Detection
by Anna Paleczek, Bartłomiej Szafraniak, Łukasz Fuśnik, Andrzej Brudnik, Dominik Grochala, Stanisława Kluska, Maria Jurzecka-Szymacha, Erwin Maciak, Piotr Kałużyński and Artur Rydosz
Sensors 2021, 21(13), 4387; https://0-doi-org.brum.beds.ac.uk/10.3390/s21134387 - 26 Jun 2021
Cited by 6 | Viewed by 2105
Abstract
Controlling environmental pollution is a burning problem for all countries more than ever. Currently, due to the increasing industrialization, the number of days when the limits of air pollutants are over the threshold levels exceeds 80–85% of the year. Therefore, cheap and effective [...] Read more.
Controlling environmental pollution is a burning problem for all countries more than ever. Currently, due to the increasing industrialization, the number of days when the limits of air pollutants are over the threshold levels exceeds 80–85% of the year. Therefore, cheap and effective sensors are always welcome. One idea is to combine such solutions with cars and provide real-time information about the current pollution level. However, the environmental conditions are demanding, and thus the developed sensors need to be characterized by the high 3S parameters: sensitivity, stability and selectivity. In this paper, we present the results on the heterostructure of CuO/SnOx and SnOx/CuO as a possible approach for selective NO2 detection. The developed gas sensors exhibited lower operating temperature and high response in the wide range of NO2 and in a wide range of relative humidity changes. Material characterizations and impedance spectroscopy measurements were also conducted to analyze the chemical and electrical behavior. Full article
(This article belongs to the Special Issue Thin Film Gas Sensors)
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Review

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45 pages, 92265 KiB  
Review
P-Type Metal Oxide Semiconductor Thin Films: Synthesis and Chemical Sensor Applications
by Abderrahim Moumen, Gayan C. W. Kumarage and Elisabetta Comini
Sensors 2022, 22(4), 1359; https://0-doi-org.brum.beds.ac.uk/10.3390/s22041359 - 10 Feb 2022
Cited by 43 | Viewed by 9747
Abstract
This review focuses on the synthesis of p-type metal-oxide (p-type MOX) semiconductor thin films, such as CuO, NiO, Co3O4, and Cr2O3, used for chemical-sensing applications. P-type MOX thin films exhibit several advantages over n-type MOX, [...] Read more.
This review focuses on the synthesis of p-type metal-oxide (p-type MOX) semiconductor thin films, such as CuO, NiO, Co3O4, and Cr2O3, used for chemical-sensing applications. P-type MOX thin films exhibit several advantages over n-type MOX, including a higher catalytic effect, low humidity dependence, and improved recovery speed. However, the sensing performance of CuO, NiO, Co3O4, and Cr2O3 thin films is strongly related to the intrinsic physicochemical properties of the material and the thickness of these MOX thin films. The latter is heavily dependent on synthesis techniques. Many techniques used for growing p-MOX thin films are reviewed herein. Physical vapor-deposition techniques (PVD), such as magnetron sputtering, thermal evaporation, thermal oxidation, and molecular-beam epitaxial (MBE) growth were investigated, along with chemical vapor deposition (CVD). Liquid-phase routes, including sol–gel-assisted dip-and-spin coating, spray pyrolysis, and electrodeposition, are also discussed. A review of each technique, as well as factors that affect the physicochemical properties of p-type MOX thin films, such as morphology, crystallinity, defects, and grain size, is presented. The sensing mechanism describing the surface reaction of gases with MOX is also discussed. The sensing characteristics of CuO, NiO, Co3O4, and Cr2O3 thin films, including their response, sensor kinetics, stability, selectivity, and repeatability are reviewed. Different chemical compounds, including reducing gases (such as volatile organic compounds (VOCs), H2, and NH3) and oxidizing gases, such as CO2, NO2, and O3, were analyzed. Bulk doping, surface decoration, and heterostructures are some of the strategies for improving the sensing capabilities of the suggested pristine p-type MOX thin films. Future trends to overcome the challenges of p-type MOX thin-film chemical sensors are also presented. Full article
(This article belongs to the Special Issue Thin Film Gas Sensors)
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19 pages, 4860 KiB  
Review
Synthesis Methods of Obtaining Materials for Hydrogen Sensors
by Izabela Constantinoiu and Cristian Viespe
Sensors 2021, 21(17), 5758; https://0-doi-org.brum.beds.ac.uk/10.3390/s21175758 - 26 Aug 2021
Cited by 8 | Viewed by 4019
Abstract
The development of hydrogen sensors has acquired a great interest from researchers for safety in fields such as chemical industry, metallurgy, pharmaceutics or power generation, as well as due to hydrogen’s introduction as fuel in vehicles. Several types of sensors have been developed [...] Read more.
The development of hydrogen sensors has acquired a great interest from researchers for safety in fields such as chemical industry, metallurgy, pharmaceutics or power generation, as well as due to hydrogen’s introduction as fuel in vehicles. Several types of sensors have been developed for hydrogen detection, including resistive, surface acoustic wave, optical or conductometric sensors. The properties of the material of the sensitive area of the sensor are of great importance for establishing its performance. Besides the nature of the material, an important role for its final properties is played by the synthesis method used and the parameters used during the synthesis. The present paper highlights recent results in the field of hydrogen detection, obtained using four of the well-known synthesis and deposition methods: sol-gel, co-precipitation, spin-coating and pulsed laser deposition (PLD). Sensors with very good results have been achieved by these methods, which gives an encouraging perspective for their use in obtaining commercial hydrogen sensors and their application in common areas for society. Full article
(This article belongs to the Special Issue Thin Film Gas Sensors)
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