Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 14: Metal Substrates: Epitaxy and Growth

O 14.10: Talk

Monday, March 26, 2007, 16:30–16:45, H39

Alloying and dealloying in pulsed laser deposited Pd on Cu(001) — •Holger Meyerheim, Elena Soyka, and Jürgen Kirschner — Max-Planck-Institut f. Mikrostrukturphysik, Weinberg 2, 06120 Halle

Using surface x-ray diffraction we have studied the geometric structure of ultra thin Pd films grown at room temperature on Cu(001) by pulsed laser deposition (PLD) in the coverage regime between 0.4 and 4 monolayers (ML). We find a complicated growth mechanism characterized by alloying, dealloying and Pd-agglomeration above an alloyed structure. The growth sequence is governed by the balance of the free surface energy, the strain energy and the activation energy for interlayer exchange. Up to about 2 ML, the interface formation is characterized by an alloying-dealloying mechanism, where Pd is incorporated into the Cu substrate for less than half filled layers, but expelled if the Pd coverage is close to a complete layer. In this case the top layer is composed of Pd. Above 2 ML, Pd agglomeration sets in characterized by Pd-rich alloy layers covered by Pd-layers. Interlayer spacings linearly depend on the Pd-concentration (x) in the Pd(x) Cu(1-x) alloy layers. Our study shows that the film structure is inhomogeneous with respect to both, layer composition and interlayer spacings. It thus provides new structure informations for the strain relief mechanism developed for PLD grown Pd/Cu(001). So far, layer-by-layer growth of a homogeneous non-alloyed Pd-film was assumed as concluded by reflection high electron diffraction and scanning tunneling microscopy [1]. [1] Y. Lu et al., PRL 94, 146105 (2005).