Change In Electrical Resistance Research Articles

Interface Engineering-Driven Room-Temperature Ultralow Gas Sensors with Elucidating Sensing Performance of Heterostructure Transition Metal Dichalcogenide Thin Films.

In this report, we investigate the room-temperature gas sensing performance of heterostructure transition metal dichalcogenide (MoSe2/MoS2, WS2/MoS2, and WSe2/MoS2) thin films grown over a silicon substrate using a pulse laser deposition technique. The sensing response of the aforementioned sensors to a low concentration range of NO2, NH3, H2, CO, and H2S gases in air has been assessed at room temperature. The obtained results reveal that the heterojunctions of metal dichalcogenide show a drastic change in gas sensing performance compared to the monolayer thin films at room temperature. Nevertheless, the WSe2/MoS2-based sensor was found to have an excellent selectivity toward NO2 gas with a particularly high sensitivity of 10 ppb. The sensing behavior is explained on the basis of a change in electrical resistance as well as carrier localization prospects. Favorably, by developing a heterojunction of diselenide and disulfide nanomaterials, one may find a simple way of improving the sensing capabilities of gas sensors at room temperature.

Phase evolution and electrical resistance properties in vanadium dioxide nanobeams with mechanical deformation-induced strain gradients

Understanding the effect of strain on the physical properties of vanadium dioxide (VO2) is crucial for its effective use in flexible devices exposed to various strains. Stress (or strain) applied to VO2 plays a critical role in modulating its electrical and optical properties. Herein, we investigate the structural and electronic responses of VO2 nanobeams to bending deformation using interfacial adhesion between the VO2 and substrate, which can provide a route for understanding the correlation between the structural inhomogeneity and electrical properties associated with the strain gradient. The temperature-dependent phase evolution associated with the strain gradient in the bent nanobeam is resolved by characteristic Raman shifts and synchrotron diffraction, combined with stress analyses using a finite element method. The electrical resistance change and electro-thermal simulations reveal that the strain gradient-induced multiple phases in the bent nanobeam result in a higher resistance in the insulating state region, a higher transition temperature, a much broader transition range, and a smaller Joule heating effect, compared to the straight nanobeam. Our results may provide insight into the impact of the strain gradient in correlated materials, and can enable the deliberate control of physical properties using the strain gradient in nanostructures for flexible device applications.

Size-induced metal–insulator transition temperature decrease of VO2 nanoparticles obtained by laser irradiation in water

Vanadium dioxide (VO2) is a highly attractive and multifunctional material for technological applications due to its metal–insulator transition, which is accompanied by several orders of magnitude changes in electrical resistivity and optical transmissivity. In this work, we report on the metal–insulator transition of VO2 nanoparticles which are produced by a simple, efficient, and low-cost two-step preparation method based on infrared laser irradiation of V2O5 powder dispersed in water and subsequent stoichiometric stabilization by vacuum annealing at 773 K. VO2 nanoparticles have an average size of 36 nm with facet-like contours and undergo a structural phase transition from a monoclinic to a tetragonal phase, accompanied by a metal–insulator transition occurring around 323 K, which is about 17 K lower than bulk VO2. No evidence of the formation of intermediary metastable phases is observed. Our findings reveal that the size of VO2 nanoparticles is a key parameter to moving the transition closer to room temperature, which is important for many applications.

Surface-Catalyzed Zinc Oxide Nanorods and Interconnected Tetrapods as Efficient Methane Gas Sensing Platforms

