Relative Resistance Change Research Articles

Strain and damage monitoring in SBR nanocomposites under cyclic loading

Abstract In the present work a comparative study of the piezoresistivity behavior of two series of elastomeric nanocomposites, based on Styrene-Butadiene Rubber (SBR), reinforced with carbon black (CB) and carbon nanotubes (CNTs) has been performed. The relative resistance change with strain was recorded under monotonic and cyclic testing, revealing different response between CB and CNTs. The piezoresistivity response was more repeatable for the elastomeric nanocomposites which have been previously deformed and relaxed under zero stress. Moreover, the strain softening behavior of the materials under loading-unloading was examined by employing a rubber-softening empirical model developed in previous works.

Hybrid normal metal/ferromagnetic nanojunctions for domain wall tracking

Hybrid normal metal/ferromagnetic, gold/permalloy (Au/Py), nanojunctions are used to investigate magnetoresistance effects and track magnetization spatial distribution in L-shaped Py nanostructures. Transversal and longitudinal resistances are measured and compared for both straight and 90° corner sections of the Py nanostructure. Our results demonstrate that the absolute change in resistance is larger in the case of longitudinal measurements. However, due to the small background resistance, the relative change in the transversal resistance along the straight section is several orders of magnitude larger than the analogous longitudinal variation. These results prove that hybrid nanojunctions represent a significant improvement with respect to previously studied all-ferromagnetic crosses, as they also reduce the pinning potential at the junction and allow probing the magnetization locally. In addition, unusual metastable states with longitudinal domain walls along Py straight sections are observed. Micromagnetic simulations in combination with a magnetotransport model allow interpretation of the results and identification of the observed transitions.

3D Printing of Free‐Standing Stretchable Electrodes with Tunable Structure and Stretchability

Free‐standing stretchable electrodes with high stretchability and resistance stability are desired for future wearable electronic applications. However, it is very difficult to achieve high stretchability (typically restricted by the substrate) and meanwhile maintain low resistance change upon stretching. Innovative designs and fabrication strategies need to be developed to meet the required characteristics. We report the successful fabrication of free‐standing wavy elastic electrodes achieving very high stretchability (>300% for PDMS) and outstanding resistance stability (only 5% relative resistance change at 100% strain), simultaneously. We systematically studied designs with different joining angles and shapes to optimize the electrode performances. The 3D free‐standing electrodes with outstanding stretchability and electrical stability has great potential for further optimizations and applications in future stretchable and wearable electronic devices.

Anisotropic magnetothermoelectric power of ferromagnetic thin films

In this article, we report the measurements of the magnetothermoelectric power (MTEP) in metallic ferromagnetic thin films of Ni80Fe20 (Permalloy; Py), Co and CrO2 at temperatures in the range of 100K to 400K. In 25nm thick Py films and 50nm thick Co films both the anisotropic magnetoresistance (AMR) and MTEP show a relative change in resistance and thermoelectric power (TEP) of the order of 0.2% when the magnetic field is reversed, and in both cases there is no significant change in AMR or MTEP after the saturation field has been reached. Surprisingly, both Py and Co films have opposite MTEP behaviour although both have the same sign for AMR and TEP. The data on half metallic ferromagnet CrO2 films show a different picture. Films of thickness of 100nm were grown on TiO2 and on sapphire. The MTEP behavior at low fields shows peaks similar to the AMR in these films, with variations up to 1%. With increasing field both the MR and the MTEP variations keep growing, with MTEP showing relative changes of 1.5% with the thermal gradient along the b-axis and even 20% with the gradient along the c-axis, with an intermediate value of 3% for the film on sapphire. It appears that the low-field effects are due to the magnetic domain state, and the high-field effects are intrinsic to the electronic structure of CrO2 and intergarian tunnelling magnetoresistance that contributes to MTEP as tunnelling-MTEP. Our results will stimulate the research work in the field of spin dependent thermal transport in ferromagnetic materials to further develop spin-Caloritronics.

