Simultaneous Electrical Resistance Research Articles

Conduction mechanism in undoped and antimony doped SnO2 based FSP gas sensors

The conduction mechanism in highly porous thick film SnO2 sensing layers, obtained by a direct deposition technique using FSP (flame spray pyrolysis) and the role of antimony (Sb) additives is investigated by simultaneous DC electrical resistance and work function changes measurements in various ambient atmospheres. The results have shown that the conduction mechanism changes according to the ambient atmosphere from a depletion layer controlled one to flat band situation and to an accumulation layer controlled one. In comparison to former studies performed on polycrystalline thick film layers, obtained from pre-processed powders, the measurements indicate that the grain size of the sensing material has a big influence on the conduction mechanism. In the case of undoped FSP-SnO2 sensors the studies showed that the grains are fully depleted in oxygen containing atmospheres. By increasing the number of free charge carriers in the bulk of the semiconductor, it was found that the addition of Sb changes the conduction mechanism dramatically. In contrast to the undoped material, there is a direct switch from a conduction mechanism controlled by the depletion layer to the degenerated semiconductor surface situation. Additionally, an initial upwards band bending is observed, even in the absence of atmospheric oxygen, which indicates a surface effect of Sb.

Simultaneous measurement of pressure evolution of crystal structure and superconductivity in FeSe0.92 using designer diamonds

Simultaneous high-pressure X-ray diffraction and electrical resistance measurements have been carried out on a PbO-type α-FeSe0.92 compound to a pressure of 44 GPa and temperatures down to 4 K using designer diamond anvils at synchrotron source. At ambient temperature, a structural phase transition from a tetragonal (P4/nmm) phase to an orthorhombic (Pbnm) phase is observed at 11 GPa and the Pbnm phase persists up to 74 GPa. The superconducting transition temperature (TC) increases rapidly with pressure reaching a maximum of ∼28 K at ∼6 GPa and decreases at higher pressures, disappearing completely at 14.6 GPa. Simultaneous pressure-dependent X-ray diffraction and resistance measurements at low temperatures show superconductivity only in a low-pressure orthorhombic (Cmma) phase of the α-FeSe0.92. Upon increasing pressure at 10 K near TC, crystalline phases change from a mixture of orthorhombic (Cmma) and hexagonal (P63/mmc) phases to a high-pressure orthorhombic (Pbnm) phase near 6.4 GPa where TC is maximum.

Conduction mechanisms in SnO 2 based polycrystalline thick film gas sensors exposed to CO and H 2 in different oxygen backgrounds

The conduction mechanism in polycrystalline SnO 2 thick sensing films was modeled and experimentally investigated by means of simultaneous DC electrical resistance and work function changes measurements under CO and H 2 exposure in different oxygen backgrounds. It was shown that, according to the composition of the ambient atmosphere, the conduction changes from the case in which it is controlled by the surface depletion layers to a situation in which the main contribution comes from free charge transport in the surface accumulation layer. This is significant for the interpretation of work function changes measurements results because the relation between the different measured electrical resistance and surface band bending depends on the conduction model. Furthermore, the CO sensing mechanism dependence on the oxygen amount in the ambient was explained.

Influence of humidity on CO sensing with p-type CuO thick film gas sensors

A model for the detection of CO in the presence of humidity is proposed for thick porous film gas sensors based on p-type CuO. The sensing mechanism is investigated by means of simultaneous DC electrical resistance and work function changes measurements combined with appropriate modeling of the conduction in the polycrystalline sensing film. The experiments were performed at 150 °C in dry and humid air backgrounds. The conclusion is that, very similarly to the case of undoped SnO 2, the explanation of the cross-interference of water in the CO detection is the fact that both react with pre-adsorbed oxygen ions.

Effect of carbon black nanoparticle intrinsic properties on the self-monitoring performance of glass fibre reinforced composite rods

Self-monitoring composite rods, made of an internal conductive core surrounded by an external structural skin, were manufactured and tested. Both parts were made of glass fibre-epoxy. Electrical conductivity was achieved in the inner core by incorporating as an alternative high surface area or low surface area carbon black in the resin. Self-monitoring performance was assessed by simultaneous mechanical and electrical resistance measurements. The aim was to correlate the electrical resistance variation to stress. Only one type of material showed appropriate self-monitoring properties, since increase of electrical resistance was recorded at increasing loading (both monothonic and cyclic tensile loading), while electrical resistance recovery at high loads was found in the other case. Calorimetric analysis, rheological measurements and SEM observations were carried out to explain this result. Filler dispersion seems to be the key feature affecting the self-monitoring properties. Only high surface area nanoparticles can ensure self-monitoring reliability.

