  Alkali metal dosing (AMD) has been widely used as a way to control doping
without chemical substitution. This technique, in combination with angle
resolved photoemission spectroscopy (ARPES), often provides an opportunity to
observe unexpected phenomena. However, the amount of transferred charge and the
corresponding change in the electronic structure vary significantly depending
on the material. Here, we report study on the correlation between the sample
work function and alkali metal induced electronic structure change for three
iron-based superconductors: FeSe, Ba(Fe$_{0.94}$Co$_{0.06}$)$_{2}$As$_{2}$ and
NaFeAs which share a similar Fermi surface topology. Electronic structure
change upon monolayer of alkali metal dosing and the sample work function were
measured by ARPES. Our results show that the degree of electronic structure
change is proportional to the difference between the work function of the
sample and Mulliken's absolute electronegativity of the dosed alkali metal.
This finding provides a possible way to estimate the AMD induced electronic
structure change.
