Gas Sensor Applications Research Articles

Impact of Copper Doping on Nanocrystalline SnO<sub>2</sub> Thin Films Synthesized by Sol-Gel Coating and Chemical Bath Deposition for Gas Sensor Applications

Impact of Copper Doping on Nanocrystalline SnO<sub>2</sub> Thin Films Synthesized by Sol-Gel Coating and Chemical Bath Deposition for Gas Sensor Applications

Conductivity optimisation of graphene oxide-M13 bacteriophage nanocomposites: towards graphene-based gas micronano-sensors

Graphene oxide (GO) and M13 bacteriophage can self-assemble to form ultra-low density porous structures, known as GraPhage13 aerogels (GPA). Due to the insulating nature of GPA and the challenges in producing highly conductive aerogels, it is paramount to explore ways to enhance the conductivity of GPA. Herein, we have developed a method to enhance the conductivity of GPA, via the integration and optimisation of 5 nm and 20 nm diameter gold nanoparticles (AuNPs) into the aerogel structure and systematically analysed the morphology, composition and spectroscopic properties of the resulting GPA-Au nanocomposite. The fabricated GPA-Au nanocomposites exhibited remarkable increases in conductivity, with the integration of 5 nm AuNPs leading to a 53-fold increase compared to GPA, achieving a performance of up to 360 nS/cm, which is within the range suitable for miniaturised semiconductor devices. The mechanism behind the conductivity enhancement was further investigated and attributed to GO-AuNP interactions increasing the carrier density by introducing new energy levels in the GO band gap or shifting its Fermi level towards the conduction band. These findings demonstrate the potential of functionalised AuNPs to significantly improve the electrical properties of GPA, paving the way for their application in gas sensors for biological and chemical detection and a new range of advanced semiconductor devices.

Conduction in yttrium iron garnets with nickel dopant: Potential for sensor applications

Doped yttrium iron garnet materials exhibit semiconducting behavior and have potential applications in resistive-based sensors, including thermoresistive and gas sensors. In this study, we synthesized Ni-doped yttrium iron garnet samples using the sol-gel method combined with heat treatment. The crystal structure, morphology, and Ni incorporation into the crystal lattice were investigated using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Raman spectroscopy. The saturation magnetization of the samples in the ground state was measured in a Physical Property Measurement System (PPMS) at 5 K. The experimental magnetic moments deviate significantly from the values calculated based on the cation distribution models, suggesting the occupation of Ni2+ and Fe2+ at the octahedral and tetrahedral sites, respectively, with the latter due to oxygen vacancies. We investigated the resistivity, magnetoresistance effect, and hydrogen sensing properties to elucidate the conduction mechanism. At room temperature, the resistivity of the samples decreased sharply as the oxygen vacancy concentration increased, from ∼108 Ωcm in sample x = 0 to ∼106 Ωcm in sample x = 0.08. The resistance of the samples increased when exposed to hydrogen gas, supporting the prediction from the magnetization data that the samples exhibit n-type semiconductor characteristics. The samples showed good sensitivity to H2 gas. At 250°C, sample x = 0.08 exhibits a response of S =11.5, the response time (τres. ∼8 s), and recovery time (τrec. ∼22 s) at 100 ppm hydrogen concentration.

In-doped ZnO films deposited by modified SILAR method for enhanced ethanol gas sensor application

The rapid and skillful detection of toxic gases is a crucial requirement for the advancement of gas sensors. In this study, we fabricated undoped and In-doped (1 %, 3 %, and 5 % by weight) ZnO films using a two-step modified SILAR deposition technique. The ethanol gas sensing properties of both undoped and In-doped ZnO films were examined across a range of operating temperatures (from room temperature, 27 °C–200 °C) and concentrations (1 ppm–50 ppm). Of all the films, those doped with 5 % Indium exhibited the most stable, reproducible, and highest response, achieving 86.27 % at 50 ppm ethanol at an operating temperature of 100 °C. Compared to the undoped ZnO films, all Indium-doped ZnO films demonstrated significantly shorter response times (17 s) and recovery times (19 s). The response of all the deposited films to various gases such as acetone, methanol, toluene, xylene, and formaldehyde was lower than their response to ethanol. The mechanism behind the enhanced sensing characteristics of the Indium-doped ZnO films is explored. Additionally, the impact of humidity on sensor performance was investigated. This study reveals that 5 % In-doped ZnO films hold great potential as materials for ethanol gas sensing applications.