Thermal-induced percolation in high-density polyethylene/carbon black composites

The networking of carbon black in high-density polyethylene melt has been traced by simultaneous electrical resistance ( R) and dynamic storage modulus ( G′) testing. Thermal-induced dynamic percolation was observed for both R and G′ as a function of annealing time. The influence of temperature and filler volume fraction on percolation times to R and G′ was investigated, and activation energies of dynamic percolation were determined. The percolation times were longer than the terminal relaxation time, and activation energies of dynamic percolation were significantly higher than those of viscous flow and molecular relaxation of the composites. A first order kinetics aggregation model was introduced into the classical percolation theory to account for the dynamic percolation. The contribution of filler networking was evaluated quantitatively.

A high temperature cell for simultaneous electrical resistance and neutron diffraction measurements

An in situ cell that allows the electrical resistance of a sample pellet to be measured while performing neutron diffraction experiments has been developed at the ISIS pulsed neutron source. The sample is held between two spring loaded platinum electrodes embedded in a boron nitride clamp assembly with the resistance measured using the four-probe method. An outer quartz glass jacket allows the atmosphere within the sample enclosure to be controlled, and the entire device can be accommodated within a standard ISIS neutron furnace for measurements at temperatures up to 1270 K. The operation of this cell is illustrated using data for the structural, magnetic, and electrical properties of chalcopyrite CuFeS(2) collected over the temperature range of 398-873 K on the Polaris powder diffractometer at ISIS.

In-situ combined X-ray diffraction and electrical resistance measurements at high pressures and temperatures in diamond anvil cells

A method of simultaneous X-ray diffraction and electrical resistance measurements of materials in a diamond anvil cell has been developed. The experimental arrangement for the electrical measurements uses a gasket as a part of the electrode scheme. Application of the new methodology is demonstrated on the examples of the study of high-pressure high-temperature behavior of Pr and Fe–Ni alloys. Simultaneously obtained diffraction and resistance data provide the different, from earlier studies, interpretations of the topology of the dhcp–fcc phase transition in the phase diagram of Pr. Namely, the shape of a hysteretic region is mostly defined by kinetics of the dhcp phase growth rather than by thermodynamic driving force at the fcc to dhcp phase transformation. The results of combined X-ray diffraction and resistance measurements of Fe0.8Ni0.2 alloy up to 18 GPa and 425 K are reported along with the complementary resistance measurements of Fe0.9Ni0.1 alloy.

Electrical characterization of Schottky diodes based on boron doped homoepitaxial diamond films by conducting probe atomic force microscopy

A large planar tungsten carbide (WC) Schottky diode on p-type homoepitaxial diamond was mainly investigated on a microscopic level by atomic force microscopy (AFM) and conducting probe atomic force microscopy (CP-AFM), allowing simultaneous topographic and local electrical resistance imaging measurements. These techniques revealed the existence of a specific microstructure on the WC Schottky contact consisting of electrically insulating islands surrounded by conductive paths. The islands are found to be insulating in the whole range of explored bias [−5 V, +5 V], whereas the current flowing between the islands is 1000 times lower at a reverse bias of −5 V than at a forward bias of +5 V, in agreement with the rectifying ratio found from macroscopic current–voltage (I–V) measurements. CP-AFM provides a prospective imaging tool which is well suited for analyzing the local electrical properties and instabilities of Schottky junctions.

Monitoring of directional solidification with simultaneous measurements of electrical resistance and temperature

In this paper, we present the efficiency of simultaneous electrical resistance and temperature (ERT) measurements for monitoring the position, X, and the growth rate, V, of the solidification front during the directional solidification of alloys. On a laboratory device for directional solidification (Bridgman-type furnace), the eutectic Pb–Sn alloy was solidified at five different pulling rates, V P, with a constant imposed temperature gradient, G P. During directional solidification, the electrical resistance and the temperature changes were measured simultaneously in the experimental samples. The results of the experiments show that simultaneous measurement of ERT enables not only the determination of the average growth rate, V, during directional solidification but also its fluctuation over the total measurement length of the sample.

Study of the stress-assisted two-way memory effect of a Ti–Ni–Cu alloy using resistivity and thermoelectric power techniques

The stress-assisted two-way memory effect has been studied for successive cycles in a Ti–Ni–Cu alloy for two different thermo-mechanical treatments: recovery annealed (TT425) and fully recrystallized. Simultaneous tensile strain and electrical resistance measurements have been performed as a function of temperature and for different applied stresses. The thermoelectric power (TEP) in the stressed martensitic state has also been measured. For the treatment TT425 corresponding to 30% cold drawing followed by 425 °C annealing, a stable reversible strain ε m-β of 4.5% at maximum is found. A relatively low plastic strain ε p occurs for stresses above 125 MPa, which increases with the number of thermal cycles. For the recrystallized treatment, the maximum amplitude of the reversible strain is almost the same but a quite large plastic strain occurs even at 50 MPa and strongly increases with the number of cycles, reaching 12% for 20 cycles at 200 MPa. It is shown that the electrical resistivity change, associated with the reverse transformation, increases linearly with the reversible strain ε m-β. This effect is related to the electrical resistivity anisotropy of the martensite, with the slope being slightly different for the two treatments. In addition, the resistivity is relatively insensitive to the plastic strain. The TEP and the resistivity are sensitive to the orientation of the martensite, but the TEP also strongly depends on the plastic strain.

