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Open AccessArticle

Porous MgNiO₂ Chrysanthemum Flower Nanostructure Electrode for Toxic Hg²⁺ Ion Monitoring in Aquatic Media

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Sensors 2023, 23(18), 7910; https://doi.org/10.3390/s23187910 - 15 Sep 2023

Viewed by 234

Abstract

A simple hydrothermal synthesis approach was used to synthesize porous MgNiO₂ Chrysanthemum Flowers (CFs) nanostructures and applied as a sensing electrode for quick detection of hazardous mercury (Hg²⁺ ions). The morphological, structural, and electrochemical properties of MgNiO₂ CFs were investigated. [...] Read more.

A simple hydrothermal synthesis approach was used to synthesize porous MgNiO₂ Chrysanthemum Flowers (CFs) nanostructures and applied as a sensing electrode for quick detection of hazardous mercury (Hg²⁺ ions). The morphological, structural, and electrochemical properties of MgNiO₂ CFs were investigated. The morphological characteristic of MgNiO₂ CFs, with a specific surface area of 45.618 m²/g, demonstrated strong electrochemical characteristics, including cations in different oxidation states of Ni³⁺/Ni²⁺. Using a three-electrode system for electrochemical detection, the MgNiO₂ CFs based electrode revealed a good correlation coefficient (R²) of ~0.9721, a limit of detection (LOD) of ~11.7 μM, a quick response time (10 s), and a sensitivity of 8.22 μA∙μM⁻¹∙cm⁻² for Hg²⁺ ions over a broad linear range of 10–100 μM. Moreover, the selectivity for Hg²⁺ ions in tap water and drinking water was determined, and a promising stability of 25 days by MgNiO² CFs electrode was exhibited. The obtained results indicate that the developed MgNiO₂ CFs are a promising electrode for detecting hazardous Hg²⁺ ions in water and have the potential to be commercialized in the future. Full article

(This article belongs to the Special Issue Thin Film Materials and Nanostructure Devices for Sensing Applications)

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Open AccessArticle

Preparation of Hybrid Films Based in Aluminum 8-Hydroxyquinoline as Organic Semiconductor for Photoconductor Applications

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María Elena Sánchez Vergara

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Luis Alberto Cantera Cantera

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Citlalli Rios

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Roberto Salcedo

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Octavio Lozada Flores

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Ateet Dutt

Sensors 2023, 23(18), 7708; https://doi.org/10.3390/s23187708 - 06 Sep 2023

Viewed by 242

Abstract

In the present work, we have investigated an organic semiconductor based on tris(8-hydroxyquinoline) aluminum (AlQ₃) doped with tetracyanoquinodimethane (TCNQ), which can be used as an organic photoconductor. DFT calculations were carried out to optimize the structure of semiconductor species and to [...] Read more.

In the present work, we have investigated an organic semiconductor based on tris(8-hydroxyquinoline) aluminum (AlQ₃) doped with tetracyanoquinodimethane (TCNQ), which can be used as an organic photoconductor. DFT calculations were carried out to optimize the structure of semiconductor species and to obtain related constants in order to compare experimental and theoretical results. Subsequently, AlQ₃-TCNQ films with polypyrrole (Ppy) matrix were fabricated, and they were morphologically and mechanically characterized by Scanning Electron Microscopy, X-ray diffraction and Atomic Force Microscopy techniques. The maximum stress for the film is 8.66 MPa, and the Knoop hardness is 0.0311. The optical behavior of the film was also analyzed, and the optical properties were found to exhibit two indirect transitions at 2.58 and 3.06 eV. Additionally, photoluminescence measurements were carried out and the film showed an intense visible emission in the visible region. Finally, a photoconductor was fabricated and electrically characterized. Applying a cubic spline approximation to fit cubic polynomials to the J-V curves, the ohmic to SCLC transition voltage

V_{ON}

and the trap-filled-limit voltage

V_{TFL}

for the device were obtained. Then, the free carrier density and trap density for the device were approximated to

n_{0} = 4.4586 \times 10^{19} \frac{1}{m^{3}}

and

N_{t} = 3.1333 \times 10^{31} \frac{1}{m^{3}}

, respectively. Full article

(This article belongs to the Special Issue Thin Film Materials and Nanostructure Devices for Sensing Applications)

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Open AccessArticle

Hydrogen Gas Sensing Properties of Mixed Copper–Titanium Oxide Thin Films

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Sensors 2023, 23(8), 3822; https://doi.org/10.3390/s23083822 - 08 Apr 2023

Viewed by 865

Abstract

Hydrogen is an efficient source of clean and environmentally friendly energy. However, because it is explosive at concentrations higher than 4%, safety issues are a great concern. As its applications are extended, the need for the production of reliable monitoring systems is urgent. [...] Read more.

