title: Channels of oxygen diffusion in single crystal rubrene revealed.
abstract: Electronic devices made from organic materials have the potential to support a more ecologically friendly and affordable future. However, the ability to fabricate devices with well-defined and reproducible electrical and optical properties is hindered by the sensitivity to the presence of chemical impurities. Oxygen in particular is an impurity that can trap electrons and modify conductive properties of some organic materials. Until now the 3-dimensional profiling of oxygen species in organic semiconductors has been elusive and the effect of oxygen remains disputed. In this study we map out high-spatial resolution 3-dimensional distributions of oxygen inclusions near the surface of single crystal rubrene, using Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). Channels of diffused oxygen are found extending from uniform oxygen inclusion layers at the surface. These channels extend to depths in excess of 1.8 μm and act as an entry point for oxygen to diffuse along the ab-plane of the crystal with at least some of the diffused oxygen molecularly binding to rubrene. Our investigation of surfaces at different stages of evolution reveals the extent of oxygen inclusion, which affects rubrene's optical and transport properties, and is consequently of importance for the reliability and longevity of devices.
authors.affiliation: London Centre for Nanotechnology, 17-19 Gordon Street, London, WC1H 0AH, UK and Department Electronic & Electrical Engineering, UCL, Roberts Building, London, WC1E 7JE, UK. robert.j.thompson@ucl.ac.uk.
authors.forename: Robert J
authors.identifier: http://orcid.org/0000-0002-1458-5922
authors.initials: RJ
authors.lastname: Thompson
authors.affiliation: Department Materials, Imperial College London, Royal School of Mines, Exhibition Road, London, SW7 2AZ, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Bennett
authors.affiliation: Department Materials, Imperial College London, Royal School of Mines, Exhibition Road, London, SW7 2AZ, UK.
authors.forename: Sarah
authors.initials: S
authors.lastname: Fearn
authors.affiliation: London Centre for Nanotechnology, 17-19 Gordon Street, London, WC1H 0AH, UK.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Kamaludin
authors.affiliation: School of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore.
authors.forename: Christian
authors.initials: C
authors.lastname: Kloc
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas at Dallas, 800 W. Campbell Rd, TX 75080-3021, USA.
authors.forename: David S
authors.initials: DS
authors.lastname: McPhail
authors.affiliation: Department Electronic & Electrical Engineering, UCL, Roberts Building, London, WC1E 7JE, UK. robert.j.thompson@ucl.ac.uk.
authors.forename: Oleg
authors.initials: O
authors.lastname: Mitrofanov
authors.affiliation: London Centre for Nanotechnology, 17-19 Gordon Street, London, WC1H 0AH, UK and Department Electronic & Electrical Engineering, UCL, Roberts Building, London, WC1E 7JE, UK. robert.j.thompson@ucl.ac.uk.
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Curson