Simultaneous Resistance Measurements Research Articles

Sensing mechanisms of CO and H2 with NiO material – DRIFTS investigations

The response of nickel oxide gas sensors towards CO and H2 and the underlying gas sensing mechanisms were investigated with special focus on the influence of ambient humidity interference. Surface reactions were tracked by using diffuse reflectance infrared Fourier transformation spectroscopy with simultaneous resistance measurements. The sensor response to both gases is barely influenced by the background humidity. Spectroscopic results reveal that the underlying processes at the surface are almost identical for CO and H2 reception and similar to the effect of the removal of oxygen. Accordingly, the detection of the analytes is based purely on the reduction and oxidation of the oxide material instead of the formation of analyte specific surface species.

Influence of Ni interlayer on hydrogen absorption and cyclicity in Gd thin films

The Pd/Gd bilayers and Pd/Ni/Gd trilayers were prepared onto glass substrates by magnetron sputtering. Detailed XPS in-situ studies of the Pd/Gd bilayers allowed to estimate the thickness of the mixed layer at about 4 nm. Further studies showed that the additional Ni interlayer can significantly reduce the interface mixing during the deposition process, leading to the formation of a rather narrow Ni–Gd interface. The structure of the obtained layers before and after the hydrogenation was examined by the standard X-ray diffraction method. The hydrogenation kinetics was studied in-situ at room temperature and pressure up to 1 bar using simultaneous measurements of resistivity and optical transmittance. Furthermore, hydrogen absorption by electrochemical method was monitored using optical transmittance. It was found that the use of an additional 4 nm Ni layer significantly improved the cyclicity of the hydrogen absorption/desorption from the electrolyte, while maintaining low switching time (10 s).

Effect of interfacial mixed layer on hydrogen absorption in yttrium thin films

Pd/Y bilayers and Pd/Ti/Y trilayers were prepared in a UHV chamber by DC/RF magnetron sputtering. The characterization of the Pd-Y and Ti-Y interfaces was performed immediately after the deposition using in-situ X-ray photoelectron spectroscopy (XPS). The results indicated significant interface mixing for the Pd/Y bilayers. Further studies showed that the additional Ti layer deposited between the palladium and yttrium layers can significantly reduce the mixing of the Pd-Y layers during the deposition process at room temperature, leading to the formation of a sharp Ti-Y interface. The structure of the obtained layers before and after the hydrogenation was examined by the standard X-ray diffraction method. The hydrogenation kinetics was studied in-situ at room temperature and pressure up to 1 bar using simultaneous measurements of resistivity and optical transmittance. It was found that for a thickness of Ti equal to 5 nm, the shortest transition time to the YH3 phase was obtained while maintaining a short switching time.

Operando monitoring of a room temperature nanocomposite methanol sensor.

The sensing of volatile organic compounds by composites containing metal oxide semiconductors is typically explained via adsorption-desorption and surface electrochemical reactions changing the sensor's resistance. The analysis of molecular processes on chemiresistive gas sensors is often based on indirect evidence, whereas in situ or operando studies monitoring the gas/surface interactions enable a direct insight. Here we report a cross-disciplinary approach employing spectroscopy of working sensors to investigate room temperature methanol detection, contrasting well-characterized nanocomposite (TiO2@rGO-NC) and reduced-graphene oxide (rGO) sensors. Methanol interactions with the sensors were examined by (quasi) operando-DRIFTS and in situ-ATR-FTIR spectroscopy, the first paralleled by simultaneous measurements of resistance. The sensing mechanism was also studied by mass spectroscopy (MS), revealing the surface electrochemical reactions. The operando and in situ spectroscopy techniques demonstrated that the sensing mechanism on the nanocomposite relies on the combined effect of methanol reversible physisorption and irreversible chemisorption, sensor modification over time, and electron/O2 depletion-restoration due to a surface electrochemical reaction forming CO2 and H2O.

Fabrication of polypyrrole/tin oxide/graphene nanoribbon ternary nanocomposite and its high-performance ammonia gas sensing at room temperature

In this study, the polypyrrole (PPy)/tin oxide (SnO2)/graphene nanoribbon (GNR) ternary nanocomposites are successfully synthesized using in situ chemical oxidative polymerization. In doing so, the SnO2 nanoparticles fabricated using a solvothermal reaction are coated on the surface of the GNR. The gas sensing performances of nanocomposites at room temperature are estimated by a homemade dynamic test system, equipped with a simultaneous resistance measurement platform. The response value of the PPy/SnO2/GNR sensor containing 3-wt% SnO2 nanoparticles with an exposure of 1-ppm NH3 is 92.7, which is roughly three times greater than that of a pure PPy sensor. This composite sensor can sensitively detect the NH3 between concentrations of 0.6 and 2 ppm at room temperature. The PPy/SnO2/GNR sensor also has higher repeatability and selectivity when exposed to 1- and 2-ppm NH3 at room temperature than existing sensor. Due to the outstanding repeatability and selectivity, it is evident that the PPy/SnO2/GNR nanocomposite sensor is a promising gas sensing material for the detection of the hepatic or kidney disease in human breath.

