[Wien] Calculating XPS spectra in Wien2k

[Pierre-Emmanuel Lippens]

At 11:19 18/09/2008, you wrote:
>Realy not a good idea,
>  if you have C on the surface, what C is it ? CO, hydrocarbon, 
> graphite ? All have a different binding energy of the C 1s !
>I suggest, if youre sample is not to be supposed to contain C, you 
>should clean it.


This is not my own choice (I am not XPS experimentalist) but what I 
have read in some XPS papers.

The main point: experimental calibration of the binding energy scale 
requires a reference energy.

C1s is surely not the most accurate choice. From discussions with XPS 
users: this peak is used because, if you don't clean your C free 
sample, you have C that may originate from contamination in the 
analysis chamber (vacuum pump oil) and this C is not expected to form 
chemical bonds with the sample.

But as you said in your email you can have other C on the surface and 
the reference is not expected to be very accurate.


>XPS energies have to be calibrated using the Au (or Ag) Fermi energy !!!!!

A better choice than C1s but unfortunately not used by all the XPS 
experimentalists...



>and the other question: And for an insulator when the extra 1/2 (or 
>1) electron goes into the
>conduction band and E_F changes....?
>An insulater will most probably charge if you do XPS, and the 
>energies do not tell you much.

Can we consider that charge mainly shifts the energy scale? What is 
the effect on the binding energy differences for a given sample?

Pierre