Abstract
We have investigated the initial growth of the first two epitaxial layers of PTCDA on a Ag(111) surface consisting of a distribution of flat (111) terraces, separated by single atomic steps or step bunches with a few point defects. By utilizing the low-energy electron microscopy (LEEM) technique in both bright and dark field modes, we are able not only to follow the growth of the first layers but also to distinguish between different rotational and mirror domains and their influence on the growth of subsequent layers. Thus, we learn much about diffusion lengths and barriers, domain sizes, and about the influence of domain boundaries and nucleation centers. The results give deep insight into the growth dynamics, the influence of step orientation, and the quality of the resulting epitaxial layers and lead to the conclusion that the morphology of the substrate surface is likely to be the most influential parameter for the homogeneity of epitaxial layers.
Highlights
The understanding and tailoring of thin organic films and their interfaces to inorganic materials is a field of high scientific interest
We have investigated the initial growth of the first two epitaxial layers of PTCDA on a Ag(111) surface consisting of a distribution of flat (111) terraces, separated by single atomic steps or step bunches with a few point defects
As example with respect to the system studied here, we just refer to earlier work where it has been found that the photoluminescence yield of a film of 30 ordered layers of 3,4,9,10-Perylenetetracarboxylicacid-Dianhydride (PTCDA) on Ag(111) decreases by a factor of about 20 when the preparation temperature of the layer is changed by 80 K most experimental techniques are unable to detect a difference of layer morphology, structure, or electronic properties.[5]
Summary
The understanding and tailoring of thin organic films and their interfaces to inorganic materials is a field of high scientific interest. The ideal and perhaps only method that can answer these two questions simultaneously is low-energy-electron-microscopy (LEEM) This method yields structural data, can distinguish between different rotational domains, can discern first, second, and higher layers, has a sufficiently high lateral resolution to see single atomic steps on the surface, and can be used in a dynamic mode. The latter property means that one can watch the organic film growing, can vary parameters like temperature and deposition rate, and can monitor the growth of several domains simultaneously under identical conditions providing a kind of statistical information. The cleaning progress was checked by photoelectron emission microscopy, LEEM, low-energy electron diffraction (LEED), and X-ray photoelectron spectroscopy
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