3D printing of multiaxial force sensors using carbon nanotube (CNT)/thermoplastic polyurethane (TPU) filaments

We developed a new method to directly fabricate 3D multiaxial force sensor using fused deposition modeling (FDM) 3D printing of functionalized nanocomposite filaments. Here, 3D cubic cross shaped force sensor is suggested to measure the forces from three axes (x, y and z). The sensor has two components – a structural part and a sensing part – both of which are concurrently fabricated by 3D printing with different functional filaments. The structural part is printed with thermoplastic polyurethane (TPU) filament and the sensing part is printed with carbon nanotube (CNT)/TPU nanocomposite filament with a piezoresistivity on the surface of the structural part. The resistances of the sensing part are measured in three axial directions; Rx, Ry, and Rz and the force applied on each axis is measured by the resistance change. The 3D-printed multiaxial force sensor could detect the sub-millimeter scale deflection and its corresponding force on each axis. According to the sensing principle, when Fz=4N was applied, Rz was decreased by 2% while only 0.2% resistance change of Ry was induced. In addition, a simultaneous resistance measurement system was developed for a real-time force sensing in three axes. With its customizability, rapid manufacturing, and economic feasibility, this manufacturing approach allows direct fabrication of multiaxial sensors without additional assembly or integration processes.

English

We report on the simultaneous measurement of resistivity and Seebeck coefficients in samples of Pd81Ge19 ribbons prepared by the melt spinning technique method and having a typical dimension of 40.0 mm × 1.75 mm × 0.028 mm. The investigation was performed using a new completely automated device in a large temperature range (from room to 700°C). Structural changes, crystallization times and heat treatments on several samples of the same composition were followed as a function of temperature. Seebeck coefficients, reported for the first time in these samples, varied roughly between -2 and -21 µV/K in the temperature range of 25 to 700°C, while the electrical resistivity varied roughly between 35 and 120 µΩ.cm in agreement with the literature. Complementary differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) experiments were also carried out and confirm the phase transitions observed by the above mentioned techniques. Key words: Seebeck coefficient, melt spinning technique, crystallization temperature, electrical resistivity, phase transitions.

Simultaneous measurement of resistively and optically detected nuclear magnetic resonance in theν=2/3fractional quantum Hall regime

We observe nuclear magnetic resonance (NMR) in the fractional quantum Hall regime at Landau level filling factor $\nu=2/3$ from simultaneous measurement of longitudinal resistance and photoluminescence (PL). The dynamic nuclear spin polarization is induced by applying a huge electronic current at the spin phase transition point of $\nu=2/3$. The NMR spectra obtained from changes in resistance and PL intensity are qualitatively the same; that is, the Knight shift (spin polarized region) and zero-shift (spin unpolarized region) resonances are observed in both. The observed change in PL intensity is interpreted as a consequence of the trion scattering induced by polarized nuclear spins. We conclude that both detection methods probe almost the same local phenomena.

Annealing-induced rheological and electric resistance variations in carbon black-filled polymer melts

Annealing-induced viscoelastic and electric conduction variations were traced by simultaneous measurement of resistance and dynamic modulus to carbon black (CB)-filled high-density polyethylene, polystyrene, and polypropylene at elevated temperatures. The resistance decay during annealing the melts is closely related to terminal relaxation of polymer chains and the temperature-mediated interfacial tension between CB and the matrix. On the other hand, a time–temperature–concentration superposition principle was disclosed to evolution of dynamic modulus for the filled melts at different temperatures and CB volume fractions. Annealing the filled melts causes a liquid-to-solid-like transition and the differences in kinetic constant for evolution of dynamic modulus among the three systems at the same condition are involved in interfacial tension.

Electrical resistivity and TDR methods for soil moisture estimation in central Italy test-sites

Summary In this study, the feasibility of the resistivity method for the study of the spatial and temporal soil moisture variations in the Vallaccia catchment (central Italy), covering an area of about 56 km 2 , was investigated. Correlation and regression analyses were performed over a 1 year data set of simultaneous soil electrical resistivity and soil moisture measurements, acquired in eight different sites with a Resistivimeter Syscal Junior and a portable Time Domain Reflectometer (TDR), respectively. Measurements acquired in-time by continuous Frequency Domain Reflectometer (FDR) sensors were also used and compared with simultaneous resistivity measurements. The statistical analyses were conducted not only for the whole data set, but also separately for each sampling day, for each sampling site and considering spatially averaged data. Results showed a good correlation between resistivity and soil moisture measurements, revealing the capability of resistivity measurements to infer soil moisture spatial and temporal variability with a root mean square error equal, on average, to 4.4% vol/vol. In comparison with TDR, the resistivity method gives information integrated on a greater volume of soil and the measurements are easier and quicker to be carried out. Therefore, this method can be considered as an alternative tool to be employed for qualitative and quantitative soil moisture monitoring in small to medium catchments.

