Electronic devices made from organic materials have the p
otential to support a more ecologically friendly
and affordable future. However, the ability to fabr
icate devices with well-defined and reproducible
electrical and optical properties is hindered by the sen
sitivity to the presence of chemical impurities.
Oxygen in particular is an impurity that can trap elect
rons and modify conductive properties of some
organic materials. Until now the 3-dimensional profili
ng of oxygen species in organic semiconductors
has been elusive and the effect of oxygen remains disput
ed. In this study we map out high-spatial
resolution 3-dimensional distributions of oxygen inclusi
ons 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 a
t the surface. These channels extend to depths
in excess of 1.8
μ
m 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 bindin
g to rubrene. Our investigation of surfaces at
different stages of evolution reveals the extent of o
xygen inclusion, which affects rubrene's optical and
transport properties, and is consequently of importance
for the reliability and longevity of devices.