What is the Work Function?: Definition and Factors that Determine the Work Function

This chapter handles the definition of the work function, the origin of the work function and factors that determine the work function. The work function is discussed based on potential energy difference of electrons between in solids and at vacuum, which results in the involvement of surface electrostatic potential. Band bending at the surface (not at the interface) is explained in the frame of surface electrostatic potential, and negative electron affinity is also explained. The influence of the image force on electronic potential is also discussed. By introducing the jellium model, which assumes solids to be uniformly distributed ion cores (positive charges) and homogenous electron gas, it is shown that the work function is comprised of two terms, bulk derived term and surface derived (surface electrostatic potential derived) term. Both terms are related to Wigner–Seitz radius. The surface derived term is further discussed in crystalline structures, as well as the influence of surface roughness. Other practical factors such as the influence of temperature on the work function and inhomogeneity of work function have also been discussed.