Relative Resistance Change Research Articles

Elaboration of SWNTs-based gas sensors using dispersion techniques: Evaluating the role of the surfactant and its influence on the sensor response

This paper describes the preparation of the CNTs-based gas sensors, which are achieved by the utilisation of aqueous dispersions of carbon nanotubes (CNTs) using NaDDBS as a surfactant. The sensors are made of IDEs (Interdigitated electrodes) on which the CNTs dispersion are dropcast deposited. The sensing layers are characterized by Raman and IR spectroscopy as well as SEM analysis and electrical characterization (I–V). Finally, the sensor response and relative resistance change (ΔR/R) versus concentration under low NO2 gas concentrations are reported. The sensor performance is evaluated by focusing on the influence of the surfactant and the annealing process on the final sensor. The effect of the surfactant has been investigated in order to establish the optimal conditions for the realization of the sensors using dispersion route. Although the use of surfactant provides stable dispersions, the annealing treatment of the sensor before sensing experiments need to be correctly tuned for good sensor performance. Indeed, even if the presence of surfactant does not drastically hinder the sensor response, a major problem comes from its residue after decomposition under certain annealing conditions (≥300°C). In fact the surfactant residue seems to obstruct active sites on the sensor surface and therefore render the sensor unusable. Lower annealing conditions (≤150°C) seem to be the optimum.

Large piezoresistance of single silicon nano-needles induced by non-uniaxial strain

Silicon (Si) nanostructures may play an important role in future nanoelectronics. Here, arrays of single vertically aligned Si nano-needles (SiNNs) are fabricated and found to exhibit a significant piezoresistance effect under large non-uniaxial strain. The experiments were performed by in situ manipulating of the SiNNs in a scanning electron microscope. The method enables us to determine the piezoresistance effect under the combined action of compressive and tensile strains, which is different from reported works on the piezoresistance effect of Si nanostructures under uniaxial/biaxial strains. This has given rise to an opportunity to further explore the physical origins responsible for the piezoresistance of Si. The relative change in resistivity under the non-uniaxial strain was calculated from the experimental I-V data. The results show that a greater piezoresistance effect can be achieved as compared with that of Si nanowires under uniaxial strain. We propose that the suppression of inter-valley scattering and the change of electron concentration caused by the energy band shift are the main reasons for the large piezoresistance effect.

Measurement of microstructure changes in 9Cr–1Mo and 2.25Cr–1Mo steels using an electromagnetic sensor

This paper presents results from a multi-frequency electromagnetic sensor used to characterize the microstructural changes in 9Cr–1Mo and 2.25Cr–1Mo power generation steels after tempering and elevated temperature service exposure. The electromagnetic sensor can detect the microstructural changes in both steels due to the corresponding relative permeability and resistivity changes. The low-frequency inductance value is particularly sensitive to the different relative permeability values of both steels.

Design, Modeling and Simulation of CMOS-MEMS Piezoresistive Cantilever Based Carbon Dioxide Gas Sensor for Capnometry

This paper reports design, modeling and simulation of MEMS based sensor working in dynamic mode with fully differential piezoresistive sensing for monitoring the concentration of exhaled carbon dioxide (CO2) gas in human breath called capnometer. CO2 being a very important biomarker, it is desirable to extend the scope of its monitoring beyond clinical use to home and ambulatory services. Currently the scope of capnometers and its adaption is limited by high cost, large size and high power consumption of conventional capnometers . In recent years, MEMS based micro resonant sensors have received considerable attention due to their potential as a platform for the development of many novel physical, chemical, and biological sensors with small size, low cost and low power requirements. The sensor is designed using 0.35 micron CMOS technology. CoventorWare and MATLAB have been used as simulation software. According to the developed model and simulation results the resonator has resonant frequency 57393 Hz and mass sensitivity of 3.2 Hz/ng. The results show that the longitudinal relative change of resistance is 0.24%/µm while the transverse relative change of resistance is -0.03%/µm.