Remaining Useful Lifetime Estimation for Power MOSFETs Under Thermal Stress With RANSAC Outlier Removal

Reliability of power converters is crucial for mission critical systems. Among the components that are susceptible to failure, power semiconductor devices are one of the major causes of the power converter failures. This paper focuses on the remaining useful lifetime (RUL) estimation of degraded power MOSFETs, which are stressed by thermal cycling. The relative change in on-state resistance is identified as the fault signature. A data-driven RUL estimation algorithm based on a linear approximation model is proposed. The empirical coefficients are estimated by the classical least squares, where the outliers are removed by random sample consensus (RANSAC) algorithm. A sliding window approach is used to track the nonlinearities. The window size, threshold value, and number of samples used by RANSAC are optimized with the genetic algorithm. The accuracy of the proposed RUL estimation tool is verified on a number of thermally aged discrete power MOSFET data.

Fully Printed Silver‐Nanoparticle‐Based Strain Gauges with Record High Sensitivity

This paper describes a strategy to impart brittle conductive patterns composed of silver nanoparticles with high stretchability and structure‐dependent electrical characteristics. Silver nanoinks are printed on an elastomeric polyurethane acrylate substrate in the form of planar serpentine structures that can effectively mitigate strain concentration. The relative changes in resistance (∆R/R 0) and stretchability are found to strongly depend on the serpentine radius (r) that determines the strain relieving efficiency. Features with small radius of curvature show colossal ∆R/R 0 and hold great promise as ultrasensitive stretchable strain gauges. A record high gauge factor of 107 is achieved at 12% strain with r = 200 µm. Devices with larger radius of curvature exhibit higher stretchability and much more stable conductance, thus can be used as stretchable conductors. The results demonstrate the versatile functionalities that can be acquired from conventional materials by judicious structural designs.

Effect of annealing on the performance of nickel thermistor on polyimide substrate

In this study, a nickel thermistor pattern integrated with copper electrodes on polyimide substrate is fabricated by photolithography and magnetron sputtering techniques. The effect of annealing treatment on the performance of the nickel thermistor on polyimide substrate is evaluated. It is found that the performance of nickel thermistor is significantly improved by annealing treatment. The relative change of resistance increases with the increasing annealing temperature and time when the annealing temperature is below 360°C. The temperature range over which the temperature coefficient of resistance (TCR) remains linear is long when the annealing temperature is 350°C. The adhesion strength between the nickel thermistor and the polyimide substrate significantly increases after annealing treatment, but decreases when the annealing temperature and time increase. From the experimental results, the appropriate annealing temperature and time are obtained to meet required resistance, TCR, adhesion strength of the nickel thermistor.

(Invited) Electrodeposited Carbon Nanotube Ropes, Decorated with Electrodeposited Pd Nanoparticles for Fast, Sensitive, and Wide-Range, H2 Sensors

Hydrogen (H2) gas sensors that are sensitive, rapid-responding, stable, selective, compact, and inexpensive are needed to support the operation of fuel cell-electric automobiles. Palladium absorbs hydrogen to form a hydride (PdHx ) with x saturating at 0.67 and since 1869 it has been known that the electrical resistivity of this hydride increases linearly with x by a factor of 1.8 – 1.9 over the range from x = 0 to 0.67. This property of PdHx was first exploited for hydrogen sensing by Hughes and Schubert in 1992. As hydrogen gas sensors, Pd thin film resistors are elegant in their simplicity and cheap, but they are much too slow. One solution is to use a Pd nanowire as a resistive H2 sensor instead of a film. In this talk, we describe a second approach involving palladium (Pd) nanoparticle (NP)-decorated carbon nanotube (CNT) ropes (or CNT@PdNP). In the devices we prepare here, the Pd NPs have a mean diameter below 6 nm and are highly dispersed on the CNT surfaces. Both the Pd NPs and the CNT ropes are prepared by pulsed electrodeposition methods. Such CNT@PdNP ropes produce a relative resistance change 20 - 30 times larger than is observed at single, pure Pd nanowires. Thus, CNT@PdNP rope sensors improve upon all H2 sensing metrics (speed, dynamic range, and limit- of-detection), relative to single Pd nanowires which heretofore have defined the state- of-the-art in H2 sensing performance. Specifically, response and recovery times in air at [H2] ≈ 50 ppm are one sixth of those produced by single Pd nanowires with cross- sectional dimensions of 40 × 100 nm Pd. The LODH2 is <10 ppm versus 300 ppm, and the dynamic range (10 ppm – 4%) is nearly twice that afforded by the Pd nanowire. CNT@PdNP rope sensors are prepared by the dielectrophoretic deposition of a single semiconducting CNT rope followed by the electrodeposition of Pd nanoparticles with mean diameters ranging from 4.5 (± 1) nm to 5.8 (± 3) nm. The diminutive mean diameter and the high degree of diameter monodispersity for the deposited Pd nanoparticles are distinguishing features of the CNT@PdNP rope sensors described here, relative to prior work on similar systems. Figure 1