Interplay of H2, water vapor and oxygenat the surface of SnO2 based gas sensors – An operando investigation utilizing deuterated gases

The surface reactivity toward hydrogen and water vapor of three different (in grain size and amount of OH groups on the surface, different synthesis route) undoped tin dioxide materials (SnO2 Ac, SnO2Cl, SnO2 Cl K) was investigated at 300°C by applying simultaneous resistance measurements and DRIFTS (diffuse reflectance infrared spectroscopy). The changes of the surface species, i.e. OH groups, were examined due to exposure to hydrogen H2/deuterium D2, watervapor H2O/deuterated water vaporD2O and carbon monoxide CO. A possibility to minimize IR related disturbing phenomena in the absorbance spectra is the use of deuterated gases (D2, D2O): everything which deals with OH groups/water related species is shifted in the IR spectrum. We were able to show that the reaction with those reducing gases can be traced back to the reaction with adsorbed oxygen. There was no evidence for a direct reaction of the test gas with OH groups or in case of H2, a direct reaction with (lattice) oxygen to hydroxyl groups.

Label-free electrical discrimination of cells at normal, apoptotic and necrotic status with a microfluidic device

As a label-free alternative of conventional flow cytometry, chip-based impedance measurement for single cell analysis has attracted increasing attentions in recent years. In this paper, we designed a T-shape microchannel and fabricated a pair of gold electrodes located horizontally on each side of the microchannel using a transfer printing method. Instant electric signals of flowing-through single cells were then detected by connecting the electrodes to a Keithley resistance and capacitance measurement system. Experimental results based on the simultaneous measurement of resistance and capacitance demonstrated that HL-60 and SMMC-7721 cells could be differentiated effectively. Moreover, SMMC-7721 cells at normal, apoptotic and necrotic status can also be discriminated in the flow. We discussed the possible mechanism for the discrimination of cell size and cell status by electrical analysis, and it is believed that the improvement of detection with our design results from more uniform distribution of the electric field. This microfluidic design may potentially become a promising approach for the label-free cell sorting and screening.

Characterization of carbon black‐filled immiscible polypropylene/polystyrene blends

AbstractThe electrical and rheological behaviors of carbon black (CB)‐filled immiscible polypropylene (PP)/polystyrene (PS) blends were investigated. The compounding sequence influences the phase morphology of the ternary CB/PP/PS composites and the distribution of CB aggregates. Simultaneous measurements of resistance and dynamic modulus were carried out to monitor the phase coalescence of the ternary composites and CB migration and agglomeration in the PS phase during annealing at temperatures above the melting point of PP. The variation of resistivity is mainly attributed to CB agglomeration in the PS phase and the interfacial region, while the variation of dynamic modulus is regarded as the superimposition of the phase coalescence and CB agglomeration in the PS phase. The ternary composites with the majority of CB particles distributed in the interfacial region show the lowest conductive percolation threshold and the most stable resistivity–temperature performance during heating–cooling cycles. Copyright © 2011 Society of Chemical Industry

Conductive and viscoelastic behaviors of carbon black filled polystyrene during annealing

Aggregation of carbon black (CB) aggregates in polystyrene melt was traced by simultaneous measurement of resistance ( R) and dynamic storage modulus ( G′) as a function of annealing time. There existed a dynamic resistance percolation in the time evolution of R while G′ increased gradually during the whole experimental time scale. Dynamic resistance and modulus percolation models were used to model the time-dependent R and G′, respectively. Furthermore, the time evolution of G′ was explained with a combination of the kinetic cluster–cluster aggregation model and the first order kinetics aggregation model. It was found that the aggregation of CB aggregates in the molten polystyrene has a close relation with the terminal relaxation of polystyrene molecules. The results indicated that the interfacial tension between polystyrene molecules and CB plays a crucial role in driving CB to aggregate.

