Browsing by Author "Benthem, Klaus van"

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Electron microscopic investigations of the bonding behaviour of metals on SrTiO3 substrates
(2002) Benthem, Klaus van; Rühle, Manfred (Prof. Dr. Dr. h.c.)
The microscopic and electronic structure of interfaces between SrTiO3 in its cubic phase and thin films of Pd, Ni and Cr have been investigated to gain insights into the bonding characteristics between the ceramic substrate and the different 3-d transition metals. The interfaces were investigated by various transmission electron microscopy techniques, such as conventional TEM, high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). The electronic structure of the different interfaces was analysed in terms of electron energy-loss near-edge structures (ELNES). These are theoretically described by site and symmetry projected unoccupied densities of states (PDOS). For the Pd/SrTiO3 interface, density functional theory was used to calculate PDOS spectra on the basis of several different atomistic structure models. A comparison to experimental ELNES data showed the presence of a TiO terminated interface structure. This result is in agreement with previuous theoretical studies. The adhesion between the thin Pd films and the SrTiO3 substrate was found to be formed by Pd-d with O-p hybridizations. For the Ni/SrTiO3 and Cr/SrTiO3 interfaces, which are considered as more reactive systems, the bonding behaviours were analysed only on the basis of experimental ELNES data. It was concluded that a 2-dimensional reaction layer of NiO composition froms the adhesion at the Ni/SrTiO3 interface, whereas for the Cr/SrTiO3 interface no reaction layer was found. At this interface, ELNES spectra show Cr-O hybridizations together with an electron transfer across the interface. Comparing results obtained for the different metal/SrTiO3 interfaces, it becomes obvious that the wetting of the (100)SrTiO3 surface is best for Cr, followed by Ni and Pd. Cr-O bonds are suggested to be stronger then the Ni-O and Pd-O bonds since not only a covalent but also a significant ionic bonding contribution is present.