Comparative study of Ag, Au, Pd, and Pt adsorption on Mo and $\mathrm{Ta}\left(112\right)$ surfaces

The structural, energetic, and electronic properties of low-coverage phases of Ag, Au, Pd, and Pt atoms adsorbed on the (112) surface of Mo and Ta are investigated from first principles. On $\mathrm{Mo}\left(112\right)$ the binding energy of adatoms increases with coverage (for dimers, linear trimers, and infinite chains) which means the prevalence of attractive interactions between adatoms in the same trough and their clustering. This is at variance from the behavior on the Ta surface where the binding per adatom in dimers or trimers is decreasing or not altered compared to a single atom adsorption. Consequently, on $\mathrm{Mo}\left(112\right)$ adatom chains form in the furrows as experimentally observed, whereas on $\mathrm{Ta}\left(112\right)$ the adatoms are more likely to form a scattered, random pattern. Pd and Pt adsorbates are predicted to mix and alloy with $\mathrm{Ta}\left(112\right)$ atoms.

Figure 1

Geometry of the original adatom structures on the $\mathrm{bcc}\left(112\right)$ surface showing the $5\times 2$ unit cell applied in the calculations. The adatom sites in atomic furrows correspond to positions occupied by substrate atoms in the bulk.

Figure 2

(Color online) Change in the vertical relaxation of interlayer distance of the outermost layers of (112) surface of Mo (full symbols) and Ta (open symbols) upon adsorption of Ag, Au, Pd, and Pt.

Figure 3

(Color online) The adatom-surface distance for single atom adsorption versus empirical covalent radius (Ref. 8) of the adatom. Circles represent the distance to the center of gravity of the uppermost layer while diamonds are the distance to the second atomic layer (beneath the adatoms). Filled and open symbols mark the results for $\mathrm{Mo}\left(112\right)$ and $\mathrm{Ta}\left(112\right)$ surfaces, respectively.

Figure 4

(Color online) Calculated dipole moments, $\mu$, for various adatom structures on the Mo and $\mathrm{Ta}\left(112\right)$ surfaces. Filled symbols are for the compact chain structures, while the open triangles represent the sparse structures (see Fig. 1). The full squares to the right represent the results for infinite chains (0.5 ML).

Figure 5

(Color online) The local density of electronic states on Ag, Au, Pd, and Pt atoms adsorbed on $\mathrm{Mo}\left(112\right)$ and $\mathrm{Ta}\left(112\right)$. The states on a monomer, a dimer atom, and the central atom of a trimer are shown, respectively. Each row displays the LDOS on a different adatom. The energies are plotted relative to the Fermi level.

Figure 6

(Color online) The full density of electronic states for the clean and adsorbate-covered (Ag, Au, Pd, Pt) $\mathrm{Mo}\left(112\right)$ and $\mathrm{Ta}\left(112\right)$ slabs.