Scanning Microscopy


A Monte Carlo method using Mott cross-sections for elastic scattering and a modification of the Bethe continuous-slowing-down by inelastic scattering at inner- shell electrons has been used to calculate linescans across surface edges and steps using a two-detector system for SE and BSE with exit momenta to the right (detector A) and to the left (detector B). The step height h=10R, R, R/2, R/5 and R/10 (R = electron range) and the inclination angles 𝛂=30°- 80° of edges and steps have been varied to get information about the influence of these quantities on the linescans. The signals contain contributions by surface tilt contrast, electron diffusion contrast, self-shadowing of the specimen and 'mutual illumination' caused by backscattered electrons re-entering the specimen. The latter results in a larger increase of the signal for an extended step relative to a surface edge with the same angle 𝛂

The difference signals A-B contain information about the surface profile. The SE A-B signal is in first order proportional to tan 𝚽 and the BSE A-B signal is proportional to sin 𝚽 where 𝚽 denotes the local surface tilt angle. Reconstructions of the surface profile using the calculated signals show the errors caused by signal contributions different to pure surface tilt contrast.

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