[La-Lu]

I have been trying to look into this for a good while. I think I have read every paper on this topic back to the 60s. What I have been able to figure out until now:

- Electropositive material implantation/adsorption into/on a sample surface lowers the work function.
- This is because a positive electric dipole layer is formed at the surface.

But WHY does the work function become lower, in terms of how are the electrons/charge densities actually causing this??

I am getting into all sorts of different subtopics (DFT, Smoluchowski effect, quantum stuff...) but I think there muse be an easy explanation. Like some very basic chemistry rule that I am overlooking or something. Probably I am simply too ignorant on the basics. I would really appreciate if someone could point me in the right direction.

Thank you in advance.