Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Struktur und Dynamik Poster: Mi., 14:00–16:30 M-P140
Energy-dispersive X-ray reflectivity for real-time growth studies of organic
thin films
Stefan Kowarik 1,2 , Alexander Gerlach 1,2 , Frank Schreiber 1 , Wolfram
Leitenberger 3 , Ullrich Pietsch 4
1 Tübingen University, Institute for Applied Physics, 72076 Tübingen, Germany –
2 Oxford University, Physical and Theoretical Chemistry, Oxford OX1 3QZ, UK –
3 Potsdam, Institute for Physics, 14469 Potsdam, Germany – 4 Siegen University, Department
of Physics, 57068 Siegen, Germany
We employ energy-dispersive as well as angle-dispersive X-ray reflectivity to study
the growth and structure of the organic semiconductors rubrene and pentacene in in
situ and real time. Following the surface morphology of rubrene films during organic
molecular beam deposition, we find relatively smooth films (surface roughness below
∼15 ˚A for thicknesses up to at least 600 ˚A) and a significant delay before the onset
of roughening. This anomalous roughening in the beginning and crossover to normal
roughening later during growth may be related to conformational changes of rubrene
in the early stages of growth. Studying pentacene in real-time during growth with
energy-dispersive reflectometry we can follow the growth oscillations for a wide range
in q-space including the anti-Bragg point. These growth oscillations give a detailed
picture of the crossover from layer-by-layer growth for the first pentacene monolayers
to roughening for thicker films. Finally, we discuss the chances and limitations of energy
dispersive as compared to conventional angle-dispersive measurements [1].
[1] S. Kowarik et al., PCCP 8 (2006) 1834
Fig. 1: Following the evolution
of the X-ray reflectivity
during pentacene thin film
growth with energy dispersive
measurements allows to determine
the growth mode.