Abrupt Change In Resistivity Research Articles

Experimental study of rill bank collapse

AbstractRill bank collapse is an important component in the adjustment of channel morphology to changes in discharge and sediment flux. Sediment inputs from bank collapse cause abrupt changes in flow resistance, flow patterns and downstream sediment concentrations. Generally, bank retreat involves gradual lateral erosion, caused by flow shear stress, and sudden bank collapse, triggered by complex interactions between channel flow and bank and soil water conditions. Collapse occurs when bank height exceeds the critical height where gravitational forces overcome soil shear strength. An experimental study examined conditions for collapse in eroding rill channels. Experiments with and without a deep water table were carried out on a meandering rill channel in a loamy sand and sandy loam in a laboratory flume under simulated rainfall and controlled runon. Different discharges were used to initiate knickpoint and rill incision. Soil water dynamics were monitored using microstandpipes, tensiometers and time domain reflectometer probes (TDR probes). Bank collapse occurred with newly developed or rising pre‐existing water tables near rill banks, associated with knickpoint migration. Knickpoint scour increased effective bank height, caused positive pore water pressure in the bank toe and reduced negative pore pressures in the unsaturated zone to near zero. Matric tension in unsaturated parts of the bank and a surface seal on the ‘interrill’ zone behind the bank enhanced stability, while increased effective bank height and positive pore water pressure at the bank toe caused instability. With soil water contents >35 per cent (sandy loam) and >23 per cent (loamy sand), critical bank heights were 0·11–0·12 m and 0·06–0·07 m, respectively. Bank toe undercutting at the outside of the rill bends also triggered instability. Bank displacement was quite different on the two soils. On the loamy sand, the failed block slid to the channel bed, revealing only the upper half of the failure plane, while on the sandy loam the failed block toppled forwards, exposing the failure plane for the complete bank height. This study has shown that it is possible to predict location, frequency and magnitude of the rill bank collapse, providing a basis for incorporation into predictive models for hillslope soil loss or rill network development. Copyright © 2006 John Wiley & Sons, Ltd.

Highly Oriented VO[sub 2] Thin Films Prepared by Sol-Gel Deposition

Highly oriented VO 2 thin films were grown on sapphire substrates by a sol-gel method which includes a low-pressure annealing in an oxygen atmosphere. This reduction process effectively promotes the formation of the VO 2 phase over a relatively wide range of pressures below 100 mTorr and temperatures above 400°C. X-ray diffraction analysis showed that as-deposited films crystallize directly to the VO 2 phase without passing through intermediate phases. VO 2 films have been found to be with [100]- and [010]-preferred orientations on Al 2 O 3 (1012) and Al 2 O 3 (1010) substrates, respectively. Both films undergo a metal-insulator transition with an abrupt change in resistance, with different transition behaviors observed for the differently oriented films. For the [010]-oriented VO 2 films a larger change in resistance of 1.2 X 10 4 and a lower transition temperature are found compared to the values obtained for the [100]-oriented films.

Phase coexistence in the metal–insulator transition of a VO 2 thin film

Vanadium dioxide (VO 2) shows a metal–insulator transition (MIT) near room temperature, accompanied by an abrupt resistivity change. Since the MIT of VO 2 is known to be a first order phase transition, it is valuable to check metallic and insulating phase segregation during the MIT process. We deposited (100)-oriented epitaxial VO 2 thin films on R-cut sapphire substrates. From the scanning tunneling spectroscopy (STS) spectra, we could distinguish metallic and insulating regions by probing the band gap. Optical spectroscopic analysis also supported the view that the MIT in VO 2 occurs through metal and insulator phase coexistence.

Modeling of resistance changes based on the free volume in VLSI interconnection electromigration

A well-known model for the rate of heterogeneous nucleation and growth of a second-phase precipitate in a solid matrix has successfully been applied to analyze the electromigration process in Al thin-film interconnects. The change of resistance is considered resulting mainly from the scattering of electrons by atoms around the vacancies or voids at grain boundaries. Free volume is introduced to describe the behavior of these atoms and to simplify the complicated scattering process by means of the effective scattering cross section of the free volume. The quantitative relation between the scattering cross section and the resistance change is established, and from which the resistance revolution can be characterized during different electromigration stages. Comparison of our simulation results with experimental data shows good agreement and our model can explain the previously unexplained abrupt resistance change phenomena.

