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

tel-00751814, version 1 - 14 Nov 2012
Appendixes
Preparation of the pre-tip. The pre-tip is special tip on which a powder grain is maintained
(see Figure 4 (a)). Pre-tips are usually made of tungsten. The electropolishing is performed in
90% H2O and 10% of NaOH electrolyte. In the present case, the “micro-loop” method was
used. Afterwards, in order to facilitate and insure a better fixation of the powder grain on the
pre-tip, a “flat area” at the apex of pre-tip is done using the focused ion beam (FIB). The
diameter of the flat area is about 3 to 6 µm.
Fixation of the powder grain on the pre-tip. This is realized by means of
micromanipulators (under optical microscope, see Figure 4 (b)). The powder grain is fixed on
the pre-tip using special silver glue (see Figure 4 (a)). It should be mentioned that the size of a
powder grain that will be processed by FIB must not exceed 10 to 13 µm in diameter. Above
these sizes, the milling time is too long.
(a)
Powder grain
Tungsten pre-tip
Figure 4. (a) Tungsten pre-tip with a powder grain at the end (b) SEM image of a
micromanipulator used to fix a powder grain on the pre-tip.
Milling the final shape by FIB. The powder is transformed into sharp needle-like tip by
annular milling FIB. For this final preparation LEO 1530 and NVISION 40 SEM microscopes
of the GPM laboratory were used under the supervision of F. Cuvilly.
The basic idea of the ion milling using the FIB technique is the following: the sample (pre-
tip) is aligned parallel to and centred on the column of the ion beam. The ion beam scan the
end of the specimen in a circular annular pattern [1]. A general scheme is shown on Figure 5
(a). The milling is generally performed in a series of stages with successively smaller inner and
outer diameters of the mask and decreasing the ion current. Finally, the connection between the
tungsten pre-tip and the powder particle (silver glue) is additionally reinforced by the
deposition of a layer of platinum, Figure 5 (b).
(b)
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