Work Function, Contact Potential, and Kelvin Probe AFM

We already used the term work function when we introduced the tunneling barrier height in STM. The work function can be considered as the energy difference between the vacuum level and the Fermi level of a metal. Here we will see that also a surface term contributes to the work function. The work function is a measurable quantity and the operative definition of the work function is that it is the energy required to remove an electron from the bulk Fermi level of a metal to a certain distance from the solid.