Novel CdFe2O4 nanoparticles facile synthesis and their applications towards practical ammonia detection: an effect of annealing

Cadmium ferrite (CdFe2O4) nanoparticles were synthesized via a simple co-precipitation method, and the effect of annealing temperature over the prepared samples’ structural, morphological, and optical properties was analyzed by varying the temperatures 700, 800, and 900 °C. The x-ray diffraction (XRD) studies revealed that the prepared samples are highly crystalline in nature and belong to a cubic spinel crystal structure, and the crystallite size increases from 32 to 59 nm with respect to the increasing temperature. The surface morphology of the ferrite samples showed the uniformly distributed highly agglomerated particles with larger voids for the ferrite nanoparticles annealed at 900 °C. Optical properties of the prepared CdFe2O4 samples were carried out by diffused reflectance spectroscopy (DRS) and the optical band gap of the samples were found to be 2.57, 2.55 and 2.53 eV. The Vibrating sample magnetometer (VSM) studies at room temperature showcased that the nanoparticle samples possess ferromagnetic behavior, and the magnetization (Ms), Coercivity (Hc), and Retentivity (Mr) values were found to be 27.5 × 10−3 emu g−1, 237.60 Oe, and 1976 × 10−6 emu/g for the CdFe2O4 sample annealed at 900 °C. The gas sensing studies were carried out with the presence of target gas ammonia, and its significant sensing parameters such as gas responsivity (S%), rise time, and recovery times were determined, and these values of CdFe2O4 samples annealed at 900 °C were observed to be 1610%, 7.1 s, and 2.2 s. Our findings strongly suggest that the CdFe2O4 samples annealed at 900 °C hold significant promise as a multifunctional material, particularly in gas-sensing applications. This potential opens an exciting avenue for further research and development.

Fast and selective isoprene gas sensor: Influence of polystyrene size and role of the au catalyst on gas sensing properties

Sacrificial methods using polystyrene (PS) templates are extensively applied in various research fields, particularly for fabricating gas sensors. The many processing advantages of these methods, such as a uniform particle size distribution, ease of manipulation, and potential for functionalization enable the fabrication of intricate nanostructures with precise control of the geometry and surface-area-to-volume ratio. Nevertheless, no previous study has investigated the fundamental correlation between the size of the PS particles used as a template and the performance of the resulting functional gas sensor. In this study, we fabricated In2O3 hollow hemispheres (HHs) with PS template sizes ranging from 200 to 3000 nm to explore the essential aspects for gas sensor applications. Notably, compared to In2O3 thin films, In2O3 HHs-based sensors prepared using a 3000 nm PS template exhibited a larger surface area, particularly when formed in a monolayer, and achieved an enhanced gas response to C2H5OH by approximately 132 times. By decorating In2O3 HHs with Au nanoparticles, the detection of C5H8 at 350 ℃ among various volatile organic compounds was significantly enhanced (increase ratio = 31.7), achieving a response of 483 and a theoretical detection limit as low as 743 parts per trillion (ppt). In addition, the highly porous structure with Au decoration achieved an extremely short response time of less than 2 s. These unprecedented results provide critical insights into conventional sensor technologies and pave the way for potential health-monitoring applications and bioelectronics.

Pure and Ce-Doped MnO2–ZnO Nanocomposites for Colossal Dielectric Energy Storage and Gas Sensing Applications

Pure and Ce-Doped MnO2–ZnO Nanocomposites for Colossal Dielectric Energy Storage and Gas Sensing Applications

Simulations of Infrared Reflectivity and Transmission Phonon Spectra for Undoped and Doped GeC/Si (001).

