Resistance Measurement Technique Research Articles

Inherent sensing and interfacial evaluation of carbon nanofiber and nanotube/epoxy composites using electrical resistance measurement and micromechanical technique

Inherent sensing of load, micro-damage and stress transferring effects were evaluated for carbon nanotube (CNT) and carbon nanofiber (CNF)/epoxy composites (with various added contents) by an electro-micromechanical technique, using the four-point probe method. Carbon black (CB)/epoxy composites, with conventional nanosize material added, were used for the comparison with CNT and CNF composites. Subsequent fracture of the carbon fiber in the dual matrix composites (DMC) was detected by acoustic emission (AE) and by the change in electrical resistance, Δ R due to electrical contacts of neighboring CNMs. Stress/strain sensing of the nanocomposites was detected by an electro-pullout test under uniform cyclic loading/subsequent unloading. CNT/epoxy composites showed the best sensitivity to fiber fracture, matrix deformation and stress/strain sensing, whereas CB/epoxy composite exhibited poorer sensitivity. From the apparent modulus (as a result of matrix modulus and interfacial adhesion), the stress transferring effects reinforced by CNT was highest among three CNMs. The thermodynamic work of adhesion, W a as found by dynamic contact angle measurements of the CNT/epoxy composite as a function of added CNT content was correlated and found to be consistent with the apparent mechanical modulus. Uniform dispersion and interfacial adhesion appear to be key factors for improving both sensing and mechanical performance of nanocomposite. Thermally treated-CNF composites exhibited a slightly higher apparent modulus, whereas higher testing temperatures appeared to lower the apparent modulus.

Influence of calcium sulfate state and fineness of cement on hydration of Portland cements using electrical measurement

The influence of calcium sulfate state and fineness of cement on hydration of Portland cement was studied using electrical resistivity measurement. The bulk resistivity curve of the paste from the abnormal cement mainly with hemihydrate had a characteristic abnormal peak and rapid increase in early period. The resistivity measurement technique can be used to discriminate abnormal setting. For normal cement with gypsum, the increase in fineness of the Portland cement decreases the minimum resistivity due to a higher ionic concentration and increases the 24 hour resistivity due to a reduction in macroscopic pore size. The setting time, compressive strength, pore structure of pastes made from different cements were carried out to compare the influence of water to cement ratio, calcium sulfate state and fineness. It is found that the electrical and mechanical properties are strongly affected by the initial porosity, the presence of hemihydrate or gypsum, and the fineness of cement.

Substrate dependent growth studies of MgB2 films by electrocrystallization

The comparative study of MgB2 film growth on Al2O3 and glass substrate by electrocrystallization technique is discussed. The precursor magnesium films were deposited by vacuum evaporation method. These magnesium films were then used as electrode for the growth of MgB2 films by electrocrystallization. The structural, morphological and superconducting properties of the electrocrystallized MgB2 films on Al2O3 substrate were examined by using XRD, SEM and electrical resistivity measurement techniques and compared with that of MgB2 films grown on glass substrate. The films deposited on Al2O3 substrates showed enhanced crystallinity and relatively higher Tc value compared to films deposited on glass substrates.

06/01517 Pulsed laser deposition-assisted patterning of aligned carbon nanotubes modified by focused laser beam for efficient field emission: Saurakhiya, N. et al. Carbon, 2005, 43, (10), 2128–2133

In this study, the optimized conditions of electrophoretic deposition (application potential, application time and concentration of stable graphene oxide (GO) suspension) for development of ultra-thin graphene film on copper substrate are introduced. The current density and deposition efficiency analysis, Ohm resistance measurement, SEM, FTIR and AFM techniques were done on prepared samples. The electrical conductivity of graphene coated copper substrate was increased three times more than bare copper. All of the carried tests showed that by increasing the key parameters of EPD, the average thickness of electrodeposited GO layers are increased continually so that the GO concentration effect is the most evident factor. The minimum sheet resistance and average thickness of electrodeposited RGO layers with uniform wrinkled morphology are achieved at EPD conditions of 2 V in 10 s and annealed at 200 °C for 1 min. The results of this research manifested that the EPD technique is a promising route to a low cost and well controllable method to fabricate a very conductive electrode base for electro-optical devices.

