46
potential and concentration of cations in solution. The properties of adatoms have
been studied at a constant potential by various in situ optical techniques, scanning
tunneling and atomic force microscopies, and ex situ surface-physics techniques
[33]. Various overlayer lattices have been identified for different coverages of
adatoms.
A coadsorption of metal ions and anions is often observed in UPD. A wellknown system is UPD of Cu on Au(111) in sulfate solutions showing two UPD
peaks (see Fig. 5.6). The charge under the first peak corresponds to the formation of
a mixed layer of copper and sulfate. Only at the second peak near 0.03 V a monolayer of copper is adsorbed.
One of the most fascinating systems showing coadsorption in UPD deposition, in
which five ordered adlayer phases are formed, involves Tl UPD on Au(111) in the
presence of bromide anion in solution (Fig. 5.8) [38]. At the most positive potential
around 0.8 V, Br
−
is adsorbed as a rotated hexagonal adlayer. At more negative
potentials, UPD of Tl commences, Br phase gets disordered. Between two sharp
peaks, a mixed TlBr ordered adlayer (√13 × √13) forms with TlBr 2 stochiometry.
At even more negative potential, 3(3 × √3) forms, followed by c(p × √3), both with
TlBr stoichiometry. At the most negative potentials, Tl forms rotated hexagonal
phase without bromide present in ordered phase [38].
Jovic et al. have studied the influence of various anions on the thermodynamics
and kinetics of the UPD process on the Ag(111) surface [39]. The effects of perchlorate, acetate, and citrate anions on the kinetics of UPD of Pb are in line with their
adsorbability. The kinetics of the reaction in all the solutions investigated are under
mixed activation and growth control.
Fig. 5.7 UPD of Pb on Au(hkl) from surfaces in [11
– 0] zone. (From [37] with permission)
i, µA
cm =2
i, µA
cm =2
(110)
(551) = 3(110)-(111)
(331) = 3(111)-(111) = 2(110)-(111)
(221) = 4(111)-(111)
(332) = 6(111)-(111)
(111)
(554) = 10(111)-(111)
5 Important Electrosorption Reactions
potential and concentration of cations in solution. The properties of adatoms have
been studied at a constant potential by various in situ optical techniques, scanning
tunneling and atomic force microscopies, and ex situ surface-physics techniques
[33]. Various overlayer lattices have been identified for different coverages of
adatoms.
A coadsorption of metal ions and anions is often observed in UPD. A wellknown system is UPD of Cu on Au(111) in sulfate solutions showing two UPD
peaks (see Fig. 5.6). The charge under the first peak corresponds to the formation of
a mixed layer of copper and sulfate. Only at the second peak near 0.03 V a monolayer of copper is adsorbed.
One of the most fascinating systems showing coadsorption in UPD deposition, in
which five ordered adlayer phases are formed, involves Tl UPD on Au(111) in the
presence of bromide anion in solution (Fig. 5.8) [38]. At the most positive potential
around 0.8 V, Br
−
is adsorbed as a rotated hexagonal adlayer. At more negative
potentials, UPD of Tl commences, Br phase gets disordered. Between two sharp
peaks, a mixed TlBr ordered adlayer (√13 × √13) forms with TlBr 2 stochiometry.
At even more negative potential, 3(3 × √3) forms, followed by c(p × √3), both with
TlBr stoichiometry. At the most negative potentials, Tl forms rotated hexagonal
phase without bromide present in ordered phase [38].
Jovic et al. have studied the influence of various anions on the thermodynamics
and kinetics of the UPD process on the Ag(111) surface [39]. The effects of perchlorate, acetate, and citrate anions on the kinetics of UPD of Pb are in line with their
adsorbability. The kinetics of the reaction in all the solutions investigated are under
mixed activation and growth control.
Fig. 5.7 UPD of Pb on Au(hkl) from surfaces in [11
– 0] zone. (From [37] with permission)
i, µA
cm =2
i, µA
cm =2
(110)
(551) = 3(110)-(111)
(331) = 3(111)-(111) = 2(110)-(111)
(221) = 4(111)-(111)
(332) = 6(111)-(111)
(111)
(554) = 10(111)-(111)
5 Important Electrosorption Reactions