Following this are electronics to shape the voltage into a pulse that can be counted.

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EDS spectrum for NIST glass K309 (Goldstein et al, Fig.

Associated electronics produce instantaneously a spectrum, i.e.

X-ray Relatively inexpensive; there are probably EDS detectors in the world for every 1 WDS (electron microprobe) Operator should be aware of the limitations of EDS, mainly the specific spectral artifacts, and the poor spectral resolution for some pairs of elements, and general lack of quality control of results.

Components: thin window (Be, C, B); SiLi crystal, FET (field effect transistor: initial amp), cold finger, preamp, vacuum, amp and electronics (single channel analyzer).

Be: The most common EDS detector window has been made of Be foil 7.6 mm (0.3 mil) thick.

It allows good transmission of X-rays above 1 keV.

It is strong enough to withstand venting to atmospheric pressure, and opaque to optical photons.

Thin - Ultrathin: For transmission of light element X-rays ( This plots shows the transmittance of X-rays thru different types of window material.

Quantum BN 0.25 um, diamond 0.4 um).

The higher the transmission number, the better Windowless: Here there is no film, and there is a turret that allows swapping with a Be window.

Difficult to use as oil or ice can coat the detector surface.

X-ray hits the SiLi crystal, producing a specific number of electron-hole pairs proportional to X-ray energy; e.g.

V, so for incident Fe Ka, 6404 eV, 1685 e-hole pairs are produced.

With a bias applied across the crystal, the holes are swept to one side, the electrons to the other, producing a weak charge.

This photoelectron then creates electron-hole pairs as it scatters inelastically.

If Auger, it scatters inelastically and produces electron-hole pairs.

In either case, the energy will end up as electron-hole pairs.

The result, in sum, is the conversion of all the X-rays energy into electron-hole pairs -- with 2 exceptions.

Fig 9.5 Reed; Fig 5.22 Goldstein.

Since this X-ray removes 1.74 keV of energy, the signal generated (electron-hole pairs) by the incident X-ray will be 1.74 keV LOW.

This will produce a small peak on the EDS spectrum 1.74 keV below the characteristic X-ray peak.

The Fe and Cu peaks are from excitation of metal in chamber or sample holder by BSE or Ti X-rays.

Note the sharp drop in the background intensity on the high side of the Ti Kb peak ( Ti K absorption edge, red arrow).

Ti Ka and Ti KaKb explained shortly.) Note the scale of the spectrum: the Ti Ka max is 1.3 million counts.

These effects are generally weak, but evident when you are looking for minor elements.

Then ADC (analog to digital converter) outputs data to the screen as a spectrum display.

The FET(preamplifier) changes the charge (capacitance) into a tiny voltage (millivolts).

The output of the FET is shown below at (b) where the x axis is time and y is voltage.

The jump represents the presence of a voltage proportional to the number of electron-hole pairs generated by each X-ray, so Photon 2s jump is of a higher energy than Photon 1s jump which is higher than Photon 3s jump.

Eds Peaks Table