Exploring the phonon characteristics of novel group-IV binary XC (X = Si, Ge, Sn) carbides and their polymorphs has recently gained considerable scientific/technological interest as promising alternatives to Si for high-temperature, high-power, optoelectronic, gas-sensing, and photovoltaic applications. Historically, the effects of phonons on materials were considered to be a hindrance. However, modern research has confirmed that the coupling of phonons in solids initiates excitations, causing several impacts on their thermal, dielectric, and electronic properties. These studies have motivated many scientists to design low-dimensional heterostructures and investigate their lattice dynamical properties. Proper simulation/characterization of phonons in XC materials and ultrathin epilayers has been challenging. Achieving the high crystalline quality of heteroepitaxial multilayer films on different substrates with flat surfaces, intra-wafer, and wafer-to-wafer uniformity is not only inspiring but crucial for their use as functional components to boost the performance of different nano-optoelectronic devices. Despite many efforts in growing strained zinc-blende (zb) GeC/Si (001) epifilms, no IR measurements exist to monitor the effects of surface roughness on spectral interference fringes. Here, we emphasize the importance of infrared reflectivity Rω and transmission Tω spectroscopy at near normal θi = 0 and oblique θi ≠ 0 incidence (Berreman effect) for comprehending the phonon characteristics of both undoped and doped GeC/Si (001) epilayers. Methodical simulations of Rω and Tω revealing atypical fringe contrasts in ultrathin GeC/Si are linked to the conducting transition layer and/or surface roughness. This research provided strong perspectives that the Berreman effect can complement Raman scattering spectroscopy for allowing the identification of longitudinal optical ωLO phonons, transverse optical ωTO phonons, and LO-phonon-plasmon coupled ωLPP+ modes, respectively.

Reusable gasochromic gas sensor with enhanced selectivity for acidic gases via surface-engineered all-inorganic perovskite nanocrystals

The use of strong acids is crucial for the fabrication of highly integrated semiconductor devices. To effectively detect and alert against the potential hazards of acid gas leakage, considerable advancements have been made to enhance gas sensor sensitivity. However, most available gas sensors only detect cations (H+), making it challenging to precisely identify the specific types of acids present. Cesium lead halide perovskite nanocrystals, renowned for their exceptional optical properties, have emerged as promising candidates for gas-sensing applications. Nonetheless, concerns regarding reuse stability persist. In this study, surface engineering via solution-phase ligand exchange is conducted to address halide vacancies and prevent acid-induced structural degradation. The resulting surface-modified perovskites exhibit remarkable gasochromic sensitivity and selectivity towards HCl and HNO3. Furthermore, the vivid emission properties of these perovskites enable the visual detection of danger without the need for additional warning equipment. Finally, the reusability of the gas sensors is evaluated, and the perovskite-based sensors are recyclable.

Synthesis of Sn-ZnO nanostructures on MgO by hybrid pulsed laser ablation and RF magnetron sputtering tandem system for CO gas-sensing application

An exceptional method of incorporating Sn ions into Zinc Oxide (ZnO) using a tandem system of Pulsed Laser Deposition (PLD) and Radio-Frequency Magnetron Sputtering (RFMS) to synthesize and functionalize ZnO nanostructures is demonstrated in this study for gas-sensing application. The RFMS power was varied up to 50 W to sputter a pure Sn metal target, while simultaneously or successively growing ZnO nanostructures on a templated MgO < 0001 > substrate and on an Au-plated Al2O3 gas sensor, via PLD process at the substrate temperature of 700 °C in 100–500 millitorr oxygen/argon gas background. The morphologies of the grown Sn-ZnO nanostructures were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and X-ray Diffraction (XRD), and while their chemical/oxidation states and optical properties were analyzed by X-ray photospectroscopy (XPS) and photoluminescence (PL), respectively. For simultaneous deposition, the resulting (0002)-dominated 2D grain-like ZnO nanostructures were influenced by the interaction of the dynamic PLD plasma with static RFMS plasma at different powers. For successive growth, at 50 W-RF power, a remarkable increase in the sensor response to 50-ppm carbon monoxide (CO) gas was observed at 250 °C, which could be attributed to the creation of more adsorption sites in the Sn-ZnO depletion region caused by the replacement of some Zn sites with Sn ions in the ZnO matrix. This study, therefore, exhibits the viability of this hybrid system to design, synthesize, and functionalize Sn-ZnO nanomaterials, either by simultaneous/successive deposition, for gas-sensing applications.

