I synthesized gold nanoparticle thin films under four conditions, three of them show agglomerated islands, like any metallic particle observed before, highly agglomerated. However this fourth condition presents with a lot of circles and round objects ( as in attachement).
what it could be this structures in your opinion? is it gold nanoparticles? why are they so monodisperesed ?
Can you provide more details about the synthesis? Like method, substrate, conditions...
It looks like normal nanoparticles created by thermal annealing (solid state dewetting) of a thin gold film. However, I am curious why they seem to be under the surface. Thus, more details will be useful.
Tomas Lednicky I used sparking discharge of gold wires, the condition in foto attached was collected nanoparticles under magnetic field and under nitrogen flow. Spark discharge is aerosol metal melt process, where we use high voltage to melt tip of wire ( electrode) and I collect them on the quartz substrate. but because I use magnetic field, they are charged and trapped, usually they are agglomerated.
Thank you, unfortunatelly I dont have any experience with this technique, but it seems plausable that you can trap them in the subtrate as they seems to be from SEM images. I just look for some papers about this technique, and it seems temperature plays a role in the agglomeration - maybe this may be your case.
To conclude, beside SEM, I would perform any chemical analysis (EDX, XPS) to be sure it is gold. Optical spectroscopy may also help, those AuNPs on quartz should have the distinguish absorbance somewhere about 600nm (blue/purple-ish look).
Yes, perform analysis EDX, XPS , as Tomas Lednicky , said, above.
What are the conditions(' differences), dear Stefan Ručman , in that 'fourth synthesis' (sample 4d.pdf) ?
Ioannis Samaras I used magnetic field and nitrogen flow, yes I did UV Vis, XPS, and EDX, it shows gold. but other 3 are clearly agglomerated.
My opinion is that the particals are thin or somehow embeded inside in the substrate. I do not know the method so I do not know if it is possible. Any way in both case can be useful to decrease the acceleration voltage (AV) of the SEM beam. 15 kV electrons can penetrate 200 nm of Au. In case the particals are thin you will see them more clearly at for example 2 kV with details of its structure (2 kV electron beam does not penetrate through 20 nm of Au). In case the particles are inside of the substrate you will lose the signal from the particles at low kV. The fact that the particles are thin is more probable, because you see them in XPS, which means the particles are on the surface.
Jakub Kolar thank you so much, so in your opinion they look fade because SEM voltage is too high?
This can be the reason. You can still see the cracks on the surface even at the "particles". This is why I believe that you are looking through the particles or the particles are under the surface. In both cases the particles can look fade and in both cases going down with AV can bring you a different view, which will help you to understand the nature of your sample.
Just to add to the nanoparticles placement/depth. You can also try angle resolve measurements for both SEM or XPS to find out where they are or if they are covered or not.
My personal opinion is they are under because cracks in the substrate are much more detailed. And I dont think you can get so thin AuNP so you can see so well through them, especially with technique that melts gold for which I would expect more or less spherical particles (not flakes). I works with 40nm thick ones and they are not "transparent".
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