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.

One-dimensional defects are created in [001] and [110] oriented TiO 2 single crystals by uniaxial pressure. Transmission electron microscopy (TEM) characterization shows them to preferably lie on {110} planes. Electrical properties studied as a function of oxygen partial pressure reveal their infl uence on ionic and electronic charge carriers. At high oxygen partial pressures (1 bar-10 − 5 bar) the conductivity due to positive charge carriers is strongly enhanced, e.g., the ionic conductivity is increased by more than two orders of magnitude, when the electrical measurement axis lies on the slip plane. In contrary, no changes are observed when the measurement axis does not lie on the slip planes. At low oxygen partial pressures ( < 10 − 15 bar), irrespective of orientation and presence of dislocation, there is no change in the n-type conductivity. The observed phenomena can be well explained within the space charge model, assuming the dislocation cores to exhibit an excess negative charge (increased titanium vacancy concentration). The present study gives a clear correlation between line defects and point defect concentrations in such an oxide for the fi rst time.

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.

We demonstrate that the growth of F16CuPc 1-D nanostructures can be directed by templates of gold nanoparticles. The growth occurs via vapor-phase transport, whereby the gold nanoparticles act as nucleation sites for F16CuPc molecules and promote their anisotropic growth. The F16CuPc 1-D structures adopt diameters of approximately 15-30 nm independent of the nanoparticle size. This approach enables a technologically simple and inexpensive fabrication of very uniform organic 1-D structures (aspect ratio of approximately 30) and precise control of their location and packing density.

The influence of line defects (dislocations) on the electrical properties of polycrystalline TiO2 was investigated. Line defects were created in TiO2 during spark plasma sintering at 1000 °C and 400 MPa. TEM characterisation indicates dislocations to be preferably oriented on {110} and {101} planes. The measured electrical conductivity as a function of oxygen partial pressure and temperature revealed that the dislocations play a vital role in modifying the defect chemistry of TiO2. The presence of dislocations enhanced the ionic conductivity over a wide range of oxygen partial pressures. The observed changes can be interpreted in terms of negatively charged dislocation cores and adjacent space charge accumulation layers. The present findings point towards an alternative method to tune the electrical properties of ionic solids.

Recently, artificial ion conductors have been prepared by growing epitaxial heterolayers consisting of BaF2-CaF2 using molecular beam epitaxy. The ionic conductivity of these heterolayers shows a strong dependence on the layer thickness [N. Sata, S. Eberman, K. Eberl, and J. Maier, Nature 408, 996 (2000)]. In this paper three such heterolayers with different spacings (sample A: 80 nm, sample B: 10 nm, sample C: 1 nm) are investigated by conventional transmission electron microscopy and high-resolution transmission electron microscopy. The spacings are chosen such that they fall into the three conductivity regimes observed in N. Sata et al. (l > 50 nm; 8 < l < 50 nm; l < 8 nm). In accordance with conductivity studies, the samples with spacings of 10 nm or greater (A,B) are epitaxial and continuous, whereas in the case of extremely small spacing (C) the continuity of the layers is destroyed by formation of a column-like structure. Analytical electron microscopy reveals that, instead of forming multilayers, Ca and Ba separate in different columns in sample C. The structure properties of sample A (large l) are quite ideal: Planar interfaces with regular arrays of misfit dislocations with their Burgers vectors on the interface are observed. In the case of sample B (medium l) the lattice misfit is accommodated, in addition, by wavy interfaces associated with dislocations characterized by a Burgers vector that makes a large angle to the interfaces. The (111) lattice spacing very close to the interfaces is markedly changed due to this novel relaxation mechanism in the multilayer. The influences of the crystallographic defects on the ionic conductivity are also discussed.

The relationships between organic semiconductor morphology and device stability of organic field-effect transistors (FETs) are very complex and not yet fully understood. Especially for obtaining high-performance, air-stable n-channel FETs, gaining a deep insight into possible degradation mechanisms can help improve their air stability. Here, we investigate the performance and stability of organic n-channel FETs based on solution-grown single-crystalline ribbons of the conjugated semiconductor bis(1H,1H-perfluorobutyl)-dicyano-perylene tetracarboxylic diimide (C 3 F 7 CH 2 -PTCDI-(CN) 2 ). The FETs show an electron mobility of 0.25 cm 2 /(V s) in air and an on/off ratio up to 1 Â 10 7 . Their mobility does not significantly change when devices are stored in air for more than 5 weeks. This excellent air stability stands in contrast to FETs based on thin evaporated polycrystalline films of the same compound that degrade by more than an order of magnitude during the same 5 week period. We attribute this striking difference in air stability to the grain boundaries in the polycrystalline films and discuss different possible degradation mechanisms.