The model system Pd/TiO2 (110) was used to evaluate the correlation between metal encapsulation and electronic structure of TiO2 crystals. We observed encapsulation of Pd clusters supported on TiO2 crystals, which were heavily Ar+ sputtered, Nb-doped, or reduced by vacuum annealing. In contrast, encapsulation was not observed on unreduced, undoped, or slightly sputtered TiO2 crystals. Our results indicate a strong dependence of the encapsulation process on the electron density in the conduction band of TiO2 and on the space charge formed at Pd/TiO2 interfaces. This behavior is controlled by the initial position of the Fermi energy level (EF) of the metal and the oxide before contact is established. We proved that encapsulation reactions are favored by n-type doping of the oxide and a large work function of the metal. On the basis of this mechanism, we conclude on general trends controlling encapsulation reactions of oxide-supported metal clusters and the strong metal-support interaction (SMSI).
Spherical carbon onions are generated by irradiating graphitic carbon soot with Ne+ ions of 3 MeV energy. Under continued irradiation, a transformation of their cores to cubic diamond crystals is observed. In comparison to earlier electron irradiation experiments, the yield of diamond is much higher. The output of the irradiation experiment is characterized by electron microscopy and electron energy loss spectroscopy. Knock-on displacements of carbon atoms by Ne+ ions are assumed to be responsible for a self-compression of the onions, leading to the nucleation of diamond in their cores. The increased diamond yield is explained by the higher displacement cross-section, the higher energy transfer, and the higher total beam current on the specimen.
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.
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