Investigation of effects of ionizing radiation exposure on material properties of organic semiconducting oligomer – Pentacene

Abstract

Organic semiconducting materials are known for their chemical affinity and sensitivity to environmental conditions. In this manuscript we investigate the changes in various material properties of a very well-known organic semiconducting oligomer – pentacene, upon exposure to ionizing radiation of γ-rays using Cobalt-60 radiation source. The changes in the optical properties were observed by studying UV–Visible Absorbance spectra of the pentacene thin-film. The effects on the valance electronic structure of the pentacene were studied by ultraviolet photoelectron spectroscopy of pristine pentacene, and after exposure of the same to different total-doses of ionizing radiation. Moreover, X-ray photoelectron spectra of the material were recorded to study the core-level changes in the pentacene when exposed to ionizing radiation. These photoelectron spectroscopy techniques suggested p-type doping into the material and presence of newly generated oxidized energy-states in the energy band gap of the material upon exposure to ionizing radiation. Electrostatic force microscopy imaging was done to observe the changes in the electrical properties of pentacene thin-film which suggested an increase in the conductivity upon exposure to ionizing radiation. Moreover, the effect of newly generated oxidized energy-states, in the band gap of the material, on the hopping transport in the pentacene thin-film was studied by measuring changes in the resistance as a function of temperature before and after different total-doses of ionizing radiation, and observing the changes in the slope. Thus, exposure to ionizing radiation is proposed here as a controlled method of doping the organic semiconducting materials and changing their conductivity. Moreover, the changes in the electrical properties of the thin-film upon exposure to ionizing radiation enable its use in sensors for determining ionizing radiation using organic electronic devices as sensors.