Calculation of the vibration properties of the Pd/Au (111) ordered surface alloy in its stable domain

¹ LPEC, Université du Maine, Av. Olivier Messiaen, 72085 Le Mans Cedex 09, France
² LPCQ, Université Mouloud Mammeri, B.P. N° 17, 15000 Tizi-Ouzou, Algérie

^a e-mail: rabah_abo@yahoo.fr

Abstract

In the present paper, a calculation is presented for the vibration properties of the ordered surface alloy alloy Au(111) − (√3×√3)R30° − Pd, which is a stable system in the temperature range of 500K to 600K. This surface alloy is formed by depositing Pd atoms onto the Au(111)surface, and annealing at higher temperatures. The matching theory is applied to calculate the surface phonons and local vibration densities of states (LDOS) for the clean Au (111) surface, and for the Au(111) − (√3×√3)R30° − Pd surface alloy. Our theoretical results for the surface phonon branches of the clean Au (111) surface compare favorably with previous ab initio results and experimental data. In contrast, there are no previous results for the vibrational LDOS for the atomic Au site in a clean Au (111) surface, or results for the surface phonons and vibration spectra for the surface alloy. The surface phonons are calculated for the clean Au (111) surface and the ordered surface alloy along three directions of high symmetry, namely, $\overline{\Gamma {\rm M}},\overline{\text{MML:MK}}$, and $\overline{K\Gamma }$. The phonon branches are strongly modified from the Au (111) surface to the surface alloy. In particular a remarkable change takes place for the LDOS between the clean Au (111) surface and the surface alloy, which may find its origin in the charge transfer from Au atoms to Pd atoms.