EDS Windows: Past, Present, and Future

Dr. Patrick Camus, Director of Research and Innovation

EDS window

Silicon Nitride Window on SDD

For many years, the only x-ray window material available for EDS was Be. These performed well for energies above ~2keV but in SEM and STEM, low x-ray energy performance was non-existent. For select STEM applications, windowless installations became the norm.

Then alternative materials with low x-ray energy transmission became available, including BN and diamond. Ultimately ultrathin polymer windows became the standard for both SEM and STEM installations. TEM windowless were still an option, but cleanliness with cryogenically-cooled SiLi detectors and oil diffusion pumps still caused reliability problems.

With the advent of SDD performance, including reduced cooling needs, windowless operation is once again becoming fashionable for STEM and is a consideration for SEM. The use of an oil-free pumping system on the microscope is a true reliability advantage for the SDD.

But cooled detectors can still become contaminated with enough age. When they do, they must be fully replaced. Is there a better choice between windowless and ultrathin polymer windows on SDD?

A new material for windows is being produced which has more low x-ray energy transmission than polymer but is still not as good as windlowless, but it affords more safety for the SDD: Silicon nitride. Preliminary tests indicate a 2-5x increase in low x-ray energy intensity and stable mechanical and chemical stability.

Look for these windows on select SDDs for specialized applications.

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