Diplomarbeit Diplom-Ingenieur - Institut für Halbleiter

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For the JEM 2011 FasTEM with a Cs of 1mm and 200keV electrons with a λ of
2.5·10 -2 Å this equation leads to a resolution of 2.3 Å which is equal to the specified
resolution by JEOL [35].
3.5 Sample Preparation
The aim of sample preparation is the production of thin enough samples. Electrons
can only pass through samples thinner than about 100nm. For HRTEM imaging, the
sample must be even thinner and should be only a few nanometers thick if it should be
simple to interpret the images. The sample holder of the Jeol JEM2011 FastTem
requires samples with a diameter of 3mm. These small disks are thinned to the
necessary thickness. For a detailed description of the Sample Preparation see [40].
One distinguishes between two kinds of preparations concerning the direction of
view with respect to the layer structure of the specimen. With a cross sectional sample
(X-specimen) one looks along a direction in the plane with the layer of interest. With
a plan view (P-specimen) sample one looks along a direction perpendicular to the
layer. The material is cut with a wire saw or an ultrasonic cutting device [37]. After
the fabrication of the blank shape (for our sample holder a disk with a diameter of
3mm), it is thinned by grinding on a rotation wheel to about 150 μm. The next step is
done with the so called dimple grinder [38]. A rotating wheel grinds a dimple in the
middle of the rotating disk such that a supporting ring remains. The thinnest area is in
the middle of the dimple and is about 10 μm thick. The last step of thinning is done by
ion milling with argon ions [39] down to 10 nm or less.
The Ar ions are accelerated with 2-3kV for the sputtering process and thus result in
a heating of the sample during the thinning. The sputtering time for the thinning
process varies strongly because grinding with the dimple grinder is only accurate on
the μm scale. The transferred load of heat can cause additional annealing of the
sample. Specimens of un-annealed samples show in some case the beginning stage of
QD precipitation. But this could also be an effect of the CdTe overgrowth. The
additional transferred heat has no effect for annealed samples with QDs in the
equilibrium shape.
r
Sch = s
1
4
3
4
0. 66C
λ
(3.25)