Do UPS, you can identify the work function.

From Wikipedia, the free encyclopedia

 " In solid-state physics, the work function is the minimum thermodynamic work (i.e. energy) needed to remove an electron from a solid to a point in the vacuum immediately outside the solid surface."

The electron work function is generally measured by:

1. Thermoemission;

2. Contact Potential Difference;

3. Photoemission,

" The Fermi energy is a concept in quantum mechanics usually referring to the energy difference between the highest and lowest occupied single-particle states in a quantum system of non-interacting fermions at absolute zero temperature. In a Fermi gas, the lowest occupied state is taken to have zero kinetic energy, whereas in a metal, the lowest occupied state is typically taken to mean the bottom of the conduction band."

 thanks for your contribution on uncover this issue for me

Dear Xue,

You can also take a look to an interesting discussion (and many others related)  in the following link below:

http://physics.stackexchange.com/questions/1042/how-would-i-calculate-the-work-function-of-a-metal?lq=1

wow, it is really very helpful. Thank you!