Temperature dependence of the 2D-3D transition in the growth of PTCDA on Ag(111): A real-time X-ray and kinetic Monte Carlo study

We present a real-time X-ray scattering study of the growth modes in organic molecular-beam epitaxy. We have studied the model system 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) on Ag(111) and find a temperature-dependent transition from layer-by-layer growth to islanding. The transition smears out for low substrate temperatures, T , implying that the degree of the layer-by-layer growth of the wetting layer decreases with decreasing T . This behavior has been analyzed quantitatively and reproduced by kinetic Monte Carlo simulations. The implications and consequences of our findings for the understanding of the organic molecular-beam epitaxy are discussed.