Scanning Electron Microscopy and X-Ray Microanalysis

390

23

only of the X-ray bremsstrahlung that occurs at all photon ener-

gies, Eν, up to the incident beam energy, E 0 (Duane–Hunt limit).

Inspecting this spectrum starting at high photon energy, as the

photon energy Eν decreases, the intensity of the continuum, Icm,

increases, a consequence of the physics of the generation of the

bremsstrahlung, which has the following form:

Iicm≈ BZE()Ev

.

0 / −^1

(23.2)

where iB is the beam current, and Ż is the average atomic

number of the target. For a given material, the mass

absorption coefficient increases as the photon energy

decreases. Absorption is an exponential effect, so that even-

tually the increased absorption overwhelms the increase in

the continuum intensity so that the intensity reaches a max-

imum. For boron with E 0 = 20 keV this maximum occurs at

approximately 1.3 keV. Because of the effect on the electron

range and the subsequent X-ray absorption, the exact loca-

tion of the maximum in bremsstrahlung intensity depends

on beam energy as well as the specific element(s) acting as

the absorber. Moreover, for complex compositions the

numerous characteristic peaks are superimposed on the

Fe

(n

ormali

ze

d weight

percent)

1 s

0

10

20

30

40

50

60

70

80

020406080100 120140

Bulk K411 All Geometries

Raw analytical to tal (weight percent)

Analysis with a compromised sample shape: raw analytical total for all forms

Analysis of K411: Bulk polished and All Geometries

Raw analytical total (weight percent)

Mg (normali

ze

d we

ight

pe

rcent)

Analysis of K411: Bulk polished and All Geometries

1 s

0

2

4

6

8

10

12

020406080100 120 140

Bulk K411

All Geometries

a

b

. Fig. 23.11 Calculated nor-
malized concentrations as a
function of the raw analytical
total from the suite of spectra
obtained from the various geo-
metric shapes: a Fe, b Mg

Chapter 23 · Analysis of Specimens with Special Geometry: Irregular Bulk Objects and Particles