Nanostructured metal oxide semiconductors have proven to be promising for the gas sensing domain. However, there are challenges associated with the fabrication of high-performance, low-to-room-temperature operation sensors for methane and other gases, including hydrogen sulfide, carbon dioxide, and ammonia. The functional properties of these semiconducting oxides can be improved by altering the morphology, crystal size, shape, and topology. Zinc oxide (ZnO) is an attractive option for gas sensing, but the need for elevated operating temperatures has limited its practical use as a commercial gas sensor. In this work, we prepared ZnO nanorod (ZnO-NR) arrays and interconnected tetrapod ZnO (T-ZnO) network sensing platforms as chemiresistive methane sensors on silicon substrates with platinum interdigitated electrodes and systematically characterized their methane sensing response in addition to their structural and physical properties. We also conducted surface modification by photochemical-catalyzed palladium, Pd, and Pd-Ag alloy nanoparticles and compared the uniformly distributed Pd decoration versus arrayed dots. The sensing performance was assessed in terms of target gas response magnitude (RM) and response percentage (R) recorded by changes in electrical resistance upon exposure to varying methane concentration (100–10,000 ppm) under thermal (operating temperatures = 175, 200, 230 °C) and optical (UV A, 365 nm illumination) excitations alongside response/recovery times, and limit of detection quantification. Thin film sensing platforms based on T-ZnO exhibited the highest response at 200 °C (RM = 2.98; R = 66.4%) compared to ZnO-NR thin films at 230 °C (RM = 1.34; R = 25.5%), attributed to the interconnected network and effective bandgap and barrier height reduction of the T-ZnO. The Pd-Ag-catalyzed and Pd dot-catalyzed T-ZnO films had the fastest response and recovery rates at 200 °C and room temperature under UV excitation, due to the localized Pd nanoparticles dots resulting in nano Schottky barrier formation, as opposed to the films coated with uniformly distributed Pd nanoparticles. The experimental findings present morphological differences, identify various mechanistic aspects, and discern chemical pathways for methane sensing.

Strong Connection of Single-Wall Carbon Nanotube Fibers with a Copper Substrate Using an Intermediate Nickel Layer.

Lightweight carbon nanotube fibers (CNTFs) with high electrical conductivity and high tensile strength are considered to be an ideal wiring medium for a wide range of applications. However, connecting CNTFs with metals by soldering is extremely difficult due to the nonreactive nature and poor wettability of CNTs. Here we report a strong connection between single-wall CNTFs (SWCNTFs) and a Cu matrix by introducing an intermediate Ni layer, which enables the formation of mechanically strong and electrically conductive joints between SWCNTFs and a eutectic Sn-37Pb alloy. The electrical resistance change rate (ΔR/R0) of Ni-SWCNTF/solder-Cu interconnects only decreases ∼29.8% after 450 thermal shock cycles between temperatures of -196 and 150 °C, which is 8.2 times lower than that without the Ni layer. First-principles calculations indicate that the introduction of the Ni layer significantly improves the heterogeneous interfacial bond strength of the Ni-SWCNTF/solder-Cu connections.

Electro-mechanical behavior of self-sensing textile-reinforced composites for in situ structural health monitoring

Advanced engineering materials like glass fabric-reinforced composites (GFRC) are frequently utilized in automotive components, civil structures, aviation sectors, etc. Contrary to metals, the anisotropic nature of composites makes it difficult to forecast damage and failure under real-time loads. GFRC is employed in this work to demonstrate structural health monitoring (SHM) using a reduced graphene oxide (rGO) coated glass fabric piezo-resistive sensor. The sensor was embedded in the GFRC composite to detect changes in the fractional electrical resistance under flexural strain. The developed composite specimens were subjected to three-point bending to examine the piezo-resistive performance. Throughout testing, the effect of sensor width and relative positions in the thickness direction within the composite specimen on strain and damage detection was assessed. The results of the tests revealed that these parameters were responsively associated with the piezo-resistance of the developed sensor. This study concluded that the developed piezo-resistive sensor has the potential to be used as a strain and damage detection mechanism for glass fabric-reinforced composite structures for disparate applications.

Piezoresistive behavior in cement-based sensors: Nonlinear modeling and preliminary application

Self-sensing cement sensors detect stress/strain by measuring the fractional change in electrical resistivity. However, neglecting the nonlinear portion of the FCR-stress/strain curves may limit monitoring range. Existing functional models lack versatility and physical meanings of parameters. A new model based on Ramberg-Osgood relation, incorporating the gauge factor, fractional change in resistance, and strain was proposed to cover linear and nonlinear regions. To validate the model, compression and tension cement sensors made of ultra-high toughness cementitious composite and multi-walled carbon nanotubes were tested. Results from various types of cement-based sensors validated the model's versatility. A four-point bending test on a C70 steel-reinforced concrete beam with an embedded cement sensor confirmed the feasibility of the proposed functional model.

