A. C. Dürr

High structural order in thin films of the organic semiconductor diindenoperylene

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 A 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°.

Morphology and interdiffusion behavior of evaporated metal films on crystalline diindenoperylene thin films

We present a transmission electron microscopy (TEM)/Rutherford backscattering spectrometry (RBS)/x-ray-diffraction (XRD) study of Au evaporated on crystalline organic thin films of diindenoperylene (DIP). Cross-sectional TEM shows that the preparation conditions of the Au film (evaporation rate and substrate temperature) 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 ≈120 °C the Au film starts to reorder and shows sharp (111)-diffraction features. In addition, temperature dependent RBS measurements indicate that the Au/DIP interface is thermally essentially stable against diffusion of Au in the DIP layer up to ≈100 °C on the time scale of hours, dependent on the Au thickness.

Thermal stability and partial dewetting of crystalline organic thin films: 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(111)

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 (PTCDA) on Ag(111). 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 Tg≲350 K are metastable, while films deposited at Tg≳350 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.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 (PTCDA) on Ag(111). 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 Tg≲350 K are metastable, while films deposited at Tg≳350 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.

Optically induced electron transfer from conjugated organic molecules to charged metal clusters

c ¨ Abstract The formation of small gold clusters at the initial stage of the metal growth on a thin film of the conjugated organic semiconductor diindenoperylene (DIP) leads to charging during ultraviolet photoemission spectroscopy (UPS) investigations. Additional irradiation of the sample with visible light was successfully applied to re-establish charge neutrality on the sample surface. By varying the light energy, we demonstrate that the optical formation of excitons and yor polarons results in efficient electron transfer from DIP to the positively charged Au clusters and thus the elimination of charging in UPS. This allows the collection of reliable information on the interface electronic structure. 2003 Elsevier Science B.V. All rights reserved.

Optimized preparation of cross-sectional TEM specimens of organic thin films

We present a route for the preparation of cross-sectional TEM specimens of crystalline organic thin films which minimizes the mechanical, chemical and thermal load of the organic film during preparation and allows to take TEM images with molecular resolution. A typical example of a thin film of diindenoperylene capped with a thin layer of gold is shown to demonstrate the application of the technique for the investigation of metal-organic interfaces.