High temperature selective sensing of hydrogen with MgO-modified SrMoO4 micro-fibers

Micro-fibers of Mg-doped SrMoO4 (SrMoO4/MgO) were synthesized using a two-step hydrothermal technique. The SrMoO4/MgO micro-fibers were used as the sensing material within a solid-state, resistive-type sensor architecture. The material showed selective detection of hydrogen (H2) up to 1000°C with high sensor response and stability for the given concentrations. The maximum relative resistance change values (Rmax) for SrMoO4/MgO for 4000ppm H2 in a N2 atmosphere (1% O2) were −31, −85, and −87.5 for 600, 800 and 1000°C, respectively. At 1000°C, and the same background atmosphere, the Rmax was only −2.5 and −12.5 to 4000ppm CO and 2000ppm SO2, respectively. Chemical characterization showed that the Mg was dissolved into the SrMoO4 structure, in addition to residual MgO precipitate found within the final SrMoO4 powder. The surface MgO was shown to affect the H2 adsorption and dissociation processes in addition to high selectivity for H2 in comparison to SO2 and CO, while the dissolved Mg contributed to the alteration of the electronic properties, where the Schottky barrier height, band gap, and work function were all lowered. These combined effects resulted in the favorable sensitivity and high selectivity to H2, and also contributed to the increased stability at the elevated sensing temperatures.

Electromechanical properties of a yarn strain sensor with graphene-sheath/polyurethane-core

This paper reports on the fabrication of a new yarn strain sensor based on commonly used polyurethane yarn which is easily incorporated into textile structures by using textile technologies for wearable applications. By integrating graphene/poly(vinyl alcohol) composites as the conductive sheath around yarn, and polyurethane yarn as the elastic core by using a layer-by-layer assembly method that is simple, scalable and low in cost, the merits of both types of materials are incorporated to fabricate sensors with enhanced performance. The combined effects of graphene concentration and number of coatings on sensor properties are elucidated, and on that basis, the electromechanical properties can be modified by adjusting the parameters. The sensors are characterized in terms of sensitivity, resistivity, linearity, repeatability, hysteresis and thermal stability. There are two sensors (graphene concentration of 0.8 wt% and 1.0 wt%, and 12 and 9 cycles of coating respectively) with high sensitivity (gauge factor of 28.48 and 86.86, respectively), good linearity between the change in relative resistance and applied strain (correlation coefficient of 0.95 and 0.97, respectively), good repeatability (repeatability error of 2.03% and 1.81%, respectively), low hysteresis (hysteresis error of 7.03% and 9.08%, respectively) and excellent thermal stability (within the range of 25 °C–310 °C).

Reversible electrochemical modification of the surface of a semiconductor by an atomic-force microscope probe

A technique for reversible surface modification with an atomic-force-microscope (AFM) probe is suggested. In this method, no significant mechanical or topographic changes occur upon a local variation in the surface potential of a sample under the AFM probe. The method allows a controlled relative change in the ohmic resistance of a channel in a Hall bridge within the range 20–25%.

Highly moisture and weak-acid resistant Ga-doped ZnO films with titanium dioxide co-doping fabricated by magnetron sputtering

In this work, we proposed a strategy to improve the damp-heat stability and weak-acid resistance of gallium doped zinc oxide (GZO) thin films by co-doping TiO2 into GZO targets. Results showed that GZO thin films with a 0.2wt% TiO2 co-doping in the target (GTZO) exhibited a resistivity of 5.1×10−4Ω·cm and an average transmittance of 82.9%. The relative change in sheet resistance was as low as 5.1% after 24h damp heat treatment in conditions of 97% relative humidity at 121°C. A craterlike textured surface with a high haze value was not found in GTZO thin films after dipping in 1vol% HCl solution for 10min. These results showed that GTZO thin films have great potential for use as transparent electrode in extreme outdoor conditions.

