adsorption/desorption processes, structural and morphological evolutions, reconstruction of surfaces, changes in the electronic structure, etc. In two particular
situations STM can also play the active role—atomic/cluster manipulations and
the Atomic Switch. In the first case due to physical interactions and local heating
generated between tip and substrate single (or group of) atoms can be removed/
added and/or dragged on surfaces [5]. This technique has been further developed for
nanostructuring i.e. STM lithography [8–10].
The Atomic Switch is the second and maybe the latest development in applications of STM. It has been invented by Terabe et al. and uses STM for inducing
electrochemical transformations at surfaces, related with mass and charge transfer
[11–13]. This technique is applied in the information technology for storing information and performing neuromorphic operations [14, 15].
A limiting factor for the applications of STM is the requirement for the samples to
be electronically conductive. Thus, samples with insufficient electronic conductivity
e.g. insulating oxides and purely ionic solid electrolytes are in principle not accessible by this technique. To avoid the restriction, several different approaches have
been used. For example, insulating oxides can be reduced prior to STM experiments.
Reduction can be achieved either by variation of the deposition conditions, or by
annealing in reducing atmosphere. Alternatively, oxides can also be deposited very
thin (few monolayers) or can be doped with foreign elements in order to increase
their electronic conductivity to a sufficient level, however, without changing their
structure. Many examples can be found using various oxides such as NiO, SrTiO 3 ,
TiO 2 , BaO, ZnO, Nb-STO, CeO 2 etc. but also for super ionic conductors [16–22].
In this chapter the use of the STM in electrochemical studies in the role of an
active electrode will be demonstrated and discussed. Based on the Atomic Switch
approach and also using it in combination with the other STM modes this technique
provides the opportunity for site-invariant electrochemical studies with highest
lateral, mass and charge resolution, using time as critical kinetic parameter. Theoretical discussion and particular examples will highlight this application.
2 (Sub-)Nanoscale Electrochemical Studies
Electrochemical studies at the nano- and sub-nanoscale are essential for mechanistic
understandings of processes occurring in variety of applications within the fields of
energy conversion and storage, sensors, (electro)catalysis, smart devices,
nanoelectronics and information technology [23]. The small dimensions of electrodes and solid electrolytes and related small amounts of exchanged mass and
charge challenge the sensitivity of the modern equipment. In addition, electrochemical experiments in nanoscale cells are accompanied by extreme conditions: Applying voltages even in the lower range of up to 1 V, corresponds to e.g. electric fields in
the range of 10
7
–10
8 V m
–1 and current densities varying between j ~ (10
4
–10
9 )
A cm
–2 . Moreover, non-trivial effects can appear, deviating from expectations and
theories formulated for macroscopic samples. Thus, even insulating thin films of
74
I. Valov et al.
situations STM can also play the active role—atomic/cluster manipulations and
the Atomic Switch. In the first case due to physical interactions and local heating
generated between tip and substrate single (or group of) atoms can be removed/
added and/or dragged on surfaces [5]. This technique has been further developed for
nanostructuring i.e. STM lithography [8–10].
The Atomic Switch is the second and maybe the latest development in applications of STM. It has been invented by Terabe et al. and uses STM for inducing
electrochemical transformations at surfaces, related with mass and charge transfer
[11–13]. This technique is applied in the information technology for storing information and performing neuromorphic operations [14, 15].
A limiting factor for the applications of STM is the requirement for the samples to
be electronically conductive. Thus, samples with insufficient electronic conductivity
e.g. insulating oxides and purely ionic solid electrolytes are in principle not accessible by this technique. To avoid the restriction, several different approaches have
been used. For example, insulating oxides can be reduced prior to STM experiments.
Reduction can be achieved either by variation of the deposition conditions, or by
annealing in reducing atmosphere. Alternatively, oxides can also be deposited very
thin (few monolayers) or can be doped with foreign elements in order to increase
their electronic conductivity to a sufficient level, however, without changing their
structure. Many examples can be found using various oxides such as NiO, SrTiO 3 ,
TiO 2 , BaO, ZnO, Nb-STO, CeO 2 etc. but also for super ionic conductors [16–22].
In this chapter the use of the STM in electrochemical studies in the role of an
active electrode will be demonstrated and discussed. Based on the Atomic Switch
approach and also using it in combination with the other STM modes this technique
provides the opportunity for site-invariant electrochemical studies with highest
lateral, mass and charge resolution, using time as critical kinetic parameter. Theoretical discussion and particular examples will highlight this application.
2 (Sub-)Nanoscale Electrochemical Studies
Electrochemical studies at the nano- and sub-nanoscale are essential for mechanistic
understandings of processes occurring in variety of applications within the fields of
energy conversion and storage, sensors, (electro)catalysis, smart devices,
nanoelectronics and information technology [23]. The small dimensions of electrodes and solid electrolytes and related small amounts of exchanged mass and
charge challenge the sensitivity of the modern equipment. In addition, electrochemical experiments in nanoscale cells are accompanied by extreme conditions: Applying voltages even in the lower range of up to 1 V, corresponds to e.g. electric fields in
the range of 10
7
–10
8 V m
–1 and current densities varying between j ~ (10
4
–10
9 )
A cm
–2 . Moreover, non-trivial effects can appear, deviating from expectations and
theories formulated for macroscopic samples. Thus, even insulating thin films of
74
I. Valov et al.