Real-time observation of oxidation and photo-oxidation of rubrene thin films by spectroscopic ellipsometry

TL;DR

This study uses spectroscopic ellipsometry to monitor in real-time how rubrene thin films oxidize and photo-oxidize, revealing significant optical property changes and faster photo-oxidation under illumination, with insights into diffusion mechanisms.

Contribution

It provides the first real-time spectroscopic ellipsometry analysis of rubrene oxidation and photo-oxidation, highlighting the impact of illumination on oxidation rates and optical properties.

Findings

Photo-oxidation is significantly faster than oxidation without light.

Optical absorption changes indicate oxidation-induced modifications in rubrene.

Photo-oxidation involves non-Fickian diffusion mechanisms.

Abstract

We follow in real-time and under controlled conditions the oxidation of the organic semiconductor rubrene grown on SiO_2 using spectroscopic ellipsometry. We derive the complex dielectric function epsilon_1 + i epsilon_2 for pristine and oxidized rubrene showing that the oxidation is accompanied by a significant change of the optical properties, namely the absorption. We observe that photo-oxidation of rubrene is orders of magnitude faster than oxidation without illumination. By following different absorption bands (around 2.5eV and 4.0eV for pristine rubrene and around 4.9eV for oxidized rubrene) we infer that the observed photo-oxidation of these films involves non-Fickian diffusion mechanisms.