SPP and conductivity calculation for CNTs


#1

Hi,
I am a newbie to the field of anything here (since I am totally from computer science), but there is a requirement for me to know about a structure and its behavior when irradiated with THz EM waves. Thus as a first step, I want to calculate the conductivity of an Arm chair CNT array on a metal-dielectric-CNT structure. This will help us understand how we can have a receiving nano structure. As a first step, I am trying to have a rectangular platinum metal plate lower layer and a CNT uppet layer with a dielectric inbetween. Something like in the FIG1 here. When I tried to create 3 objects, I am not able to create a layered structure of the 3 materials. That is, I want the metal in the botto, a dielectric on it and the CNT on top of the dielectric. I am only able to design something as in the file attached here. Please help me on to start.


Thanks
Ram.


#2

Hi Ram,

Thank you for posting your question here.

I took a quick look at your file, I think the problem with the structure is that you had Metal and CNT exactly the same size. In this case, the software will only recognize one or the other, you can learn the behavior of the mesh order here (https://kb.lumerical.com/en/index.html?materials_mesh_order_optical.html). Also, if they are supposed to be structures with different geometry/dimension, you will need to modify it geometry.

What kind of results are you hoping to reproduce? I can try to see if there is any relevant examples that we have in the KB.

In the meantime, I would encourage you to watch this introductory video, if you havent done so (https://www.lumerical.com/support/courses/fdtd_introductory_webinar_video.html)


#3

Hi,

Thank you for your reply.

I am trying to know what is the behaviour of a structure like a CNT or Graphene–dielectric–Metal when triggered by a frequency, like an optical (THz). In other words, I want to know, at what frequency, my structure would resonate (Surface Plasmon Resonance) at the Graphene/CNT-Dielectric interface. I found one relevant example (https://kb.lumerical.com/en/metamaterials_graphene_absorber.html (this is the same kind of structure which we need, but I want to examine the SPR property)) and some references regarding this, but I have to build on it to suit my need.

Can you point me to some references which have examined SPR?

Thanks

Ram.


#4

The graphene model we have right now is only for a flat sheet of graphene. The current model does not have the full capability of representing a carbon nanotube.
https://kb.lumerical.com/en/index.html?other_application_graphene_simulation_tips.html

Not sure if these example are exactly what you are looking for, but I think they may be able to get you started.
https://kb.lumerical.com/en/index.html?other_application_graphene_exciting_tm_sp.html
https://kb.lumerical.com/en/index.html?other_application_exciting_a_te_surface_plasmon.html


#5

Hi,
Thanks for your reply. I have one more question. I tried building a structure and adding monitors to it, just to see the results in the layout. But I am unable to get any result on this structure and I am not sure where I am going wrong. The source and monitors seems to be right. Attached here is the project file and the text results. Please let me know where I am probably going wrong.

And how can I change the external environment permittivity? I want to mimic a liquid medium instead of vacuum. Thus I want the structure to be simulated in a water permittivity. Please let me know on these two queries. It would be helpful.
Graphene_Dielectric_Metal.fsp (667.4 KB)
Graphene_Dielectric_Metal_p0.log (3.9 KB)

Thanks


#6

Hi @narayan

Looks like there quite a few critical issues in your simulation.

There is no object in the simulation region, not even the source, nor monitors. Therefore, there simulation was not meaningful. You will need to bring the objects to inside the simulation region (the orange box).

The Pt material only has data up to about 2 um. So I am not sure if the fit has a good representation for longer wavelengths, likely not. You will probably want to find some material from literature for the longer wavelengths in order to have a good representation of the material.

Since the wavelength range is very large, the software needs to injects a long pulse. Based on the signal vs time plot, it is obvious that the simulation time is too short for the simulation. You will need to increase the “simulation time” in the FDTD region for the simulation to run reasonably.

On the other hand, I noticed that you had a very thick graphene layer (1um). This is way beyond the usual graphene thickness (~ nm). I am not sure if the graphene model will provide some good representation for graphene material to you, likely not. I guess you will need a reference to obtain some bulk material properties to represent graphene for this thickness range.

For your other questions, the background index can be changed here.

Edited file here Graphene_Dielectric_Metal.fsp (300.1 KB)

Graphene is not an easy material to work with, I can imagine that the simulation you need to deal with might have some challenges. My feedback is that you should start with something simple as an excise to learn our software. There are lot of advantages to play with some simple simulations first, easier to debug, less things to go wrong, etc. It will actually save you time down the road. I’d recommend you to play with this simple simulation, and we can discuss any questions you may have regarding this example. There is also a demo in this video which I think you should try to reproduce too. I think it isn’t the most efficient to start simulating your own model right now.

I hope this helps


#7

Thank you very much. I will try to get back after the basic tutorial.