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
explained.
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
apparent.
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.
The promising field emission properties of carbon nanotubes, or CNTs, have resulted in them being identified as desirable sources for electron microscopes and other electron beam equipment. A new process to grow single CNTs aligned to the electron-optical axis inside electron source modules has been developed. The process involves putting the entire source-suppressor module inside a plasma-enhanced chemical vapour deposition reaction chamber. This is a process which can be scaled up to mass production. The resultant CNT electron sources were inserted into an electron microscope for imaging. Though current stability was found to be comparable to the tungsten cold-field emitter (with a maximum-minimum variation of 3-7% of the mean current over one hour), the reduced brightness was found to be an order of magnitude greater than a typical Schottky source (at 3×109 Acm2sr-1) with a kinetic energy spread of 0.28 eV. Imaging with a CNT source has produced a marked improvement in resolution when compared to a Schottky source using the same electron-optics. The properties measured show that the CNT source compares favourably with and in some cases improves upon other sources available today. In particular, the CNT source would be of most benefit to low-voltage, high-resolution microscopy.
A new type of electrostatic electron energy analyzer is described that can acquire an electron energy spectrum in 'one shot.' It uses a hyperbolic field to focus electrons emitted from a solid in the energy range 50 eV to 2500 eV into a dispersive plane of about 50 mm length. An expression for the energy resolution is given and the effect of side and base plates on the behavior of the device is discussed. The main intended area of application for this type of analyzer is parallel data acquisition in Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The potential to acquire a spectrum is just a few seconds is possible with this device.
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