Electrical measurements bulk resistivity

See 2-3.1. Electrical conduction through solids takes place both through the bulk material and over the surface. In most cases surfaces have different physical and chemical properties than the bulk, for example due to contamination or moisture. Volume and surface resistivity can be separately measured for solid materials such as antistatic plastic sheet. Powders represent a special case since although both surface and bulk conduction occur, their contributions cannot be individually measured and the volume or bulk resistivity of a powder includes surface effects. 

The bulk (or volume) specific resistance p is one of the most useful electric properties that can be measured. Specific resistance is a physical quantity that may differ by more than 1023 in readily available materials. This unusually wide range of conductivity is basic to the wide use of electricity and many electric devices. Conductive materials, such as copper, have p values of about 10-6 ohm cm, while good insulators, such as polytetrafluoroethylene (PTFE) and low-density polyethylene (ldpe), have p values of about 1017 ohm cm. 

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. 

The Rb based on the sample cannot be calculated correctly, since the electric charge transfer resistance and the electric double layer in an electrode interface are also detected as a resistance, even if bias voltage is impressed to the measurement cell in order to measure the ionic conductivity. For the ionic conductivity measurement, a dc four-probe method, or the complex-impedance method, is used to separate sample bulk and electrode interface [4]. In particular, the complex-impedance method has the advantage that it can be performed with both nonblocking electrodes (the same element for carrier ion and metal M) and blocking electrodes (usually platinum and stainless steel were used where charge cannot be transferred between the electrode and carrier ions). The two-probe cell, where the sample is sandwiched between two pohshed and washed parallel flat electrodes, is used in the ionic conductivity measurement by complex-impedance method as shown in Figure 6.1. 

By the process described above, a plasma film could be obtained that had high enough electrical conductivity to allow direct electrodeposition of copper. The bulk resistivity of film measured by a four-point probe was 2.6 x 10 " ohm-cm for the copper-containing polymer film when deposition was stopped after 18 min at HOW. This value is critical if a uniform electrolytic deposit is to be obtained. For safety, deposition was carried out until a total film thickness of 150nm was obtained, giving a nearly pure metallic layer thick enough to allow subsequent electroplating. 

Electrical methods. The electrical methods of measuring temperature are based on two facts, firstly, that the resistance of a conductor varies with the temperature, and secondly, that the electromotive force which is produced at a point of contact between two different metals or alloys is hkewise a function of the temperature. If, therefore, we close a circuit consisting of two wires of different metals, so that there are two joints in the circuit where two metals meet, a current will flow in general so long as these joints are not at the same temperature. If the temperature of the one joint is known, a measurement of the electromotive force enables us to determine the temperature of the other. On account of the great sensibility of electrical measurements, it is possible to measure very small differences of temperature by either of these methods. They have the further advantage over the first and second methods, that we are enabled by their means to measure very high and very low temperatures in a most convenient manner. The small bulk occupied by a thermocouple is often important from an experimental point of view, and for this reason thermocouples are preferable in some cases to all other forms of thermometer. 

This paper describes some recently completed work on the electrical conductivity of paper. A reliable method of measuring bulk conductivity of paper, where the contact resistance is reduced to negligible values, has been developed. A study of the effect of some papermaking variables, such as the type of pulp, the degree of refining and the fiber orientation, on the bulk conductivity of paper is reported. Finally, an investigation has been made into the current transient phenomena exhibited by paper upon the application of an electric field. These transient currents were interpreted as the transport of ionic species within a water associated fibrous network making up the paper. 

Electrical Measurements. The electrical properties of polymers have much in common with mechanical properties. They can be divided into static properties equivalent to direct current properties and dynamic properties resulting from alternating current measurements. The most used parameter is the volume or bulk resistivity (ASTM-D257-75b) which is the resistance in ohms of a material 1 cm thick and 1 cm2 area. Bulk resistivity is one of only a few properties that vary nearly 1025 in typical use (materials with values above 10 ohm-cm for polystyrene to 10 5 ohm-cm for copper). 

In the tests using the conductive silicone rubber, which has electric resistance of about 50 (2, it is corrected so that the voltage derived from the bulk resistance of non-swollen conductive rubber corresponds to the degree of separation of 0. The effect of swelling phenomena on the measured voltage is described later. 

FIGURE 6.15 Enhanced setup for measuring contact resistance and bulk resistance within one measurement. Bulk properties can be obtained from a separate potential measurement across two needles electrically insulated from the main circuit. (Adapted from Kreuz, C. 2008. Dissertation PEM-BrennstofFzellen mit spritzgegossenen Bipolarplatten aus hochgefiilltem Graphit-Composite, Gerhard-Mercator-University in Germany, 04/2008.)... 

An electrical equivalent circuit model, composed of a resistor and a capacitor which were connected in series, was adopted to represent the soymilk-electrode system. High frequency impedance measurements presented an increase in resistance and constant value in reactance for different coagulation times. This resistance is attributed to the bulk resistance of soymilk mixture and changed minimally when the coagulation process is finished [50]. 

In practice, the figure of merit for conductors is resistivity, which is the inverse of conductivity. Resistivity is the ability of a material to resist the passage of current (units are ohm-centimeters for bulk resistivity, as illustrated for metals in Table 8.1). Surface resistance or line resistance is expressed in ohms. The common expression for thick film conductors is sheet resistivity (expressed in milliohms per square), which is the electrical resistance measured across opposing sides of a square for a normalized thickness. 

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 ... 

Figure 7.16 shows the results of an oscillographic measurement on PbO in a time range in which the interfacial process can be observed and the bulk process appears as a jump. The mechanistic interpretation of the bulk resistance was largely the subject of the previous chapters. The source of bulk capacitance has been discussed briefly above. We now wish to address interfacial layer parameters in more detail. First we neglect the influence of electrical capacitances by referring to the steady state and concentrate on the resistive parameters. Similarly, when we will discuss capacitive effects later on (Section 7.3.3) we will ignore Faradaic effects. The combination of both will, in a linear response approximation, be performed by a parallel... 

The terms resistance and resistivity are both used when referring to the resistance of an object to current flow. Surface resistance is the measure of electrical resistance along the surface of an object. However, the current flow is not limited to the surface of the object. Some of the current passes through the bulk of the object from one electrode to the other electrode. Surface resistivity includes the dimensions of the object in its measurement (Eig. 2c). 

The electrical-resistance measurement has nothing to do with the electrochemistry of the corrosion reaction. It merely measures a bulk property that is dependent upon the specimens cross-section area. Commercial instruments are available (Fig. 28-5). 

Ebbesen and Ajayan [16] measured a conductivity of the order of 10 2 Ocm in the blaek eore bulk material, inferring that the carbon arc deposit contains electrically conducting entities. A subsequent analysis of the temperature dependenee of the eleetrieal resistivity of similar bulk materials [17,18] revealed that the resistivities were strongly sample dependent. 

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