Marion Kelsch

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.

Structures of BaF2-CaF2 heterolayers and their influences on ionic conductivity.

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.

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.

Enhanced ionic conductivity in polycrystalline TiO2 by ‘‘one-dimensional doping’’

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.

Materials News: Interfacial chemistry and atomic arrangement of ZrO2 − La2/3Sr1/3MnO3 pillar-matrix structures

We studied ZrO2 − La2/3Sr1/3MnO3 pillar–matrix thin films which were found to show anomalous magnetic and electron transport properties. With the application of an aberration-corrected transmission electron microscope, interfacial chemistry, and atomic-arrangement of the system, especially of the pillar–matrix interface were revealed at atomic resolution. Minor amounts of Zr were found to occupy Mn positions within the matrix. The Zr concentration reaches a minimum near the pillar–matrix interface accompanied by oxygen vacancies. La and Mn diffusion into the pillar was revealed at atomic resolution and a concomitant change of the Mn valence state was observed.

Cross-sectional characterization of electrodeposited, monocrystalline Au nanowires in parallel arrangement.

Cross-sections of cylindrically shaped nanowires are fabricated using a focused ion beam technique. They are oriented such that the electron beam direction is parallel to a low-index zone axis for high- resolution imaging. In this configuration the direction of gold nanowire growth can be determined using electron diffraction.

Magnetic properties of [NdFeBx/Nbz]n multilayer films

This article presents the systemic relationship between microstructure and magnetic properties of NdFeB single layer and [NdFeBx/Nbz]n multiplayer films. Temperature dependence on coercivity was fitted to a modified nucleation model to study the magnetization reversal process of films. The microstructure parameters (αK) determined the deteriorating effect of the microstructure on coercivity. The highest values of the single- and multilayer films were 0.46 and 0.69, respectively. It proved that the Nb spacer layer improved the grain boundary of the Nd2Fe14B matrix effectively.

Electron-Beam-Induced Antiphase Boundary Reconstructions in a ZrO2-LSMO Pillar-Matrix System.

The availability of aberration correctors for the probe-forming lenses makes simultaneous modification and characterization of materials down to atomic scale inside a transmission electron microscopy (TEM) realizable. In this work, we report on the electron-beam-induced reconstructions of three types of antiphase boundaries (APBs) in a probe-aberration-corrected TEM. With the utilization of high-angle annular dark-field scanning transmission electron microscopy (STEM), annular bright-field STEM, and electron energy-loss spectroscopy, the motion of both heavy element Mn and light element O atomic columns under moderate electron beam irradiation are revealed at atomic resolution. Besides, Mn segregated in the APBs was observed to have reduced valence states which can be directly correlated with oxygen loss. Charge states of the APBs are finally discussed on the basis of these experimental results. This study provides support for the design of radiation-engineering solid-oxide fuel cell materials.

Materials News: Interfacial chemistry and atomic arrangement of ZrO{sub 2} − La{sub 2/3}Sr{sub 1/3}MnO{sub 3} pillar-matrix structures

We studied ZrO2 − La2/3Sr1/3MnO3 pillar–matrix thin films which were found to show anomalous magnetic and electron transport properties. With the application of an aberration-corrected transmission electron microscope, interfacial chemistry, and atomic-arrangement of the system, especially of the pillar–matrix interface were revealed at atomic resolution. Minor amounts of Zr were found to occupy Mn positions within the matrix. The Zr concentration reaches a minimum near the pillar–matrix interface accompanied by oxygen vacancies. La and Mn diffusion into the pillar was revealed at atomic resolution and a concomitant change of the Mn valence state was observed.

Interfacial chemistry and atomic arrangement of ZrO2 − La2/3Sr1/3MnO3 pillar-matrix structures

We studied ZrO2 − La2/3Sr1/3MnO3 pillar–matrix thin films which were found to show anomalous magnetic and electron transport properties. With the application of an aberration-corrected transmission electron microscope, interfacial chemistry, and atomic-arrangement of the system, especially of the pillar–matrix interface were revealed at atomic resolution. Minor amounts of Zr were found to occupy Mn positions within the matrix. The Zr concentration reaches a minimum near the pillar–matrix interface accompanied by oxygen vacancies. La and Mn diffusion into the pillar was revealed at atomic resolution and a concomitant change of the Mn valence state was observed.