Four-point probe method

The most typical way to measure the in-plane electrical conductivity of a diffusion layer is through the use of the four-point probe method. A small current is applied across the sample material a separate set of voltage measuring probes that are in touch with the material are used to measure the resulting voltage drop in order to calculate the resistance. With these values, the in-plane resistivity, p, can be calculated with the following equation [9,233] ... 

Emissive spectral features were consistent with those previously reported for CdS Te (6-13) and confirmed (Roessler s correlation, (12)) that the Te concentration was <100 ppm. TheA,5x5xl mm samples had resistivities of A,2 ohm-cm (four point probe method) and were oriented with the 5x5 mm face perpendicular to the c-axis. Samples were first etched with 1 10 (v/v) Br2/MeOH and then placed in an ultrasonic cleaner to remove residual Br2. The electrolyte was either sulfide, 1M 0H /1M S2-, or polyselenide, typically 5M 0H /0.1M Se2 /0.001M Se22- short optical pathlengths (<0.1 cm) were used to make the latter essentially transparent for A >500 nm. Electrode and electrolyte preparation as well as electrochemical and optical instrumentation employed have been described previously (8). Electrolytes were magnetically stirred and blanketed under N2 during use. 

The resistivity of a free-standing bulk sample was measured by depositing Pt electrodes by FIB and by employing the four point probe method [8], The resistivity of the bulk was 10 - 15 Q cm. The carrier concentration was estimated to be less than 1016 cm 3 by the plasmon-coupled mode in the Raman spectrum. These electrical measurements show that the crystal is of relatively high purity. 

Hall voltage was measured by a four-point probe method for the samples shaped like a cross, using dc current and dc magnetic field. 

The most convenient way to determine the resistivity routinely is by the four point probe method as described by Valdes254. The resistivity can be calculated from the sheet resistance by ... 

To measure the surface resistivity of paper, a variant of a four-point probe method proposed by Cronch 15 was used. This approach has proven to be reliable, avoiding the effects of contact resistance by employing an electrostatic voltmeter (utilizing contactless probes) to measure the surface potential of paper subject to a constant current. 

This article has addressed a number of issues relating to the electrical properties of paper or fibrous structures. It was shown that reliable measurement methods are now available for estimating both the bulk and surface conductivities of paper. In the case of the bulk conductivity, a new in situ pressure conductivity cell was described which significantlyreduces contact resistance. The surface conductivity can be determined by the application of a modified four-point probe method first used on paper by Cronch<15). It was shown that the degree of refining has a small effect on the bulk conductivity of paper. 

Figure 13.13 Arrangement in the four-point probe method of measurement of resistance of semiconductors for (a) rectangular specimen and (b) a disc. The spacing, s, of the probes is much smaller than the dimensions of the specimen. The current is measured between the outer probes, and the voltage drop is measured between the inner two probes...

High-purity A1 was obtained in the form of 60.3-mm-diameter bar stock. The bar stock was then extruded into a tube 24.4-mm OD and 19.8-mm ID. The extrusion was carried out at room temperature with a spider die arrangement. With a standard four-point probe method, the resistivity ratio, P298k/P4.2k of the extruded high-purity A1 tube was about 1700. 

Determined by the four-point probe method on compressed pellets at room temperature. 

In the past, the four-point probe method (36) has been used to measure the conductivity of the non-woven fiber mat and crosschecked with measurements of the conductivity of cast films produced from the same solution. Figure 3 shows the effect of the weight percentage content of HCSA-PANI on the room temperature conductivity obtained from the HCSA-PANl/PEO electrospun fibers and the film (34).. 

The chemical composition of the resultant film was confirmed by X-ray fiuorescence (XRF ZSX lOOe, Rigaku Co.) analysis. The crystallographic orientation, lattice parameters, and film thickness were evaluated by high-resolution x-ray diffraction (HR-XRD ATX-G, Rigaku-Co.) measurements, o- and 5" were measured by the dc four-point probe method and the conventional steady state method, respectively. Sputtered Au electrodes were used for ohmic contacts. 