Development of an impedimetric immunosensor for the determination of 3-amino-2-oxazolidone residue in food samples

The use of furazolidone in food animals has been banned in European Union (EU) because of its carcinogenicity and mutagenicity on human health, but its continued misuse is widespread. Therefore, there is an urgent need for a simple, reliable, and rapid method for the detection of its marker residue, 3-amino-2-oxazolidinone (AOZ), in food products. In this regard, a sensitive and reliable electrochemical method was presented to detect AOZ based on a novel label-free electrochemical impedimetric immunosensor to address this need. The immobilization of monoclonal antibody against AOZ (denoted as AOZ-McAb) on the gold electrode was carried out through a stable acyl amino ester intermediate generated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosuccinimide (NHS), which could condense antibodies on the self-assembled monolayer (SAM). The detection of AOZ was performed by measuring the relative change in charge transfer resistance before and after AOZ and AOZ-McAb immunoreaction by electrochemical impedance spectroscopy (EIS). Under the optimized conditions, the relative change in charge transfer resistance was proportional to the logarithmic value of AOZ concentrations in the range of 20.0 to 1.0 × 10 4 ng mL −1 ( r = 0.9987). Moreover, the proposed immunosensor has a high selectivity to AOZ alone with no significant response to the metabolites of other nitrofuran antibiotics, such as 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), semicarbazide (SEM), and 1-aminohydantoin hydrochloride (AHD). This protocol has been applied to detect AOZ in food samples with satisfactory results.

TEMPORAL CONTEXT, PREFERENCE, AND RESISTANCE TO CHANGE

According to behavioral momentum theory, preference and relative resistance to change in concurrent-chains schedules are correlated and reflect the relative conditioned value of discriminative stimuli. In the present study, we explore the generality of this relation by manipulating the temporal context within a concurrent-chains procedure through changes in the duration of the initial links. Consistent with previous findings, preference for a richer terminal link was less extreme with longer initial links across three experiments with pigeons. In Experiment 1, relative resistance to change and preference were related inversely when responding was disrupted with response-independent food presentations during initial links, replicating a previous finding with rats. However, more food was presented with longer initial links, confounding the disrupter and initial-link duration. In Experiment 2, presession feeding was used instead and eliminated the negative relation between relative resistance to change and preference, but relative resistance to change was not sensitive to relative terminal-link reinforcement rates. In Experiment 3, with more extreme relative terminal-link reinforcement rates, increasing initial-link duration similarly decreased preference and relative resistance to change for the richer terminal link. Thus, when conditions of disruption are equal and assessed under the appropriate reinforcement conditions, changes in temporal context impact relative resistance to change and preference similarly.

Behavior of Sputtered Indium–Tin–Oxide Thin Film on Poly-Ethylene Terephthalate Substrate Under Stretching

In this work, two different sheet resistances, 100 and 60 Ω per square of DC-Magnetron sputtered indium tin oxide (ITO) thin film on poly ethylene terephthalate (PET) substrate were stretched up to 15% of the original length under three different strain rates, 0.01, 0.1, and 1.0 min-1. The cracks development during stretching was monitored using optical microscope. Two types of cracks were observed: in the first type, cracks initiated perpendicularly to the tensile load and propagated towards the edge of the sample, which was observed at 4% strain for both sheet resistances and different strain rates. In the second type, cracks initiated from the first type cracks and propagated perpendicularly to it towards the next original crack. The cracks intensity for both types of cracks was investigated. The intensity of both cracks type increases with the strain and sheet resistance. The electrical resistance was measured every 1% strain during stretching. The relative electrical resistance change (ΔR/R0) was plotted against strain at different strain rates. It could be concluded that, the relative electrical resistance change under high strain rate is higher at the beginning of the stretching process, but after a certain strain, the relative electrical resistance change under the lower strain rate accelerated till the film becomes non-conductive while the relative electrical resistance change under high strain rate is in acceleration process until reaching non-conductive condition. Analysis of Variance (ANOVA) results showed that the strain and the sheet resistance are significant factors on the relative electrical resistance change at 95% confidence level. The strain rate was not significant factor in the range considered. No two factor interactions are significant as well.

Multifilament fibres of poly(ɛ-caprolactone)/poly(lactic acid) blends with multiwalled carbon nanotubes as sensor materials for ethyl acetate and acetone

Conductive poly(ɛ-caprolactone) (PCL) + 4% multiwalled carbon nanotubes (MWCNTs)/poly(lactic acid) (PLA) = 50/50 wt% blend multifilament fibres were melt-spun and a woven textile was made by a handloom with the conductive fibres in weft direction. The fibres were tested for cyclic liquid sensing in ethyl acetate and acetone as two moderate solvents and in ethanol as a poor solvent. The liquid sensing responses, namely the relative resistance changes R rel relating the resistance change to the initial resistance of the samples on contact with ethyl acetate and acetone, were fast ( R rel higher than 16 after 100 s), with high amplitudes ( R rel higher than 23 after 500 s), and well reproducible. At the same time, the fibres were resistant against these solvents. The response to ethanol was also reproducible, however, very slow and with low amplitude. PLA was found to crystallize during the immersion process, whereas in PCL the crystalline domains transformed into amorphous ones as studied by Wide Angle X-ray Diffraction. The crystallization of PLA does not influence negatively the liquid sensing properties which can be assigned to the finding that the MWCNT are predominantly localized in the PCL phase as confirmed by Scanning Electron Microscopy. In the final step, a textile based on those fibres was prepared and its sensing behaviour was investigated on ethyl acetate and acetone clearly showing that such textiles are suitable to detect these solvents.

