I'm synthesizing gold nanorods but in my UV-vis spectra I saw that transversal absorption is higher than the longitudinal one. Actually, in the range where the longitudinal absorption is located, there are some other "bands" and it makes me think that I have a mixture of different aspect ratios. Does the presence of difference sizes could increase the absorption of the transversal plasmon?
The position of the longitudinal mode for Au nanorods is usually very sensitive to the axis ratio (it shifts toward longer wavelengths when shape anisotropy increases).The position of the transverse mode is usually less sensitive. So if you have a polydisperse distribution of nanorods, the interpretation of the data has to be done carefully. Are the nanorods in a solution (random orientation) or grown on a substrate (with a well controlled orientation)? At which wavelengths are located the maximum of the absorption bands you have measured?
Thanks. The transversal one is located at ~535 nm and the longitudinal one at ~800nm and the nanorods are in water.
Thanks,
Indeed, all the synthesis that Im using have a large production of gold spheres, maybe Im doing something wrong on my synthesis.
Such peak positions might indeed indicate that you have a mixture of "large" spherical NPs (from Mie theory, about 60-70 nm diameter) plus rather elongated nanorods (elongated enough to make the longitudinal resonance peak in the NIR). Also the shape of the peaks might give you some info. Do you have an example of spectrum? What about the other bands you were talking about?
It is maybe due to spherical NPs is higher than NRs and also the length of NR is very less.
Usually, the longitudinal plasmon absorption band is around 800 nm while the transverse plasmon absorption band is around 535 nm. If the intensity of the transverse plasmon absorption is higher than that of the longitudinal one, there are a lot of spherical nanoparticles in the solution more than the nanorods.
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