Europhys. Lett.
Volume 71, Number 2, July 2005
Page(s) 276 - 282
Section Condensed matter: structural, mechanical and thermal properties
Published online 15 June 2005
Europhys. Lett., 71 (2), pp. 276-282 (2005)
DOI: 10.1209/epl/i2005-10075-5

Making a noble metal of $\chem{Pd}$

E. Hüger1 and K. Osuch2, 3

1  Institute of Physics, Technische Universität Clausthal D-38678 Clausthal-Zellerfeld, Germany
2  Department of Physics, University of South Africa - Unisa 0003, South Africa
3  Faculty of Physics, Warsaw University of Technology Koszykowa 75, 00-662 Warsaw, Poland

received 2 March 2005; accepted in final form 18 May 2005
published online 15 June 2005

We present theoretical and experimental data concerning the possibility of inducing in $\chem{Pd}$ properties characteristic of a noble metal. A free-standing $\chem{Pd(100)}$ monolayer expanded to the lattice constant of 3.30$\un{\AA}$ exhibits an atomic-like electronic structure, having its d-valence states almost full, like the noble metals $\chem{Cu}$, $\chem{Ag}$ or $\chem{Au}$. To prevent de-population of the d-states, we deposit the $\chem{Pd}$ ML on a $\chem{Nb(100)}$ substrate passivated by a pseudomorphic $\chem{S}$ monolayer. The weak interaction with the $\chem{S}$-capped $\chem{Nb(100)}$ surface causes the centre of the d-states of the $\chem{Pd}$ monolayer to lie much closer to the Fermi level than in bulk $\chem{Pd}$. As a result, the weakly bonded $\chem{Pd}$ monolayer becomes more reactive than bulk $\chem{Pd}$. However, when $\chem{Pd}$ is deposited directly on the $\chem{Nb(100)}$ surface, the strong, direct bonds between $\chem{Pd}$ and $\chem{Nb}$ push the d-band centre of the monolayer toward lower binding energies, resulting in $\chem{Pd}$ reactivity comparable to that of the noble metal $\chem{Ag}$.

68.43.-h - Chemisorption/physisorption: adsorbates on surfaces.
82.80.Pv - Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.).
73.20.At - Surface states, band structure, electron density of states.

© EDP Sciences 2005