Kinetics of pinhole nucleation and growth in magnetic tunnel junctions

Tunnel junctions with different pinhole probabilities were obtained by varying natural oxidation condition. In pinhole-free junctions, the observed abrupt changes in magnetoresistance and junction resistance with increasing bias current are the signature of dielectric breakdown, and are attributed to the process of pinhole nucleation. On the contrary, low RA junctions show gradual changes in magnetoresistance and junction resistance with voltage, indicating the absence of pinhole nucleation, but only the process of pinhole growth starting from the inherent pinholes. Experimentally, the activation energy of pinhole growth (EG∼0.3 eV) is found to be much lower than that of pinhole nucleation (EN∼0.6eV), which explains the easy breakdown behavior observed in low RA junctions.

Current-induced spin-wave excitations in a single ferromagnetic layer.

Evidence for a current-induced spin-transfer torque effect has been investigated in a series of point contacts to single ferromagnetic layers. At specific current densities, abrupt resistance changes, similar to those attributed to current-induced spin-wave excitations in multilayers, have been observed for one current polarity. The critical current for these resistance changes depends linearly on the external field applied perpendicular to the layer. The observed effect is interpreted as a current-driven heterogeneous instability in an otherwise uniform ferromagnetic layer.

Tunable Magnetoresistance in InAs/Ferromagnet Hybrid Devices

Metal-oxide semiconductor field-effect transistors with ferromagnetic source- and drain-electrodes are fabricated on InAs. Tailored micromagnetic behavior of the ferromagnetic electrodes is achieved by use of a specific shape as well as in-plane external magnetic fields and is measured by magnetic-force microscopy. The field-effect in transistors with electrodes of defined magnetization is determined as a function of the gate voltage. The amplitude and the sign of abrupt resistance changes observed at points of irreversible switching of the ferromagnetic contacts' magnetization can be tuned by the gate voltage providing evidence for spin-polarized transport.

Device for Oil Spill Detection on Water Surfaces

An electrochemical device for oil spill detection on water surfaces based on conductometric principles is described measuring the abrupt big change of resistivity if the water level is covered by an oil layer. This detection device consists of two copper wire electrodes fixed on a support floating on the water layer and connected by cable with the monitoring unit giving a two level answer: “Yes” or “No”, on ev. oil spill presence. The system is used on many places in this country for purposes of river water surveillance.

Device for Oil Spill Detection on Water Surfaces

An electrochemical device for oil spill detection on water surfaces based on conductometric principles is described measuring the abrupt big change of resistivity if the water level is covered by an oil layer. This detection device consists of two copper wire electrodes fixed on a support floating on the water layer and connected by cable with the monitoring unit giving a two level answer: “Yes” or “No”, on ev. oil spill presence. The system is used on many places in this country for purposes of river water surveillance.

An effective medium model applied to the conductivity of La–Ca–Mn–O across the phase transition temperature

Colossal magnetoresistance is closely related to (but is not) the abrupt change of electrical resistivity in the vicinity of Curie temperature, which is caused by the temperature-dependent paramagnetic–ferromagnetic phase transition and concurrent change of electrical conducting mechanism. A model equation based on the effective medium theory is presented to explain the abrupt change of resistivity in the vicinity of Curie temperature of La–Ca–Mn–O (LCMO). It is assumed that LCMO is in the form of mixture of ferromagnetic and paramagnetic phase in the magnetic transition region. The main ingredients of the equation are a simple effective medium theory and a function for the temperature-dependent fraction of ferromagnetic phase. This model fits very well to the measured resistance–temperature curves of La 0.7Ca 0.3MnO 3.

Instrumentation effects on the detection of resistance transients during accelerated testing of VLSI interconnects

Some researchers have proposed using noise as an interconnect reliability tool. Often, however, noise spectral density has been used without concurrently examining the fluctuations in the time-domain which generate the noise spectra. Recently, the presence of abrupt changes in resistance (ACR's) has been documented in VLSI interconnects at accelerated stressing conditions. These ACR's are investigated here to identify their impact on typical spectra produced in noise measurements. Three results are reported in this paper, First, the presence of ACR's usually coincides with generation of 1//spl Fscr//sup 2/ noise. Second, the location of the ACR in the Fast Fourier Transform window is significant. Third, cross-correlation techniques can be used to identify ACR's in the time-domain signal.

