There are many reports in which the authors have been saying that the presence of defects in graphene are responsible for their improved conductivity and/or improved electron transfer rate, but they are not giving any details about the relationship among these three (defects. electronic conductivity and electron transfer rate constants).
In my opinion the electronic conductivity should be decreased with increasing defects as the conjugation of the sp2 skeleton will be disturbed and band gap will be introduced which makes the graphene a semi-metal and even a semiconductor too.
I would, humbly, disagree as well as agree with your view point.
But first –disagree:The conductivity should increase as:
It is attributed to the defect induced mid-gap states, which creates a region exhibiting metallic behaviour around the vacancy defects.This “ sort of” metallic behaviour is expected to increase the electrical conductivity.
An idea regarding formation of this sort of metallic bands as reported in literature looks plausible as:
Normally,a Unit cell of grapheme has two identical carbon atoms and two zero-energy states: one in which the electron resides on atom A, the other in which the electron resides on atom B. Both states exist at exactly zero energy. However, if the two atoms in the unit cell are not identical, the situation changes as it can alter the potential felt at atom A versus atom B enough for the electrons to develop a mass and accompanying band gap of about 30 meV*.The mass can be positive or negative. An arrangement that slightly raises the energy of an electron on atom A relative to atom B gives it a positive mass, while an arrangement that raises the energy of atom B produces a negative electron mass. The two versions behave alike and are indistinguishable via optical spectroscopy. An electron traveling from a positive-mass region to a negative-mass region must cross an intermediate region where its mass once again becomes zero. This region is gapless and, therefore, metallic.
Now I agree with your view point on the fact that:
[i]No details about the relationship among these three (defects. electronic conductivity and electron transfer rate constants) is available in literature.
[ii] Again, sp2 to sp3 change over should cause a decrease,BUT ,PERHAPS, THE SORT OF METALLIC CHARACTER OVERWEIGHS IT TO RESULT SOME INCREASE IN CONDUCTIVITY. Yes , it needs further investigation.
*Fuhrer, M. S. (2013). "Critical Mass in Graphene". Science340 (6139): 1413–1414.
I think there are two different effects:
1. Mobility is decreased by defects, as you say, because scattering rates are typically increased.
2. Defects in some cases can effectively behave as dopants, therefore increasing carrier concentration.
Conductivity is the product of mobility and carrier concentration, so it can either increase or decrease depending on which effect is dominant
Dear all,
would you please visit the RG-page of Dr. Mahboobeh Nosrati below, I have uploaded good reference on graphene. Regards
https://www.researchgate.net/profile/Mahboobeh_Nosrati
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