• SEs provide information on the surface topography of the sample.• If a SE is generated close to the sample surface, it can leave the sample with a high probability and can be collected at the detector.• SEs generated deep in the sample's volume will be absorbed with a high probability and cannot escape to the detector.• The features of the sample cause a variation in the secondary electrons yield and accounts for direct information on the topography.• The contrast of secondary electron images depends mainly on the tilt angle and topography of the specimen surface.