materials such as Ta 2 O 5 , HfO 2 , SiO 2 etc. turn at nanoscale from high-k materials
with insulating macroscopic properties into ionic or mixed ionic-electronic electrolytes at the nanoscale, blurring borders of macroscopic definitions for insulators,
semiconductors and electrolytes [24].
The development of the field of nanoelectrochemistry has been especially accelerated by re-discovering the resistive switching memories and their applications not
only as non-volatile memory but as building units for neuromorphic applications,
alternative logic operations and beyond von Neumann computing [25, 26]. One of
the reasons for this acceleration is the focus of both academia and industrial interest
on the nanoscale processes. In other areas where electrochemistry plays an inevitable
role such as energy conversion and storage or catalysis, industrial research and
development targets typically middle and large scale applications, whereas academia
aims microscopic understandings. In contrast, in the case of resistive switching
memoires (and the Atomic Switch as a part of it) the interest and efforts of both
academia and industry are concentrated on research and development of devices,
cells and structures with lowest possible size, fastest kinetics, and highest scalability.
This joint interest is especially productive and pushes forward the equipment
development, fundamental research and technology/applications.
In that sense the Atomic Switch is used not only for information processing and
storage, but can be a powerful tool for fundamental research of nanoscale electrochemical processes with highest precision.
3 Using the Atomic Switch
As any STM based technique, the Atomic Switch in generally can work only with
materials providing a sufficient electronic conductivity. In a macroscopic sense solid
materials (excluding metals) can be categorised as insulators, semiconductors/mixed
ionic-electronic conductors and ionic conductors. As discussed above after appropriate treatment such as doping, annealing etc., most solid thin films can be used for
STM studies. An example illustrating some of these materials related to the use of
Atomic Switch is shown in Fig. 1.
Metals and highly doped semiconductors are usual materials choice for STM
studies. However, within the Atomic Switch concept also ionic conductors and even
materials considered macroscopic insulators can be modified in a way to become
suitable for this technique without significantly changing their ionic transport characteristics and preserving their crystallographic structure.
For example RbAg 4 I 5 is a superionic solid conductor with the highest reported room
temperature ionic (Ag
+
) conductivity, being measured in the order of 0.1 Ω
–1 cm
–1
[27, 28]. It provides a very suitable model system for studies on kinetics of electrode
processes in solids. However, the low electronic conductivity of this material,
suppressing the quantum mechanical tunnelling, is in principal not supporting STM
studies. A way to avoid this restriction is using a doping approach, selectively increasing the electronic conductivity, without influencing the Ag
+ partial conductivity. It has
been shown that small amount of Fe (0.1 at.%) introduced in RbAg 4 I 5 are able to
Nanoscale Electrochemical Studies: How Can We Use the Atomic Switch
75
with insulating macroscopic properties into ionic or mixed ionic-electronic electrolytes at the nanoscale, blurring borders of macroscopic definitions for insulators,
semiconductors and electrolytes [24].
The development of the field of nanoelectrochemistry has been especially accelerated by re-discovering the resistive switching memories and their applications not
only as non-volatile memory but as building units for neuromorphic applications,
alternative logic operations and beyond von Neumann computing [25, 26]. One of
the reasons for this acceleration is the focus of both academia and industrial interest
on the nanoscale processes. In other areas where electrochemistry plays an inevitable
role such as energy conversion and storage or catalysis, industrial research and
development targets typically middle and large scale applications, whereas academia
aims microscopic understandings. In contrast, in the case of resistive switching
memoires (and the Atomic Switch as a part of it) the interest and efforts of both
academia and industry are concentrated on research and development of devices,
cells and structures with lowest possible size, fastest kinetics, and highest scalability.
This joint interest is especially productive and pushes forward the equipment
development, fundamental research and technology/applications.
In that sense the Atomic Switch is used not only for information processing and
storage, but can be a powerful tool for fundamental research of nanoscale electrochemical processes with highest precision.
3 Using the Atomic Switch
As any STM based technique, the Atomic Switch in generally can work only with
materials providing a sufficient electronic conductivity. In a macroscopic sense solid
materials (excluding metals) can be categorised as insulators, semiconductors/mixed
ionic-electronic conductors and ionic conductors. As discussed above after appropriate treatment such as doping, annealing etc., most solid thin films can be used for
STM studies. An example illustrating some of these materials related to the use of
Atomic Switch is shown in Fig. 1.
Metals and highly doped semiconductors are usual materials choice for STM
studies. However, within the Atomic Switch concept also ionic conductors and even
materials considered macroscopic insulators can be modified in a way to become
suitable for this technique without significantly changing their ionic transport characteristics and preserving their crystallographic structure.
For example RbAg 4 I 5 is a superionic solid conductor with the highest reported room
temperature ionic (Ag
+
) conductivity, being measured in the order of 0.1 Ω
–1 cm
–1
[27, 28]. It provides a very suitable model system for studies on kinetics of electrode
processes in solids. However, the low electronic conductivity of this material,
suppressing the quantum mechanical tunnelling, is in principal not supporting STM
studies. A way to avoid this restriction is using a doping approach, selectively increasing the electronic conductivity, without influencing the Ag
+ partial conductivity. It has
been shown that small amount of Fe (0.1 at.%) introduced in RbAg 4 I 5 are able to
Nanoscale Electrochemical Studies: How Can We Use the Atomic Switch
75