Signals collected by bse detector comes from materials penetrated by electron beam. The higher the kV the greater the penetration. So my question is, contrast in color seen in the image due to different atomic weight of element are contributed not only from the surface but also bulk material? If this is true, for image of material with multi grains, the contrast seen on the grain is not representation of the composition of the grain? (Since, signal is also from material below the grain?)
Dear San Ty,
please have a look at the answers of a similar question from some days ago here on RG:
https://www.researchgate.net/post/How_to_analyze_colour_in_scanning_electron_microscopy_result_of_barrium_hexaferrite?_ec=topicPostOverviewFollowedQuestions
In addition to the forgoing answers in the link the BSE signal might be additionally from below (in case of small grains), but it is also influenced by surface contamination/adhesion of gas and water molecules as well as due to surface orientation, surface curvature and surface roughness. Although the BSE signal depends on the representation of the composition of the grains the compositions cannot be deduced.
You have use XPS and/or XRF, EDX for elemental and XRD for structural analysis of your grains.
At least EDX and XRD also don't image the surface only but the first few micrometers. Of course, everything depends on the energy of the radiation...the composition (NOT DENSITY!), the orientation (in case of very clean surfaces only) and on the topography. Contaminations are usually to weak in order to influence this signal, but all is relative.
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