I’ve deposited thin TiO2 (~200 nm) films on SiO2 substrates. Later, Au nanoparticles were formed on the surface of TiO2 thin films. How can I observe LSPR? I measured absorbtion spectra using UV-VIS spectrophotometer and observed increase of absorbtion spectra around 630 nm. However, absorbtion spectra of thin TiO2 films without Au nanoparticles have interference fringes (minimums around ~370 nm and ~600 nm). So, how can I be sure that I observe LSPR around 630 nm. Perhaps there is a better method of measurement?
Dear Mantas,
I think one of the effective method is to measure the absorption spectrum.
In order to be sure that the increased absorption is due to the surface plasmons
you need only to change the gold nano particle size to shift its resonance frequency. If the absorption frequency shifts accordingly then this will be an evidence that the absorption is that of the gold particles.
Best wishes
Dear Mantas,
I think one of the effective method is to measure the absorption spectrum.
In order to be sure that the increased absorption is due to the surface plasmons
you need only to change the gold nano particle size to shift its resonance frequency. If the absorption frequency shifts accordingly then this will be an evidence that the absorption is that of the gold particles.
Best wishes
Dear Mantas,
Abdelhalim and Omar are right, but in the case you cannot change easily the gold particle´s size, may be you could try different approaches. There are specific techniques to measure LSPRs, like SNOM, Scanning Near Field Optical Microscopy, EELS Electron Energy Loss Spectroscopy (in this case it could be complicated if you want to keep the particles on top of your TiO2/SiO2 substrate, because EELS is a transmission technique and requires very thin films. Another technique is CL CathodeLuminiscence. All this equipment is expensive and may be is not easy to access.
Raman could provide you some qualitative information about if you have or not LSPRs, by adding some Raman active molecule to your system in low concentration, by measuring the Raman signal over a substrate without Au NP´s you should get a low intensity Raman spectrum, and when you do the same measurement over the sample with Au NP´s you should see a quite better spectrum, due to SERS, which is caused by the interaction of LSPRs with the molecules in close proximity to the AuNP´s,
Hope it helps.
Best
As I understand if you use UV-Vis Spectrophotometer it has one reference and one measurement line, using TiO2 on Silica has reference can remove the peaks due to these materials and what you will have is only effect from gold NPs. I use UV 3600 model from Shimadzu and it works pretty well.
Thank you all for the advices. They are definitely useful, but I would like to ask one more question. What do you think if I form thinner TiO2 films (50 nm - 80 nm)? Would it help to prevent interference fringes in visible spectra?
One thing you have to bear in mind is that reflectivity oscillations due to Fabry-Perot effect manifest themselves in non absorbing regions and are relatively weak due to the low F factor of the cavity. LSPR are usually very strong, and should have OD values well above these variations. You can try increasing the density of Au NPs tto see if the feature you observe near 630 nm increases, in which case you can attribute it to the LSPR
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