QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: simCity on July 11, 2013, 12:29

Title: Contact resistance of graphene-Ni interface
Post by: simCity on July 11, 2013, 12:29

Hi,

I read the tutorial on the contact resistance of graphene-Ni interface (http://quantumwise.com/publications/tutorials/builder/174-graphene-nickel-interface).

I tried to do the same simulation and got 8,97009044626000e-06 A current for 0.1 V meaning that the resistance is 1.1148e+004 Ohms. However I couldn't understand if I did it right as I couldn't see a resistance value in the mentioned paper (http://arxiv.org/pdf/1202.0171v2.pdf). The graphene and nickel contact overlap length is 3.74 Angstrom. Is my result consistent with the results of the mentioned paper?

Thanks in advance,
Jim

Title: Re: Contact resistance of graphene-Ni interface
Post by: Anders Blom on July 21, 2013, 23:19

In the full paper in Phys. Rev. B. 85, 165442 (2012) we compute the resistance to be about 600 Ohm*micrometer. The model in the tutorial is slightly different.

Title: Re: Contact resistance of graphene-Ni interface
Post by: simCity on July 23, 2013, 09:07

Thank you for your answer.

However if the contact resistance is expected to be around 600Ohm*um according to ATK results then for 3.74 Angstrom of contact length, the resistance is calculated as: (600Ohm*micrometer)/(3.74E-4micrometer)=1.6Megaohms, right?. But in my simulation what ATK calculated was 8,97009044626000e-06 A current for 0.1 V meaning that the resistance is 1.1148e+004 Ohms. Hence could you please give an idea where this difference comes from?

Thanks in advance.

Title: Re: Contact resistance of graphene-Ni interface
Post by: Anders Blom on August 1, 2013, 00:09

The contact resistance is estimated from the zero-bias conductance, using Eq. (1) in PRB 85, 165442 (2012), and not from the I-V curve. Even so, any difference to your results can be due to many reasons, like different geometry, different k-point sampling and other parameters, and even different basis sets.

Title: Re: Contact resistance of graphene-Ni interface
Post by: kstokbro on August 1, 2013, 12:49

Our contact resistance is calculated in the linear response regime, thus, you should reproduce our value for a very small bias, let say 0.01 Volt.

The graphene is a semi-metal, and to describe the transmission spectrum around the fermi level requires many k-points. You need to check the convergence of transmission spectrum with k-point sampling, we used several hundred k-points.

Title: Re: Contact resistance of graphene-Ni interface
Post by: Anders Blom on August 1, 2013, 13:05

And we used a customized basis set. Perhaps we could publish it, but I don't have the Python code for it. Do you have it, Kurt?

Title: Re: Contact resistance of graphene-Ni interface
Post by: simCity on September 20, 2013, 09:09

Thanks, I'll give a try for the small voltage values as you pointed out...