If i am depositing the TOP metal contacts of Au/Cr with the thickness 250 nm/3-5 nm. Cr is used as an adhesion layer and very thin (3-5 nm). Cr is first in contact with the film. Than how i can determine the workfunctions of the electrodes. Should i need to consider the workfunctions of the Au only or the Cr only. Or I haveto take the average of the both.
It depends on how you are using the electrodes whether the work function whether is that of the surface or the bulk material.
If I am not mistaken you are using a glass coated slide as an electrode, since only the surface is interacting with the solution the chromium does not affect the experiment (you could test this by using a different adhesion layer eg. platinum, titanium). If your setup is more like the paper you cited Fig. 2 than you will need to account for the chromium.
Hope that helps,
Chris
Only consider the surface effect, the work function of the surface is determined by the outermost layer of 1-3 atoms or molecules. So, if the electrodes works as a surface not a bulk, i think you don't need to account for the Cr. In additon, you can measure the work function of Au and Au/Cr or Au/(other adhesion layer) by KPFM to quantitatively analyze this problem.
Hope that helps,
Hao
As was pointed out before, it depends on which WF you're interested in. If you mean WF as measured from the top surface (e.g. the famous photoelectric effect experiment) then this would indeed be the WF of gold.
Since you refer to your film as a top contact, I assume that you refer to a device underneath it (e.g. this is a gate electrode, or a contact). In that case you'd be interested in the WF as "seen" by the substrate. This is often referred to as an Effective WF (EWF), especially in the context of Schottky contacts and MOS gates.
If this is indeed the case, the EWF is determined by the bottom few monolayers of the metal (i.e. a much thinner layer than your 3nm of Cr), meaning that you expect to get the EWF of Cr.
HOWEVER, this is not necessarily the case, and you need to consider several other possibilities:
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