NEAR-FIELD OPTICAL THERMOMETRY

Far-field optical thermometry techniques have spatial resolution limited by diffraction to the order of the radiation wavelength. We report progress on near-field optical thermometry (NFOT) that targets spatial resolution better than 50 nm. A tapered, single-mode optical fiber scans nanometers above electronic microstructures, which are heated using transient electrical currents. The fiber tip releases about 1 nW of radiation power from a steady probe laser, and the reflected radiation is used to measure the local temperature. Simultaneous electrical resistance thermometry is used to estimate the relative importance of temperature dependent optical properties of the sample and thermal expansion of the sample and tip. This work provides guidance for implementing other NFOT techniques using radiation transmission and infrared emission.

The catastrophic phase of electromigration: surface diffusion, island formation, and film thinning

In situ transmission electron microscope investigation have been carried out on ultrahigh vacuum evaporated Al thin films using a specially designed heating stage. Standard photolithographic methods were used to form narrow metal stripes on oxidized silicon substrates which were then thinned from the rear. A linear temperature ramp was applied while simultaneous electrical resistance and temperature measurements were made. A video camcorder and standard photographic methods were used to record microstructural changes during current stressing. In large grained films clear evidence for surface diffusion was obtained. Thinning of the foil occurs on the cathode end and proceeds in channels in a direction, more or less, towards the cathode. Meanwhile atom motion occurs towards the anode. Simultaneously, islands are nucleated and grow in the thinned regions of the foil as a result of atom-atom and atom-cluster interactions. It is concluded that in these suspended stripes, surface or interface diffusion processes during electromigration testing make important contributions in the regime just prior to catastrophic failure.

Relation between resistivity and corrosion rate of reinforcements in carbonated mortar made with several cement types

Many years ago Stratfull and colleagues suggested the measurement of concrete resistivity as an indirect indication for active corrosion of the reinforcements. Their results were obtained from potential mapping measurements in chloride contaminated concrete. In the present paper results of corrosion rate and simultaneous electrical resistance values of rebars in mortar fabricated with six different types of cements are given and the relation between those values is presented. The specimens were carbonated in order to promote active corrosion of the rebars. They were held in chambers with different relative humidities. The results of this study indicate a strong relation-ship between the corrosion rate measured on the rebars (by means of Polarization Resistance method) and the electrical resistance of the concrete, which suggests a method of estimating the rebar corrosion rate from the simple measurement of the electrical resistance when rebars are depassivated. The relation between i corr and R ohm obtained is quite similar in all the cases and suggests that the concrete electrical resistivity may act as a “controlling” factor of the corrosion rate.

Low-temperature structural phase transition in La2CuO

Simultaneous electrical resistance and x-ray diffraction measurements have been made on samples of ${\mathrm{La}}_{2}$Cu${\mathrm{O}}_{4}$. The resistance data show a local maximum near 36 K; the x-ray data reveal a low-temperature structural transition which is correlated with the electrical anomaly. In addition to the new diffraction pattern, remnants of the orthorhombically distorted ${\mathrm{K}}_{2}$Ni${\mathrm{F}}_{4}$ structure of the parent phase are seen in varying amounts in all samples at low temperatures. These observations are in agreement with recent theoretical predictions.

The effects of adsorbed water on the electrical resistance and the length of saran charcoal rods—A preliminary account

An investigation has been made into the dimensional and electrical perturbations produced in cylindrical Saran carbon rods upon the adsorption of water vapour. Two independent experimental techniques have been used: 1. (a) conductivity changes only, were examined in the temperature range 0–50°C, and 2. (b) a sensitive adsorption extensometer was constructed to measure simultaneous length and electrical resistance changes, in the temperature range −40-25°C. From the data, the effect of adsorbed water on the coefficient of thermal expansion of a rod, and on an activation energy for electrical conduction were deduced. A qualitative interpretation of the main experimental findings is put forward.

High Pressure X-ray Diffraction Studies on Barium

Simultaneous x-ray diffraction and electrical resistance measurements on barium establish, with certainty, that Bridgman's 78-kb resistance transition is identical with his 59-kb volumetransition. During this transition, the bodycentered cubic structure changes to hexagonalclose packed. Lattice parameters for the latter structure at 62 kb (volume scale) are: a = 3.90 A, c = 6.15 A, and c/a = 1.58. Compression (AV/Vo) at 62 kb is 0.359 + 0.005 compared to 0.345 previously reported by Bridgman. Below the transition, at 49 kb, compression is 0.300 +/- 0.005 compared to Bridgman's 0.288. Bridgman's 17-kb volume transition was not detected by x-ray diffraction.