Synergistic effects of Mg doping on TiO2 for improved toxic gas sensing performance at room temperature

The gas sensing characteristics of magnesium (Mg)-doped titanium dioxide (TiO2) films were investigated using a spray pyrolysis method. TiO2 Thin films with varying Mg doping concentrations (0, 2.5, and 5 weight percentages) were deposited and tested for their gas detection ability to organic compounds such as ethanol, butanol, toluene, xylene, and formaldehyde at room temperature. Results disclosed that introducing Mg into TiO2 enhanced the gas sensing characteristics, particularly for formaldehyde. Mg-doped TiO2 film improved the change in electrical resistance during gas adsorption, leading to an increased response in formaldehyde detection. Additionally, XRD revealed the crystal structure, while Raman spectroscopy provided insights into molecular vibrational modes of the fabricated films. FESEM allowed for high-resolution imaging of surface morphology, and atomic force microscope assessed surface roughness and other properties of the as deposited samples. UV-Vis spectroscopy was utilized to examine the optical characteristics. The collective results strongly indicated that the introduction of Mg significantly improved the gas-sensing capabilities of TiO2 films, making them highly promising for various gas-sensing applications.

Utilizing cluster percolation theory to analyze electrical resistivity jumps in high-entropy alloy thin films containing small atoms

The high-entropy alloy thin films (HEATFs) with non-metal small atoms have obvious characteristics of adjustable properties. However, the mismatch phenomenon of phase-transition and electrical resistivity jump usually occur during the interstitial-filling. To explain this phenomenon, a new method is proposed that transforms the multi-color percolation of HEATFs to two-color percolation. The [N/O-M6] clusters with high electrical resistivity and [▫-M6] clusters with low electrical resistivity in (NbMoTaW)100-xNx and (NbMoTaWV)100-xOx films are equivalent to black and white spheres, respectively (M and ▫ ▫-M6]) reaches the face-centered-cubic and amorphous percolation thresholds of 0.198 and 0.27, respectively, a conductive percolation path is formed, contributing to a significant reduction in electrical resistivity. This work enables it possible to predict the composition at sudden change in electrical resistivity of HEATFs with non-metallic small atoms, which has great significance for the functional composition design.

In-situ monitoring of carbon fiber-reinforced plastic manufacturing using electrical resistance during infusion

Carbon fiber reinforced plastics (CFRPs) have been widely applied in various fields such as aerospace, vehicles, and civil infrastructure, even though their manufacturing time, labor, and cost are burdensome compared to other materials. However, studies on monitoring systems for composite manufacturing are limited. The spotlight is biased toward CFRP design and functional nanocomposites. Therefore, in this study, an in-situ monitoring system of a CFRP is proposed to investigate the vacuum-assisted resin infusion process in real time using electrical resistance changes. Specifically, two electrode types namely Cu tape and silver paste, were comparatively analyzed under several vacuum bag pressures. Resin impregnation was then investigated on the scale of a carbon fiber single tow and laminae. Impregnated resin increases the thickness of the laminae, thereby increasing the electrical resistance. Moreover, the curing behavior of the resin was correlated with changes in its electrical resistance so that the viscosity and degree of curing of the resin could be identified. The proposed method enables the detection of not only the resin front, but also the degree of curing.

Investigating the Influence on the Electro-Conductive Properties of Leather as a Result of Natural Aging

Conductive leather and its use in smart products have found a lot of interest. Leather behaves as a good insulator, so it was treated with electrically conducting polypyrrole using a chemical polymerization technique to give it conductive characteristics. The electro-conductive properties are obtained by using the double in–situ oxidative polymerization of pyrrole. The electrical properties of conductive samples are studied using the Van Der Pauw method as a measuring method. The conductive leather transformation process was carried out during the 2018-2020 period, and the conductive leather samples were preserved in room conditions until the year 2023. The effect of natural ageing on the electro-conductive properties of conductive leather is the focus of this research. The results show that environmental factors influence polymer breakdown and stability, by causing an increase in electrical resistance. The changes in electrical surface resistance, as the effect of the ageing factor, vary from 39.8% to 129.9%. Those changes in electrical resistance indicate that ageing is one of the major concerns in the electrical properties and stability of conductive leather samples, so the performed measurements have importance in providing information for the researchers and designers regarding the conductivity changes over time as a result of natural ageing, which would like to work with conductive leather on smart products.

