45
Hamelin and co-workers reported a detailed study of the underpotential deposition of lead on gold stepped surfaces [37]. Systematic changes in the UPD were
observed as a function of the crystallographic orientation. Figure 5.7 shows the data
for the surfaces from the [11
– 0] zone.
Adlayer structures depend on the size of substrate and adsorbate atoms, coverage, and strength of interaction. Gold has an fcc lattice, and the Au(111) surface
forms a triangular lattice with a lattice constant of 2.89
°
A. Copper atoms are smaller
than gold atoms, and they adsorb in the threefold hollow sites (see Fig. 4.1), forming
a triangular lattice commensurate with that of the substrate, that is, the lattices of the
adsorbate and of the surface layer of the substrate are related by a simple mathematical transformation – otherwise the adsorbate lattice is said to be incommensurate.
The metal adsorbates with atoms that are smaller than those of the substrate tend
to form commensurate layers, while adsorbates with bigger atoms tend to form
incommensurate monolayers. In addition, pure UPD layers tend to form close to the
bulk deposition potential, while structures at higher potentials are usually mixed
layers containing both the metal ions and anions. No alloying within the monolayer
coverage was found, in agreement with the gas phase data.
Following demonstration of the strong dependence of the UPD of metals on the
crystallographic orientation of the electrode surface, this phenomenon attracted an
unabated attention. The coverage of foreign adatoms is determined by the electrode
Fig. 5.6 Cyclic
voltammetry (a) and
charge deposited on the
electrode during Cu UPD
on Au(111) surface. The
insets show predicted
surface structures. (From
[33] with permission)
5.3 Underpotential Deposition (UPD) of Metals and Catalytic Properties of Surfaces…
Hamelin and co-workers reported a detailed study of the underpotential deposition of lead on gold stepped surfaces [37]. Systematic changes in the UPD were
observed as a function of the crystallographic orientation. Figure 5.7 shows the data
for the surfaces from the [11
– 0] zone.
Adlayer structures depend on the size of substrate and adsorbate atoms, coverage, and strength of interaction. Gold has an fcc lattice, and the Au(111) surface
forms a triangular lattice with a lattice constant of 2.89
°
A. Copper atoms are smaller
than gold atoms, and they adsorb in the threefold hollow sites (see Fig. 4.1), forming
a triangular lattice commensurate with that of the substrate, that is, the lattices of the
adsorbate and of the surface layer of the substrate are related by a simple mathematical transformation – otherwise the adsorbate lattice is said to be incommensurate.
The metal adsorbates with atoms that are smaller than those of the substrate tend
to form commensurate layers, while adsorbates with bigger atoms tend to form
incommensurate monolayers. In addition, pure UPD layers tend to form close to the
bulk deposition potential, while structures at higher potentials are usually mixed
layers containing both the metal ions and anions. No alloying within the monolayer
coverage was found, in agreement with the gas phase data.
Following demonstration of the strong dependence of the UPD of metals on the
crystallographic orientation of the electrode surface, this phenomenon attracted an
unabated attention. The coverage of foreign adatoms is determined by the electrode
Fig. 5.6 Cyclic
voltammetry (a) and
charge deposited on the
electrode during Cu UPD
on Au(111) surface. The
insets show predicted
surface structures. (From
[33] with permission)
5.3 Underpotential Deposition (UPD) of Metals and Catalytic Properties of Surfaces…