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Thin Film Materials and Nanostructure Devices for Sensing Applications

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

Deadline for manuscript submissions: closed (1 June 2024) | Viewed by 25107

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Dr. Hugo Aguas

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Guest Editor

Department of Materials Science, Faculty of Science and Technology, New University of Lisbon and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
Interests: materials; photovoltaics; thin-film silicon; perovskites; microfluidics; SERS; biosensors
Special Issues, Collections and Topics in MDPI journals

Dr. Matteo Tonezzer

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Department of Chemical and Geological Sciences, Università di Cagliari, 09042 Monserrato, CA, Italy
Interests: OMBE; supersonic molecular beam deposition; CVD; PECVD; field effect transistor; OFET; metal oxides; metal oxide nanowires; organic thin films; small conjugated molecules; gas sensors; liquid sensors; biosensors; environmental monitoring; hybrid sensors; functionalized nanomaterials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In this Special Issue, we intend to receive contributions in the field of thin film science and technology applied to sensor devices, with particular emphasis on the use of nanomaterials and nanotechnology. Examples of practical applications, but not only are, light intensity sensors, non-visible radiation sensors, strain sensors, temperature sensors, solar cells, photodiodes, image sensors, biosensors, air quality sensors, bacteria sensors, etc. With the developments in many of today’s applications such as industry 4.0, biomedicine, the automobile industry, home automation, food, water, and air quality, etc., sensors have come to play a very important role in people's lives. It is important, therefore, to understand their physical operating principles, manufacturing technology, characteristics, stability, sensitivity, etc., as well as the different areas of application. Therefore, in this Special Issue, we welcome all contributions of original research, short communications, conceptual and review articles, both in theoretical, modeling and experimental aspects related to Thin-Film Materials and Nanostructure Devices for Sensing Applications, including the development of advanced materials, methods, properties, devices and their applications. This Special Issue will cover the following, although it is not strictly limited to this list:

Synthesis and advanced characterization of thin film materials;
Development of thin-film-based devices and sensors;
Thin film materials for photonic, magnetophotonic and magnetoplasmonic sensors;
Development and characterization of thin film micro / nanostructures for sensing;
Growth mechanisms of thin film materials and the effects of process parameters on film and sensing properties;
Thin film materials and surface engineering to improve sensing properties;
Improvements in material stability and improved light absorption;
Thin film coatings for smart materials;
Thin film materials for photovoltaic (PV) cells.

Dr. Hugo Aguas
Dr. Matteo Tonezzer
Guest Editors

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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.

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Keywords

Sensors
Biosensors
Photonics
Solar cells
Thin films
Smart materials
Nanomaterials

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Published Papers (13 papers)

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Research

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10 pages, 5546 KiB

Open AccessCommunication

Enhancing the Longevity and Structural Stability of Humidity Sensors: Iron Thin Films with Nitride Bonding Synthesized via Magnetic Field-Assisted Sparking Discharge

by Stefan Ručman, Posak Tippo, Arisara Panthawan, Niwat Jhuntama, Nidchamon Jumrus and Pisith Singjai

Sensors 2024, 24(17), 5466; https://doi.org/10.3390/s24175466 - 23 Aug 2024

Viewed by 637

Abstract

Developing long-lasting humidity sensors is essential for sustainable advancements in nanotechnology. Prolonged exposure to high humidity can cause sensors to drift from their calibration points, leading to long-term accuracy issues. Our research aims to develop a fabrication method that produces stable sensors capable of withstanding the environmental challenges faced by humidity sensors. Traditional iron-based nanoparticles often require complex treatments, such as chemical modification or thermal annealing, to maintain their properties. This study introduces a novel, one-step synthesis method for iron-based thin films with exceptional stability. The synthesized films were thoroughly characterized using X-ray photoelectron spectroscopy (XPS) to evaluate their phase stability and nitride formation. The method proposed in this study employs an electrical sparking discharge process within a pure nitrogen atmosphere under a 0.2 T magnetic field, producing thin films composed of nanoparticles approximately 20 nm in size. The resulting films demonstrate superior performance in humidity sensing applications compared to conventional methods. This straightforward and efficient approach offers a promising path toward robust and sustainable humidity sensors. Full article

