Hello Community,
I am struggeling at the moment with the correct concept of the link between the sheet resistance of graphene and the improvement of the dirac point after a annealing step.
So what I do:
I grow graphene, transfer it (with different solvents and/or bubble transfer) onto Si/SiO2-wafer. Then I measure the sheet resistance via TLM contacts and I try to find the dirac point via gate measurements. After this procedure I anneal the sample at 150°C/300°C for 1h/3h under Argon atmosphere. After the treatment I repeat the measurement steps and compare the results. I always see the same trend:
The sheet resistance increases while the dirac point gets closer to 0V.
Now for my understanding:
When I anneal my samples I (hopefully) get rid of residues (dirt, PMMA, etc) at the samples surface. Also, I get rid of possible dopants (O2, H2O,...). If I counteract the doping, I would argue that the sheet resistance should really increase, because the conductivity of my charge carriers decreases. But if I get rid of all the PMMA I would argue that the sheet resistance should go down. I am a little bit confused why the sheet resistance increases drastically. Also I have not found any literatur where this is discussed (increase in sheet resistance while dirac gets closer to 0V --> improvement).