The scaling exponents alpha, beta, and 1/z in thin films of the organic molecule diindenoperylene deposited on SiO2 under UHV conditions are determined. Atomic-force microscopy, x-ray reflectivity, and diffuse x-ray scattering were employed. The surface width displays power law scaling over more than 2 orders of magnitude in film thickness. We obtained alpha = 0.684+/-0.06, beta = 0.748+/-0.05, and 1/zeta = 0.92+/-0.20. The derived exponents point to an unusually rapid growth of vertical roughness and lateral correlations. We suggest that they could be related to lateral inhomogeneities arising from the formation of grain boundaries between tilt domains in the early stages of growth.

We report extraordinary structural order along the surface normal in thin films of the organic semiconductor diindenoperylene (DIP) deposited on silicon–dioxide surfaces. Cross-sectional transmission electron microscopy (TEM), noncontact atomic force microscopy (NC–AFM), as well as specular and diffuse x-ray scattering measurements were performed to characterize thin films of DIP. Individual monolayers of essentially upright-standing DIP molecules could be observed in the TEM images indicative of high structural order. NC–AFM images showed large terraces with monomolecular steps of ≈16.5 Å height. Specular DIP Bragg reflections up to high order with Laue oscillations confirmed the high structural order. A semi-kinematic fit to the data allowed a precise determination of the oscillatory DIP electron density ρel.,DIP(z). The mosaicity of the DIP thin films was obtained to be smaller than 0.01°.

We present a study of the morphology, structure, and electronic properties of interfaces formed between Au and the organic semiconductor diindenoperylene ͑DIP͒ employing transmission electron microscopy ͑TEM͒, atomic-force microscopy ͑AFM͒, x-ray diffraction, and ultraviolet photoelectron spectroscopy ͑UPS͒. Pronounced islanding of the DIP films deposited on Au is found by AFM as well as by TEM. In addition, TEM images show individual monolayers of DIP with the long molecular axis parallel to the substrate, suggesting a lying-down phase ͑-phase͒. TEM images also show the formation of Au clusters and a certain degree of Au interdiffusion into the DIP film after Au deposition on DIP. Specular and grazing incidence x-ray diffraction show the coexistence of standing phase ͑-phase͒ and -phase with a preferred growth of the -phase. UPS is used to study the evolution of the electronic structure of the DIP-on-Au and Au-on-DIP interfaces. DIP is found to physisorb on Au. The energy difference between substrate Fermi level and the DIP highest occupied molecular orbital at the interface is 1.0 eV. This hole-injection barrier increases to 1.45 eV away from the interface because of decreased screening by the metal and possible changes in molecular conformation. For Au deposition onto DIP, UPS traces the formation of Au clusters as a function of Au coverage. These clusters percolate only for Au coverages higher than 32 Å to give a continuous metal surface coverage and conductivity. The interaction between the Au clusters and DIP is also found to be of physisorptive nature.

The planar organic molecule 3,4,9,10-perylenetetracarboxylic dianhydride ͑PTCDA͒ deposited on Ag͑111͒ has been used as a model system for organic molecular-beam epitaxy ͑OMBE͒. The crystal structure and morphology of thin films in the range of 50-200 Å have been examined in detail as a function of the growth parameters by x-ray diffraction and noncontact atomic force microscopy. Evidence for the coexistence of ␣and ␤-like structures has been found for a variety of growth conditions. A growth temperature-dependent morphology transition from smooth films to well-separated islands has been observed which can be related to changes of the crystal structure. These changes of the crystal structure can be rationalized similar to the Nishiyama-Wassermann and the Kurdjumov-Sachs relations. The island density and size show a similar temperature-dependent behavior as observed for MBE-grown inorganic thin films. A rate-equation-based analysis is used to estimate an effective diffusion barrier for the surface self-diffusion of PTCDA.

The interfacial properties of metal contacts on organic substrates are strongly determined by the preparation conditions of the gold film. A gold–diindenoperylene (DIP) interface has been studied as a model system for metal contacts on organic electronic devices. The Figure juxtaposes the two deposition methods used, whereby only the first method leads to a well‐defined interface with only a slight amount of diffusion of the gold film into the DIP layer.

We present a transmission electron microscopy ͑TEM͒/Rutherford backscattering spectrometry ͑RBS͒/x-ray-diffraction ͑XRD͒ study of Au evaporated on crystalline organic thin films of diindenoperylene ͑DIP͒. Cross-sectional TEM shows that the preparation conditions of the Au film ͑evaporation rate and substrate temperature͒ strongly determine the interfacial morphology. In situ XRD during annealing reveals that the organic layer is thermally stable up to about 150°C, a temperature sufficient for most electronic applications. The x-ray measurements show that the ''as-grown'' Au layer exhibits a large mosaicity of around 10°. Upon annealing above Ϸ120°C the Au film starts to reorder and shows sharp ͑111͒-diffraction features. In addition, temperaturedependent RBS measurements indicate that the Au/DIP interface is thermally essentially stable against diffusion of Au in the DIP layer up to Ϸ100°C on the time scale of hours, dependent on the Au thickness.

The thermal stability and dewetting effects of crystalline organic thin films on inorganic substrates have been investigated for a model system for organic epitaxy, 3,4,9,10-perylenetetracarboxylic dianhydride ͑PTCDA͒ on Ag͑111͒. The thin films deposited under a variety of growth conditions have been annealed stepwise and studied by in situ x-ray diffraction and noncontact atomic force microscopy. It has been found that comparatively smooth films deposited at temperatures T g Շ350 K are metastable, while films deposited at T g տ350 K are stable against annealing on a time scale of several hours. The thermal expansion of thin PTCDA films and bulk samples has been determined.

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