The contact resistance force relationship of an intrinsically conducting polymer interface

Investigations on contact connector materials for different applications such as in the automotive industry have focused toward the increasing interest of using conducting polymers, as compared to conventional metallic contacts. The aim is to achieve overall improvements in performance as well as cost effectiveness. Currently, extrinsic conducting polymers (ECPs) are employed as conductive coats or adhesives at contact interfaces. However, frictional abrasion within the metal doped polymer (ECP) causes fretting corrosion, which leads to instability in the contact resistance. To overcome this, intrinsically conducting polymers (ICPs) are explored. Hemispherical contact coatings were fabricated using poly(3,4-ethylenedioxythiopene) (PEDOT) or polyaniline/polyvinylchloride (PANI/PVC) commodity blends. Contact resistances were taken using four-wire resistance measurement techniques. The conductivities of in-house fabricated ICP contacts were found to be in the range of 10-2 Smiddotcm-1. The response relating the change of contact resistance under varying compression force appeared to be repeatable with minimum deviation of 2%. The surface profiles of the ICP contacts were also recorded by an optical confocal system. The initial investigation results presented in this paper were used to evaluate and validate the hypothesis of employing ICP contacts to eliminate or minimize wearing and fretting effects

Investigation of electroconductivity of lithium pentaferrite

Using a double-probe spreading resistance measurement technique combined with a layer-by-layer analysis, temperature dependences of electroconductivity of polycrystalline lithium pentaferrite (LPF), which is produced via a ceramic-production technological process, are investigated. It is shown that the electroconductivity activation energy of LPF is controlled by the height of grain-boundary potential barrier due to different degrees of grain boundary and grain bulk oxidation. A relationship is established between the value of the electroconductivity activation energy of LPF and the processes of its oxygen exchange with the surrounding medium during thermal annealing.

Superconductivity in the copper-poor region of the Ca(Cu, Si)2−x system

We report the discovery of superconducting materials Ca(Cu,Si)2−x. The results of magnetic susceptibility and electrical resistivity measurements on two phase Ca–Cu–Si samples with nominal compositions CaCu0.25Si1.75, CaCu0.33Si1.67 and CaCu0.25Si1.7 provide evidence for bulk superconductivity in a hexagonal AlB2-type majority fraction of the sample volume. Powder X-ray diffraction patterns indicate that the minor impurity phase is the element Si which has no effect on the superconductivity. CaCuxSi2−x samples with excess Cu component (x⩾0.4) showed no evidence of superconductivity for T⩾1.8K. Under the annealing conditions required for the fabrication of the AlB2-type superconductor, the best sample with the nominal composition CaCu0.25Si1.7 annealed for three days at 1000°C exhibits the transition temperature Tc∼3.2K, as determined by magnetic susceptibility and electrical resistivity measurement techniques.

OHMIC CONTACTS TO SIC

In this chapter, the most significant results obtained in the last decade in the field of ohmic contacts to SiC are reviewed. First, the basic concepts related to the physics of ohmic contacts and to the contact resistance measurement techniques are briefly reported. Then, some aspects concerning the formation of low resistance (10-5-10-6 Ω cm 2) ohmic contacts on n-type and for p-type SiC are discussed, focusing on Ni -based and Al/Ti -based contacts. Examples of innovative applications on practical devices are also reported, as the simultaneous formation of ohmic contacts on n- and p-type SiC for vertical power MOS devices, obtained adding Al to a standard Ni contact, and a single-metal technology for ohmic and rectifying contacts in MESFETs, using Ti or Ni without post-deposition annealing.

