To prevent EDS detector from condensation and contamination (e.g. water and hydrocarbons) building up on the cooled silicon crystal surface of the EDS detector, in the early EDS systems the detector is usually isolated from the microscope column by a thick (8~10-μm) beryllium (Be) `window'. Removal of the Be window is possible only in an ultra-clean environment; otherwise, contaminants will degrade the performance of the EDS detector.

Table 3924 lists the transmission (absorption) of X-rays in different energy ranges by Be window. Therefore, such conventional EDS was only usable for X-rays generated from chemical elements whose atomic number is from 11 (sodium, Na) upwards. Figure 3924a shows the schematic illustration of an EDS detector. The “window” can be Be window in thickness of 7 to 12 µm. However, the Be material in the window can attenuate the x-ray signal.

Table 3924. Transmission of X-rays in different energy ranges by Be window.

Figure 3924a. Schematic illustration of EDS detector.

Furthermore, the comparison of various EDS detectors with windowless, ultra-thin window, atmospheric thin window, and beryllium window is listed on a table on page3923.

Note that, in the low energy region of the spectrum, the attenuation caused by the detector window induces an abrupt roll-off in the spectrum.

Figure 3924b shows the detection limits attainable for EDS measurements with both Be-window and windowless detectors. For low atomic numbers, the windowless EDS provides higher sensitivity, while the sensitivities for elements with high atomic numbers are the same for both detectors.