I have fabricated Ag nanoantenna arrays on glass. It consists of cylindrical nanoantennas at constant separation in symmetrical environment. I have observed a splitting of single particle resonance dip in transmission spectra when the periodicity of the array is increased.
What could be the reason behind the splitting (or two dips) in transmission spectra? I am attaching the image of the transmission spectra for three different periodicities.
Dear Upkar,
It could be related to the onset of the first diffraction order. You have a periodicity of 450nm and a glass substrate, so I assume a refractive index n = 1.5. Then, the first diffraction order should appear around 675nm, in good agreement with your data.
Regards!
Dear Miguel,
Then what about the broader dip in the lower wavelength region??
Well, there you have a mixture of modes and it is difficult to come to a conclusion without doing a field analysis. In principle, at the lower wavelength range the first order diffraction mode is propagating and it could take away some power from the zeroth-order (which I assume is the curve you are plotting)
Dear Upkar,
In your experiments, as you are decreasing the period of your nanocylinders, there is a red shift in the plasmonic resonance. It is quite expected because as you decrease the period or spacing between two plasmonic particles, their near field starts to overlap with each other. Therefore, the near field of each particle each affected by the near field of its adjacent particle and the experimental results can only explained by considering these coupled particles instead of individual.
For more details, you can go through J. Phys. Chem. B 2005, 109, 3195-3198.
Dear Arunanadan,
It is other way round here. As I am increasing the period from 350 to 450nm, the dip is moving towards longer wavelength region (as you can see from the graph).
Br,
Upkar
yes you are correct Upkar, I think that I saw the graph in hurry. For this pattern of your results, I do not have any suggestions.
Hi Upkar,
If I understand well your structure, these are two kinds of resonances due to the longitudinal and transverse nature of surface plasmon resonance (SPR) of cylindrical Ag nano rods (antenna). One is due to dipole contribution and second one a multi polar contributions.
The longer wavelength peak shift as a function of length of the rod is expectory. But in your case the length of the rod is fixed, so there should be contribution from the periodicity.
This kind of periodic plasmonic structures are well studies to great extent by prof. Jermy J.baumberg from University of Cambridge. Better your refer to their publications.
Here is the home page of the group.
http://www.phy.cam.ac.uk/people/baumbergj.php
Good luck
Sriram.G
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