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

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12 pages, 5560 KiB

Open AccessArticle

Preparation and Mechanism Analysis of High-Performance Humidity Sensor Based on Eu-Doped TiO₂

by Ling Zhang, Chu Chen and Hongyan Zhang

Sensors 2024, 24(13), 4142; https://doi.org/10.3390/s24134142 - 26 Jun 2024

Viewed by 1107

Abstract

TiO₂ is a typical semiconductor material, and it has attracted much attention in the field of humidity sensors. Doping is an efficient way to enhance the humidity response of TiO₂. Eu-doped TiO₂ material was investigated in both theoretical simulations and experiments. In a simulation based on density functional theory, a doped Eu atom can increase the performance of humidity sensors by producing more oxygen vacancies than undoped TiO₂. In these experiments, Eu-doped TiO₂ nanorods were prepared by hydrothermal synthesis, and the results also confirm the theoretical prediction. When the doping mole ratio is 5 mol%, the response of the humidity sensor reaches 23,997.0, the wet hysteresis is 2.3% and the response/recovery time is 3/13.1 s. This study not only improves the basis for preparation of high-performance TiO₂ humidity sensors, but also fills the research gap on rare earth Eu-doped TiO₂ as a humidity-sensitive material. Full article

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

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8 pages, 1447 KiB

Open AccessCommunication

Broadband Eddy Current Measurement of the Sheet Resistance of GaN Semiconductors

by Ghania Belkacem, Florent Loete and Tanguy Phulpin

Sensors 2024, 24(5), 1629; https://doi.org/10.3390/s24051629 - 1 Mar 2024

Viewed by 1045

Abstract

Although the classical four-point probe method usually provides adequate results, it is in many cases inappropriate for the measurement of thin sheet resistance, especially in the case of a buried conductive layer or if the surface contacts are oxidized/degraded. The surface concentration of dislocation defects in GaN samples is known to challenge this kind of measurement. For the GaN sample presented in this study, it even totally impaired the ability of this method to even provide results without a prior deposition of gold metallic contact pads. In this paper, we demonstrate the benefits of using a new broadband multifrequency noncontact eddy current method to accurately measure the sheet resistance of a complicated-to-measure epitaxy-grown GaN-doped sample. The benefits of the eddy current method compared to the traditional four-point method are demonstrated. The multilayer-doped GaN sample is perfectly evaluated, which will allow further development applications in this field. The point spread function of the probe used for this noncontact method was also evaluated using a 3D finite element model using CST-Studio Suite simulation software 2020 and experimental measurements. Full article

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

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16 pages, 20855 KiB

Open AccessArticle

Tungsten Oxide Coated Liquid Metal Electrodes via Galvanic Replacement as Heavy Metal Ion Sensors

by Sagar Bhagwat, Leonhard Hambitzer, Richard Prediger, Pang Zhu, Ahmed Hamza, Sophia K. Kilian, Sebastian Kluck, Pegah Pezeshkpour, Frederik Kotz-Helmer and Bastian E. Rapp

Sensors 2024, 24(2), 416; https://doi.org/10.3390/s24020416 - 10 Jan 2024

Cited by 1 | Viewed by 1812

Abstract

Gallium liquid metals (LMs) like Galinstan and eutectic Gallium-Indium (EGaIn) have seen increasing applications in heavy metal ion (HMI) sensing, because of their ability to amalgamate with HMIs like lead, their high hydrogen potential, and their stable electrochemical window. Furthermore, coating LM droplets with nanopowders of tungsten oxide (WO) has shown enhancement in HMI sensing owing to intense electrical fields at the nanopowder-liquid–metal interface. However, most LM HMI sensors are droplet based, which show limitations in scalability and the homogeneity of the surface. A scalable approach that can be extended to LM electrodes is therefore highly desirable. In this work, we present, for the first time, WO-Galinstan HMI sensors fabricated via photolithography of a negative cavity, Galinstan brushing inside the cavity, lift-off, and galvanic replacement (GR) in a tungsten salt solution. Successful GR of Galinstan was verified using optical microscopy, SEM, EDX, XPS, and surface roughness measurements of the Galinstan electrodes. The fabricated WO-Galinstan electrodes demonstrated enhanced sensitivity in comparison with electrodes structured from pure Galinstan and detected lead at concentrations down to 0.1 mmol·L⁻¹. This work paves the way for a new class of HMI sensors using GR of WO-Galinstan electrodes, with applications in microfluidics and MEMS for a toxic-free environment. Full article

