In your SEM picture, bumps are brighter than base material, which means they contain an element whose atomic weight is greater than zirconium and yttrium. So it can't be Al2O3, but rather HfO2, which is always present in ZrO2.

Dear Gyunam Kim

These are most likely contamination from the thermal treatment, sample processing, etc. Alternatively, these can be new grain growth or phase transformation when dealing with ZrO2.

I have to strongly disagree with Vadim Verlotski answer, as his response is predicated on the detector, which is SEI (secondary electron image) and not BEI (backscatter electron image). These bumps are bright due to the surface topography (not the elemental composition) as in the features are raised on the surface. HfO2 is extremely difficult to extract from ZrO2 due to the inherent similarities, but this is typically in solid solution with ZrO2 and separation does not typically occur on a micro level.

I would suggest to repeat the experiment and conduct EDS/EDX spot analysis on the features and the matrix for both samples, possibly before and after heat treatment to see if the features are from the treatment. I'd use this iterative process to backtrack to see where the features are coming from.

Cheers and good luck!

Dear all.

Thanks to Vadim Verlotski for your sincere answer, and I really appreciate your answer by taking your time. However, I think I must perform SEM analysis once again, by kind advice from Alec Ladonis , and EDS spot analysis will be conducted right now. I will feedback your thankful opinions soon.

Thanks!

Dear Alec Ladonis,

you are right, I made a mistake, I thought it was a BSI image. By the way, it would be interesting to see this material in BSI.

Vadim Verlotski Well, it turned out the bumpy features had slightly darker contrast comparing to ZrO2 matrix, so I am currently confused. :(

Alec Ladonis Sadly, the spot analysis data for the bumpy feature and ZrO2 matrix were exactly the same, only C (for carbon tape), O, Zr were observed. (of course for Au and Cu for sputtering and substrate, respectically).

So, It seems that these bumpy features might be an outcome from ZrO2, but I have no clue right now. Additionally, I just found out that this 5.5Y mol% ZrO2, whether thermally etched or not, both had these bumps.

The fracture surface did not have these bumps, and only the free surface they were observed. Any suggestions would be so helpful.

Thanks!

Hi Gyunam,

are you sure they are bumps, but not open pores? Depending on geometry, on SED pictures both might look pretty similar sometimes.

Dmitry Bogachov Hello. sorry for late reply. I am pretty sure that those abnormal structures are bumps, not open pores.

Vadim Verlotski Alec Ladonis Sorry for late feedback. From followed investigation, these bumpy structures might be Au nano island, which may have been derived from sputtering process before taking SEM image. Here follows a related article;

https://opg.optica.org/oe/fulltext.cfm?uri=oe-21-4-4126&id=249216

Would this 'Au nano-island' phonomenon to be plausible candidate for bumpy structure? I am looking forward to hear your opinions.

Thanks for your concerns and ideas.

Why not?! If the layer is too thick, you might have side effects like this on the surface. Worth to say that at their size on your photo, you should already be able to identify enrichment of these pimples by your sputter material with the help of EDS. Is there any noticeable difference in specta?