SEM Contrast Dependence on Surface
Structure/Surface-topography Contrast
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SEs created at an  inclined surface or close to a surface step have an  increased probability of escape from the surface, resulting in  surface-topography contrast  [2].

Differences of energy and angular distributions of secondary electrons (SE) from reconstructed surfaces had been detected from SEs which had very low kinetic energy (normally ≤ 10 eV). For instance, SEs emitted from 7 x 7 - Si ( 111), x - Ag and 5 x 2 - Au surfaces, excited by a 15 keV primary electron beam, had been measured in an ultrahigh-vacuum (UHV) chamber [1]. SE from 7 x 7 and x-Ag surfaces showed angular dependence nearly proportional to cos (Θ), described by Equation [4832], with Θ denoting the emission angle referred to surface normal: while those from 5 x 2-Au decrease more rapidly with 0. The latter can be explained by an additional field between the sample and the detector,  resulting from the larger work function of 5 x 2-Au.

Angular dependence of secondary electron (SE) for a surface reconstructed Si

Figure 4826 (a) Angular dependence of secondary electron (SE) for surface of 7 x 7 Si( 111 ). Inset shows the experimental configuration. The primary electron (PE) beam is incident normally to the surface. [1]

 

[1] Akira Endo and Shozo Ino, Surface Science 346 (1996) 40-48.
[2] L. Reimer, Scanning Electron Microscopy, second edition, Springer, New York, 1998.

 

 

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