How Are Allowed Wave Vectors Calculated in Carbon Nanotubes?

In summary, you can find the allowed wave vectors in a CNT by using an sp3s* tight binding approach and taking into account the chirality of the CNT.
  • #1
rejinisaac1
11
0
how does one find the allowed wave vectors in a CNT? I'm trying to use an sp3s* tight binding approach to compute the current through a CNT. While writing the off diagonal elements, is exp^{ik.R} a necesaary prefix? If so what value of k does one have to take?
 
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  • #2
I can't remember, but you can find a number of textbooks on the subject that will detail the process.

EDIT: My notes aren't in order about my sources but Nature Nanotechnology Vol 2 Ocober 2007 had a review article of CNT that has a large list of references. By the way, I thought graphene was sp2 bonded or is that only when it is in graphite?
 
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  • #3
i was referring to this book named 'physical properties of carbon nanotubes' by saito and dresselhaus. Page 47 of this book shows 2 vectors K1 and K2. The allowed vectors are shown parallel to K1. So are the values of K1 the allowed wave vectors of the in the first brillouin zone of the CNT under consideration? Sorry, couldn't attach the book as its around 14 MB.
 
  • #4
This depends on the chirality of the CNT. However, it is my recollection that yes, the propagation only occurs along one direction. However, the wave numbers that are allowed are more than one and are discrete. Unfortunately, I don't have complete notes on the derivation although I went over it about 6 months ago.

If you can find a 3D picture of the band structure, I believe that you will see that the the metallic CNT only has the conduction and valence bands meeting at one point (well, I think it's four points actually but I think it only counts as one point when using the Brillouin vectors. So this single point accounts for the single direction of the k vector and the periodicity of the Brillioun (How do you spell this guy's name fer crying out loud?) lattice is the cause of the discrete wave numbers that are possible I believe.

But if you are just interested in calculating the current that is dependent upon the situation. The CNT's are capable of ballistic transport, under these conditions the CNT's have zero resistance but there is a contact resistance due to the fact that there are only two conducting bands from the pi-bands. This results in a contact resistance of 12.9 kiloohms. This is only useful under specific conditions. In addition, I believe Burke has developed a transmission line model for the current if you are interested in an AC excitation. That's Peter J. Burke of UC-Irvine.
 
  • #5
The equation of the allowed wave vectors for a CNT is given by


K= k*( K1/|K1|) + nK2

-pi/T< k <=pi/T

n=0,1,2,3...N

How does one construct K ? Run a loop of k from -pi/T to pi/T for a given value of n?
 

FAQ: How Are Allowed Wave Vectors Calculated in Carbon Nanotubes?

What are the allowed wave vectors of CNT?

The allowed wave vectors of CNT, or carbon nanotubes, are determined by the size and structure of the tube. They can range from 0 to 2π/a, where a is the lattice parameter of the tube. This range is known as the first Brillouin zone.

How are wave vectors related to the electronic structure of CNT?

The electronic structure of CNT is closely related to the allowed wave vectors. The electronic band structure of CNT is determined by the periodicity of the tube, which is related to the allowed wave vectors in the first Brillouin zone.

What is the significance of the allowed wave vectors in CNT?

The allowed wave vectors in CNT play a crucial role in determining the electronic and optical properties of the tube. They also determine the symmetry of the tube, which can affect its mechanical and thermal properties.

How do the allowed wave vectors differ between metallic and semiconducting CNT?

The allowed wave vectors for metallic and semiconducting CNT differ due to their different electronic band structures. Metallic CNT have a continuous band structure, allowing for a larger range of allowed wave vectors, while semiconducting CNT have a band gap, limiting their allowed wave vectors.

Can the allowed wave vectors of CNT be modified?

Yes, the allowed wave vectors of CNT can be modified through different methods such as doping or strain engineering. These modifications can alter the electronic and optical properties of the tube, making it a promising area of research for potential applications in nanoelectronics and optoelectronics.

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