Investigating the Influence on the Electro-Conductive Properties of Leather as a Result of Natural Aging

Conductive leather and its use in smart products have found a lot of interest. Leather behaves as a good insulator, so it was treated with electrically conducting polypyrrole using a chemical polymerization technique to give it conductive characteristics. The electro-conductive properties are obtained by using the double in–situ oxidative polymerization of pyrrole. The electrical properties of conductive samples are studied using the Van Der Pauw method as a measuring method. The conductive leather transformation process was carried out during the 2018-2020 period, and the conductive leather samples were preserved in room conditions until the year 2023. The effect of natural ageing on the electro-conductive properties of conductive leather is the focus of this research. The results show that environmental factors influence polymer breakdown and stability, by causing an increase in electrical resistance. The changes in electrical surface resistance, as the effect of the ageing factor, vary from 39.8% to 129.9%. Those changes in electrical resistance indicate that ageing is one of the major concerns in the electrical properties and stability of conductive leather samples, so the performed measurements have importance in providing information for the researchers and designers regarding the conductivity changes over time as a result of natural ageing, which would like to work with conductive leather on smart products.

Investigating the Influence on the Electro-Conductive Properties of Leather as a Result of Natural Aging

Conductive leather and its use in smart products have found a lot of interest. Leather behaves as a good insulator, so it was treated with electrically conducting polypyrrole using a chemical polymerization technique to give it conductive characteristics. The electro-conductive properties are obtained by using the double in–situ oxidative polymerization of pyrrole. The electrical properties of conductive samples are studied using the Van Der Pauw method as a measuring method. The conductive leather transformation process was carried out during the 2018-2020 period, and the conductive leather samples were preserved in room conditions until the year 2023. The effect of natural ageing on the electro-conductive properties of conductive leather is the focus of this research. The results show that environmental factors influence polymer breakdown and stability, by causing an increase in electrical resistance. The changes in electrical surface resistance, as the effect of the ageing factor, vary from 39.8% to 129.9%. Those changes in electrical resistance indicate that ageing is one of the major concerns in the electrical properties and stability of conductive leather samples, so the performed measurements have importance in providing information for the researchers and designers regarding the conductivity changes over time as a result of natural ageing, which would like to work with conductive leather on smart products.

Effect of high temperature on macroscopic properties and microstructure of metallurgical coke

Coke produces powder in high-temperature environments, which leads to a decrease in coke strength and affects the smooth operation of blast furnace. To study the effect of high temperature on the macroscopic properties and microstructure, two types of coke were heated to 1100–1400 °C in conditions that simulated a blast-furnace heating regime. The results showed that the weight of the tamping coke (T-coke) and top-charging coke (TC-coke) was reduced by 9.04 g and 8.7 g, respectively, and the coke strength after reaction was reduced by 4.23% and 3.86% with an increase in temperature from 1100 °C to 1400 °C. In addition, the electrical resistance of T-coke and TC-coke decreased from ambient temperature to 1400 °C. The rate of change in electrical resistance had a negative correlation with the coke strength after reaction, which decreased as the change in electrical resistance increased. Comparing the optical texture index, carbon layer spacing, carbon structure parameters, and percentage of large pores in the coke with the heating temperature, it was found that high temperatures led to a decrease in the anisotropic texture of the coke, an increase in the degree of graphitization, partial conversion of amorphous carbon to graphitic carbon, and an increase in the percentage of large pores. Furthermore, the larger the pore area of the coke, the smaller were its pore wall hardness and elastic modulus. These results suggest that a decrease in anisotropic texture and an increase in large pores and the degree of graphitization decrease resistance to temperature, leading to lower strength after reaction.

