Van der Pauw

Thus electrical conductivity is commonly measured in units of S/cm (0 cm ). Various experimental methods have been used to measure the electrical conductivity of conductive polymers, eg, 4-probe method. Van der Pauw method, etc, and are well documented in the Hterature. 

An example of the temperature dependence of donor neutralization is shown in Fig. 3. Devices with a square van der Pauw geometry were exposed to H° for 30 min. at different temperatures. Hydrogenation reduces the free-electron concentration over the entire investigated temperature range, with a maximum reduction of approximately 40% at 140°C. In... 

S. Hafizovic and O. Paul. Temperatru e-dependent thermal conductivities of CMOS layers by micromachined thermal van der Pauw test structures . Sensors and Actuators A97-98 (2002), 246-252. 

Fig. 1. The relationship of the sample and the various pieces of equipment necessary to automatically measure the current, and the parallel and perpendicular voltages. A standard contact configuration is shown in the main drawing, whereas a van der Pauw configuration is shown in the inset. The lock-in amplifier is used in ac photoconductivity measurements. [From Look and Farmer (1981), copyright by The Institute of Physics.]...

Measurements of electrical resistivity were made at 25 °C using the Van der Pauw technique (7) on discs 0.05 cm thick, which were cut from the cylindrical compacts. Four contacts were made to the perimeter... 

The number of characterization techniques that are sufficiently sensitive for this material and preferably impurity species or defect structure specific is rather small. Variable temperature Hall effect measurements in the Van der Pauw (1958) configuration allow the determination of (NA - ND). The... 

Table 10 compiles multipoint methods named after van der Pauw and Valdes, which allow conductivity detection of complex geometries. (See specialist Ref.295 for more details.)... 

Experimental configuration and evaluation formulae of the methods named after van der Pauw and Valdes.296,297 Reprinted from J. Maier, Physical Chemistry of Ionic Materials. Ions and Electrons in Solids, (2004). Copyright 2004... 

The factor A is a function of molar masses of zinc, aluminum, and oxygen atoms and additionally slightly depends on C Ai(wt). For our needs, k can be approximated by the constants A metaiiic = 2.3-2.4 and Ayompound = 1.5-1.6 for metallic and ceramic targets as well as for the compound film, respectively. Carrier concentration and mobility were determined by van der Pauw Hall effect measurements [105]. 

The crystal symmetry of most organic metals is low, often only monoclinic, and the principal axes of the conductivity tensor (cr) are not precisely defined. However, in practice the conductivity along the chain direction (cr,) is particularly high, usually 300 to 2500 (Q-cm) 1 at room temperature, while that in one direction perpendicular to the chains (07) is very low [2]. Therefore, these two directions must be very close to the principal axes of ex. The third perpendicular direction has intermediate conductivity (07). So in the situation, where > 07, which is quite common, the principal axes of the conductivity and resistivity (p) tensors are known reasonably well. When measuring these quantities on a single crystal, care must be taken either to ensure that the current distribution is uniform, or alternatively, special methods such as those of Montgomery [11] or van der Pauw [12] must be used. Some insight into these problems can be obtained by consideration of the equivalent isotropic sample [11,13]. 

Fig. 5.19 Electrode configurations for resistivity measurement (a) 2-terminal, (b) 4-terminal in line, (c) 4-terminal Montgomery and (d) 4-terminal van der Pauw.

The analysis of van der Pauw can be used for arbitrary electrode arrangements on thin samples of anisotropic materials of any shape and has been widely used in studies of conjugated polymers, where only small and irregular samples are available. Four electrodes are attached, as shown in Fig. 5.19(d). The resistance values Ry and R2 are measured as for the Montgomery method. The volume resistivity is then calculated from these values as... 

We investigated the transport properties of ZnO single erystals and PLD thin films by Hall measurements using the van der Pauw method. ... 

L. J. van der Pauw, "A Method of Measuring Specific Resistivity and Hall Effect of Discs... 

IR spectra were taken at room temperature (300 K) and liquid-helium temperatures (5-15 K), using a Bomem DAS Fourier transform infrared (FTIR) spectrometer and an InSb detector. For the low-temperature measurements, a Janis continuous-flow liquid-helium cryostat with wedged, IR-transparent windows was utilized. Hall-effect measurements, in the Van der Pauw geometry, were performed at room temperature using a system from MMR Technologies. Wires were attached to the ZnO using silver paint, which provided adequate Ohmic contacts for the electron concentrations (10 cm ) in these samples. 

Koopman-Esseboom C, Morse DC, Weiglas-Kuperus N, Lutke-Schipholt I, van der Pauw CG, Tuinstra LGMT, Brouwer A, Sauer PJJ (1994) Pediatr Res 36 468... 

---