I have been trying to look at blue silver nanoparticles (AgNPs), which are supposed to have a prism shape, on transmission electron microscopy (TEM). However, I have been seeing irregularly-shaped nanoparticles (size ~ 50 - 80 nm) for the majority of time on TEM. I do see some prism shapes but there weren't that many. These AgNPs were prepared fresh and were put on TEM grid within a few days so there should not be degradation due to aging. Also, the UV-Vis spectrum agrees with previously published papers. Just to be sure, I tried putting on AgNPs on the shiny side of the copper grid and also the dull side. I did not see the differences. Could you advise me how you would prepare AgNPs on copper grids ? Thank you!
[Silver Nanoparticles Synthesis (chemical reaction method)]
- Silver nitrate
- Trisodium citrate
- Hydrogen peroxide
- Sodium borohydride
[TEM sample preparation]
- Copper grid with formvar and carbon coated
1) 5 uL of AgNPs were put on the grid
2) Let the grid dry under air in dark
We have followed this paper and obtained good results using photo-induced conversion. The process takes approximately 7 days to complete and requires very little preparation.
I'm surprised that you're using TEM for this study of particles of 50 - 80 nm size as SEM will be perfectly adequate. TEM requires a thin slice of material typically. Have you considered that you're simply looking at different planes or slices of the prisms akin to the cubes in Claude Bragdon's A primer of higher space (the fourth dimension)?
Reference: Plate 30 in
Claude Bragdon A primer of higher space (the fourth dimension) Rochester, N.Y., The Manas Press, 1913. See attached.
I have used TEM for particles up to 100 nm without problems so don't think it will have a significant effect on what you observe.
Thank you for your response, Dr. Sokolov and Dr. Rawle!
Dr. Rawle, the thickness of these prisms are typically 20 nm or less so the electron beam can easily pass through. I also thought about the fact that I might be seeing the cross-sectional images at various angles. Fig. 1 is when I was successfully able to see many prismic AgNPs. If the AgNPs are not perfectly aligned to the plane of the grid, they will look uneven yet they still look triangle.
Fig. 2 is an example of when I see irregularly shaped AgNPs along with few prisms. Most of the particles are completely rounded. This patter was the same throughout the grid.
The same AgNP sample solution was put on to the grid for Fig. 1 and another grid for Fig 2 using the same method so the pattern of shapes should have been the same. For the majority of time, the results will look like Fig 2.
Dr. Sokolov, thank you for the paper! I will check it out.
For TEM you can actually use either side of the copper grid and it shouldn't be a problem.
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