Development of a bright, highly coherent
field ion source
Persons involved in this theme:
Franz Hasselbach, Hubert Kraus and Uwe Maier, Universität Tübingen,
Institut f. Angewandte Physik, Auf der Morgenstelle 12,
D-72076 Tübingen, Germany
Short abstract:
Field ion sources are the most promising candidates when small virtual
source sizes and high brightness are indispensable, e.g., for high
current focused ion spots of nanometer size or if a virtual source of
atomic dimensions is needed for the coherent illumination of an ion
optical biprism, as in our present application. The development of the
ion source presented here, bases on the formation of a supertip, i.e.
a protrusion consisiting of a small number of tungsten atoms on an
<111>
-oriented tungsten fieldemission tip with relatively large radius
of curvature of the apex. For our application in an ion interferometer
long wavelengths corresponding to relatively low extraction voltages of
1 - 5kV are desirable. This has been reached by choosing a radius of the
tungsten tip smaller than that giving the highest possible brightness.
The present source is emitting into a single spot of angular diameter of
1 degree only, compared to about 20 degrees of the very sharp single or
few atom nanotips developed by Fink. The brightness at 77K is 1000A/sqrcm Gsr.
By going to temperatures of about 10 - 20K and increasing
the pressure the brightness is expected to increase about 1 - 2 orders
of magnitude. This will be sufficient for observing ion
interferences. Our supertips can be prepared in an UHV chamber, exposed
to air and transferred into another apparatus, e.g., our biprism
interferometer or an ion beam lithography device without altering their
excellent features.
Einen allgemeinen Überblick über das Prinzip der Ionen Mikroskopie
gibt es hier.
Members of the group