Probing inhomogeneities in nanoscale organic semiconductor films: Depth profiling using slow positron beam and X-ray reflectivity techniques

Depth profiling studies in 200 nm organic semiconductor (OSC) films on quartz substrate have been carried out using slow positron beam and X-ray reflectivity (XRR) techniques with the objective of examining structural inhomogeneities in as-deposited film and those annealed at high temperature. Grazing incidence X-ray diffraction and atomic force microscopy measurements are carried out to examine the crystallinity and surface morphology, respectively. In general, annealing is seen to modify the morphology and nanostructure. However, a significant inhomogeneity in nanostructure, marked by a disordered layer with low density region is observed in the film annealed at 200 °C from positron as well as XRR measurements. This study highlights the sensitivity of these techniques to defects and inhomogeneities in nanoscale that may have profound influence on device performance.