Late growth stages and post-growth diffusion in organic epitaxy: PTCDA on Ag(111)

TL;DR

This study investigates late-stage growth and post-growth diffusion of PTCDA on Ag(111), revealing temperature-dependent diffusion effects and morphology changes through in situ x-ray measurements and modeling.

Contribution

It provides new insights into the morphology evolution and diffusion processes in organic epitaxy, especially during late growth stages and after growth.

Findings

Intensity oscillations during growth observed via x-ray measurements.

Post-growth diffusion causes intensity increase and morphology change.

Models successfully reproduce observed intensity and morphology evolution.

Abstract

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.