Mechanical-electrical coupling behaviors of 3-D carbon fiber angle-interlock woven composites under quasi-static and cyclic tension

Mechanical-electrical coupling behaviors of carbon fiber composites is important to structure health monitoring (SHM). Here, we investigated the mechanical–electrical coupling behaviors of 3D carbon fiber angle-interlock woven composites (3DAWC) under tensile loading. Different loading modes including monotonic, cyclic, and fatigue tests were adopted to find the relationship between electrical resistance and tension damages. We also developed a mechanical–electrical constitutive model to reveal the relationship between internal damage modes and the electrical resistance. The tensile deformation and damage of the 3DAWC lead to the increase of the electrical resistance. The increased range is related to the degree of the deformation, damage, and damage accumulation. The transition point of the electrical resistance change represents the initial point of warp yarn longitudinal damages. The irreversible deformation of warp yarns leads to an increase in resistance after unloading. The stress–strain curve and the resistance vs. strain curve can be obtained simultaneously to reveal the internal structural deformation and inner damage mechanisms.

An Experimental Approach to Assess the Sensitivity of a Smart Concrete

Structural health monitoring of concrete infrastructure is a critical concern for timely repair and maintenance. This study provides an innovative approach utilizing smart concrete integrated with multi-walled carbon nanotubes (MWCNTs) to enhance electrical conductivity. The smart concrete’s self-sensing capability is assessed through fractional change in electrical resistance (FCR) measured using a four-probe technique. Four-point bending and compressive tests explore the material’s response to cyclic and monotonic loads. Additionally, the impact of saturation levels on self-sensing sensitivity is investigated through compressive tests on varying saturation degrees. Remarkably, a substantial correlation between crack mouth opening displacement (CMOD) and FCR is observed during cyclic bending tests, where FCR increases significantly (from 0.019% to 154%) as CMOD rises from 0.004 mm to 0.55 mm. Digital image correlation (DIC) further validates CMOD measurements and their correlation with FCR. Moreover, this study reveals that amplitude of loading and degree of saturation have a significant effect on the self-sensing of the smart concrete. In saturated conditions, the self-sensing response of the material is insensitive to the mechanical strain, while with reduction in the saturation degree, a quasi-linear response is observed. To assess the sensitivity of the smart concrete, stress and strain sensitivities were evaluated, revealing a noteworthy enhancement of approximately 33% and 50% in stress and strain sensitivity, respectively, as saturation levels decreased. The self-sensing response of the material is very sensitive to the mechanical strain during monotonic loading and damage. These findings indicate the potential of smart concrete as a promising tool for comprehensive, real-time structural health monitoring for infrastructure during its entire life.

Nanostructured Vanadium Dioxide Materials for Optical Sensing Applications.

Vanadium dioxide (VO2) is one of the strongly correlated materials exhibiting a reversible insulator-metal phase transition accompanied by a structural transition from a low-temperature monoclinic phase to high-temperature rutile phase near room temperature. Due to the dramatic change in electrical resistance and optical transmittance of VO2, it has attracted considerable attention towards the electronic and optical device applications, such as switching devices, memory devices, memristors, smart windows, sensors, actuators, etc. The present review provides an overview of several methods for the synthesis of nanostructured VO2, such as solution-based chemical approaches (sol-gel process and hydrothermal synthesis) and gas or vapor phase synthesis techniques (pulsed laser deposition, sputtering method, and chemical vapor deposition). This review also presents stoichiometry, strain, and doping engineering as modulation strategies of physical properties for nanostructured VO2. In particular, this review describes ultraviolet-visible-near infrared photodetectors, optical switches, and color modulators as optical sensing applications associated with nanostructured VO2 materials. Finally, current research trends and perspectives are also discussed.