Assessment of titanium - tungsten iron oxide and their gas sensor application

Assessment of titanium - tungsten iron oxide and their gas sensor application

Promising CO2 gas sensor application of zinc oxide nanomaterials fabricated via HVPG technique

Highly effective gas sensors for detecting a range of hazardous and toxic gases were successfully applied in the present study using Zinc oxide (ZnO) nanomaterials. In this work, the horizontal vapor phase growth (HVPG) technique was perfectly capable of the synthesis of zinc oxide (ZnO) nanomaterials. The effect of the growth time with different dwell times was discussed by comparing the SEM-EDX analysis and photoluminescence characterization of the samples. Magnetic field (AMF) was also incorporated to determine the effect of AMF on the synthesis of ZnO nanomaterials. The results showed that the ZnO nanorods and root-like shapes are formed with more than 5 μm length and a few nm diameters. The optimum parameter showed the sensors are shiner than the less effective sensor when applied. The introduction of an external magnetic field led to a reduced energy band gap by a maximum of 15 %. The non-AMF band gap energy value is observed to be between 3.51 and 3.58 eV, while the value obtained using AMF is found to be between 2.94 and 3.22 eV. During the CO2 gas sensor test, AMF ZnO nanomaterial samples exhibited higher voltage and gradient compared to non-AMF samples.

NO sensing properties of MoS2/WSe2 heterostructure at room temperature under UV light irradiation

Transition metal dichalcogenides (TMDs) have recently sparked interest in gas-sensing applications. Generally, the kinetics of gases show minimal reactivity when the sensor is operable at room temperature (RT). Photon excitation is a potential solution for enhancing gas kinetics at RT. The present study delves gas sensing properties of MoS2/WSe2 heterostructure, emphasizing its effectiveness in detecting a broad range of NO concentration (0.1 ppm to 10 ppm) at room temperature using UV-light (266 nm & 355 nm) as a catalyst. The results reveal a remarkable 13x & 5x amplification in NO detection at 10 ppm for MoS2/WSe2 heterostructure compared to pristine WSe2 and MoS2, which were primarily tested. The highest relative sensor response of 95.4 % is reported for 10 ppm of NO gas at RT under 266 nm illumination. The sensing results revealed a substantial reduction in the limit of detection (LOD) to around 16 ppb, followed by a swift response speed of 10.31/14.38 seconds. The synergistic combination of WSe2 and MoS2 and their high specific surface area enhance NO sensitivity under UV exposure. The fabricated device holds substantial importance in environmental monitoring and healthcare, paving the way for real-time data acquisition in gas sensing.

First principle investigation on gas sensing properties of MoS2/ZnO heterojunction

MoS2/ZnO heterojunction is theoretically constructed based on density functional theory (DFT). The adsorption and electrical properties of MoS2/ZnO heterojunction after adsorbing six toxic gas molecules (CO, NO, NO2, SO2, H2S and NH3) are investigated, including adsorption energy, energy gap, density of states, charge density difference, planar-average charge density, total charge density, work function and recovery time. The results suggest that the adsorption energy of MoS2/ZnO for six gas molecules are significantly increased compared with intrinsic MoS2. Especially, the adsorption energy of the heterojunction for NO2, SO2, H2S and NH3 reach to −0.88, −0.98, −0.79 and −1.08 eV, respectively, indicating that the adsorption behavior is changed from physisorption to chemisorption. In addition, after adsorption of gas molecules (CO, NO, NO2, SO2, H2S and NH3), the energy gap of MoS2/ZnO is decreased to 0.793, 0.964, 0.834, 0.864, 0.804 and 0.770 eV, respectively, which indicates that the conductivity of MoS2/ZnO is improved. The adsorption distance (D) is also decreased after adsorption gases, especially for H2S gas molecule (0.797 Å). In addition, the work function (WF) of adsorption system is decreased and the charge transfer is increased. These results indicate that the interaction between MoS2/ZnO and gas molecules is stronger than that of intrinsic MoS2. Therefore, MoS2/ZnO has potential application for gas sensor to detect toxic gas molecules.

