Work Function and Inner Potential Change

The work function of a surface is the separation in energy between Ep and the vacuum level. The work function often changes when dipoles form at the surface. If the negative end of the dipole is toward the vacuum, the work function reduces, and vice versa. The mufiSn-tin inner potential constant corresponds to the net quantity of electrons around the atom [79]. For metal surfaces with chemisorbed oxygen, the work function often reduced by about 1.2 eV, and such a reduction depends on the phases and adsorbate exposures [24, 80]. 

Zhang et al. [81] detected that the work function of a Gd(OOOl) surface reduces from 3.3 to 2.5 eV upon oxygen chemisorption. Moreover, they noted that the work function decreases quickly upon exposure to oxygen and the reduction rate slows down when the oxygen coverage is over 0.5 ML. Occasionally, work function of a surface increases at higher oxygen exposures. 

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