X
spatial distortion due to foreshortening. The
true three-dimensional nature of the speci-
men can be recovered by applying the tech-
niques of stereomicroscopy, which invokes
the natural human visual process for stereo
imaging by combining two independent views
of the same area made with small angular dif-
ferences.- Other properties which can be accessed by
SEM imaging: (1) crystal structure, including
grain boundaries, crystal defects, and crystal
deformation effects (e.g.,. Fig. 8 ); (2) mag-
netic microstructure, including magnetic
domains and interfaces; (3) applied electri-
cal fields in engineered microstructures; (4)
electron-stimulated optical emission (cath-
odoluminescence), which is sensitive to low
energy electronic structure.
Measuring the Elemental
Composition
The beam interaction with the specimen produces
two types of X-ray photon emissions which com-
pose the X-ray spectrum: (1) characteristic X-rays,
whose specific energies provide a fingerprint that
is specific to each element, with the exception of H
and He, which do not emit X-rays; and (2) con-
tinuum X-rays, which occur at all photon energies
from the measurement threshold to E 0 and form a
background beneath the characteristic X-rays.
This X-ray spectrum can be used to identify and
quantify the specific elements (excepting H and
He, which do not produce X-rays) present within
the beam-excited interaction volume, which has
dimensions ranging from approximately 100 nm
to 10 μm depending on composition and beam
energy, over a wide range of concentrations (C,
expressed in mass fraction):
“Major constituent”: 0.1 < C ≤ 1
“Minor constituent”: 0.01 ≤ C ≤ 0.
“Trace constituent”: C < 0.The X-ray spectrum is measured with the semi-
conductor energy dispersive X-ray spectrometer
(EDS), which can detect photons from a threshold
of approximately 40 eV to E 0 (which can be as high
as 30 keV). Vendor software supports collection
and analysis of spectra, and these tools can be aug-
mented significantly with the open source software
National Institute of Standards and Technology
DTSA II for quantitative spectral processing and
simulation, discussed in this textbook.
Analytical software supports qualitative X-ray
microanalysis which involves assigning the char-
acteristic peaks recognized in the spectrum to
specific elements. Qualitative analysis presents
significant challenges because of mutual peak
interferences that can occur between certainSE MAG: 500 X HV: 20.0 kV WD: 11.0 mm BSE MAG: 500 X HV: 20.0 kV WD: 11.0 mm20 mm2 0 mm. Fig. 5 Topographic contrast as viewed with different detectors: Everhart–Thornley (positive bias) and semiconductor
BSE (sum mode); silver crystals; E 0 = 20 keV; Bar = 20 μm
SEM HV: 15.0 kV WD: 9.42 mm
View field: 439 mm Det: SE 100 mm. Fig. 6 Visualizing the third dimension. Anaglyph ste-
reo pair (red filter over left eye) of pollen grains on plant
fibers; E 0 = 15 keV; coated with Au-Pd; Bar = 100 μm
Scanning Electron Microscopy and Associated Techniques: Overview