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DS: Fachverband Dünne Schichten

DS 54: Nanoengineered Thin Films

DS 54.6: Vortrag

Donnerstag, 17. März 2011, 19:15–19:30, GER 38

Phase transitions in nano-grained close-packed Pd thin films — Erwin Hüger¹, •Tomas Kana^2,3, and Mojmír Šob^4,2 — ¹Institute of Metallurgy, Clausthal University of Technology, D-38678 Clausthal-Zellerfeld, Germany — ²Institute of Physics of Materials, Academy of Sciences of the Czech Republic, CZ-616 62 Brno, Czech Republic — ³Faculty of Mechanical Engineering, Brno University of Technology, CZ-616 69 Brno, Czech Republic — ⁴Department of Chemistry, Faculty of Science, Masaryk University, CZ-611 37 Brno, Czech Republic

Using ab initio density functional calculations, we analyze experimental data and corresponding energy barriers of phase transitions in the (1120) oriented hcp Pd thin films grown on W(001) and Nb(001) substrates. We elucidate the feasibility of the experimentally observed phase transformation between the hcp and double hcp (dhcp) structures and absence of the hcp–fcc transformation in those films. The proposed model of the experimentally observed hcp–dhcp transformation preserves the existing domain topology of the Pd films and exhibits a sufficiently low energy barrier. On the other hand, the orthogonal pattern of rectangular domains induced by the four-fold symmetry of the substrate surface hinders the hcp Pd phase to convert back to the ground-state fcc phase, although there exists a transformation path exhibiting a very low energy barrier between the hcp and fcc structures. This path, however, would break the domain arrangement and, therefore, it cannot be accomplished. In this way, the hcp crystalline phase is locked inside of nanograins.