For take SEM image in the BSE mode should sample surface be smooth or not necessary?
Depends on your task. For example, if you observe fracture surface and want to see phase with (significantly) higher Z - then no polishing for sure. If you are studying phase distribution then polishing is necessary (much better separation of Z contrast from topographical contrast). And so on. Just bear in mind that for not polished specimen you have not just Z contrast in BSE mode, but topographical one also.
BSE carry information about the chemical composition of the sample, and is going to give you a higher contrast (brighter for higher Z) image compared to SE mode. You can image a surface without polishing. I guess you confused the BSE mode of SEM with Electron Backscatter Diffraction EBSD.
Dear Dilek IŞIK ,
Thanks.no confuse. I know the BSE mode differ than EBSD pattern. If sample surface be rough ,doesn't make topography (SE mode ) overlap and noise in the chemical composition (BSE mode ) of the sample?
In fact the sample preparation for a SEM analysis with BSE is an issue. With a flat sample you can maximize the contrast due to chemical composition and collect a significant image. In many cases the powders are put into a resin and the surface is then flattened to reproduce the best experimetal conditions.
Depends on your task. For example, if you observe fracture surface and want to see phase with (significantly) higher Z - then no polishing for sure. If you are studying phase distribution then polishing is necessary (much better separation of Z contrast from topographical contrast). And so on. Just bear in mind that for not polished specimen you have not just Z contrast in BSE mode, but topographical one also.
Dear Vladimir Dusevich ,
thanks.for not polished specimen Z contrast in BSE mode than topographical in SEM image distinguishable?
It depends on difference in Z. For big differences even very uneven surface is not a problem. For smaller differences you may be out of luck.
Dear Vladimir Dusevich ,
thanks.have you any SEM image about your comments that send me:[email protected]
All the best,
Abbas
BSE images are used for chemical contrast therefore a flat surface is to be preferred in order to avoid absorption from topographic features in the sample. It is also true, however, that BS electrons are collected at a very high angle (close to 180° in fact they are back-scattered!), so they are not that sensitive to small topographic features and they are "bounced" back from the sample in a straight line. By contrast Secondary electrons are collected at a low angle in order to enhance topographic features (if you want to see a needle on the floor, you look and shine a light parallel to the floor).
In the long run experience will tell you how flat a sample must be for reliable results in BSE, depending on the material you are working with , naturally!
As Vladimir pointed out: it depends what you want to see.
Already the very important application of GSR (gun shot residue) shows that topography seems to be "relative". No problem at all to find the tiny particles for a later investigation by EDS if the atomic number contrast is big enough.
The first task is always ask yourself which kind of signal is collected by the detector detector. Then an answer is often quite simple and possible limitations become more clear. Qualitatively the use of BSE at fractured surfaces is useful but nobody would seriously try to interpret the reflected intensity seriously in a quantitative manner.
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