2-D inversion of VES data in Saqqara archaeological area, Egypt

The interpretation of actual geophysical field data still has a problem for obtaining a unique solution. In order to investigate the groundwater potentials in Saqqara archaeological area, vertical electrical soundings with Schlumberger array have been carried out. In the interpretation of VES data, 1D resistivity inversion has been performed based on a horizontally layered earth model by El-Qady (1995). However, some results of 1D inversion are not fully satisfied for actual 3D structures such as archaeological tombs. Therefore, we have carried out 2D inversion based on ABIC least squares method for Schlumberger VES data obtained in Saqqara area. Although the results of 2D cross sections were correlated with the previous interpretation, the 2D inversion still shows a rough spatial resistivity distribution, which is the abrupt change in resistivity between two neighboring blocks of the computed region. It is concluded that 3D interpretation is recommended for visualizing ground water distribution with depth in the Saqqara area.

In-situ electromigration studies using resistometry

The effect of electromigration on unpassivated aluminum thin films has been studied using the resistometry method. Interim information during current-stressing can be obtained by this method. Ultimate open-circuit failure has also been monitored by the presence of a very large increase in resistance. The relations between the mean-time-to failure (MTTF) with the current density and with the ambient temperature have been determined. From the resistometry measurements, it was found that there are three stages of temporal evolution for sputtered films. An abrupt resistance change of about 0.02–0.04% was observed in the films under low or moderate current density. Subsequently, a randomly fluctuating period followed, where the fluctuating amplitude was about 0.01%. Finally, a fatal stage with an abrupt and tremendous resistance increase was reached until an open-circuit failure occurred. For sputtered films under high stressing-current density (J ≥ 2.35 MA cm-2), and for all evaporated films, the initial stage of abrupt resistance change essentially disappeared. From the scanning electron microscopy (SEM) micrograph, film thinning, surface coarsening, voids in irregular shape, and continuous cracks were found near the cathode. “Fan-shape” erosion appeared in the cathode under high current density. In the anode, hillocks parallel to the conductor direction were observed. Perpendicular extrusions extending out of the conductor were also present.

Thermal Transition Effects and Electrochemical Properties in Organic Coatings: Part 1 — Initial Studies on Corrosion Protective Organic Coatings

Abstract Thermal effects in a high-performance fusion-bonded epoxy (FBE) powder coating on steel were measured by electrochemical means. Experimental performance of the coating in immersion indicated the coating resistance as acquired by electrochemical noise methods (ENM), electrochemical impedance spectroscopy (EIS), and direct current resistance (RDC) measurements decreased in an Arrhenius manner with increasing temperature up to the glass transition temperature (Tg) of the immersed coating film. Coating resistance then abruptly decreased more rapidly. The abrupt change in film resistance (a coating transport property) at Tg was seen in all three film resistance measures. Using independent differential scanning calorimetry (DSC) experiments, Tg was shown to be that of the water-plasticized film and not of the dry film. Calculation of film capacitance values from EIS indicated increased water uptake with temperature consistent with water-plasticization as seen in Tg measurements. Data implied that use o...

A phase transition with an abrupt electrical resistivity change around 800 K in BaBi 0.5Pb 0.5O 3

Seebeck coefficient and electrical resistivity were measured in a temperature range of 300–1100 K in air for BaBi 1− x Pb x O 3 ( x=0, 0.25, 0.5, 0.75 and 1.0). The increase in Pb content led to the change in electrical conduction behavior from p-type semiconducting to n-type metallic and to n-type semimetallic, consistent with that in electronic structure previously reported on this alloy system. Two phase transitions were found at ∼650 K and ∼800 K for BaBi 0.5Pb 0.5O 3 from the temperature dependence of the electrical resistivity. With increasing temperature, the temperature dependence of the electrical resistivity for BaBi 0.5Pb 0.5O 3 showed a semiconductor-to-metal transition at ∼650 K with the continuous change in the resistivity and a metal-to-metal transition with an abrupt resistivity drop over ∼1.5 digits in a temperature range of 750–850 K (∼800 K). Combined with the powder X-ray diffraction (XRD) and Seebeck coefficient data, it is discussed that the semiconductor-to-metal transition at ∼650 K is due to the continuous proportionation of Bi cations into the chemical states closer to Bi 4+, and the metal-to-metal transition at ∼800 K may be due to the formation of a single chemical state with Bi 4+ which leads to the disappearance of the pseudogap at E F and the formation of a normal metal.

Deposition of Highly Conductive n+ Silicon Film for a-Si:H Thin Film Transistor

ABSTRACTPlasma enhanced chemical vapor deposition of phosphorus-doped n+ silicon film over a wide range of process conditions has been studied. The deposited films were characterized with SIMS, Raman, and XRD. An unusually abrupt change of resistivity over a small SiH4(1% PH3) flow rate has been observed and was correlated to the variation of the film's morphology from amorphous to micrycrystalline. The grains are less than 50 Å in size and has strong <111> orientation. Amorphous silicon thin film transistors with microcrystalline n+ source and drain contacts have consistently good device characteristics. However, the contact resistance is comparable to the channel resistance when the channel length approaches 1 micrometer.

