...I wish to give an account of some investigations
led to the conclusion that the carriers of negative electricity are bodies,
which I have called corpuscles, having a mass very much smaller than that
of the atom of any known element, and are of the same character from
whatever source the negative electricity may be derived.
Joseph John Thomson from his Nobel Prize Award Address, 1906
We talk about single-electronics whenever it is possible to control the movement and position of a single or small number of electrons. To understand how a single electron can be controlled, one must understand the movement of electric charge through a conductor. An electric current can flow through the conductor because some electrons are free to move through the lattice of atomic nuclei. The current is determined by the charge transferred through the conductor. Surprisingly this transferred charge can have practically any value, in particular, a fraction of the charge of a single electron. Hence, it is not quantized.
This, at first glance counterintuitive fact, is a consequence of the displacement of the electron cloud against the lattice of atoms. This shift can be changed continuously and thus the transferred charge is a continuous quantity (see left side of Fig. 1.1).
If a tunnel junction interrupts an ordinary
conductor, electric charge will
move through the system by both a continuous and discrete process. Since
only discrete electrons can tunnel through junctions, charge will
accumulate at the surface of the electrode against the isolating layer,
until a high enough bias has built up across the tunnel junction (see
right side of Fig. 1.1). Then one electron will be
transferred. K. Likharev  has coined the term
as an analogy of this process. In other words, if a single tunnel
junction is biased with a constant current I, the so called
Coulomb oscillations will
appear with frequency f = I/e,
where e is the charge of an electron
(see Fig. 1.2).
The current biased tunnel
junction is one very simple circuit, that shows the controlled transfer
of electrons. Another one is the electron-box
(see Fig. 1.3).
It is easily understandable, that these single-electron phenomena, such as Coulomb oscillations and
Coulomb blockade, only matter, if the Coulomb energy is bigger than the
thermal energy. Otherwise
thermal fluctuations will disturb the motion of
electrons and will wash
out the quantization effects. The necessary condition is
where kB is Boltzmann's constant and T is the absolute temperature. This means that the capacitance C has to be smaller than 12 aF for the observation of charging effects at the temperature of liquid nitrogen and smaller than 3 aF for charging effects to appear at room temperature. A second condition for the observation of charging effects is, that quantum fluctuations of the number of electrons on an island must be negligible. Electrons need to be well localized on the islands. If electrons would not be localized on islands one would not observe charging effects, since islands would not be separate particles but rather one big uniform space. The charging of one island with an integer number of the elementary charge would be impossible, because one electron is shared by more than one island. The Coulomb blockade would vanish, since no longer would a lower limit of the charge, an island could be charged with, exist. This leads to the requirement that all tunnel junctions must be opaque enough for electrons in order to confine them on islands. The `transparency' of a tunnel junction is given by its tunnel resistance RT which must fulfill the following condition for observing discrete charging effects
where h is Planck's constant. This should be understood as an order-of-magnitude measure, rather than an exact threshold.
Therefore, these effects are experimentally verifiable only for very small high-resistance tunnel junctions, meaning small particles with small capacitances and/or very low temperatures. Advanced fabrication techniques, such as the production of granular films with particle sizes down to 1 nm, and deeper physical understanding allow today the study of many charging effects at room temperature .
Based on the Coulomb blockade many interesting devices are possible, such as precise current standards , very sensitive electrometers , logic gates  , and memories   with ultra low power consumption, down-scalability to atomic dimensions, and high speed of operation. Altogether, single-electronics will bring new and novel devices and is a very promising candidate to partly replace MOS technology in the near future.