Thermal annealing effects on polyaniline studied by electrically detected magnetic resonance

The effects of thermal treatments in inert atmosphere on polyaniline films have been investigated by electrically detected magnetic resonance (EDMR). For small electric fields (F<1000 V cm−1) and coplanar contacts, a resonance line is observed by EDMR (approximately 0.24 mT), for larger fields, a second broader resonance line is observed (1.6 mT), with similar g-factors (2.003). The narrow line, which is similar to the conventional electron spin resonance (ESR) signal, is not present for sandwich contacted samples. The broader line is temperature independent, and assigned to polarons. The protonation is observed to decrease the EDMR signal intensity from 10−3 to 10−6 for a change in conductivity from 10−9 to 10−5 Ohm−1 cm−1, without a change in line shape. The broad EDMR signal is not sensitive to the presence of oxygen or moisture, as is the case of ESR and conductivity. The present results are in agreement with polyaniline being a heterogeneous material composed of crystallites embedded in an amorphous network, and indicate that ESR signal may be due to surface states.