The effect of temperature on the corrosion of mild steel in acidic media in the presence of some sulphur-containing organic compounds

The effects of methylthiourea (MTU), phenylthiourea (PTU) and thiobenzamide (TBA) on the corrosion of mild steel in 0.1 M H 2SO 4 solution at temperatures of 30 °C, 40 °C and 50 °C have been studied. AC impedance, polarization resistance measurement and polarization curves measurement techniques have been used to obtain experimental data. The percent inhibition efficiency (IE%) and activation energy ( E a) have been determined in the presence and in the absence of these compounds. The results showed that all compounds have good inhibtion properties at all temperatures studied. The value of activation energy ( E a) found in the presence of PTU and TBA is smaller than that in the uninhibited solution while it is greater in the presence of MTU. The reasons that cause the deviation of a Nyquist plot from a semicircle have been investigated. Differential capacitance ( Q dl) has been used instead of double layer capacitance ( C dl) to represent the experimental deviations of a Nyquist plot from a semicircle. Whether the difference in real impedance at lower and higher frequencies correspond with the charge transfer resistance ( R t) has been discussed by taking the resistance contribution of diffuse layer into account. The resistance measured with AC impedance technique has been divided into charge transfer resistance ( R t) and diffuse layer resistance ( R d). The corrosion current density ( i corr) values have been determined by making use of the variation of corrosion potential with pH.

A general Weibull model for reliability analysis under different failure Criteria-application on anisotropic conductive adhesive joining technology

In this paper, a generic four-parameter model has been developed and applied to the anisotropic conductive adhesive (ACA) flip-chip joining technology for electronics packaging applications. The model can also be used to predict any minimum failure cycles if the maximum acceptable failure criterion (in this case, a preset electrical resistance value) is set. The original reliability testing from which the test data was obtained was carried out on flip-chip anisotropically conductive adhesive joints on an FR-4 substrate. In the study, nine types of ACA and one nonconductive film (NCF) were used. In total, nearly 1000 single joints were subjected to reliability tests in terms of temperature cycling between -40/spl deg/C and 125/spl deg/C with a dwell time of 15 min and a ramp rate of 110/spl deg/C/min. The reliability was characterized by single contact resistance measured using the four-probe method during temperature cycling testing up to 3000 cycles. A single Weibull model is used for two failure definitions defined as larger than 50 m/spl Omega/ and larger than 100 m/spl Omega/ respectively using the in situ electrical resistance measurement technique. The failure criteria are incorporated into this Weibull model. This paper shows the flexibility and usefulness of Weibull distribution in this type of applications.

Formation of highly textured (1 1 1) Bi 2O 3 films by anodization of electrodeposited bismuth films

Highly textured bismuth oxide (Bi 2O 3) thin films have been prepared using anodic oxidation of electrodeposited bismuth films onto stainless steel substrates. The Bi 2O 3 films were uniform and adherent to substrate. The Bi 2O 3 films were characterized for their structural and electrical properties by means of X-ray diffraction (XRD), electrical resistivity and dielectric measurement techniques. The X-ray diffraction pattern showed that Bi 2O 3 films are highly textured along (1 1 1) plane. The room temperature electrical resistivity of the Bi 2O 3 films was 10 5 Ω cm. Dielectric measurement revealed normal oxide behavior with frequency.

Electrical resistivity measurement of liquid metals

Two facilities for the complete noninvasive measurement of the electrical resistivity of liquid metals above the melting temperature and in the undercooled liquid state below the melting temperature are presented: a ground-based facility that was built up in our laboratory and the microgravity facility TEMPUS. Both facilities are unique in combining the containerless positioning method of electromagnetic levitation with the contactless, inductive resistivity measurement technique, thereby enabling for the first time measurements in the undercooled liquid state of a metal. The principles and technical realizations of the levitation and measurement technique of both facilities are presented. Furthermore, experimental resistivity data for Cu60Ni40 as well as Co80Pd20 alloy are presented which indicate atomic ordering effects in the undercooled melt.