Potential for multi-application advancements from doping zirconium (Zr) for improved optical, electrical, and resistive memory properties of zinc oxide (ZnO) thin films

Transition metal-doped Zinc oxide (ZnO) thin films with an optimal wide band gap and semiconducting nature find numerous applications in optoelectronic devices, gas sensors, spintronic devices, and electronics. In this study, Zirconium (Zr) doped ZnO thin films were deposited on ITO (Indium Tin oxide) coated glass substrate using RF-magnetron sputtering. Optical and electrical properties were examined for their potential use in resistive random-access memory (RRAM) applications. X-ray Diffraction (XRD), UV–vis spectroscopy, x-ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM) and Scanning electron microscopy (SEM) were used to investigate structural, optical, and compositional properties and roughness respectively. The results demonstrate that the films possess crystalline properties. Additionally, an augmentation in Zr concentration correlates with an elevation in the optical band gap, ascending from 3.226 eV to 3.26 eV, accompanied by an increase in Urbach energy from 0.0826 eV to 0.1234 eV. The film with the highest Zr content among all the films demonstrated the best electrical performance for resistive memory applications. Incorporating Zr as a dopant shows enhancement in the electrical performance and such ZnO films with optimum concertation of Zr can potentially be used in RRAM. ZnO being a versatile host material, its doping with Zr may extend its applications in catalysis, gas sensing, energy storage, and biomedical engineering. ZnO thin films employ zirconium (Zr) as a dopant, which is a novel way to improve the material’s characteristics. Although ZnO has been thoroughly researched, adding Zr presents a novel technique to enhance optical, electrical, and resistive memory characteristics all at once that has not been fully investigated.

DFT Study on the Janus ZrSSe Monolayer for Its Potential Application in NO Gas Sensing.

The growth of industry has resulted in increased global air pollution, necessitating the urgent development of highly sensitive gas detectors. In this work, the adsorption of the Janus ZrSSe monolayer for CO, CO2, NH3, NO, NO2, and O2 was studied by first-principles calculations. First, the stability of the ZrSSe monolayer is confirmed through calculations of cohesive energy and AIMD simulations. Furthermore, the calculations indicate that the Se layer exhibits higher selectivity and sensitivity toward gas molecules compared to the S layer. Specifically, among the gases adsorbed on the Se layer, NO has the shortest adsorption distance (1.804 Å), the lowest adsorption energy (-0.424 eV), and the greatest electron transfer (0.098 e). Additionally, density of states analysis reveals that adsorption of NO, NO2, and O2 on the Janus ZrSSe monolayer can induce a transition from a nonmagnetic to a magnetic state. The adsorption of NO not only alters the magnetic state but also induces a transition from a semiconductor to metal, which is highly advantageous for gas sensing applications. There results suggest that the Janus ZrSSe monolayer has the potential to serve as a highly sensitive detector for NO gas.

Investigating the adsorption performance of agricultural greenhouses hazardous gases on Rh doped HfX2 (X=S, Se) monolayers through DFT for potential gas sensor applications

This study uses density functional theory to study the adsorption performance of agricultural greenhouses hazardous gases on Rh doped HfX2 (X=S, Se) monolayers. After multiple geometric optimizations, the most stable adsorption configuration was found. The results indicate that the adsorption energy of Rh doped HfX2 monolayers is very stable for adsorbing small molecule gases. The change in the total density of states of the adsorption system reveals the transfer and recombination of electrons during the adsorption process, and the partial density of states helps to understand the interactions between bonding atoms. Molecular orbital analysis shows that LUMO is mainly concentrated near Hf atoms, while HOMO is mainly concentrated near X atoms, Rh atom, and gases. By calculating the work function, the interaction strength and electron transfer mechanism between the adsorbent and the metal surface are revealed. In addition, the recovery time indicates that HfX2 and Rh-HfSe2 are excellent adsorbents for these four gases at room temperature, but when HfS2 operates at 473 K, it will be an efficient and excellent gas sensor for the four gases. Thus, Rh-HfS2 can be a feasible resistance sensing material for Cl2 and SO2. This DFT results provide a theoretical basis for potential gas sensor applications of Rh doped HfX2 (X=S, Se) monolayers, leading to the design and development of more efficient greenhouse gas identification sensor devices.

