  The late growth stages and the post-growth diffusion of crystalline organic
thin films have been investigated for 3,4,9,10-perylenetetracarboxylic
dianhydride (PTCDA) on Ag(111), a model system in organic epitaxy. In situ
x-ray measurements at the anti-Bragg point during the growth show intensity
oscillations followed by a time-independent intensity which is independent of
the growth temperature. At T > 350 K, the intensity increases after growth up
to a temperature-dependent saturation value due to a post-growth diffusion
process. The time-independent intensity and the subsequent intensity recovery
have been reproduced by models based on the morphology change as a function of
the growth temperature. The morphology found after the post-growth diffusion
processes has been studied by specular rod measurements.