Surface conductivity of insulators: a resistivity measurement technique undervacuum

A method of resistivity measurement for insulators, previously described by Liesegang andSenn (1995 J. Appl. Phys. 77 5782; 1996 J. Appl. Phys. 80 6336), has been demonstrated toproduce measurements not only in good agreement with established results in the literaturebut also with improved accuracy. The method is based on monitoring the discharge of acharged sample of an insulator through a grounded boundary. The measurements, however,were performed under atmospheric conditions and so the results were influenced byatmospheric effects such as temperature and moisture. By confining a sample to a vacuumand charging it via a custom built electron gun, we here extend the established method ofLiesegang and Senn to a more controlled environment. In this paper, we numerically solvethe potential and transport equations for the axial–cylindrical geometry of thesystem and present comparisons of theory and experiment through derived valuesof the resistivity, carrier depth and diffusion constant for a range of insulatorsamples. We also use asymptotic solutions via a theory of Burgers equation shockwaves, as discussed in Holcombe et al (2004 J. Phys. Condens. Matter 16 5999),to derive resistivity values and again draw comparisons. The results presentedhere are also compared with previously obtained or literature measurements ofresistivity.

Phase equilibria and γ′-L1 2 phase stability in the Ni-rich portion of Ni–Fe–Si and Ni–Fe–Al systems

Stable and metastable phase equiliblia among γ-FCC, γ′-L1 2 Ni 3Si and δ-Ni 31Si 12 phases in the Ni–Fe–Si system and among γ-FCC, γ′-L1 2 Ni 3Al and β-B2 NiAl phases in the Ni–Fe–Al system were examined. The stable phase diagrams in the Ni-rich portion were determined by energy dispersion X-ray spectroscopy (EDX) and electron probe microanalysis (EPMA) using specimens fully annealed at temperatures in the interval 700–1300 °C. On the other hand, the γ/γ′ metastable phase equilibria were investigated by the electrical resistivity (ER) measurement technique, transmission electron microscopic (TEM) observation and TEM–EDX analysis. It was confirmed that the metastable γ′ phase coherently precipitates in the γ matrix due to aging even in the specimens with a high Fe composition over 60 at.%, and that both the γ′-Ni 3Si or γ′-Ni 3Al phase fields extend not only toward the Ni 3Fe portion but also toward the Fe 3Si or Fe 3Al portion, forming metastable (Ni,Fe) 3Si or (Ni,Fe) 3Al intermetallic compound with the L1 2 structure.

Electrochemical and quantum chemical studies of some sulphur-containing organic compounds as inhibitors for the acid corrosion of mild steel

The influence of thioacetamide (TAcA), thiourea (TU) and thiobenzamide (TBA) on the corrosion of mild steel in 0.1 M H 2SO 4 solution has been studied in relation to the concentrations. The CS NH 2 group is the common main group for these compounds and they differ only having different groups on the other side of the thiocarbonyl group. Electrochemical impedance spectroscopy (EIS) and polarization resistance measurement ( R p) techniques have been used to obtain experimental data. The results showed that these compounds revealed a good corrosion inhibition, thiobenzamide being the most efficient and thioacetamide the least. The correlation between the molecular structures and corrosion inhibition efficiencies of TAcA, TU and TBA has been investigated using ab initio quantum chemical calculations. The structures of these compounds have been optimized, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, LUMO–HOMO energy gap and molecular orbital densities have been computed. The relations between the inhibition efficiency and quantum chemical parameters have been discussed. It was seen that there is a clear relation between the increase in corrosion inhibition and the increase of HOMO energy level. The highest values of the HOMO densities were found in the vicinity of the sulphur atom indicating it as most probable adsorption center.

A portable meter for measuring low frequency currents in the human body.

A portable meter has been developed for measuring low frequency currents that flow in the human body. Although the present version of the meter was specifically designed to measure 50/60 Hz "contact currents," the principles involved can be used with other low frequency body currents. Contact currents flow when the human body provides a conductive path between objects in the environment with different electrical potentials. The range of currents the meter detects is approximately 0.4-800 microA. This provides measurements of currents from the threshold of human perception (approximately 500 microA(RMS)) down to single microampere levels. The meter has a unique design, which utilizes the human subject's body impedance as the sensing element. Some of the advantages of this approach are high sensitivity, the ability to measure current flow in the majority of the body, and relative insensitivity to the current path connection points. Current measurement accuracy varies with the accuracy of the body impedance (resistance) measurement and different techniques can be used to obtain a desired level of accuracy. Techniques are available to achieve an estimated +/-20% accuracy.

