Capacitor electrostatic energy

Figure 1. The tunneling of a single electron (SE) between two metal electrodes through an intermediate island (quantum dot) can be blocked of the electrostatic energy of a single excess electron trapped on the central island. In case of non-symmetric tunneling barriers (e.g. tunneling junction on the left, and ideal (infinite-resistance) capacitor on the right), this device model describes a SE box .

We now turn to the potential dependence of electrosorption of neutral molecules, considering first the model developed by Frumkin. This is a phenomenological model, which depends on considerations of the changes in the electrostatic energy of the interphase caused by adsorption. Assuming that measurements are taken in concentrated solutions of a supporting electrolyte, we can neglect diffuse-double-layer effects and focus our attention on the Helmholtz part of the double layer, considered as a parallel-plate capacitor. In the pure solvent the... 

The derivation of the Frumkin isotherm is rather involved and is not given here. We note only that it is based on ealculating the difference in electrostatic energy of charging the double-layer capacitor with and without the adsorbed species. The final result is as follows ... 

The electric capacitor provides an intuitive example of dipole because it is often used as component (dipolar) of an electric circuit and also because it is often considered as made up of two electric charges (two poles) between which an electric field is established. This is a system able to store capacitive (electrostatic) energy and to see it varying when it is connected to another dipole. 

The electrostatic energy, W, expressed in joules (J), stored in a capacitor is given by the following equation ... 

Presently, electrostatic energy analysers have fully replaced magnetic ones, since the former have many practical advantages. An electrostatic analyser consists essentially of two concentric cylindrical capacitor electrodes, that produce a well-defined radial electric field. 

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