Molecular dynamics study of influence of vacancy types defects on thermal conductivity of β-SiC

A molecular dynamics technique has been used to study the impact of single vacancies and small vacancy clusters/microvoids on thermal conductivity of Si and β-SiC. It is found that single vacancies reduce thermal conductivity more significantly than do microvoids with the same total number of vacancies in the crystal. The vacancy concentration dependence of the relative change of thermal resistivity of both Si and SiC changes from linear at low concentrations to square-root at higher values. In contrast, the dependence on the volume fraction of microvoids switches from square-root at small swelling values to nearly linear dependence at higher swelling. In the case of SiC the results obtained for vacancies and microvoids agree reasonably well with experimental values. The computational results are compared with the commonly used Debye–Callaway model.

Study on the Sensing Property of Carbon-Coated Filaments

This paper analyzes sensitivity, linearity, repeatability, strain relaxation of Carbon-coated Filaments (CCFS) in resistance tensile strain to evaluate CCFS’s sensing property. The results show that the relative resistance changes present two stages, change is stable in 0-6mm tensile range, while it amplitude increases in 6-15mm. CCFS’s linearity is better as number of filament increasing, while sensitivity is lower; if number is the same, CCFS sensitivity reduces as twist’s increasing. The 12F CCFS has poor repetitiveness and seriously flabby phenomenon when tensile change greatly.

A study on crack propagation and electrical resistance change of sputtered aluminum thin film on poly ethylene terephthalate substrate under stretching

This work is designed to study crack development and resistance changes in aluminum thin films under stretching. Crack development and relative electrical resistance change (∆R/R 0) of aluminum thin film on 127-μm poly ethylene terephthalate substrates were investigated as a function of engineering strain. Four thicknesses were considered for the aluminum thin films: 50, 100, 200, and 500 nm. The engineering stress–engineering strain curves were very similar for all thicknesses. Three strain rates were considered in this study: 0.1 min − 1 , 0.5 min − 1 and 1.0 min − 1 . Before the yield point, there was no stress difference under different strain rates. However, after the yield point, stress was higher at a higher strain rate. It was found that ∆R/R 0 was very sensitive to the film thickness. Optical microscope images at high magnification showed that cracks were observed at 2% strain for 100, 200, and 500 nm-thick films and at 8% strain for the 50 nm-thick films. Short lateral cracks (perpendicular to the original cracks) were observed at 20% strain for the 100 and 200 nm thick films and at 30% for the 500 nm thick films.

Environmental monitoring of leaks using time-lapsed long electrode electrical resistivity

Abstract Highly industrialized areas pose challenges for surface electrical resistivity characterization due to metallic infrastructure. The infrastructure is typically more conductive than the desired targets and will mask the deeper subsurface information. The risk of this occurring may be minimized if steel-cased wells are used as long electrodes in the area near the target. We demonstrate a method of using long electrodes to electrically monitor a simulated leak from an underground storage tank with both synthetic examples and a field demonstration. Although the method of using long electrodes has been proposed by others, no time-lapse resistivity data have been collected, modeled, and analyzed within a nuclear waste tank farm environment. Therefore, the main objective of this work was to test whether the long electrode method using steel-cased wells can be employed to spatially and temporally track simulated leaks in a highly industrialized setting. A secondary objective was to apply a time-lapse regularization procedure in the inverse modeling code, similar to the 4D tomography approach by Kim et al. (2009), and to test the procedure's effect on the quality of the outcome regarding plume intensity and position. For the synthetic examples, a simple target of varying electrical properties was placed beneath different types of layers of low resistivity to simulate the effects of the infrastructure. Both surface and long electrodes were tested on the synthetic domain, and the test cases covered a variety of survey parameters including low and high electrode density, noise, array type, and the explicit location of the wells relative to the target. All data were processed in four dimensions, where the regularization procedure was applied in both the time and space domains. The synthetic test case showed that the long electrode resistivity method could detect relative changes in resistivity that was commensurate with the differing target properties. The surface electrodes, on the other hand, had a more difficult time matching the original target's footprint unless the electrodes were distributed at a greater density on the surface. The simulated tank leak in the field experiment was conducted by injecting a high conductivity fluid in a perforated well within the S tank farm at the Hanford Site, and the resistivity measurements were made before and after the leak test. The field results showed a lowered resistivity feature develops south of the injection site after cessation of the injections. The parameter used in the time-lapsed inversion had a strong influence on the differences in inverted resistivity between the pre- and post-injection datasets, but the interpretation of the target was consistent across all values of the parameter. The long electrode electrical resistivity monitoring (ERM) method may provide a tool for near real-time monitoring of leaking underground storage tanks given a sufficient density of wells.