Hydrogen is an efficient source of clean and environmentally friendly energy. However, because it is explosive at concentrations higher than 4%, safety issues are a great concern. As its applications are extended, the need for the production of reliable monitoring systems is urgent. In this work, mixed copper–titanium oxide ((CuTi)Ox) thin films with various copper concentrations (0–100 at.%), deposited by magnetron sputtering and annealed at 473 K, were investigated as a prospective hydrogen gas sensing material. Scanning electron microscopy was applied to determine the morphology of the thin films. Their structure and chemical composition were investigated by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The prepared films were nanocrystalline mixtures of metallic copper, cuprous oxide, and titanium anatase in the bulk, whereas at the surface only cupric oxide was found. In comparison to the literature, the (CuTi)Ox thin films already showed a sensor response to hydrogen at a relatively low operating temperature of 473 K without using any extra catalyst. The best sensor response and sensitivity to hydrogen gas were found in the mixed copper–titanium oxides containing similar atomic concentrations of both metals, i.e., 41/59 and 56/44 of Cu/Ti. Most probably, this effect is related to their similar morphology and to the simultaneous presence of Cu and Cu₂O crystals in these mixed oxide films. In particular, the studies of surface oxidation state revealed that it was the same for all annealed films and consisted only of CuO. However, in view of their crystalline structure, they consisted of Cu and Cu₂O nanocrystals in the thin film volume. Full article

(This article belongs to the Special Issue Thin Film Materials and Nanostructure Devices for Sensing Applications)

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Open AccessArticle

Effect of Fractal Topology on the Resistivity Response of Thin Film Sensors

by

Gregory Kopnov

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Sudhansu Sekhar Das

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Alexander Gerber

Sensors 2023, 23(5), 2409; https://doi.org/10.3390/s23052409 - 22 Feb 2023

Cited by 1 | Viewed by 720

Abstract

We discuss the effect of topological inhomogeneity of very thin metallic conductometric sensors on their response to external stimuli, such as pressure, intercalation, or gas absorption, that modify the material’s bulk conductivity. The classical percolation model was extended to the case in which [...] Read more.

We discuss the effect of topological inhomogeneity of very thin metallic conductometric sensors on their response to external stimuli, such as pressure, intercalation, or gas absorption, that modify the material’s bulk conductivity. The classical percolation model was extended to the case in which several independent scattering mechanisms contribute to resistivity. The magnitude of each scattering term was predicted to grow with the total resistivity and diverge at the percolation threshold. We tested the model experimentally using thin films of hydrogenated palladium and CoPd alloys where absorbed hydrogen atoms occupying the interstitial lattice sites enhance the electron scattering. The hydrogen scattering resistivity was found to grow linearly with the total resistivity in the fractal topology range in agreement with the model. Enhancement of the absolute magnitude of the resistivity response in the fractal range thin film sensors can be particularly useful when the respective bulk material response is too small for reliable detection. Full article

(This article belongs to the Special Issue Thin Film Materials and Nanostructure Devices for Sensing Applications)

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Open AccessFeature PaperArticle

The Comparison of InSb-Based Thin Films and Graphene on SiC for Magnetic Diagnostics under Extreme Conditions

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Sensors 2022, 22(14), 5258; https://doi.org/10.3390/s22145258 - 14 Jul 2022

Cited by 3 | Viewed by 1383

Abstract

The ability to precisely measure magnetic fields under extreme operating conditions is becoming increasingly important as a result of the advent of modern diagnostics for future magnetic-confinement fusion devices. These conditions are recognized as strong neutron radiation and high temperatures (up to 350 [...] Read more.

The ability to precisely measure magnetic fields under extreme operating conditions is becoming increasingly important as a result of the advent of modern diagnostics for future magnetic-confinement fusion devices. These conditions are recognized as strong neutron radiation and high temperatures (up to 350 °C). We report on the first experimental comparison of the impact of neutron radiation on graphene and indium antimonide thin films. For this purpose, a 2D-material-based structure was fabricated in the form of hydrogen-intercalated quasi-free-standing graphene on semi-insulating high-purity on-axis 4H-SiC(0001), passivated with an Al₂O₃ layer. InSb-based thin films, donor doped to varying degrees, were deposited on a monocrystalline gallium arsenide or a polycrystalline ceramic substrate. The thin films were covered with a SiO₂ insulating layer. All samples were exposed to a fast-neutron fluence of ≈

7 \times 10^{17}

cm⁻². The results have shown that the graphene sheet is only moderately affected by neutron radiation compared to the InSb-based structures. The low structural damage allowed the graphene/SiC system to retain its electrical properties and excellent sensitivity to magnetic fields. However, InSb-based structures proved to have significantly more post-irradiation self-healing capabilities when subject to proper temperature treatment. This property has been tested depending on the doping level and type of the substrate. Full article

(This article belongs to the Special Issue Thin Film Materials and Nanostructure Devices for Sensing Applications)

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Open AccessCommunication

Carbon-Based Nanomaterials Thin Film Deposited on a Flexible Substrate for Strain Sensing Application

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Shiuh-Chuan Her

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Yuan-Ming Liang

Sensors 2022, 22(13), 5039; https://doi.org/10.3390/s22135039 - 04 Jul 2022

Cited by 1 | Viewed by 1230

Abstract

Hybrid nanomaterial film consisting of multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelet (GNP) were deposited on a highly flexible polyimide (PI) substrate using spray gun. The hybridization between 2-D GNP and 1-D MWCNT reduces stacking among the nanomaterials and produces a thin film [...] Read more.