Near- and far-fields: source characteristics and the conducting medium in neurophysiology.

It is possible to appreciate the production of far-field potentials by considering constant current dipolar source voltage distributions in bounded volumes, especially when they are stretched in one direction, e.g., a cylinder. An essentially nondeclining voltage is detected when the recording electrodes are on opposite sides of, and relatively far from, the dipolar source. This voltage maintains its (a) latency, (b) amplitude, (c) morphology, and (d) polarity even if recordings are performed a whole body length away. These four criteria define far-field potentials. A propagating action potential (AP) can be conceptualized as a linear quadrupole or the summation of two dipoles "back-to-back" (+ - - +). The far-field components of the summated dipoles cancel resulting in the anticipated triphasic waveform for APs with only near-field characteristics, not meeting the first three criteria above. Far-field potentials can be transiently generated when any propagating AP constitutes a net "real" or "virtual" dipolar source. "Real" dipolar sources can occur if an AP encounters the termination of excitable tissue, an alteration in conduction velocity, curvature in excitable tissue resulting in a change in propagation direction, or an abrupt change in resistance of the excitable tissue. Virtual dipolar sources may be produced if an AP encounters a change in the size or shape of the extracellular medium or a transition in extracellular conductivity.

Electromigration in isolated aluminum vias probed by resistance changes and 1/f noise

1/f noise and high-resolution resistance measurements have been performed in isolated aluminum via interconnects under electromigration stress. The test structures had a volume of roughly 1 μm3 and a resistance of 0.1 Ω with an internal TiN diffusion barrier. The 1/f resistance noise of the vias was found to be larger than the 1/f noise in the connecting aluminum runners due to the high intrinsic noise, high resistivity TiN layer within the structure. The direct currents induced reversible increases and decreases in the resistance of the via due to electromigration damage but had no effect on the 1/f noise. The magnitude and polarity dependence of the dc current induced resistance changes are most consistent with the initial electromigration of copper. Above 200 °C the resistance changes became dominated by abrupt jumps in the resistance. Possible mechanisms for the abrupt resistance changes are reviewed.

Vanadium dioxide films with good electrical switching property

A novel method is described for preparing high-quality thin films which exhibit an abrupt resistivity change of 4 - 5 orders of magnitude at about ; this is the best result among those so far prepared on non-crystal substrates. To show the difference from the ordinary sol - gel method which uses vanadium alkoxide as precursor, this method has been called (by the authors) the inorganic sol - gel method, for it uses powder as precursor. This newly developed method shows some advantages in that it produces high-quality thin films (adherent, crack-free, and with good switching properties) in a cheap, simple, and reproducible way. The method consists of four processes: quenching, coating, drying and vacuum heat treatment. These processes show strong effects on the properties of the final films. In this paper, the effects of the drying process on the film blistering and the effects of film thickness, quenching temperature, and heat treatment time on the resistivity switching property were studied, and DSC, XRD, ESCA, and SEM were utilized to study the drying process and characterize the films. It was found that when the drying temperature was and heating rate was in the drying process, the final films would be blister-free and crack-free (on non-crystal substrates). It was also found that the magnitude of resistivity change at the phase transition of the samples treated at for 10 h under a pressure of 0.8 Pa increased with increasing thickness (in the thickness range 0.4 to ). When the film thickness was about , the magnitude of resistivity change of the samples treated under the same conditions was found to decrease with increasing quenching temperature. In a certain range of treatment time the magnitude of resistivity change of the samples treated at under a pressure of 0.8 Pa was found to increase with increasing heat treatment time.

Structural phase transitions in donor doped BaTiO3 and effects on PTCR behavior

In this study, in situ transmission electron microscopy studies were used to examine and characterize domain formation and phase transformation mechanisms in donor doped, PTCR BaTiO3 materials. A significant and abrupt change in resistivity occurs as a result of a non-uniform boundary structure, the result of variability in strain state and non-uniform potential energy barrier along the grain boundary. In the highly stressed grain boundary regions, the ferroelectric phase transformation is very rapid with martensitic type character. During the phase transformation process, the sudden release of stress and change in structure, in the limited number of conducting regions along the grain boundary, were found to be the dominant factors behind the driving force for a sudden and abrupt change in resistance.