Vaginal and vestibular electrical resistance as an alternative marker for optimum timing of artificial insemination with liquid-stored and frozen-thawed spermatozoa in sows

Development of a pen-side test to objectively determine the ideal time for artificial insemination (AI) in the sow would save producers time and money. Current processes rely on identification of oestrus via subjective behavioural and physiological markers that are indicative of high blood oestrogen concentrations. This study attempted to use measurements of electrical resistance (ER) in the cervical mucus to pinpoint timing of AI accurately enough to lead to equivalent pregnancy rates as a natural mating. Thirty-six sows were divided into 3 groups and observed for signs of oestrus. Seven sows did not show any oestrus behaviour and were excluded from the study. The remaining 29 sows were inseminated via natural mating and conventional oestrus detection (n = 14), or inseminated artificially with either liquid-stored semen (n = 8) or frozen-thawed semen (n = 7) according to timing indicated from electrical resistance measurements in the vagina and vestibule. Sows that were artificially inseminated on the basis of the electrical resistance readings had a lower pregnancy rate (P = 0.034) and less piglets born alive per litter (P < 0.05) than those that were naturally mated according to a conventional oestrus detection regime. However, the pregnancy rate and total piglets born alive did not differ between the two groups that underwent artificial insemination. Change in electrical resistance in the vagina has the potential to accurately predict ovulation timing, but more work is required to refine the timing of AI in relation to the readings before the technique can be adopted by industry.

Laser induced graphene for EMI shielding and ballistic impact damage detection in basalt fiber reinforced composites

Basalt fiber has been widely used in a variety of industries due to its unique properties and relatively low cost. However, the nature of electrical insulation of basalt fiber limits its application in the field of functional composite materials such as electromagnetic interference (EMI) shielding materials. Laser-induced graphene (LIG) is a form of three-dimensional carbon nanomaterial, which could be generated by scribing a laser on many carbonaceous precursors. In this work LIG film obtained by double-sided etching Polyimide (PI) paper was embedded in the basalt fiber laminates to fabricate multi-functional basalt fiber composites. The effects of LIG film insertion on Mode I and Mode II fracture toughness and out-of-plane ballistic impact resistance of basalt fiber laminates were investigated. The basalt fiber laminates with LIG inserted retain their original mechanical properties in terms of fracture toughness and impact resistance. While the conductivity and electromagnetic shielding performance of basalt fiber laminate after LIG insertion have been greatly improved. The EMI shielding effectiveness of the basalt fiber laminates is increased to ∼20 dB after one layer of LIG was inserted, and to ∼50 dB after three layers of LIG were inserted, for the X-band frequency range. The damage localization of the basalt fiber laminates was demonstrated by arraying the rectangular LIG strips in the shape of hash key and in-situ monitoring the electric resistance changes.

Experimental Evaluation of Stiffness Properties of a Quicklime-Stabilized Clay Subgrade Using a Resistivity Plate Loading Testing Device

Quicklime-mixing in soil stabilization applications for subgrade construction is crucial to its engineering performance and controlling quicklime and water content. Modern construction quality control devices and methods have improved construction quality control substantially. Certain devices, meanwhile, still need to be studied more thoroughly. This study used the resistivity plate loading device to assess the physical and stiffness properties of compacted quicklime-stabilized subgrade instantaneously and simultaneously for compaction quality control. The Taguchi L9 orthogonal array was used to design the experiment considering the dry density, test time, quicklime, and water content at various input factor levels. The pH, cation exchange capacity, conductivity, X-ray diffraction analysis (XRD), and scanning electron microscope (SEM) tests were further conducted. Analysis of the Taguchi experiment shows that the average soil electrical resistivity responses increased with dry density, test time, and quicklime content, and were highest at low water content. Whether the dry density, quicklime content, and test time are positively or negatively related to the average subgrade reaction modulus depends on the level of the water content. Regression equations are proposed to predict the average subgrade reaction modulus and soil electrical resistivity. The tested soils’ pH, conductivity, and cation ion exchange capacity properties were directly related to the test time, water, and quicklime content. The XRD showed nearly similar X-ray diffraction peaks. The SEM analysis confirmed marked changes in the microstructure of the samples that explained the changes in electrical resistivity and subgrade reaction modulus responses. The test results show that the resistivity plate loading device efficiently assesses compacted quicklime’s stiffness and physical properties at ease and instantaneously.