Piezoresistance effect of metallic glassy fibers

Smaller electrical resistance strain gauges (ERSG) are highly expected especially for micro-electro-mechanical systems while the reduction in the size of strain gauge is restricted by the relatively low resistivity and poor processability of conventional piezoresistive alloys. We investigate piezoresistive properties of a Pd40Cu30Ni10P20 metallic glassy fiber (MGF), and find that the resistivity, gage factor, elastic limit, and relative change in resistance of the MGF are superior to that of commercial crystalline ERSG piezoresistors. Combining with high flexibility, uniformity, smoothness, and nanoscale size in diameter, the MGFs are promising for submicroscale ERSGs.

Composites of carboxylate-capped TiO 2 nanoparticles and carbon black as chemiresistive vapor sensors

Titanium (IV) dioxide (TiO 2) nanoparticles (NPs) with a 1–5 nm diameter were synthesized by a sol–gel method, functionalized with carboxylate ligands, and combined with carbon black (CB) to produce chemiresistive chemical vapor sensor films. The TiO 2 acted as an inorganic support phase for the swellable, organic capping groups of the NPs, and the CB imparted electrical conductivity to the film. Such sensor composite films exhibited a reproducible, reversible change in relative differential resistance upon exposure to a series of organic test vapors. The response of such chemiresistive composites was comparable to, but generally somewhat smaller than, that of thiol-capped Au NPs. For a given analyte, the resistance response and signal-to-noise ratio of the capped TiO 2-NP/CB composites varied with the identity of the capping ligand. Hence, an array of TiO 2-NP/CB composites, with each film having a compositionally different carboxylate capping ligand, provided good vapor discrimination and quantification when exposed to a series of organic vapors. Principal components analysis of the relative differential resistance response of the sensor array revealed a clear clustering of the response for each analyte tested. This approach expands the options for composite-based chemiresistive vapor sensing, from use of organic monomeric or polymeric sorbent phases, to use of electrically insulating capped inorganic NPs as the nonconductive phase of chemiresistive composite vapor sensors.

Vapor sensing properties of thermoplastic polyurethane multifilament covered with carbon nanotube networks

The volatile organic compound (VOC) vapor sensing properties of a novel kind of thermoplastic polyurethane multifilament – carbon nanotubes (TPU–CNTs) composites is studied. And the sensing is based on changes in the electrical resistance of the composites due to vapor contact. The composites were readily obtained by adhering CNTs on the surface layer of TPU by means of simply immersing pure TPU multifilament into CNT dispersion. The uniformly formed nanotube networks on the outer layer of composite multifilament are favorable for providing efficient conductive pathways. The resulting TPU–CNTs composites show good reproducibility and fast response (within seconds) of electrical resistance change in cyclic exposure to diluted VOC and pure dry air. The vapor sensing behaviors of the composites are related to CNT content, vapor concentration, and polar solubility parameters of the target vapors. A relatively low vapor concentration of 0.5% is detectable, and a maximum relative resistance change of 900% is obtained for the composite with 0.8 wt.% CNT loading when sensing 7.0% chloroform. It is proposed that both the disconnection of CNT networks caused by swelling effects of the TPU matrix and the adsorption of VOC molecules on the CNTs are responsible for the vapor sensing behavior of TPU–CNTs composite, while the former effect plays the major role.

Polymer/carbon nanotube composites for liquid sensing: Model for electrical response characteristics

Electrically conductive polymer composites (CPCs) based on carbon nanotubes (CNTs) and polycarbonate were investigated regarding their electrical resistance change in different solvents like tetrahydrofuran, acetone, and ethyl acetate. CPCs containing 0.086 to 2.778 vol.% CNT were melt mixed using a twin-screw extruder under optimised conditions and subsequently compression-moulded. All sensing experiments revealed a resistance increase of CPCs having a U-shaped sample geometry during solvent immersion. Light microscopy investigations have shown that the diffusion of solvents into CPCs can be monitored in terms of a pronounced diffusion front, separating a swollen skin from the dry core. Based on this observed skin-core morphology, a model allowing the calculation of the time depending relative resistance change has been proposed considering several factors like diffusion parameters, composite characteristics, and geometrical values. Simulated response curves based on the model were compared with experimental data obtained on the CPCs and very good agreement was observed. Using this model the influence of CNT content and kind of solvent could be described exactly.

