question that appears is at which energetic conditions e.g. applied voltage, such
reactions will be induced. Figure 2 is visualizing these conditions assuming constant
temperature.
At equilibrium no voltage is applied and no driving force for electrochemical
reactions is present. Approaching a tunnelling distance, the Fermi level of electrons
of the STM tip and the sample, or in terms of thermodynamics their electrochemical
potentials e
μ e (tip), e
μ e (Ag), equilibrate and the condition E F (tip) ¼ E F (Ag) or, respectively, e
μ e tip
ð Þ ¼ e
μ e Ag
ð Þ is fulfilled presuming no net current flow (at zero voltage).
The main potential drop is concentrated between the STM tip and RbAg 4 I 5 surface.
An applied voltage shifts the Fermi level of the STM tip relative to the sample
(ΔE F (tip) ¼ À eΔφ) and an effective tunnelling current is induced. Electrons
coming at the RbAg 4 I 5 surface with an energy lower than the Fermi energy of the
redox reaction:
Ag
þ
þ e
À
Ð Ag
ð2Þ
i.e., E F < E F (Ag
+
/Ag) can only tunnel but cannot contribute to the electrochemical
reaction.
After exceeding the energy level of E F > E F (Ag
+
/Ag) the tunnel electrons can
overcome the energy barrier for the Ag
+ /Ag redox reaction and Ag atoms will be
formed at the electrolyte surface.
At the same moment in order to keep the electroneutrality within the solid
electrolyte at the RbAg 4 I 5 /Ag interface, an equal amount of Ag (from bottom
electrode) will be oxidized to Ag
+ entering the RbAg 4 I 5 .
Fig. 2 Atomic switch (STM) configuration and energy level positions of the half-cell redox
reactions at equilibrium state. The electrochemical potential of electrons e
μ e is given by e
μ e ¼ μ e À
zeφ (μ e is their chemical potential and φ is the electric potential) and corresponds to their Fermi
energy
78
I. Valov et al.
reactions will be induced. Figure 2 is visualizing these conditions assuming constant
temperature.
At equilibrium no voltage is applied and no driving force for electrochemical
reactions is present. Approaching a tunnelling distance, the Fermi level of electrons
of the STM tip and the sample, or in terms of thermodynamics their electrochemical
potentials e
μ e (tip), e
μ e (Ag), equilibrate and the condition E F (tip) ¼ E F (Ag) or, respectively, e
μ e tip
ð Þ ¼ e
μ e Ag
ð Þ is fulfilled presuming no net current flow (at zero voltage).
The main potential drop is concentrated between the STM tip and RbAg 4 I 5 surface.
An applied voltage shifts the Fermi level of the STM tip relative to the sample
(ΔE F (tip) ¼ À eΔφ) and an effective tunnelling current is induced. Electrons
coming at the RbAg 4 I 5 surface with an energy lower than the Fermi energy of the
redox reaction:
Ag
þ
þ e
À
Ð Ag
ð2Þ
i.e., E F < E F (Ag
+
/Ag) can only tunnel but cannot contribute to the electrochemical
reaction.
After exceeding the energy level of E F > E F (Ag
+
/Ag) the tunnel electrons can
overcome the energy barrier for the Ag
+ /Ag redox reaction and Ag atoms will be
formed at the electrolyte surface.
At the same moment in order to keep the electroneutrality within the solid
electrolyte at the RbAg 4 I 5 /Ag interface, an equal amount of Ag (from bottom
electrode) will be oxidized to Ag
+ entering the RbAg 4 I 5 .
Fig. 2 Atomic switch (STM) configuration and energy level positions of the half-cell redox
reactions at equilibrium state. The electrochemical potential of electrons e
μ e is given by e
μ e ¼ μ e À
zeφ (μ e is their chemical potential and φ is the electric potential) and corresponds to their Fermi
energy
78
I. Valov et al.