Health monitoring in continuous glass fibre reinforced thermoplastics: Manufacturing and application of interphase sensors based on carbon nanotubes

In this study, a new approach for health monitoring of GF reinforced composites is presented by incorporating percolated carbon nanotubes (CNTs) into the composites interphase. This is achieved applying CNT-filled coatings to glass fibres (GF). Taking advantage of the electrical properties of CNTs, this allows a highly localized monitoring of the composites interphase. The approach is largely independent on matrix material and can be applied to thermoplastic or thermoset resin matrix materials with minor adjustments. The resistance of CNT-coated GF yarns shows a linear dependence on the yarn length and depends on the CNT weight fraction of the coating, as well as on the amount of coating on the GF yarn. Performing tensile tests in combination with simultaneous resistance measurements on CNT-coated GF yarns embedded in a polypropylene matrix, the interphase behaviour during mechanical loading is monitored, providing information on this specific area. This allows relating interphase failure or GF breakage to the resistance data and demonstrates the potential of this approach for health monitoring of GF reinforced composites.

Evidence from neutron diffraction for superconductivity in the stabilized tetragonal phase ofCaFe2As2under uniaxial pressure

${\text{CaFe}}_{2}{\text{As}}_{2}$ single crystals under uniaxial pressure applied along the $c$ axis exhibit the coexistence of several structural phases at low temperatures. We show that the room-temperature tetragonal phase is stabilized at low temperatures for pressures above 0.06 GPa, and its weight fraction attains a maximum in the region where superconductivity is observed under applied uniaxial pressure. Simultaneous resistivity measurements strongly suggest that this phase is responsible for the superconductivity in ${\text{CaFe}}_{2}{\text{As}}_{2}$ found below 10 K in samples subjected to nonhydrostatic pressure conditions.

Inaccuracy assessment for simultaneous measurement of resistivity and permittivity applying sensitivity and transfer function approaches

Normal.dotm 0 0 1 188 1075 INGV BO 8 2 1320 12.0 0 false 14 18 pt 18 pt 0 0 false false false The present study proposes a theoretical modeling of simultaneous and noninvasive measurements of electrical resistivity and dielectric permittivity using a quadrupole probe on a subjacent medium. A mathematical–physical model is applied to the propagation of errors in the measurement of resistivity and permittivity based on a sensitivity functions tool. The findings are also compared with results of the classical method of analysis in the frequency domain, which is useful for determining the behavior of zero and pole frequencies in the linear time invariant circuit of the quadrupole. This study underlines that average values of electrical resistivity and dielectric permittivity can be used to estimate complex impedance over various terrains and concretes, especially when they are characterized by low levels of water saturation (content), and are analyzed within a bandwidth ranging only from low to middle frequencies. To meet the design specifications, that ensure satisfactory performances of the probe (inaccuracies of no more than 10%), the forecasts provided by the sensitivity functions approach are discussed in comparison with those foreseen by the transfer functions method (in terms of both the band of frequency f and the measurable range of resistivity ρ, or permittivity er).

Gallium nitride electrodes for membrane-based electrochemical biosensors

We report on the deposition of planar lipid bilayers (supported membranes) on gallium nitride (GaN) electrodes for potential applications as membrane-based biosensors. The kinetics of the lipid membrane formation upon vesicle fusion were monitored by simultaneous measurements of resistance and capacitance of the membrane using AC impedance spectroscopy in the frequency range between 50 mHz and 50 kHz. We could identify a two-step process of membrane spreading and self-healing. Despite its relatively low resistance, the membrane can be modeled by a parallel combination of an ideal resistor and capacitor, indicating that the membrane efficiently blocks the diffusion of ions.

Simultaneous measurement of resistance and viscoelastic responses of carbon black‐filled high‐density polyethylene subjected to dynamic torsion

AbstractThe conduction and viscoelastic responses to temperature are measured simultaneously for carbon black (CB) filled high‐density polyethylene (HDPE) subjected to dynamic torsion. PTC/NTC transition was correlated with the loss tangent peak and the quasi modulus plateau, which was ascribed to the filler network. The bond‐bending model of elastic percolation networks was used to reveal the structural mechanisms for the cyclic resistance changes at different temperatures. The resistance changes at lower temperatures depended on the deformation of the polymer matrix, while the changes in melting state were mainly attributed to the rearrangement of the CB network. A simple scaling law is derived to relate resistance and dynamic storage modulus in the melting region. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Strain Sensing with Nanoscale Carbon Fiber – Epoxy Composites

To study the electrical behavior of nanoscale carbon fibers (NCF)/epoxy nanocomposites under mechanical load, NCF/epoxy materials were produced using different mechanical dispersion methods like pearl mill and three roll mill. Various preliminary mechanical tests with simultaneous resistance measurements have been conducted. The influence of the filler content, the dispersion quality and the filler geometry on the electrical properties of NCF/epoxy composites was investigated as a function of the mechanical loading. The strain sensitivity strongly depended on the filler content and the filler geometry. In cyclic loading tests at low strains the resistance showed a reversible and linear behaviour. At higher strains irreversible resistance changes were observed. In addition, the specific surface resistance corresponded even during unloading with the highest strain level applied so far. This indicates the potential of NCFs/epoxy nanocomposites to monitor the loading history of a sample.