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mie scattering off gold nanoparticle in water

Posted Nov 20, 2013, 8:04 a.m. EST Version 4.4 9 Replies

Josh Cottom
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Hi.

I have been calculating the absorption and scattering cross section from a gold nanoparticle in air correctly using the example in the model exchange:

www.comsol.com/community/exchange/215/

However when I change the medium from air to water I am seeing extremely high scattering in the forward direction of the particle to a level which cannot be accurate. To specify the water I simply change the relative permittivity to 1.7689 (from n=1.33^2) set the permeability as 1 and keep the electrical conductivity as comsol states. Does anybody know where I may be going wrong?

Also as a side question, should the thickness of the medium affect the results as I am seeing large variations depending on what I set it as?

Thanks in advance,
Josh
9 Replies Last Post May 8, 2015, 12:29 p.m. EDT
Josh Cottom
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Posted: 1 decade ago Nov 21, 2013, 11:37 a.m. EST
Updated: 7 years ago Mar 22, 2018, 9:38 a.m. EDT
I think I may have worked it out but would appreciate someone double checking that it is valid as I dont have a physics background.

When running in air I defined the plane wave as E0*exp(-j*emw.k0*x) however when replacing this with water I have to change the equation to E0*exp(-j*emw.k0*1.33*x). This includes the refractive index of water in the equation to scale the wavelength. Is this the correct thing to do?

Many thanks
Josh
I think I may have worked it out but would appreciate someone double checking that it is valid as I dont have a physics background. When running in air I defined the plane wave as E0*exp(-j*emw.k0*x) however when replacing this with water I have to change the equation to E0*exp(-j*emw.k0*1.33*x). This includes the refractive index of water in the equation to scale the wavelength. Is this the correct thing to do? Many thanks Josh
Pavel Kliuiev
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Posted: 1 decade ago Jan 7, 2014, 8:18 p.m. EST
Yes. It's correct.
Yes. It's correct.
Song
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Posted: 1 decade ago Mar 13, 2014, 9:19 a.m. EDT

I think I may have worked it out but would appreciate someone double checking that it is valid as I dont have a physics background.

When running in air I defined the plane wave as E0*exp(-j*emw.k0*x) however when replacing this with water I have to change the equation to E0*exp(-j*emw.k0*1.33*x). This includes the refractive index of water in the equation to scale the wavelength. Is this the correct thing to do?

Many thanks
Josh


Dear Josh,

I've met exactly the same problem as you, and I did not work it out for a long time. I've tried what you said, and it works. Actually, I also tried to replace emw.k0 with emw.k, which is the wavevector in medium (different for different domains), and it turns out that emw.k can not give the correct result. When you plot emw.Ebz, you will see that the field is not correctly scaled inside the Au sphere. Thus, multiplying emw.k0 with the refractive index of surrounding medium, e.g., water, is correct. I believe you did a correct job.

Thanks a lot for your sharing.

Cheers,
Song
[QUOTE] I think I may have worked it out but would appreciate someone double checking that it is valid as I dont have a physics background. When running in air I defined the plane wave as E0*exp(-j*emw.k0*x) however when replacing this with water I have to change the equation to E0*exp(-j*emw.k0*1.33*x). This includes the refractive index of water in the equation to scale the wavelength. Is this the correct thing to do? Many thanks Josh [/QUOTE] Dear Josh, I've met exactly the same problem as you, and I did not work it out for a long time. I've tried what you said, and it works. Actually, I also tried to replace emw.k0 with emw.k, which is the wavevector in medium (different for different domains), and it turns out that emw.k can not give the correct result. When you plot emw.Ebz, you will see that the field is not correctly scaled inside the Au sphere. Thus, multiplying emw.k0 with the refractive index of surrounding medium, e.g., water, is correct. I believe you did a correct job. Thanks a lot for your sharing. Cheers, Song
Jeremy Lee
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Posted: 10 years ago Apr 29, 2015, 4:26 p.m. EDT
Hello guys. Thank you so much for your previous posts. I was trying to do the same thing, and I followed your instructions. The resonance did show up at the right wavelength, however, the numbers for absorption and scattering cross-sections are off. I wonder do you guys have any idea what is going on? Hopefully you will have time to reply. Thanks a lot!
Hello guys. Thank you so much for your previous posts. I was trying to do the same thing, and I followed your instructions. The resonance did show up at the right wavelength, however, the numbers for absorption and scattering cross-sections are off. I wonder do you guys have any idea what is going on? Hopefully you will have time to reply. Thanks a lot!
Josh Cottom
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Posted: 10 years ago Apr 30, 2015, 5:07 a.m. EDT

Hello guys. Thank you so much for your previous posts. I was trying to do the same thing, and I followed your instructions. The resonance did show up at the right wavelength, however, the numbers for absorption and scattering cross-sections are off. I wonder do you guys have any idea what is going on? Hopefully you will have time to reply. Thanks a lot!


