The secondary electron and backscattered electron coefficients have been measured as a function of primary beam
energy for as-inserted and cleaned pure element samples. Clearly, the effect of cleaning samples makes a significant
effect on both these key measurements needed for understanding the electron transport measurements in scannng
electron microscopy and a number of other technologies. The results from the cleaned samples suggest that the currently
accepted theory for secondary electron emission (SEE) of Baroody does not take account of an important physical effect.
We propose that the SEE in transition metals is mainly controlled by the inelastic mean free path (IMFP) of the
secondary electrons. In combination with current theories on the transport of hot electrons in transition metals, where
sensitivity to the density of empty d states is important, the apparent correlation of the work function with SEE can be
The effect of errors in the electron elastic scattering cross-section and the electron stopping power on the estimates of
backscattered electron coefficient, η, are explored for the case of Cu. It is found that percentage errors in one parameter
(e.g. stopping power) cause very similar changes in η as equal but opposite percentage errors in the other parameter (e.g.
elastic scattering cross-section).
Patterned Si surfaces, p- and n-type doped, were examined for different secondary electron yield (contrast between ptype
and n-type regions) under the electron beam of a scanning electron microscope. The contrast as a function of
primary beam energy was studied for samples with a thick oxide layer and with the layer removed using an HF solution.
It was found that the contrast between p- and n- type areas reversed on the samples with a thick oxide layer as the
primary beam energy was increased. However, after the oxide layer was removed, the contrast reversal was no longer
In addition, it was also found that regions on a patterned Si sample could reverse in contrast when the scan speed of the
electron beam was changed.
The various competing theories describing the dopant contrast effect of doped semiconductors are discussed and
compared to the results reported here and elsewhere in the literature. It is concluded that oxygen at sub-monolayer
coverage through to thick films plays an important role in the dopant contrast effect. However, adventitious carbon is
equally important where a metal-oxide-semiconductor structure could exist with the presence of these two materials.
Results from the literature using other techniques such as photoemission and field emission are also considered and it
is found that these studies give results which are inconsistent with several of the current theories which attempt to
explain the dopant contrast effect.