Synthesis, characterization, and gas-sensing application of Cd0.5Zn0.5NdxFe2–xO4 nanoparticles

Fabrication of Cd0.5Zn0.5NdxFe2–xO4 nanoparticles, with x = 0.00, 0.01, 0.02, 0.04, 0.06, and 0.08, has been carried out using a wet chemical co-precipitation method. The effect of the rare earth Nd3+ doping on the prepared ferrites was structurally investigated using x-ray diffraction (XRD) along with Rietveld refinement. The results indicate great crystallinity in the FCC Fd3m spinel structure of Cd0.5Zn0.5NdxFe2–xO4 nanoparticles. The lattice parameter increases with the increase of doping concentration from 8.5378 until 8.5432 Å and the crystallite size obtained using Debye-Sherrer, Williamson–Hall, Size-strain plot (SSP), and Halder-Wagner (H-W) methods, decreases until the solubility limit of the materials is at x = 0.04. By using transmission electron microscopy (TEM), the morphological analysis reveals the spherical shape of the samples with minor agglomeration with the aid of using a Polyvinylpyrrolidone (PVP) capping agent. The grain size ranges from 14.37 to 15.24 nm. Raman spectroscopy verifies the incorporation of Nd3+ in the octahedral sites and the decrease in particle size. The elemental composition was verified using x-ray photoelectron spectroscopy (XPS). The magnetic properties were studied using a vibrating sample magnetometer (VSM) and it shows superparamagnetic behavior with a decrease in the saturation magnetization from 2.207 to 1.918 emu g−1 and an increase in coercivity from 7.194 to 14.397 G. The prepared materials were tested as liquefied petroleum gas (LPG) sensors by studying their sensitivity, selectivity, optimum working temperature, response, and recovery times. Nd3+ doping shows a great increase in LPG sensing sensitivity 4 to 20 times than the pure samples. The doping concentration also decreases the response and recovery times.

Architectures of MoS2/SnO2 nanoflowers for NO2 gas detection

In this research, a two-step hydrothermal technique is used to fabricate a NO2 gas sensor based on MoS2 nanoflowers with SnO2 nanoparticles. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were used to determine the morphologies, nanostructures, and compositions of the materials. The nanocomposites consisting of MoS2/SnO2 demonstrated a remarkable sensing response (38.6) towards 100 ppm of NO2. Moreover, the nanocomposites showed a rapid response and recovery time (42/147 S) when exposed to 100 ppm at temperature (250 °C). The MoS2/SnO2 nanocomposites demonstrated exceptional selectivity to NO2 against CO, NH3, and H2S, as well as demonstrated good repeatability. The significant gas detection characteristics could potentially be controlled by the distinctive structures of thin layers assembled into flower-like formations of two-dimensional MoS2. The multi-joint nanostructures promote the process of transferring the electrical charge of the carrier and the response to MoS2/SnO2 and NO2. The fabricated sensors are considered as potential candidates for the commercial in the nitrogen dioxide gas-sensing applications.

Self-Assembled Ti3C2TX MXene Thin Films for High-Performance Ammonia Sensors

MXenes have emerged as a fascinating material for RT gas-sensing applications due to their outstanding properties. This work reports the design and fabrication of a high-performance ammonia sensor based on MXenes material. To improve its sensing performance, a MXenes nanosheets thin film with a thickness of ≈ 10 nm was prepared using a scalable self-assembled method. Specifically, we employed the controlled and enhanced interfacial self-assembled method to fabricate a continuous and conductive MXene ultra-thin film. The morphology and the structure of the produced MXene materials and their films were characterized by combining multi-characterization tools. Altoghether, these highlight the uniform and continuous deposition of the MXene nanosheets film on the glass substrate. The electrical characterization indicates a sheet resistance value of 4.82 × 105 Ω/sq. The fabricated devices present good RT sensing performances for NH3 detection, ranging from 1 to 20 ppm. This demonstrates the outstanding sensitivity of MXene with a value of 1.92 % for the lowest concentration (1 ppm), a fast response (179 s) and a recovery time of (612 s), which is related to the high quality of the ultra-thin MXene sensiting layer. Moreover, the sensors demonstrate high degree of stability and excellent reproducibility, make them suitable candidate for practical applications like environmental monitoring.