Coulomb-Blockade

Coulomb blockade is the disappearance of the electrical conductivity of a current path through a nano- object, because this can give or receive no electric charge because of its small electric capacity to the environment. The effect is named after Charles Augustin de Coulomb (1736-1806), but was only much later predicted and observed.

The nano- object may be a small conductive particles, a conductive island on insulator, or also a so-called quantum dot. It is between two conductors (sometimes in analogy with the field effect transistor called a " source " and " drain " ) arranged. The nano- object must have two sufficiently high electrical resistance can be contacted, which is done in practice by the quantum mechanical tunnel effect. That is, a small gap between the nano- object and the power lines exists; it can also be filled with an insulator. The electrons overcome the gap by tunneling.

If an electron to the nano- object over, then the voltage of the object changes to, the elementary charge and the electrical capacitance between the object and the environment ( including the two conductors ). With a sufficiently small object, this capacity may be so small that the energy required to increase the voltage would be greater than the electron energy is thermal excitation and the applied voltage. In this case, the electron energy not afford to go to the nano- object, and the current flow is blocked.

In order to observe the effect, so the capacitance between the nano- object and the environment must be very small and the temperature low enough that thermal excitations are not adequate for an electron can " recharge" the nano- object. For example, a metal island of 100 nanometers by 100 nanometers in size, which can be easily produced by current lithography technique on an oxide layer thickness of 1 nm and dielectric constant has a capacity of 10-15 farads. In order to observe this object Coulomb blockade, temperatures below 1 Kelvin are necessary; the applied voltage must be in the microvolt range. In still much smaller, but objects can be observed even at room temperature, a Coulomb-blockade.

The phenomenon of Coulomb blockade is the basis for the single-electron transistor.

• Nanotechnology
• Electrostatics