Regensburg 2007 – scientific programme

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DS: Fachverband Dünne Schichten

DS 3: Metal Layers and Multilayers

DS 3.5: Talk

Monday, March 26, 2007, 10:30–10:45, H34

Triple junction and interface transport in nano-crystalline Cu/Ag bi-layers — •Henning Galinski and Guido Schmitz — Institut für Materialphysik der WWU Münster, Münster, Deutschland

Cu and Ag are distinguished by strongly repulsive chemical interaction. Thus no mixing or reaction between these two elements should be expected. We investigated the chemical stability of Cu/Ag bi-layers with state-of-the-art wide angle atom probe tomography (WATAP). This method provides an extended volume of analysis so that grain boundaries are reliably located and even minor chemical modifications are detected with improved statistical significance. Bi-layer samples were deposited on tungsten substrate tips and subjected to heat treatments up to 500°C/30 min. Two surprising observations are remarkable: i) In contrast to bulk thermodynamics an intermixing zone of 1.5 nm in thickness develops at the bi-layer interface. Since its apparent activation energy amounts to only 0.3 eV, we conclude that this intermixing is not controlled by diffusion kinetics. Instead, it may be understood quantitatively by the Cahn-Hilliard approach. Thus, our experiments allow a direct measurement of the gradient term in this theory. ii) One-dimensional, worm-like segregation zones develop at both sides of the interface. The geometric analysis proves that these zones represent triple junctions of the grain boundary structure. In consequence, the measurements demonstrate that triple junctions are distinguished by remarkably large segregation factors and the triple junction diffusion coefficient can be determined in the type C kinetic regime.