The four-point probe method can be used to measure the in-plane electronic conductivity of the GDM, as shown in Figure 4.10. Two copper strips are placed near the ends of the GDM, and two copper wires separated a distance of L are placed befween the two strips. The strips and the wires are pressed against the GDM to form good contacts. A current passes from one sfrip fhrough the GDM along the in-plane direction to the other strip, and the voltage drop between the two wires is measured. Then the in-plane conductivity is... 

Figure 5.2. Conductance measurement by means of four-point-probe method. Left Basic arrangement right qdindric probe with four electrodes...

Figure 23-1. Scheme of the determination of the resistance for conducting coatings, with the collinear four-point probe method. 

Regarding the conductivity cell geometry, two configurations have been developed to measure proton conductivity the two-point probe method [52-60] and the four-point probe method [7,49,50,56,60-65]. These will be discussed in the following sections. 

To effectively eliminate interfacial impedance from conductivity measurements, a four-point probe method has been widely used [7,49,50,60-62,64]. Compared with the two-point probe configuration, two additional Pt probes... 

Figure 5.14 shows the AC impedance spectra of the Nafion 115 membrane, obtained in the four-point probe method by using Pt strips as both inner and outer probes, at room temperature and under fully hydrated conditions [60]. Each AC impedance spectrum contains one semicircle in the high-frequency domain and an arc in the low-frequency domain. Here, the low-frequency arc shrinks with increasing distance between the two voltage probes, and the whole AC impedance spectrum tends toward an ideal semicircle, which indicates that the distance between the two inner probes affects the measurement results, and that the low-firequency impedance can be reduced by increasing this distance. 

In principle, the results measured by the four-point probe method should be more accurate and reliable than those measured by the two-point probe method. However, the latter method is easier. In addition, it has been reported [56] that different measurement frequency ranges should be applied for different... 

PEM for DMFC is mainly characterized with ionic conductivity and methanol crossover. Ionic conductivity is tested with the four-point probe method. Through plane and in plane ionic conductivity is characterized with temperature and humidity [22]. Methanol crossover can be measured with diffusion cell method, pervapora-tion of methanol solution, dictating of CO amount from cathode out stream [23]. An oxidant-impermeable property is also one of the important factors in PEM for DMFC. The properties of PEM in DMFC are also characterized with an interfacial resistance, an electro-osmotic drag, methanol crossover through MEA, and so on. In this chapter, development of PEM for DMFC are discussed. Approaches for PEM in DMFC are classified as fluorinated polymer, hydrocarbon polymer, modification of polymer materials, and the technical approaches are described as well. 

A four-point probe method to measure resistivity of a layer. 

The electrical conductivity of the polymer pure and the nanocomposites was measured by four-point probe method [123]. The conductivity of the PAni/HCl was 83 S cm and for the nanocomposites was about 62 S cm. It has been noted the addition of clay directed to a Utde reduction in conductivity, unsurprisingly, owing to the presence of insulating charges between the polymer chains. However, the synthesized nanocomposite materials stiU present an excellent electrical conductivity. 

FIGURE 4-19. Experimental setup for measuring sample resistivity with four-point probe method [33]. 

Bulk electrical resistivity of the plates may be measured with a four-point probe method for sheet resistivity as described by Smits [36]. The experimental setup is shown in Figure 4-19. This method allows measurement of bulk resistivity of thin plates by applying a geometry-dependent correction factor to the measured value of voltage drop and applied current ... 

The conductivity measurements were performed using a standard four-point probe method at a constant current of 0.5 mA and ambient temperature. About 0.05 g of dried PANI salt (and nanocomposites) powders was compressed into a disk pellet of 13 nun in diameter with a hydraulic pressure at, 3000 psi to measure the conductivity. Each measurement was repeated three times and the average values reported as the result. 

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