Chapter 10
Electrochemical Manufacturing Methods
Based on Surface Inhomogeneities
at the Nanoscale
10.1 Pulse Sequences for the Regulation of Nucleation,
Growth and Post-deposition Treatment
When electrodeposition is used for producing nanoscale objects on foreign surface,
distinct objects can be obtained in the cases when the deposit does not form a uniform
layer at the substrate surface at the atomic scale. This means that the nucleation
and growth process is mostly of the Volmer–Weber type (see also Sect. 2.10.1).
In order to regulate the relative importance of the nucleation and growth rates and
to achieve a sufficient areal density of active nucleation sites, the application of
special pulse sequences may be necessary. A schematic overview of the possible
pulses is outlined in Fig. 10.1. Concerning the selection of the pulse potential values
and their interrelation with the cyclic voltammograms, a review of the topic can be
recommended [1]. The pulses listed therein are not applied in each single deposition
process, but some of them are related to a particular substrate type or post-deposition
sample treatment procedure, which will be discussed below.
The first pulse in Fig. 10.1 is an anodic pulse (A). This step is mostly applied
for pre-conditioning of the substrate. It is common when highly oriented pyrolytic
graphite (HOPG) is used as substrate in aqueous solutions. It is a common observation
that at highly oxidized step edges at the end of the basal plane of the graphene layers,
the nucleation of metals takes place with smaller activation energy than without
this anodic step. Nevertheless, it is ill-defined which kind of terminal functional
groups are produced with such a treatment. It is rather assumed that the terminal
groups are the same as those produced in the oxidation process of graphite, like
≡C–OH, = CO, –CHO and –COOH. Although these terminal groups can be partly
reduced in a forthcoming nucleation pulse, their reduction takes place typically at
a longer time scale than the metal nucleation on these active centres; therefore, the
oxidative treatment can provide favourable nucleation conditions for metal deposition
for a sufficiently long time period. The oxidative pre-treatment step seldom occurs
for metal-on-metal deposition processes since the metallic state of the substrate is
always a more favourable nucleation environment for another metal than a surface
© Springer Nature Switzerland AG 2021
L. Péter, Electrochemical Methods of Nanostructure Preparation,
Monographs in Electrochemistry, https://doi.org/10.1007/978-3-030-69117-2_10
323
Electrochemical Manufacturing Methods
Based on Surface Inhomogeneities
at the Nanoscale
10.1 Pulse Sequences for the Regulation of Nucleation,
Growth and Post-deposition Treatment
When electrodeposition is used for producing nanoscale objects on foreign surface,
distinct objects can be obtained in the cases when the deposit does not form a uniform
layer at the substrate surface at the atomic scale. This means that the nucleation
and growth process is mostly of the Volmer–Weber type (see also Sect. 2.10.1).
In order to regulate the relative importance of the nucleation and growth rates and
to achieve a sufficient areal density of active nucleation sites, the application of
special pulse sequences may be necessary. A schematic overview of the possible
pulses is outlined in Fig. 10.1. Concerning the selection of the pulse potential values
and their interrelation with the cyclic voltammograms, a review of the topic can be
recommended [1]. The pulses listed therein are not applied in each single deposition
process, but some of them are related to a particular substrate type or post-deposition
sample treatment procedure, which will be discussed below.
The first pulse in Fig. 10.1 is an anodic pulse (A). This step is mostly applied
for pre-conditioning of the substrate. It is common when highly oriented pyrolytic
graphite (HOPG) is used as substrate in aqueous solutions. It is a common observation
that at highly oxidized step edges at the end of the basal plane of the graphene layers,
the nucleation of metals takes place with smaller activation energy than without
this anodic step. Nevertheless, it is ill-defined which kind of terminal functional
groups are produced with such a treatment. It is rather assumed that the terminal
groups are the same as those produced in the oxidation process of graphite, like
≡C–OH, = CO, –CHO and –COOH. Although these terminal groups can be partly
reduced in a forthcoming nucleation pulse, their reduction takes place typically at
a longer time scale than the metal nucleation on these active centres; therefore, the
oxidative treatment can provide favourable nucleation conditions for metal deposition
for a sufficiently long time period. The oxidative pre-treatment step seldom occurs
for metal-on-metal deposition processes since the metallic state of the substrate is
always a more favourable nucleation environment for another metal than a surface
© Springer Nature Switzerland AG 2021
L. Péter, Electrochemical Methods of Nanostructure Preparation,
Monographs in Electrochemistry, https://doi.org/10.1007/978-3-030-69117-2_10
323