Question

A sample of iron is observed at 25kV and the BSE image shows a uniform-toned surface. At 0.5kV, the BSE image of the same location looks very thinks they are oxidation spots. Explain why he might think that.

In the context of Scanning Electron Microscope and energy dispersive spectroscopy

Answer 1

Ans: When the sample is exposed at high energy electron beam, there is a chance of electron loss on the surface of the sample. The image we get in high energy is uniform-toned. But when the energy is lower, the surface already has the charging effect. Therefore, there seem to have darker rounded splotches on the surface. As this is an effect of charge loss, we can say it oxidation spots But in this case, the image we are focusing is back scattered image. Charging is not apparent in BSE image. And the sample is a metal. Thus the chance of charging effect in the case of metal is lowest. At high kV, the beam penetration and the diffusion can obscure fine surface structure as the BSE increased. So, lowering the beam energy make us able to see more detailed structure in the sample