5.2 Multiple-Bath Methods
135
Co + Cu
2+
Cu + Co
2+
, which clearly leads to a deviation of the layer thicknesses
as well as their ratio from their designed values. Hence, the synchronization of the
current source applied for the deposition of a layer with the immersion process is
recommended if the deposit can undergo a cementation reaction.
It is to be emphasized that the displacement process can take place also when
the surface is not fully covered with the more noble metal and its deposition rate as
measured with the current density is smaller than that allowed by the mass transport of the reagent (in the above example, Cu
2+ ). The Cu
2+ ions not consumed by
the current applied can freely react with the uncovered Co, hence superimposing a
cementation reaction onto the deposition. Further examples for this phenomenon and
the thoughtful application of the cementation reaction will be given in Sect. 5.3.2.
The view on the possible corrosion damage during the sample transfer was,
however, strongly denied by the authors of an early work of the field dealing with
Ni/Cu multilayers [12]. Both Cu and Ni proved to be relatively inert during the rinsing
and immersion processes, and the possibly forming monolayer-thick oxide did not
prevent an epitaxial growth of the subsequent layer (which might also be caused by
the reduction of these oxides when the cathodic current pulse was applied in the next
bath). As small as 5 nm thick layers were achieved by retaining a continuous layer
structure as seen in the cross-sectional TEM images [12]. The displacement of Ni
did not seem to be a problem for multilayers produced for mechanical studies [13].
However, it has to be noted that the resistance of both Cu and Ni to both corrosion
and cementation is rather exceptional among the metal pairs considered so far.
A few examples of the cross-sectional imaging of a few dual bath-plated multilayers can be seen in Fig. 5.1. In the two cross-sectional images of the Ni/Cu multilayers, it can be seen that the relative undulation of the layers increases as the periodicity decreases. This will later be seen also for multilayers obtained with the
single-bath method.
Originally, the alternating immersion method is rendered to be a tool for multilayer
deposition with fairly large layer thicknesses where the influence of the layer degradation during the sample transfer does not impact significantly the topmost layer
exposed to the atmosphere. For producing deposits with micrometre-scale periodicity and with a limited number of bilayers (<10 repeat periods), the alternating
immersion method can be used economically and is applied still nowadays [14]. The
application of the dual bath technique for corrosion research is quite widespread.
The thickness of the constituent layers of a multilayered deposit does not have to be
in the nanometre range but can increase up to several micrometres, although thinner
layers down to about 20–40 nm proved to be optimal. This case when the less noble
metal (or the one that is not preferentially deposited) is required as a pure metal
without any impurity. Typical layer sequences in anticorrosion coatings are Zn/Co
[15], Zn/Ni [16–18] or Zn–Fe/Ni [19].
In magnetization-related studies, one of the motivations was to study layer compositions that are difficult or impossible to obtain with the single-bath method. In one
group of such materials, a Co–Zn alloy makes either the magnetic layer (in Co–
Zn/Cu multilayers [9]) or the non-magnetic layer (in Co/Co–Zn multilayers [10,
11]). Another pursuit was to obtain Ni 80 Fe 20 (Permalloy) as a constituent without
135
Co + Cu
2+
Cu + Co
2+
, which clearly leads to a deviation of the layer thicknesses
as well as their ratio from their designed values. Hence, the synchronization of the
current source applied for the deposition of a layer with the immersion process is
recommended if the deposit can undergo a cementation reaction.
It is to be emphasized that the displacement process can take place also when
the surface is not fully covered with the more noble metal and its deposition rate as
measured with the current density is smaller than that allowed by the mass transport of the reagent (in the above example, Cu
2+ ). The Cu
2+ ions not consumed by
the current applied can freely react with the uncovered Co, hence superimposing a
cementation reaction onto the deposition. Further examples for this phenomenon and
the thoughtful application of the cementation reaction will be given in Sect. 5.3.2.
The view on the possible corrosion damage during the sample transfer was,
however, strongly denied by the authors of an early work of the field dealing with
Ni/Cu multilayers [12]. Both Cu and Ni proved to be relatively inert during the rinsing
and immersion processes, and the possibly forming monolayer-thick oxide did not
prevent an epitaxial growth of the subsequent layer (which might also be caused by
the reduction of these oxides when the cathodic current pulse was applied in the next
bath). As small as 5 nm thick layers were achieved by retaining a continuous layer
structure as seen in the cross-sectional TEM images [12]. The displacement of Ni
did not seem to be a problem for multilayers produced for mechanical studies [13].
However, it has to be noted that the resistance of both Cu and Ni to both corrosion
and cementation is rather exceptional among the metal pairs considered so far.
A few examples of the cross-sectional imaging of a few dual bath-plated multilayers can be seen in Fig. 5.1. In the two cross-sectional images of the Ni/Cu multilayers, it can be seen that the relative undulation of the layers increases as the periodicity decreases. This will later be seen also for multilayers obtained with the
single-bath method.
Originally, the alternating immersion method is rendered to be a tool for multilayer
deposition with fairly large layer thicknesses where the influence of the layer degradation during the sample transfer does not impact significantly the topmost layer
exposed to the atmosphere. For producing deposits with micrometre-scale periodicity and with a limited number of bilayers (<10 repeat periods), the alternating
immersion method can be used economically and is applied still nowadays [14]. The
application of the dual bath technique for corrosion research is quite widespread.
The thickness of the constituent layers of a multilayered deposit does not have to be
in the nanometre range but can increase up to several micrometres, although thinner
layers down to about 20–40 nm proved to be optimal. This case when the less noble
metal (or the one that is not preferentially deposited) is required as a pure metal
without any impurity. Typical layer sequences in anticorrosion coatings are Zn/Co
[15], Zn/Ni [16–18] or Zn–Fe/Ni [19].
In magnetization-related studies, one of the motivations was to study layer compositions that are difficult or impossible to obtain with the single-bath method. In one
group of such materials, a Co–Zn alloy makes either the magnetic layer (in Co–
Zn/Cu multilayers [9]) or the non-magnetic layer (in Co/Co–Zn multilayers [10,
11]). Another pursuit was to obtain Ni 80 Fe 20 (Permalloy) as a constituent without