8.1 The Dynamic Bubble Template Method
263
factor can take place with a suitable UPD process (mostly with noble metal deposits)
or by double-layer charging (for any metallic deposit). The surface roughness factor
commonly achieved ranges up to several hundreds.
8.1.2 Chemical Aspects of the DHBT-Plated Metals: Deposit
Types and Bath Components
Copper is by far the most common material applied in DHBT studies [1, 2, 4, 6, 7, 12,
13, 18, 21–28]. The concentration of Cu
2+ ions reported varied between 0.05–0.8 M.
This concentration range is close to that applied for other relatively inert non-noble
metals like Ni (0.1–0.2 M [10, 14, 16, 17, 29]), Co (0.1 M [14, 16]), Sn (0.15 M [30])
and Zn (0.61 M [31]). The concentration of noble metal cations was usually lower,
such as 0.02–0.1 M [19, 32] or occasionally 0.4 M [33] for Au, 50 mM for Pt [34],
14–60 mM for Pd [3] and 10–60 mM for Ag [8, 20, 35]. Porous lead foams were
obtained from solution of 0.5–20 mM Pb
2+ concentration [36], and bismuth porous
structure in the hydrogen evolution regime proved to be successfully produced from
a solution of exceptionally small metal ion concentration of 1 mM [37]. Although
it is not possible to set up a fully systematic trend, it is apparent that the larger is
the exchange current density of the metal ion/metal system, the lower metal ion
concentration is necessary. This is in good agreement with the inclination of metals
with high exchange current density to develop dendritic deposits at current densities
near to the diffusion-limited deposition regime.
If an alloy is deposited in one single step with the DHBT method, the concentration
ranges are somewhat similar to those applied for elemental metallic porous structures.
Noble metal alloys (like Au–Pt [38], Pt–Pd [39, 40] and Pd–Au [41]) are produced
from solutions of small metal ion concentrations (c < 16 mM), and the concentration
of the precursor compound for the minor component of the noble metal alloys is
often less than 1 mM. For alloys composed of metals with significantly different
deposition potentials, some bath recipes follow the trend established for bulk alloy
deposition that the concentration of the LN metal ions is considerably larger than
that of the MN metal ions. Such examples can be seen in work in Au–Cu [42], Ni–Ag
[43] and Cu–Ni [9, 44, 45] alloy deposition with the DHBT method.
In several DHBT-related studies on alloy deposits [11, 46, 47], the data published
are not detailed enough to establish a concentration ratio—deposit composition relationship. In works where the concentration ratio of the precursor compounds was
systematically varied [15, 48, 49], it can be seen that the mole fractions of the components in the deposit are a monotonous function of their precursor ion concentration
in the solution, similarly to smooth deposits. Where detailed data are available, it
can be seen that the codeposition trends established for smooth alloys cannot be
always transferred to the DHBT method. For instance, the composition diagram of
the porous DHBT-plated Ni–Co deposit showed that the anomalous codeposition
character of the Ni–Co pair is effective at small relative Co
2+ concentration only, but
263
factor can take place with a suitable UPD process (mostly with noble metal deposits)
or by double-layer charging (for any metallic deposit). The surface roughness factor
commonly achieved ranges up to several hundreds.
8.1.2 Chemical Aspects of the DHBT-Plated Metals: Deposit
Types and Bath Components
Copper is by far the most common material applied in DHBT studies [1, 2, 4, 6, 7, 12,
13, 18, 21–28]. The concentration of Cu
2+ ions reported varied between 0.05–0.8 M.
This concentration range is close to that applied for other relatively inert non-noble
metals like Ni (0.1–0.2 M [10, 14, 16, 17, 29]), Co (0.1 M [14, 16]), Sn (0.15 M [30])
and Zn (0.61 M [31]). The concentration of noble metal cations was usually lower,
such as 0.02–0.1 M [19, 32] or occasionally 0.4 M [33] for Au, 50 mM for Pt [34],
14–60 mM for Pd [3] and 10–60 mM for Ag [8, 20, 35]. Porous lead foams were
obtained from solution of 0.5–20 mM Pb
2+ concentration [36], and bismuth porous
structure in the hydrogen evolution regime proved to be successfully produced from
a solution of exceptionally small metal ion concentration of 1 mM [37]. Although
it is not possible to set up a fully systematic trend, it is apparent that the larger is
the exchange current density of the metal ion/metal system, the lower metal ion
concentration is necessary. This is in good agreement with the inclination of metals
with high exchange current density to develop dendritic deposits at current densities
near to the diffusion-limited deposition regime.
If an alloy is deposited in one single step with the DHBT method, the concentration
ranges are somewhat similar to those applied for elemental metallic porous structures.
Noble metal alloys (like Au–Pt [38], Pt–Pd [39, 40] and Pd–Au [41]) are produced
from solutions of small metal ion concentrations (c < 16 mM), and the concentration
of the precursor compound for the minor component of the noble metal alloys is
often less than 1 mM. For alloys composed of metals with significantly different
deposition potentials, some bath recipes follow the trend established for bulk alloy
deposition that the concentration of the LN metal ions is considerably larger than
that of the MN metal ions. Such examples can be seen in work in Au–Cu [42], Ni–Ag
[43] and Cu–Ni [9, 44, 45] alloy deposition with the DHBT method.
In several DHBT-related studies on alloy deposits [11, 46, 47], the data published
are not detailed enough to establish a concentration ratio—deposit composition relationship. In works where the concentration ratio of the precursor compounds was
systematically varied [15, 48, 49], it can be seen that the mole fractions of the components in the deposit are a monotonous function of their precursor ion concentration
in the solution, similarly to smooth deposits. Where detailed data are available, it
can be seen that the codeposition trends established for smooth alloys cannot be
always transferred to the DHBT method. For instance, the composition diagram of
the porous DHBT-plated Ni–Co deposit showed that the anomalous codeposition
character of the Ni–Co pair is effective at small relative Co
2+ concentration only, but