The investigation of reversible strain and polarization effect in (011)-La0.9Ba0.1MnO3 film using field effect configuration

We have investigated the influence of the electric bias field on the magnetic and transport properties of (011)-oriented La0.9Ba0.1MnO3 (LBMO) thin film epitaxially grown on (011)-0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) single crystal substrate. It was found that strain and polarization effects induced by electric bias coexist in the whole temperature range and both of them can modulate the transport properties of (011)-LBMO on PMN–PT. The relative change of resistance ΔR/R exhibits peak values of −22% and −32% for bias fields of +12 and −12 kV/cm, respectively, around metal-insulator transition temperature, TMI. However, the sign of ΔR/R shows polarity dependence at temperature far below TMI. Further careful analysis demonstrates that these two opposite behaviors can be ascribed to the different influence of strain and polarization effects on transport properties.

Patchy nitrate promotes inter-sector flow and 15N allocation in Ocimum basilicum: a model and an experiment.

Root conductance increases under high nitrate conditions. This plasticity might increase water and nutrient transport between parallel xylem pathways, but restrictions to lateral flow - called sectoriality - are expected to limit this crossover. We simulated the effects of a high nitrate patch on root conductance, water uptake and inter-sector water transport, then empirically tested whether a high nitrate patch affects water uptake and nitrogen distribution (applied 15N as 14NH415NO3 to half the root system) within the crowns of split-root hydroponic basil (Ocimum basilicum L.). Simulations showed that at low sectoriality, the proportion of water taken up in a patch scales with the relative change in root resistance and that this fraction decreases with increasing tangential resistance. The effect of sectoriality decreased when a higher background root resistance was assumed. Empirically, water flow through excised basil roots was 1.4 times higher in the high nitrate than the no nitrate solution. In split-root basil, a nitrate patch resulted in a marginally significant increase in the proportion of water taken up from the patch and water uptake patterns significantly predicted the distribution of 15N. Our results suggest that root conductance can mediate nitrogen allocation between sectors, a previously unexplored benefit.

Passive Detection of Nitrogen Dioxide Gas by Relative Resistance Monitoring of Iron (II) Phthalocyanine Thin Films

Metal-substituted phthalocyanine (MPc) thin films have been well documented as sensitive materials for detection of nitrogen dioxide (NO2) gas. The mechanism for detection is such that a MPc thin film acting as the electron donor possesses a strong chemical adsorption affinity towards NO2 molecules acting as electron acceptors. The resulting charge-carrier complex formed significantly increases MPc thin-film conductivity. Sensors based on iron (II) phthalocyanine (FePc) thin films were fabricated by physical vapor deposition of FePc onto gold interdigitated electrodes patterned on an oxidized silicon substrate. Sensor exposure to NO2 concentrations ranging from 0.25 to 2 ppm under an ultrahigh-purity nitrogen environment was conducted. Results show that room temperature as-deposited 400-nm FePc films with no post-deposition heat treatment produced a sensor that can reliably differentiate NO2 concentrations in the range of 0.5 to 2 ppm NO2 under a nitrogen atmosphere, via passive monitoring of relative resistance change.

Characterization of phase development in non-isothermally annealed mould-cast and heat-treated Al–Mn–Sc–Zr alloys

The effect of Mn addition on microstructure and mechanical properties during isochronal annealing in the temperature range of 20 °C–570 °C of the mould-cast and heat-treated Al–Sc–Zr alloys with a various content of Mn and Zr was studied. The electrical resistometry together with the microhardness (HV0.3) measurements were compared to microstructure development. The microstructure development was examined by scanning electron microscopy, transmission electron microscopy and electron diffraction. Relative resistivity changes and the microhardness of the mould-cast and heat-treated Al–Mn–Sc–Zr alloys exhibit similar dependence on annealing temperature. Precipitation of the Al 3Sc particles is responsible for the peak microhardness in all these alloys. The microhardness decrease is slightly delayed during the isochronal annealing and during the high temperature heat treatment in the mould-cast alloy with the higher Zr-content due to a higher oversaturation of Zr. The decomposition sequence of the oversaturated solid solution of the studied Al–Mn–Sc–Zr alloys is compatible with the recently published decomposition sequence of the Al–Sc–Zr system and also with the formation of Mn,Fe-containing particles. It seems very probable that the addition of Mn does not influence the decomposition of solid solution of the ternary Al–Sc–Zr system.