Deposition and annealing effect on lanthanum sulfide thin films by spray pyrolysis

Lanthanum sulfide thin films were prepared on glass substrates from aqueous medium using spray pyrolysis technique. The effect of preparative parameters such as substrate temperature and solution concentration on the films was studied. The lanthanum sulfide films were annealed in air at 300 °C for 2 h. The films were characterized by X-ray diffraction (XRD), optical microscopy, optical absorption, electrical resistivity and thermo-emf measurement techniques. The XRD studies revealed that the as deposited films are amorphous, while annealed films are polycrystalline. The optical band gap of the as deposited film is decreased from 2.5 to 2.2 eV after annealing due to improvement in crystallinity. The electrical resistivity is of the order of 10 4–10 5 Ω cm and showed semiconducting behaviour. Thermo-emf measurement revealed that the conductivity of lanthanum sulfide is p-type.

Process during heat treatment on martensitic transformation in Ni-Ti and Ni-Ti-Cr alloys

This paper presents the effect of cooling process during heat treatment on martensitic transformation in 45% cold worked, Ti-rich, Ni-rich Ni-Ti and Ni-Ti-Cr shape memory alloys, annealed in the temperature range of 100° - 800°C. Phase transformation in water quenched and furnace cooled samples is studied in the range from +140° to -170°C, employing four-probe electrical resistivity measurement technique. The heat treatment process has a distinct effect on the martensitic transformation in these alloy systems. In the case of Ti-rich alloy two-stage martensitic transformation, A→R→M during cooling and M→A on heating, are observed in the as-received sample. For both the quenched and the furnace cooled samples this behavior persists even after annealing at 420°C. The process spreads over a temperature interval of 60°, above 0°C, whereas, after annealing above 420°C only A↔M transformation is observed. Ni-rich quenched alloy annealed below 500°C exhibits a two-stage martensitic transformation, spreading over a wide temperature interval of 150°, below +50°C. For that alloy annealed above 500°C, R-phase gradually decays narrowing the transformation region. In the furnace cooled sample, R-phase region steadily narrows, for annealing at temperatures up to 580°C, suddenly broadens for annealing above 580°C and persists prominently thereafter. In the case of Ni-Ti-Cr, though for both the processes two-stage martensitic transformation is exhibited, for quenched one, R-phase disappears for annealing temperatures above 600°C. Thus, furnace cooling is found to promote the intermediate R-phase in Ni-rich Ni-Ti and Ni-Ti-Cr alloys annealed at higher temperature also.

High resistivity measurement of SiC wafers using different techniques

To establish fast, nondestructive, and inexpensive methods for resistivity measurements of SiC wafers, different resistivity-measurement techniques were tested for characterization of semi-insulating SiC wafers, namely, the four-point probe method with removable graphite contacts, the van der Pauw method with annealed metal and diffused contacts, the current-voltage (I-V) technique, and the contactless resistivity-measurement method. Comparison of different techniques is presented. The resistivity values of the semi-insulating SiC wafer measured using different techniques agree fairly well. As a result, application of removable graphite contacts is proposed for fast and nondestructive resistivity measurement of SiC wafers using the four-point probe method. High-temperature van der Pauw and room-temperature Hall characterization for the tested semi-insulating SiC wafer was also obtained and reported in this work.

Accurate microwave technique of surface resistance measurement of large-area HTS films using sapphire quasi-optical resonator

We have developed a surface resistance (R/sub s/) measurement technique for large-area high-temperature superconducting (HTS) films using quasioptical dielectric resonators (QDR) with HTS endplates (quasioptical Hakki-Coleman resonators). In this technique, the highest Q modes, namely whispering-gallery modes, in sapphire disk sandwiched between HTS films or between one HTS film and one Cu endplate are excited at K-band frequencies. The authors report on measurement results of surface resistance of 52 mm diameter high-quality YBCO thin films. The measurement results revealed that the technique is feasible for accurate R/sub s/-measurements of large-area thin films. The method is appropriate for standard measurement of R/sub s/ at millimeter wave frequencies by analogy with classic DR-based microwave technique, although QDR-based technique has some fundamental differences.