Etude par Sonde Atomique Tomographique de la formation de nano ...

tel-00751814, version 1 - 14 Nov 2012
Appendix 2. 3DAP sample preparation methods
Appendixes
For APT analyses, samples need to be prepared in the shape of thin needles with circular
cross section and an end radius smaller than 50 nm.
In the case of bulk/massive materials, matches-shaped samples are cut with a cross-section
of approximately 300×300 μm 2 and submitted to two main electro-chemical polishing
techniques: the “double layer” and “micro-loop” polishing methods [1].
In the case of powder grains the use of a dual beam scanning electron microscope /
focused ion beam (SEM–FIB) instrument provides an alternative method for the fabrication of
APT samples [2]. All listed methods are discussed below.
a)“Double layer” method
The principle of preparation of the tip by this method is shown in Figure 2. The anode
(sample) is plugged to a positive potential (~10…18 volts) and placed into an electrolyte
composed of 25% perchloric and 75% acetic acids floating on an inert solution (Galden). The
sample should be moved up and down in order to avoid preferential etching in the area of
"electrolyte-air" interface. After some period of time, a “neck” starts to form in the active part
of the liquid (stage 1).
Stage 1
75 % acetic acid
25% perchloric acid
Galden
Figure 2. 3DAP tip preparation by the “double layer” method (from [3]).
When the “neck” is thin and long enough, the sample is placed in a second electrolyte
composed of 2% of perchloric acid and 98% ethyleneglycol monobutyl ether. A lower tension
of 4…7 volts is then applied, until the neck breaks and the lower part of the match fall down (2
stage). If the lower part of the match is long enough, it can be used to prepare a second tip
using the“micro-loop” method (see below).
Stage 2
2 % of perchloric acid
98 % of ethylene glycol
monobutylic ether
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