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

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14 pages, 5376 KiB

Open AccessArticle

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

by Mohammad Imran, Eun-Bi Kim, Dong-Heui Kwak and Sadia Ameen

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

Cited by 2 | Viewed by 1263

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. 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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17 pages, 3793 KiB

Open AccessArticle

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

by María Elena Sánchez Vergara, Luis Alberto Cantera Cantera, Citlalli Rios, Roberto Salcedo, Octavio Lozada Flores and Ateet Dutt

Sensors 2023, 23(18), 7708; https://doi.org/10.3390/s23187708 - 6 Sep 2023

Cited by 3 | Viewed by 1392

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 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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13 pages, 4252 KiB

Open AccessArticle

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

by Ewa Mańkowska, Michał Mazur, Jarosław Domaradzki, Piotr Mazur, Małgorzata Kot and Jan Ingo Flege

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

Viewed by 1906

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. 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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10 pages, 2151 KiB

Open AccessArticle

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

by Gregory Kopnov, Sudhansu Sekhar Das and Alexander Gerber

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

Cited by 3 | Viewed by 1471

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 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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17 pages, 2440 KiB

Open AccessFeature PaperArticle

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

by Semir El-Ahmar, Marta Przychodnia, Jakub Jankowski, Rafał Prokopowicz, Maciej Ziemba, Maciej J. Szary, Wiktoria Reddig, Jakub Jagiełło, Artur Dobrowolski and Tymoteusz Ciuk

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

Cited by 7 | Viewed by 2462

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 °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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12 pages, 4930 KiB

Open AccessCommunication

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

by Shiuh-Chuan Her and Yuan-Ming Liang

Sensors 2022, 22(13), 5039; https://doi.org/10.3390/s22135039 - 4 Jul 2022

Cited by 6 | Viewed by 2084

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 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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9 pages, 1127 KiB

Open AccessCommunication

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

by Shuang Liao, Peng Ye, Cheng Chen, Jie Zhang, Lin Xu and Feng Tan

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

Cited by 8 | Viewed by 2497

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 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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14 pages, 22905 KiB

Open AccessArticle

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

by Mehwish Hanif, Varun Jeoti, Mohamad Radzi Ahmad, Muhammad Zubair Aslam, Saima Qureshi and Goran Stojanovic

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

Cited by 6 | Viewed by 2623

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 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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Review

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18 pages, 5414 KiB

Open AccessReview

Physical-Vapor-Deposited Metal Oxide Thin Films for pH Sensing Applications: Last Decade of Research Progress

by Mohammad Nur-E-Alam, Devendra Kumar Maurya, Boon Kar Yap, Armin Rajabi, Camellia Doroody, Hassan Bin Mohamed, Mayeen Uddin Khandaker, Mohammad Aminul Islam and Sieh Kiong Tiong

Sensors 2023, 23(19), 8194; https://doi.org/10.3390/s23198194 - 30 Sep 2023

Cited by 4 | Viewed by 2194

Abstract

In the last several decades, metal oxide thin films have attracted significant attention for the development of various existing and emerging technological applications, including pH sensors. The mandate for consistent and precise pH sensing techniques has been increasing across various fields, including environmental monitoring, biotechnology, food and agricultural industries, and medical diagnostics. Metal oxide thin films grown using physical vapor deposition (PVD) with precise control over film thickness, composition, and morphology are beneficial for pH sensing applications such as enhancing pH sensitivity and stability, quicker response, repeatability, and compatibility with miniaturization. Various PVD techniques, including sputtering, evaporation, and ion beam deposition, used to fabricate thin films for tailoring materials’ properties for the advanced design and development of high-performing pH sensors, have been explored worldwide by many research groups. In addition, various thin film materials have also been investigated, including metal oxides, nitrides, and nanostructured films, to make very robust pH sensing electrodes with higher pH sensing performance. The development of novel materials and structures has enabled higher sensitivity, improved selectivity, and enhanced durability in harsh pH environments. The last decade has witnessed significant advancements in PVD thin films for pH sensing applications. The combination of precise film deposition techniques, novel materials, and surface functionalization strategies has led to improved pH sensing performance, making PVD thin films a promising choice for future pH sensing technologies. Full article

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

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