Recently I observed a comparatively strong contrast between grains in SEM micrographs of Yttria-stabilized Zirconia (3YSZ). Microstructure is shown in the attached file.
Both samples had been grinded and polished prior to observation. Additionally the left sample had been thermal etched to expose the grain boundaries. No conductive coating has been applied. As you can see, individual adjoining grains seem to exhibit different grey values (for the unetched sample I cranked up the contrast a little). Do we observe electron channeling contrast here? The acceleration voltage is fairly low with 1.5kV, the the beam current is in the magnitude of pA and as far as I know, channeling effects produce only a weak contrast of a few percent. Furthermore, a Everhard-Thornley Detector has been used for image formation. However, I have no expertise in ECCI/ EBSD.
Can you help me interpret the image? Is ECC possible in my configuration or do I have to consider other effects? Can you link me a good example in literature? I’ve seen micrographs in literature but operation parameters are usually at much higher acceleration voltage or experiments were carried out with completely different setups. Most of the time, contrast isn’t explained at all.
Thank you in advance! I realy hope the question is not too trivial.
The SEM I use is a Zeiss Sigma(FE-SEM), ETD bias is +300V, acceleration voltage is 1.5kV, aperture size is 30 µm, Working Distance is 3.8mm.
It (the right part) looks very interesting, just like kwown by channeling contrast images excited with high energy ions (Ga). Possibly your electron primary emergy is in a range so low, which reacts sensitively on different oriented grains near the surface. If there is time I would stepwise increase the amount of primary energy, say every 500 V. If the contrast is weakening, because of signal overlay from deeper regions, then its a hint you have channeling contrast in your presented picture.
Dear Mr. Dömling,
the energy of secondary electrons amounts to some electron volt. Essential influence on the SE current have the work function and the conductivity (here electron concentration ) of the sample. To estimate the influence of the work function I would deposit a potential grid between sample and detector (or better to apply a voltage to the sample between zero potential and sample). So you construct a simple energy analyzer. Take pictures at different voltages.
With Regard
R. Mitdank
Adding material that segregates at the grain boundary of Yttria-stabilized Zirconia (3YSZ) might solve your problem.
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