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Detection and Imaging by Electron Microscopy
Institut für Mineralogie
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
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.
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
Topography
Material contrast
Exsolution lamellae and precipitates of bright
hematite (Fe3O4) and dark ilmenite (TiFeO4).
Intersection of a tooth shows the interface
between the gold inlay and dentin.
a
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.
Metal alloy of a aircraft turbine wing
Nickel Metal Hydride
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.
SEM in the transmission mode, kidney thin section

Cells on a semiconductor