Electron backscattering from real and in-situ treated surfaces

Significant differences in backscattered electron (BSE) yields exist betwee n the surfaces cleaned by methods used in electron microscopy and spectrosc opy. These differences have been observed for Au, Cu and Al specimens, and are interpreted on the basis of simulated BSE yields. Composition and thick ness of the surface contamination layers, responsible for the differences, are estimated. The results (7 nm of carbon on Au or 3 nm of oxide on Al) re main within expectation and indicate that the BSE yield measurements and BS E images should be interpreted cautiously. Peculiar results are obtained fo r Cu, perhaps due to a different cleaning procedure, A new concept of an in formation depth for the BSE signal is introduced as a depth within which th e total BSE yield can be modelled as composed of the yields of layers propo rtional to their. thickness weighted by the escape depths. This concept pro ved satisfactory for thin surface layers and brought the information depth values 2 to 4 times smaller than first estimated, i.e. half the penetration depth.