Investigation of contact and bulk resistance of conducting polymers by simultaneous two- and four-point technique

A conventional resistance measured by two-point technique includes bulk and contact components. The contact resistance can be excluded by a four-point technique. A simultaneous use of the two- and four-point techniques allows to separate the total resistance between two electrodes for the contact and bulk parts. This approach has been used to analyze electrical coupling between metal electrodes of interdigitated structures and chemically sensitive coating formed by polyaniline (PANI). The polymer layers were deposited by electropolymerization on bare gold and platinum electrodes as well as on gold electrodes precoated by a self-assembled monolayer of 4-aminothiophenol. An exposure of the PANI films formed on interdigitated structures to gaseous HCl displays proportional changes of resistance measured by the two- and four- point techniques for platinum electrodes and for the precoated gold electrode, while a strong deviation from this proportionality was observed for the gold electrodes without precoating. The results demonstrate a high contribution of the contact resistance between PANI and bare gold electrodes into the resistance measured by the two-point technique. This contribution is small and therefore not measurable for bare platinum electrodes or for gold electrodes coated by 4-aminothiophenol. [Copyright &y& Elsevier]