As we know , when two different metals are connected electrically, the electrons in Metal A with higher fermi level will flow to metal B with lower fermi level. And finally their fermi level become identical.
Firstly,for my understanding,because the number of free electrons in metal Awith higher fermi level is larger than it in the metal B with lower fermi level ,then a net electrostatic field is generated and pointed from metal B to A， thus electrons flow from A to B under the E field.Is this correct?
Secondly,what happen to both metal's fermi level? Finally they are same ,A 's fermi level is pulled down of course,but what about B, is the fermi level of B also be pulled up to meet the fermi level of A in some value ,or just remain unchanged until the fermi level of A lower to the same level as B? If the fermi level of B doesn't change in this process, then where do those electrons come from A go? if those electrons just go into metal B, the number of free electrons in B must increase,then the fermil level must shift up,Is this case?Or the electrons from A don't increase the number of electrons in B ?
Electrons flow from a higher potential region to a lower potential region. As the fermi level of metal A is higher , it means that there are more energy states in A than B . Now when two metal are brought into contact, electronic flow will occur to balance the charge imbalance in the composite material therefore this flow will continue till the potential is same in both the system and that point in time, a barrier will be high enough to stop the flow of electron into B. Since B is also a metal, it has a empty conduction band, the electrons coming from A will fill this band till equilibrium is achieved.
As electrons leave metal A, the fermi level will change as it is the highest energy level occupied by electrons in a material at 0k.
Conduction band is nothing by higher orbitals like p,d,e,f etc , all of which can be filled up.
Ultimately any system in this universe wants to go to steady state or equillibrium.So,the junction between two metals will want to go to equillibrium energy state by exchanging energy between them.
The value of the fermi level for composite material will be different from that of either A alone or B because when two metals are in contact, they lose their individual characteristics unless there is some part of B or A which remain unchanged.
Dear Xiao Zhu
Yes, the electrons from the metal A will pass to metal B. That is, the number of electrons in the metal B will increase, and we will see a well-known phenomenon - contact potential difference. But not Fermi energy will become equal but chemical potentials μA and μB.
At low temperatures difference between the Fermi energy and chemical potential is negligible
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