Organic Molecular Beam Deposition of Pentacene on Clean Metal Surfaces

Organic Molecular Beam Deposition of Pentacene on Clean Metal Surfaces 

In this section we describe the results of a systematic study on the growth of pentacene on different types of metal surfaces. The results were obtained by combining a fairly large number of complementary techniques, including STM, atomic force microscopy (AFM), scanning electron microscopy (SEM), NEXAFS, and X-ray diffraction (XRD). These studies reveal a rather complex growth scenario which not only depends on the type of metal but also on its cleanliness and roughness. 

Generally, in the first monolayer on (coinage) metals pentacene and other planar aromatic molecules were found to adsorb with their aromatic ring plane parallel to the substrate. A detailed discussion of the molecule/metal interaction probed by means of low temperature STM can be found in Chapter 12 by Soubatch et al. The preference for such a planar adsorption geometry can be 

that in the case of bismuth the growth of upright oriented pentacene molecules has been observed - even in the very first monolayer [47]. This orientation has been explained [47] by the rather small density of states near the Fermi level of this semi-metal leading to a rather small molecule-substrate interaction which becomes comparable or even weaker than the mutual molecular interaction and thus parallels the situation observed for pentacene deposited on inert substrates such as Si02 [48]. 

In order to exclude the appearance of rotational domains in the initial stage of growth we have used a Cu(llO) substrate and have studied the growth of pentacene films on this substrate quite extensively. In fact, a highly ordered submonolayer and a saturated monolayer phase are found which exhibit a uniform alignment of the flat lying molecules with their long axes orientated parallel to the (110 )-azimuth direction of the substrate [46, 52]. 

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