Dear all
Could you, please, advice on the origin of these particulate contamination that appears to happen solely in the matter-containing region of the epoxy slice?
I'm investigating insect tissue under SEM and sadded by these type of contamination that precludes reliable observation of the cells under it. Attempts to switch between SE and BSE modes do not mediate the issue.
Interestingly, these contamination appears solely on the slice area that contains the embedded matter, while the epoxy-only area is free of this particulates (as you can see from the image). Also, this contamination happens to be present only in SEM images, since TEM measurements of sequential slices indicate absence of this type of artifact.
For sample prep the regular technique for tissue handling is used, incorporating several types of heavy metals.
Could this contamination origin from the atmospheric air? For instance, storage of the sample under atmosphere conditions result in attraction of the gases that induce the crystal growth from the pre-existing nucleation centers in the matter-containing region
What do you think?
Thanks!
Cheers,
Alex
With no BSE and TEM pictures it is difficult to discuss your problem. In addition I do not know what type of support do you have - Si wafer or Si TEM grid, but I suppose it is a wafer and I suppose for SEM you use much thicker slices, and it can lead to quite different results for postembedding staining, including creating of precipitates (for me more troubling is that I do not see any results of staining). Also contamination with soluble organic matter possible. BSE could really help to sort it out. Exposure of embedded tissue to air is harmless, at least for shorter periods of time, like a few years. By the way, for SEM you can use the same grids you observed with TEM. For better contrast place them not on Si, but above hole in a carbon stub, or on smooth plastic which contains nothing heavier than oxygen. One more thing - it looks like your specimens have a lot of tiny dimples, observation at higher magnifications could help to understand what it really is.
I have a question for that. What material was used for polishing? I have extensive experience in pressing abrasives into samples. EDS analysis would help.
I am assuming the actual sample is a biological, but I do not know that for sure. If staining is being done to the post sectioned material, the black specks may be caused by led staining, which can be caused by exposure of the led stain and sections to air during staining. Also, I note wrinkles in the section. Wrinkles can usually be eliminated by relaxing the section with a heat gun or heat wand while the sections are floating on the water in the knife boat. If no heat wand is available, solvent vapor can also work to relax the sections, just do not touch the sections them selves with either the heat wand or solvent.
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