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Detection and Imaging by Electron Microscopy
Ute Golla-Schindler, Institut für Mineralogie, D-48149 Muenster, Germany
Investigations by using electron microscopy offer the possibility to detect and image
structures in the nanoscale.
Transmission
Electron microscopy TEM
Scanning
Electron Microscopy SEM
Topography
The principle of transmission electron microscopy (TEM) is similar to
light microscopy. The imaged specimen area is illuminated at once and
can be observed with the naked eye or the signal is collected by photo
plates or a CCD camera. With TEM, structure information can be
obtained by using diffraction pattern, which allows to distinguish
between amorphous and crystalline specimen areas. High resolution
images, where atom columns can be imaged with a spatial resolution in
the range of Å are also attainable. To obtain additionally chemical
information, X-rays can be detected with an EDX detector or the
technique of energy-filtered TEM (EFTEM) can be used, which allows
the detection of monolayers and quantitative analysis in the range of nm,
especially for light elements.
Element distribution images
Material contrast
100µm
100nm
100µm
Intersection of a tooth shows the interface between the gold inlay
and dentin.
Exsolution lamellae and precipitates of bright hematite (Fe3O4) and dark ilmenite
(TiFeO4).
Fe1_I_b.pict
a
200
CCD counts x 1000
Institut für Mineralogie
In a Scanning Electron microscopy (SEM) the specimen is
scanned with a small electron probe and a simultaneous pixel by
pixel image is created. With this technique, due to the high
depth of focus, images with a three dimensional impression
which provide topographic information about the specimen
surface can be obtained, as well as material contrast information.
The achievable resolution limit is in the range of 1 nm. By
additionally collecting X-rays using an EDX (Energy dispersive
x-ray) detector, qualititative and quantitative chemical
information can be obtained down to a detection limit of 0.1%
and a resolution limit in the range of µm.
b
O K-edge
150
100
a b c
d
50
0
2µm
20 nm
Metal alloy of a aircraft
turbine wing
Nickel Metal Hydride
Cells on a semiconductor
1 µm
SEM in the transmission
mode, kidney thin section
520
540
560
Energy Loss (eV)
580
600
Collodial magnetic iron-based nanoparticles. These nanoparticles are used to enhance the
contrast between normal and diseased tissues or to indicate organ functions or blood flow. They
consist of an oxidized rim and iron core. In image (a) the rim and the core are clearly visible
and those images can be used to determine the size of each. The additional question is the
oxidation state of the rim, for which we used energy filtered TEM. Especially the near edge
structure of the O K-edge offers the possibility to distinguish between different iron oxide
minerals. Fig. (b) shows a characteristic EELS spectra of the iron oxide particles. The oxygen
K-edge displays four distinct features (a-d), where the presence of peaks at positions a and c
excludes the possibility that the rim can be FeO or -Fe2O3 respectively.
ilm
10µm
500
2 nm
High resolution TEM
HRTEM image of the interface between a large hematite
lamella and the ilmenite host. The dotted lines and small
black arrows indicate the presence of the dislocation. The
open arrow with the line show the end of the layers
affected by interface dislocations.

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