contact potential

Contact potential, also known as the volta effect, refers to the difference in electrical potential that arises when two different metals are brought into contact. This occurs because electrons flow from the metal with a less tightly bound electron structure to the one with a more tightly bound structure. This flow continues until the electrostatic potential equalizes the Fermi levels of the two metals. The magnitude of this potential difference is determined by the difference in the Fermi levels of the two metals, expressed by the equation (e\phi_{12} = W_1 - W_2), where (e) is the elementary charge, (\phi_{12}) is the contact potential, and (W_1) and (W_2) are the Fermi levels of the two metals.1

Another context for contact potential is found in vacuum tubes, where it refers to the grid bias caused by electrons lodging on the grid wires. In electrochemical reactions, the interface between an electronic conductor (like an electrode) and an ionic conductor is crucial. Here, a significant electric field exists across this interface due to charge separation, creating a potential difference.23