The Standard Four-Probe and Montgomery

To determine the value of an electrical resistance, it is necessary to measure both the current passing through the 

Depending on the contact arrangement and procedure of evaluation, different such methods have been developed. The most well-known, the standard four-probe technique, is illustrated in fig. 2. A current is applied to the outer contacts of a rectangular sample of known geometry, while the voltage drop is measured between the inner contacts. 

For this reason, the voltage contacts have been regularly interchanged with the current contacts and the resulting differences of the and R2 values have been determined /23/. This procedure has been repeated at certain intervals within the whole temperature range. As a limit for tolerance, we required agreement of the values before and after interchanging contacts within 0.1 %, for precision 

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Contacting was performed by mechanically pressing platinum contacts elastically on the film. By means of small screws, the pressure of the contacts could be adjusted. For the Montgomery method, this adjustment could be done for each of the contacts separately. Different sample holders were used for different sample sizes. For most of the conductivity experiments presented here, we used samples of 19 X 2 mm2 and 14 x 6 mm in size for the standard four-probe and Montgomery techniques, respectively. 

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