Interdigital electrodes fabricated by standard lithography on silicon chips are employed to probe the dipolar molecular dynamics and electric conduction properties of thin rhodamine films grown with two different methods. The conductivity is due to electronic charge carriers, and at around room-temperature, it is higher by 1 order of magnitude in solution-deposited films than in thermally evaporated ones. The organic material exhibits two intrinsic dynamic processes, of which the one at higher temperature is due to the orientational motion of the dipole moment of the rhodamine units, while the one at lower temperature is due to the motion of a local dipole associated with the chlorine counterions and is absent in thermally evaporated films. Our results show that thin-film dielectric spectroscopy is an easily implementable and versatile tool to extract valuable information on thin organic films.
Keywords: conductivity; dipolar relaxation; impedance spectroscopy; interdigital electrodes; molecular films; rhodamine.