Site selectivity in chemisorption of C on Pd(211)

Results of ab initio electronic structure calculations of C on Pd(211), a vicinal of Pd(111), show a hierarchy of adsorption sites with adsorption energy ranging from $-8.21\text{to}-5.46\mathrm{eV}$ (0.33 ML coverage) and scaling almost linearly with the effective coordination at the site. In the most preferred site, C atoms sit almost under the Pd step atoms and influence drastically multilayer relaxations and surface registry of Pd(211). The adsorption energy at this site is $-9.10\mathrm{eV}$ for 0.17 ML coverage. The local densities of electronic states indicate strong hybridization between C $p$ states and neighboring Pd $d$ states leading to the formation of strong covalent $\mathrm{C}\mathrm{Pd}$ bonds. The depletion of the electronic density of states of the Pd surface atoms at the Fermi level suggests a poisoning effect of C which is found to be coverage dependent. We compare the changes in the electronic structure of Pd(211) on C adsorption with those on S adsorption.

Figure 1

Adsorption sites in Pd(211) considered in this paper.

Figure 2

Correlation between the C (bold squares) and S (empty circles) adsorption energy and the number of the adsorbate-Pd bonds extracted from the calculations performed for the adsorption sites shown in Fig. 1.

Figure 3

(Color online) Geometric structures of ${\mathrm{S}}_{0.33}∕\mathrm{Pd}\left(211\right)$ and ${\mathrm{C}}_{0.33}∕\mathrm{Pd}\left(211\right)$.

Figure 4

Valence electronic density calculated for ${\mathrm{C}}_{0.33}∕\mathrm{Pd}\left(211\right)$ with the adsorption site 1 and plotted along the plane normal to the surface and including C and BNN sites.

Figure 5

The same as in Fig. 4, but plotted along the plane normal to the surface and connecting the SC and CC sites. The nucleus of the C atom is located slightly out of the plane.

Figure 6

Valence electronic density calculated for ${\mathrm{S}}_{0.33}∕\mathrm{Pd}\left(211\right)$ with the adsorption site 1 and plotted along the plane normal to the surface and including S and BNN sites.

Figure 7

(Color online) Electronic density redistribution in ${\mathrm{C}}_{0.33}∕\mathrm{Pd}\left(211\right)$ with respect to the sum of densities of non-interacting atoms. Solid red and dashed blue lines denote the positive and negative deviation, respectively.

Figure 8

(Color online) The same as in Fig. 7, but for ${\mathrm{S}}_{0.33}∕\mathrm{Pd}\left(211\right)$.

Figure 9

Local densities of C and Pd electronic states calculated for ${\mathrm{C}}_{0.33}∕\mathrm{Pd}\left(211\right)$ with the adsorption site 1 (solid line) and for clean Pd(211) (dashed line).

Figure 10

The same as in Fig. 9, but for ${\mathrm{S}}_{0.33}∕\mathrm{Pd}\left(211\right)$.

Figure 11

Local densities of C and Pd electronic states calculated for ${\mathrm{C}}_{0.17}∕\mathrm{Pd}\left(211\right)$ with the adsorption site 1 (solid line) and for clean Pd(211) (dashed line).

Figure 12

The same as in Fig. 11, but for ${\mathrm{S}}_{0.17}∕\mathrm{Pd}\left(211\right)$.