Instrument bias resolution

Although most of our discussion concerns programs that process low-resolution mass spectra, this does not indicate a bias on our part for low-resolution mass spectrometry. It is attributable rather to the fact that high-resolution work requires more in the way of instrumentation, so that low-resolution spectrometers cire much more common. Hence people tend to focus their computing research toward the greater audience of low-resolution mass spectrometiists. 

In addition, the spatial distribution of the inelastically scattered electrons carries a strong forward-bias such that the majority of the signal can be collected by the on-axis post-specimen EELS spectrometer commonly employed in the AEM. This makes EELS a far more efficient technique in terms of signal collection than XEDS, where the detector samples only a tiny fraction (< 1%) of the emitted X-ray photons. An energy resolution of less than 1 eV in the EELS spectrum is readily achievable in most commonly available instrumentation a value that is far superior to the 150 eV spectral resolution of XEDS. Finally, and perhaps most uniquely, with careful analysis, the EELS spectrum can also yield information related to the electronic structure and inter-atomic bonding present in the specimen, both of which are not detectable with the XEDS technique. 

Whenever any module in the instrumental chain is altered, the system should be checked completely. Even replacing the HT bias supply, which might not be expected to alter any of the calibrations, could have unforeseen effects on the spectrometer resolution because of electromagnetic interference with the amplifier. A complete system check is the only way to ensure complete confidence in the system. 

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