Electromodulated optical properties of the silver/pentacene/ITO thin film structure

Electromodulated optical responses of the silver/pentacene/ ITO thin film structures were characterized at various biases and temperatures. The optical transitions were perturbed by the energy shifts of the electronic states due to Stark effect induced by the modulation electric field. The modulated spectrum is strongly enhanced in the spectral regions involving the fundamental transitions and composed of the first derivatives of the unmodulated lineshapes. The field-induced change of the transmission increases with the increasing modulation voltage. The transition energies of the silver/pentacene/ ITO system can be derived from the peak positions in the electromodulated spectrum. As the temperature is increased from 25 K, the modulated transmission signal is also increased, and becomes non-monotonous as the temperature is further increased. The transition energies involving the pentacene molecular states remain almost constant as the temperature varies.