5.2 Multiple-Bath Methods
137
Ni–Fe/Cu multilayer for which a TEM study was published, indicating a periodicity
of about 50 nm (see also as Fig. 5.1c) [21]. It was found for each system containing
Co–Zn layers that the intermixing at the layer interfaces has a large impact on the
magnetization behaviour of the samples. Ni/Cu multilayers could also be obtained
with the sequential immersion method, which was the subject of a ferromagnetic
resonance study [22].
In the deposits containing both Co and Pt, the common goal is to achieve a high
magnetic anisotropy and a perpendicular magnetization [23, 24]. Since pure Co
cannot be deposited in a bath containing Pt, the sequential immersion approach can
be verified. In a study of Co/Pt deposits, the mean Co layer thickness was varied in
nearly monoatomic steps [23], which is a true challenge in the sequential immersion
method. High-quality cross-sectional TEM images showing the layer structure could
be obtained for repeat periods of at least 30 nm [24]. The magnetic properties were
measured as a function of both the mean Co layer thickness and the Co deposition
potential. The anisotropy energy of the deposit varied in the same manner as MBEgrown counterparts (i.e., linearly increasing anisotropy energy with decreasing Co
layer thickness), although the anisotropy energy values were different [23].
For the deposition of Co–Pt–P/Cu multilayers, the aim was to produce a thick
deposit containing the hard-magnetic Co–Pt–P layer by retaining its perpendicular
magnetic anisotropy [20, 25]. Without an “interrupting” layer, the growth of the hardmagnetic layer with a large thickness is not possible because of the grain coarsening
and the development of a texture with in-plane easy magnetization direction (hence
loosing the perpendicular anisotropy). Here, the materials properties of the Cu spacer
layer were not of importance but the Cu layer merely served as a fresh substrate for
the fine-grained Co–Pt–P deposition.
There are various other fields where the multiple-bath method gained some role.
In the case of Bi–Te/Bi–Se multilayer thin films with about 100 nm layer thicknesses,
the individual Bi 2 Te 3 and Bi 2 Se 3 crystal structures were both observed [26]. Although
the Seebeck coefficient of the laminated structure was not sensitive to the periodicity,
the electrical conductivity could be tuned, which impacts the figure of merit of
the deposit as a thermoelectric material. As the Bi–Te/Bi–Se multilayer structure
cannot be obtained from a single solution, this is also the case for metals that are
typically deposited from ionic liquids. Since codeposition from ionic liquids is yet
fully unexplored, metals plated from such media can be used for multilayer build-up
with the sequential immersion method only. The trial of obtaining Cu/Ta multilayer
showed an incomplete layer structure but was certainly an innovative step towards
obtaining non-conventional multilayered structures [27].
The possibility of plating more than two layer types in the multiple immersion
method was seldom exploited. An example is shown in the attempt of replacing
electroplated [Cu/Sn] N interconnects with a [Cu/Ni/Sn/Ni] N quadruple repeating
structure for modifying the intermixing properties of the easily miscible Cu/Sn interface [28]. This study showed that the presence of a Ni layer of about 70 nm between
the Cu and Sn layers gives rise to the formation of a ternary nanolayer due to the
room-temperature ageing of the layered system.
137
Ni–Fe/Cu multilayer for which a TEM study was published, indicating a periodicity
of about 50 nm (see also as Fig. 5.1c) [21]. It was found for each system containing
Co–Zn layers that the intermixing at the layer interfaces has a large impact on the
magnetization behaviour of the samples. Ni/Cu multilayers could also be obtained
with the sequential immersion method, which was the subject of a ferromagnetic
resonance study [22].
In the deposits containing both Co and Pt, the common goal is to achieve a high
magnetic anisotropy and a perpendicular magnetization [23, 24]. Since pure Co
cannot be deposited in a bath containing Pt, the sequential immersion approach can
be verified. In a study of Co/Pt deposits, the mean Co layer thickness was varied in
nearly monoatomic steps [23], which is a true challenge in the sequential immersion
method. High-quality cross-sectional TEM images showing the layer structure could
be obtained for repeat periods of at least 30 nm [24]. The magnetic properties were
measured as a function of both the mean Co layer thickness and the Co deposition
potential. The anisotropy energy of the deposit varied in the same manner as MBEgrown counterparts (i.e., linearly increasing anisotropy energy with decreasing Co
layer thickness), although the anisotropy energy values were different [23].
For the deposition of Co–Pt–P/Cu multilayers, the aim was to produce a thick
deposit containing the hard-magnetic Co–Pt–P layer by retaining its perpendicular
magnetic anisotropy [20, 25]. Without an “interrupting” layer, the growth of the hardmagnetic layer with a large thickness is not possible because of the grain coarsening
and the development of a texture with in-plane easy magnetization direction (hence
loosing the perpendicular anisotropy). Here, the materials properties of the Cu spacer
layer were not of importance but the Cu layer merely served as a fresh substrate for
the fine-grained Co–Pt–P deposition.
There are various other fields where the multiple-bath method gained some role.
In the case of Bi–Te/Bi–Se multilayer thin films with about 100 nm layer thicknesses,
the individual Bi 2 Te 3 and Bi 2 Se 3 crystal structures were both observed [26]. Although
the Seebeck coefficient of the laminated structure was not sensitive to the periodicity,
the electrical conductivity could be tuned, which impacts the figure of merit of
the deposit as a thermoelectric material. As the Bi–Te/Bi–Se multilayer structure
cannot be obtained from a single solution, this is also the case for metals that are
typically deposited from ionic liquids. Since codeposition from ionic liquids is yet
fully unexplored, metals plated from such media can be used for multilayer build-up
with the sequential immersion method only. The trial of obtaining Cu/Ta multilayer
showed an incomplete layer structure but was certainly an innovative step towards
obtaining non-conventional multilayered structures [27].
The possibility of plating more than two layer types in the multiple immersion
method was seldom exploited. An example is shown in the attempt of replacing
electroplated [Cu/Sn] N interconnects with a [Cu/Ni/Sn/Ni] N quadruple repeating
structure for modifying the intermixing properties of the easily miscible Cu/Sn interface [28]. This study showed that the presence of a Ni layer of about 70 nm between
the Cu and Sn layers gives rise to the formation of a ternary nanolayer due to the
room-temperature ageing of the layered system.