Hybrid nanomaterial film consisting of multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelet (GNP) were deposited on a highly flexible polyimide (PI) substrate using spray gun. The hybridization between 2-D GNP and 1-D MWCNT reduces stacking among the nanomaterials and produces a thin film with a porous structure. Carbon-based nanomaterials of MWCNT and GNP with high electrical conductivity can be employed to detect the deformation and damage for structural health monitoring. The strain sensing capability of carbon-based hybrid nanomaterial film was evaluated by its piezoresistive behavior, which correlates the change of electrical resistance with the applied strain through a tensile test. The effects of weight ratio between MWCNT and GNP and the total amount of hybrid nanomaterials on the strain sensitivity of the nanomaterial thin film were investigated. Experimental results showed that both the electrical conductivity and strain sensitivity of the hybrid nanomaterial film increased with the increase of the GNP contents. The gauge factor used to characterize the strain sensitivity of the nanomaterial film increased from 7.75 to 24 as the GNP weight ratio increased from 0 wt.% to 100 wt.%. In this work, a simple, low cost, and easy to implement deposition process was proposed to prepare a highly flexible nanomaterial film. A high strain sensitivity with gauge factor of 24 was achieved for the nanomaterial thin film. Full article

(This article belongs to the Special Issue Thin Film Materials and Nanostructure Devices for Sensing Applications)

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Open AccessCommunication

Comparing of Frequency Shift and Impedance Analysis Method Based on QCM Sensor for Measuring the Blood Viscosity

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Sensors 2022, 22(10), 3804; https://doi.org/10.3390/s22103804 - 17 May 2022

Cited by 3 | Viewed by 1441

Abstract

Blood viscosity measurements are crucial for the diagnosis of cardiovascular and hematological diseases. Traditional blood viscosity measurements have obvious limitations because of their expensive equipment usage and large sample consumption. In this study, blood viscosity was measured by the oscillating circuit method and [...] Read more.

Blood viscosity measurements are crucial for the diagnosis of cardiovascular and hematological diseases. Traditional blood viscosity measurements have obvious limitations because of their expensive equipment usage and large sample consumption. In this study, blood viscosity was measured by the oscillating circuit method and impedance analysis method based on single QCM. In addition, the effectiveness of two methods with high precision and less sample is proved by the experiments. Moreover, compared to the result from a standard rotational viscometer, the maximum relative errors of the proposed oscillating circuit method and impedance analysis method are ±5.2% and ±1.8%, respectively. A reliability test is performed by repeated measurement (N = 5), and the result shows that the standard deviation about 0.9% of impedance analysis is smaller than that of oscillating circuit method. Therefore, the impedance analysis method is superior. Further, the repeatability of impedance analysis method was evaluated by regression analysis method, and the correlation coefficient R² > 0.965 demonstrated that it had excellent reproducibility. Full article

(This article belongs to the Special Issue Thin Film Materials and Nanostructure Devices for Sensing Applications)

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Open AccessArticle

FEM Analysis of Various Multilayer Structures for CMOS Compatible Wearable Acousto-Optic Devices

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Mehwish Hanif

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Varun Jeoti

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Mohamad Radzi Ahmad

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Muhammad Zubair Aslam

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Saima Qureshi

and

Goran Stojanovic

Sensors 2021, 21(23), 7863; https://doi.org/10.3390/s21237863 - 26 Nov 2021

Cited by 1 | Viewed by 1693

Abstract

Lately, wearable applications featuring photonic on-chip sensors are on the rise. Among many ways of controlling and/or modulating, the acousto-optic technique is seen to be a popular technique. This paper undertakes the study of different multilayer structures that can be fabricated for realizing [...] Read more.

Lately, wearable applications featuring photonic on-chip sensors are on the rise. Among many ways of controlling and/or modulating, the acousto-optic technique is seen to be a popular technique. This paper undertakes the study of different multilayer structures that can be fabricated for realizing an acousto-optic device, the objective being to obtain a high acousto-optic figure of merit (AOFM). By varying the thicknesses of the layers of these materials, several properties are discussed. The study shows that the multilayer thin film structure-based devices can give a high value of electromechanical coupling coefficient (k²) and a high AOFM as compared to the bulk piezoelectric/optical materials. The study is conducted to find the optimal normalised thickness of the multilayer structures with a material possessing the best optical and piezoelectric properties for fabricating acousto-optic devices. Based on simulations and studies of SAW propagation characteristics such as the electromechanical coupling coefficient (k²) and phase velocity (v), the acousto-optic figure of merit is calculated. The maximum value of the acousto-optic figure of merit achieved is higher than the AOFM of all the individual materials used in these layer structures. The suggested SAW device has potential application in wearable and small footprint acousto-optic devices and gives better results than those made with bulk piezoelectric materials. Full article

(This article belongs to the Special Issue Thin Film Materials and Nanostructure Devices for Sensing Applications)

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