Friday, February 20, 2009

Electronic and magnetic properties of armchair and zigzag graphene nanoribbons

Frank J. Owens (2008). Electronic and magnetic properties of armchair and zigzag graphene nanoribbons The Journal of Chemical Physics, 128 (19) DOI: 10.1063/1.2905215

Another computational paper, this one exploring the differences between armchair and zigzag nanoribbons. Just like in carbon nanotubes, you can have two different kinds of graphene ribbon edges: armchair and zigzag, illustrated in the picture below from Nanotechweb.org (via Google):


Because you can draw two aromatic resonance structures for zigzag ribbons but only one aromatic resonance structure for armchair ribbons, zigzag ribbons are expected to be much more conductive (if you've taken sophomore organic chemistry, you can draw this out yourself). This paper does a little more math to prove this, using molecular orbital theory and a DFT program to look at how conductivity changes with nanoribbon width and doping with boron and nitrogen.

The author finds that increasing the nanoribbon width decreases the band gap (increases the conductivity) of armchair ribbons, just as expected. However, the zigzag ribbon band gap varies very much on whether the number of carbons used is even or odd, with zigzag ribbons with an even number of carbons having a lower bandgap than those with an odd number of carbons. This difference is attributed to the unpaired electron that comes with having an odd number of carbons.

Both types of ribbons exhibit possible ferromagnetism when doped, making them candidates to be magnetic semiconductors which could act as both storage and switching units.

EN#28
ResearchBlogging.org

5 comments:

nanoMan said...

Hi Rob,

I believe I was able to find a second resonance structure for the armchair edge. I suspected this might be the case because a piece of graphene can have both armchair ad zigzag edges. If you're still working on this perhaps you can help me find my error, or just take a look at the structures I've sketched

Anonymous said...

Can we please take this picture down or change it? It mixes up armchair and zigzag GNRs. It is also the first picture on google image. It propagates the wrong images of GNRs adding to confusion in what zigzag and armchair orientations look like.

Karan Singh said...

can you please tell me why the width of the armchair zigzag armchair grphene form is taken as odd and zigzag structure as even

Karan Singh said...
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Karan Singh said...
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