Scanning Electron Microscopy and X-Ray Microanalysis

269 18

18.2.2 X-Ray Energy Database: Families of X-Rays

of X-Rays

The X-ray energy database is typically accessed through
EDS software as a display of “KLM” markers showing the
position of the peak (and possibly also the corresponding
critical ionization energies) and the relative peak heights of
the members of each X-ray family, examples of which are
seen in. Figs. 18.1, 18.2, 18.3, and 18.4. The underlying
database must contain such all characteristic X-rays (for
ionization energies up to 25 keV) for all elements (except-
ing H and He which do not produce characteristic X-rays).
No elements should be excluded, all X-ray families with
photon energies below 30 keV should be included, and no
minor X-ray family members should be excluded. As an
example, a section of the DTSA-II X-ray energy database
that displays the information for gold is presented in

. Table 18.1. While it is true that many of the closely spaced
(in photon energy) and low abundance X-ray peaks cannot

be resolved by EDS because of the limited energy resolution,

these peaks are nevertheless convolved in the measured

spectrum. When a constituent is present at high concentra-

tion and is excited with adequate overvoltage, at least some

of these low abundance family members will be readily

detectable, for example, the L 3 -M 1 (Ll) and M4,5N2,3 (Mζ)

peaks, as shown for Ba in. Fig. 18.5 and the AuM4,5N2,3,

AuM 1 N1,3 and AuM 2 N 4 peaks seen in. Fig. 18.6. Note also

that the low energy performance of the silicon drift detec-

tor (SDD)-EDS is such that the Au N- family peaks are

detected.

18.2.3 Artifacts of the EDS Detection Process

Process

The EDS detection process is subject to two principal arti-

facts that must be properly cataloged to avoid subsequent

misidentification.

BaCl 2 (on C-substrate)

E 0 = 10 keV

Photon energy (keV)

Photon energy (keV)

Counts

140 000

120 000

100 000

80 000

60 000

40 000

20 000

35 000

30 000

25 000

20 000

15 000

10 000

5 000

0

0

0.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Counts

. Fig. 18.3 EDS spectrum of BaCl 2 showing Ba L-family and Ba M-family peaks

18.2 · Principles of Qualitative EDS Analysis