Hi,

How are you calculating the cross sections? A good model that helped me was the Scatterer on Substrate:

www.comsol.com/model/scatterer-on-substrate-14443

Take a look at the referenced equations in that to see if they help,

Regards,
Josh
[QUOTE] Hello guys. Thank you so much for your previous posts. I was trying to do the same thing, and I followed your instructions. The resonance did show up at the right wavelength, however, the numbers for absorption and scattering cross-sections are off. I wonder do you guys have any idea what is going on? Hopefully you will have time to reply. Thanks a lot! [/QUOTE] Hi, How are you calculating the cross sections? A good model that helped me was the Scatterer on Substrate: http://www.comsol.com/model/scatterer-on-substrate-14443 Take a look at the referenced equations in that to see if they help, Regards, Josh
Jeremy Lee
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Posted: 10 years ago May 1, 2015, 1:52 p.m. EDT


Hello guys. Thank you so much for your previous posts. I was trying to do the same thing, and I followed your instructions. The resonance did show up at the right wavelength, however, the numbers for absorption and scattering cross-sections are off. I wonder do you guys have any idea what is going on? Hopefully you will have time to reply. Thanks a lot!


Hi,

How are you calculating the cross sections? A good model that helped me was the Scatterer on Substrate:

www.comsol.com/model/scatterer-on-substrate-14443

Take a look at the referenced equations in that to see if they help,

Regards,
Josh


Thank you very much for your kind reply Josh. I really appreciate it. I followed that model and I got great results of sphere in a homogeneous environment. However, when I try to solve it for nanorods. The numbers are off again. I don't know if you have had similar problems before. But anyways, thank you very much for your help!

Best,

Jeremy
[QUOTE] [QUOTE] Hello guys. Thank you so much for your previous posts. I was trying to do the same thing, and I followed your instructions. The resonance did show up at the right wavelength, however, the numbers for absorption and scattering cross-sections are off. I wonder do you guys have any idea what is going on? Hopefully you will have time to reply. Thanks a lot! [/QUOTE] Hi, How are you calculating the cross sections? A good model that helped me was the Scatterer on Substrate: http://www.comsol.com/model/scatterer-on-substrate-14443 Take a look at the referenced equations in that to see if they help, Regards, Josh [/QUOTE] Thank you very much for your kind reply Josh. I really appreciate it. I followed that model and I got great results of sphere in a homogeneous environment. However, when I try to solve it for nanorods. The numbers are off again. I don't know if you have had similar problems before. But anyways, thank you very much for your help! Best, Jeremy
Josh Cottom
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Posted: 10 years ago May 5, 2015, 9:08 a.m. EDT
Hi,

If the sphere is giving correct results but the nanorods don't it may be due to having sharp corners in your geometry. Perhaps try rounding the corners, I found this gives much more accurate results for me.

Otherwise make sure the intop_vol and intop_surf variables as in the example model are for the correct geometry, or try reducing the mesh size.

Hope that helps,
Josh
Hi, If the sphere is giving correct results but the nanorods don't it may be due to having sharp corners in your geometry. Perhaps try rounding the corners, I found this gives much more accurate results for me. Otherwise make sure the intop_vol and intop_surf variables as in the example model are for the correct geometry, or try reducing the mesh size. Hope that helps, Josh
OpticsLabPupil
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Posted: 10 years ago May 5, 2015, 11:54 a.m. EDT
Well in case of nano rod you to take care of the fact that what polarization state of light you are incident .
For the polarization along the rod it would give different extinction cross section and for polarization perpendicular to the rod length it would give different extinction cross section.

Also meshing of rod effects the results effectively, because it happens with me



regards

Jalpa
Well in case of nano rod you to take care of the fact that what polarization state of light you are incident . For the polarization along the rod it would give different extinction cross section and for polarization perpendicular to the rod length it would give different extinction cross section. Also meshing of rod effects the results effectively, because it happens with me regards Jalpa
Jeremy Lee
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Posted: 10 years ago May 8, 2015, 12:29 p.m. EDT

Well in case of nano rod you to take care of the fact that what polarization state of light you are incident .
For the polarization along the rod it would give different extinction cross section and for polarization perpendicular to the rod length it would give different extinction cross section.

Also meshing of rod effects the results effectively, because it happens with me



regards

Jalpa


Thank you very much guys for your kind replies! I really appreciate it. The sad truth is that I am still not getting an expected value after taking care of all the possible factors that I can think of. I uploaded my project file here, if anyone can bother to take a look at it. I will really appreciate that!

I modified the model from the "Scattering on the Substrate" project. So there are some unnecessary variables, But I think now my model is describing "gold nanorod in water". The electric field looks fine, the rod is showing a longitudinal resonance, but the numbers are not matching the literature.(pubs.acs.org/doi/abs/10.1021/nn7003603)

Thank you very much in advance!

Best,

Jeremy
[QUOTE] Well in case of nano rod you to take care of the fact that what polarization state of light you are incident . For the polarization along the rod it would give different extinction cross section and for polarization perpendicular to the rod length it would give different extinction cross section. Also meshing of rod effects the results effectively, because it happens with me regards Jalpa [/QUOTE] Thank you very much guys for your kind replies! I really appreciate it. The sad truth is that I am still not getting an expected value after taking care of all the possible factors that I can think of. I uploaded my project file here, if anyone can bother to take a look at it. I will really appreciate that! I modified the model from the "Scattering on the Substrate" project. So there are some unnecessary variables, But I think now my model is describing "gold nanorod in water". The electric field looks fine, the rod is showing a longitudinal resonance, but the numbers are not matching the literature.(http://pubs.acs.org/doi/abs/10.1021/nn7003603) Thank you very much in advance! Best, Jeremy

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