Organic molecular-beam deposition of pentacene on gold substrates has been investigated using a multitechnique approach. The morphology of the organic thin films depends strongly on the substrate temperature. Pronounced dewetting and island formation are observed at room temperature. Whereas pentacene molecules adopt a planar monolayer structure, they continue to grow in an upright orientation in multilayer films as inferred from x-ray absorption spectroscopy and atomic force microscopy. These results are in pronounced contrast to a recent scanning tunneling microscopy (STM) study by Kang and Zhu [Appl. Phys. Lett. 82, 3248 (2003)] and indicate fundamental problems in the interpretation of STM measurements for organic thin films.

The growth of the polycyclic aromatic hydrocarbon perylene on (110) oriented copper substrates has been studied by means of x-ray photoelectron spectroscopy, near-edge x-ray absorption spectroscopy, and atomic force microscopy. In the monolayer regime, the molecules are orientated with their molecular plane parallel to the substrate, whereas they adopt a tilted arrangement in multilayer films. For multilayers with thicknesses exceeding 10 nm, the molecules grow in a bulk-like structure with their long axes orientated upright to the substrate surface.

Attractive materials for molecular electronics are the polycyclic aromatic hydrocarbons (PAHs), the hydrogen‐terminated segments of a graphitic plane. Since the processing of larger PAHs, for example hexa‐peri‐hexabenzocoronene, is complicated by their extremely low solubilities and very small vapor pressures, the possibility of a surface‐assisted synthesis of planar PAHs is investigated starting from diphenylacetylene (left) and hexaphenylbenzene (right), as shown in the picture.

The deposition of polycyclic aromatic hydrocarbons on substrate surfaces is a key step for using such disklike molecules in nanoelectronic devices. An alternative to the (frequently problematic) preparation by evaporation or deposition from solution is to use the substrate surface as a template for the planarization that accompanies the cyclodehydrogenation (see picture).

Polycyclische aromatische Kohlenwasserstoffe (PAHs) wie Triphenylen 1 a, Hexa-peri-hexabenzocoronen (HBC, 2 a) und sein höheres Homologes 3 (Schema 1) bilden zwei-und dreidimensionale Überstrukturen, die für das Studium von Ladungsprozessen bedeutsam sind. [1±4] Die Erzeugung von Adsorbatschichten auf Substratoberflächen, ein zentraler Schritt für die Nutzung solcher Scheibchenmoleküle in der Nanoelektronik, kann durch Aufdampfen im Ultrahochvaku-