Scanning Electron Microscopy and X-Ray Microanalysis

347 21

Si

E 0 = 20 keV

a

Coun

ts

1000000

100 000

10 000

1000

100

0.0 1.0 2.0 3.0

Photon energy (keV)

4.0 5.0 6.0 7.0 8.0 9.0 10.0

Si_20kV10nA14%DT

Si

Cr

Cu

E 0 = 20 keV

b

Count

s

1000000

100 000

10 000

1000

100

Photon energy (keV)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Si_20kV10nA14%DT

Cr_20kV10nA9%DT

Cu_20kV10nA10%DT

. Fig. 21.4 a SDD-EDS spectrum of Si (20 keV; 1000 nA-s; 0.1–20 keV = 22 million counts) with energy windows defined for Al, Cr, and Cu.
b Spectrum for Si with the spectra of Cr and Cu superimposed
. Table 21.3 Estimated limits of detection kDL for a Si
spectrum with 110 million counts (0.1–20 keV)

Element kDL ZAF CDL (mass conc) CDL (ppm)

Al 0.000115 1.12 0.000129 129

Cr 0.000133 1.01 0.000134 134

Cu 0.000113 1.00 0.000113 113

interaction volume into the K412 glass to excite secondary
fluorescence. The calculated spectrum shown in. Fig. 21.6
shows the presence of an apparent trace level of Fe (and to a
lesser extent, Ca, Si, Al, and Mg) in the Cu, corresponding to
k = 0.0028 relative to a pure Fe standard. The Fe k-ratio as a
function of beam position in the Cu is also shown in

. Fig. 21.6. Even with the beam placed in the Cu at a distance
of 40 μm from the K-412, there is an apparent Fe trace level
in the Cu of k = 0.0004, or about 400 ppm.

Range of characteristic-induced fluorescence

Range of direct electron excitation

in 75Ni-25Fe at E 0 = 25 keV

Range of secondary X-ray excitation

(characteristic fluorescence)

of Fe K-L 3 by Ni K-L 3

Ni K-L 3 in 75Ni-25Fe

10 μm

50%

75%

90%

99%

. Fig. 21.5 Range of secondary fluorescence of FeKα by NiKα in a
75Ni-25Fe alloy at E 0 = 25 keV

21.3 · Measurements of Trace Constituents by Electron-Excited Energy Dispersive X-ray Spectrometry