Influence of high intensive dry mixing and calendering on relative electrode resistivity determined via an advanced two point approach

In order to achieve a profound understanding of the production process of electrodes for lithium-ion batteries, methods to determine the (intermediate) product quality are a necessity. Therefore, a new, fast and easy to use two point method to determine the relative resistivity of dry electrodes has been established. The method is used to determine process-induced changes in the electrode’s structure. A materials testing machine is used to ensure a homogeneous and constant mechanical stress during the analysis. By applying a direct current and measuring the voltage drop the electron transport characteristic along the whole electrode cross-section, taking all battery relevant resistances into account, can be determined. The result is an easy to compare relative resistivity value including coating resistance, contact resistance between coating and adhering current collector as well as the contact resistances between sample and probe. Process-induced changes are clearly visible in the results. The influence of the main testing parameters – contact stress and applied current – is determined. To cross-check the results, an established ‘powder probe’ method is used to confirm the relative resistivity changes caused by calendering. Slight calendering of LiNiMnCoO2 cathodes leads to an increase in electrode resistivity as conductive pathways are broken by the applied shear forces. However, increasing the cathode density to 2.95g/cm3 decreases resistivity by one third compared to uncalendered electrodes by re-establishing and shortening electrical pathways. Furthermore, a relative resistivity of anodes produced with a high energy powder mixing step is measured and shows that applying too much stress to the carbon black leads to a loss in long range conductivity, resulting in electrodes with an increased resistivity of up to 50%.

All-graphene strain sensor on soft substrate

We propose a transparent and stretchable all-graphene strain sensor that can detect various types of strain induced via stretching, bending, and torsion. The sensor is fabricated by introducing single-layer graphene as a force sensing material with a conductive film composed of graphene flake for the electrode. With the exclusive use of flexible materials, the completed strain sensor is fully flexible. Using a serpentine-shaped pattern for the single-layer graphene, the sensor is capable of stretching up to 20% with a high gauge factor (42.2). In addition, the sensor provides functional extension to bi-directional responses. This sensor can detect infinitesimal strain as low as 0.1% with a relative resistance change (ΔR/R0) of ∼0.005. Finally, sensitive detection of strains induced via bending and torsion are successfully demonstrated.

Three-dimensional conformal graphene microstructure for flexible and highly sensitive electronic skin

We demonstrate a highly stretchable electronic skin (E-skin) based on the facile combination of microstructured graphene nanowalls (GNWs) and a polydimethylsiloxane (PDMS) substrate. The microstructure of the GNWs was endowed by conformally growing them on the unpolished silicon wafer without the aid of nanofabrication technology. Then a stamping transfer method was used to replicate the micropattern of the unpolished silicon wafer. Due to the large contact interface between the 3D graphene network and the PDMS, this type of E-skin worked under a stretching ratio of nearly 100%, and showed excellent mechanical strength and high sensitivity, with a change in relative resistance of up to 6500% and a gauge factor of 65.9 at 99.64% strain. Furthermore, the E-skin exhibited an obvious highly sensitive response to joint movement, eye movement and sound vibration, demonstrating broad potential applications in healthcare, body monitoring and wearable devices.

Determining the Temperature Coefficient of Reference Resistors

The influence of temperature on electrical resistance of standard resistors is presented within this paper. Electrical resistance is like any other quantity temperature dependent. This dependence is specified with the temperature coefficient, which gives the relative change of resistance with temperature. The level of resistance change is not linear as it changes with temperature, and therefore the coefficient is temperature dependent as well. At a certain temperature, its value is equal to zero—the stationary point. Use of the standard resistor at this exact temperature or in a narrow interval around it greatly reduces the influence of temperature on electrical resistance, even if the thermal conditions are not optimal. Measurements of temperature coefficient were taken on a group of standard resistors of the same type in a wide temperature range, and the temperature of the stationary point was determined. Measurements were taken by placing the resistors in an oil bath and changing its set point temperature from 18 \({^{\circ }}\hbox {C}\) to 38 \({^{\circ }}\hbox {C}\). Electrical resistance of each resistor was measured using a resistance bridge, which had its reference resistor placed in a separate thermal enclosure at a constant temperature.

