Junctions between Two Electronic Conductors

When metal/metal, semiconductor/semiconductor, or semiconductor/metal junctions are under consideration, the relative positions of the Fermi levels before contact or the work functions of two 

Ihe above arguments are easily applicable to semiconductor/metal and semiconductor/semiconductor junctions where the electronic energy level of both phases can also be represented by the Fermi level. The major difference between these two junctions and the metal/metal contact is that while in the case of the latter system, A 9 ( = develops only within several angstroms 

Now let us turn to the semiconductor/electrolyte interface, which is our main concern. In the electrolyte, there are no electrons nor holes but oxidized and/or reduced forms of a redox couple. Thus, the Fermi statistics developed for the solid state phase are not applicable and rather careful consideration of the electronic energy level of the electrolyte is required. 

In electrochemistry the energy level of a solution is represented by the redox potential. The measurement of the redox potential is carried out in an arrangement schematically shown in Fig. 3. The electrode M is in electrochemical equilibrium with a redox couple 

JS is a measure of the energy level of an electron in metal M with respect to that in Mi. In other words, E represents the energy level of the redox couple with respect to a reference electrode since = /if, where /Zf is the electrochemical potential of electron 

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