Sub-6 nm Palladium Nanoparticles for Faster, More Sensitive H2 Detection Using Carbon Nanotube Ropes

Palladium (Pd) nanoparticle (NP)-decorated carbon nanotube (CNT) ropes (or CNT@PdNP) are used as the sensing element for hydrogen gas (H2) chemiresistors. In spite of the fact that Pd NPs have a mean diameter below 6 nm and are highly dispersed on the CNT surfaces, CNT@PdNP ropes produce a relative resistance change 20-30 times larger than is observed at single, pure Pd nanowires. Thus, CNT@PdNP rope sensors improve upon all H2 sensing metrics (speed, dynamic range, and limit-of-detection), relative to single Pd nanowires which heretofore have defined the state-of-the-art in H2 sensing performance. Specifically, response and recovery times in air at [H2] ≈ 50 ppm are one-sixth of those produced by single Pd nanowires with cross-sectional dimensions of 40 × 100 nm Pd. The LODH2 is <10 ppm versus 300 ppm, and the dynamic range (10 ppm -4%) is nearly twice that afforded by the Pd nanowire. CNT@PdNP rope sensors are prepared by the dielectrophoretic deposition of a single semiconducting CNT rope followed by the electrodeposition of Pd nanoparticles with mean diameters ranging from 4.5 (±1) nm to 5.8 (±3) nm. The diminutive mean diameter and the high degree of diameter monodispersity for the deposited Pd nanoparticles are distinguishing features of the CNT@PdNP rope sensors described here, relative to prior work on similar systems.

Fabrication and gas sensing behavior of poly(3,4-ethylenedioxythiophene) coated polypropylene fiber with engineered interface

Conductive composite fibers were successfully fabricated by coating poly(3,4-ethylenedioxythiophene) (PEDOT) layers on the surface of polypropylene-graft-poly(acrylic acid) (PP-g-PAA) fibers through in situ chemical oxidative polymerization. It was found that the adhesion between the conductive PEDOT layers and the modified PP fiber substrates was significantly enhanced due to the electrostatic attractions between PEDOT chains and carboxylic groups of grafted PAA. In this study, we investigated the influence of the 3,4-ethylenedioxythiophene (EDOT) concentration and the oxidant species on the electrical conductivity of the composite fibers, and the result show that the maximum conductivities of PP-g-PAA/PEDOT composite fibers prepared with FeCl3 and iron(III) p-toluenesulfonate (FepTS) as oxidants reached 0.069S/cm and 10.09S/cm, respectively. The composite fibers were applied as a sensor for HCl and NH3 gas detection and exhibited a rapid and reversible response. The influence of the oxidant species on the sensing properties for HCl and NH3 gas detection is further discussed, and some features such as fast response time (less than 2s) and high relative resistance changes (63% for HCl and 110% for NH3 gas) were achieved.

Observation of Anomalous Resistance Behavior in Bilayer Graphene

Our measurement results have shown that bilayer graphene exhibits an unexpected sharp transition of the resistance value in the temperature region 200~250 K. We argue that this behavior originates from the interlayer ripple scattering effect between the top and bottom ripple graphene layer. The inter-scattering can mimic the Coulomb scattering but is strongly dependent on temperature. The observed behavior is consistent with the theoretical prediction that charged impurities are the dominant scatters in bilayer graphene. The resistance increase with increasing perpendicular magnetic field strongly supports the postulate that magnetic field induces an excitonic gap in bilayer graphene. Our results reveal that the relative change of resistance induced by magnetic field in the bilayer graphene shows an anomalous thermally activated property.

Composites of Fe2O3 nanosheets with polyaniline: Preparation, gas sensing properties and sensing mechanism

Fe2O3 nanosheets were in-situ deposited on the interdigitated gold electrodes by hydrothermal treatment of the electrospun nanofibers containing FeCl3 and poly(vinyl butyral). As-prepared electrode was further dip-coated with water-dispersible polyaniline (PANI) to fabricate a resistance gas sensor based on Fe2O3/PANI nanocomposite. The structure and morphology of the nanocomposite were investigated by X-ray diffraction pattern, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. It was found that the nanocomposite sensor exhibited much higher response magnitude towards low concentration of NH3 (0.5–10.7ppm) than the sensors based on either PANI or Fe2O3 at room temperature (∼20°C), indicating an obvious synergetic effect. The nanocomposite sensor was featured with ultra high response magnitude (relative resistance change of ∼3070% towards 10.7ppm of NH3) and excellent selectivity towards NH3. A sensing mechanism has been put forward, which takes into account of the conducting network comprising of bulk PANI and composites of PANI and Fe2O3 nanosheets. It was proposed that the p/n heterojunction established between Fe2O3 nanosheets and PANI coating played a major role in the highly desirable sensing performance of the composite.