ELFT HÍRADÓ

[Nagy Denes Lajos <nagy AT rmki.kfki.hu>]

Kedves Kollégák!

A KFKI RMKI és a KFKI CMRC nukleáris szerkezetkutatási szemináriumainak
következõ elõadását

                             Peter Schaaf
         Universität Göttingen, Zweites Physikalisches Institut

tartja

                 Thin Films made fast and changed fast:
   A Mössbauer Illumination of Photon- and Ion Beam-Induced Processes.

címmel.
Az elõadás helye:

                   KFKI RMKI 3. épület, tanácsterem (2. em.)

Az elõadás idõpontja:

                       2003. április 14., hétfõ, 14:30

Az elõadáson minden érdeklõdõt szeretettel látunk.

                                                  Nagy Dénes Lajos
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Az elõadás kivonata:

Thin Films are playing a more and more important role for technological
applications and there are many aspects of materials surface processing
and thin film production ranging from simple heat treatments to ion
implantation or laser surface treatments. These methods are often very
complicated, involving many basic processes and they have to be optimized
for the desired application. Nuclear methods, especially Mössbauer
Spectroscopy, can be successfully applied for this task and some examples
will be presented for ion-beam and laser-beam based processes.

Irradiating iron and steel surfaces in controlled gaseous atmospheres
(nitrogen and methane) can lead to the formation of nitride and carbide
surface layers, respectively. The evolution and abundance of each phase is
correlated to the experimental parameters such as the number of laser
pulses, the laser fluence and the ambient gas pressure. The application of
several lasers with very different pulse durations and their basic
phenomena will be presented The capability of CEMS to distinguish the
atomic surrounding in combination with its sensitivity to the surface
makes it an indispensable tool for a proper investigation and optimisation
of such surface treatments. Additional analytical techniques (CXMS, RBS,
RNRA, and XRD) have been used in order to have complementary information.
The results revealed that under proper experimental conditions, the laser
treatments can produce almost homogeneous layers of nitride/carbide, where
the composition and the structure are determined only by the parameters of
irradiation.

Furthermore, some newer developments will be presented concerning thin
iron films deposited on single crystalline silicon by pulsed laser
deposition (PLD), electron beam evaporation and also an effusion cell.
Their surfaces, interfaces and their magnetic behavior are investigated by
CEMS in the as-deposited state as well as after ion-beam and laser
treatments. The resulting changes and reactions can be accurately
determined by that. This becomes even more sophisticated by sandwiching in
some nanometer thick 57Fe marker layers. For example Ag/Fe multilayers -
especially important for GMR applications - can be prepared by pulsed
laser deposition (PLD). The Ag/Fe system is immiscible and sharp
interfaces are expected for that reason. Nevertheless, it will be
presented that some intermixing occurs which can be seen by CEMS with the
additional trick of preparing a sensitive 57Fe layer at various distances
from the interfaces. Several Ag configurations to the Fe spy-atom can be
resolved, whose abundance varies with the location of the 57Fe marker
layer.

Last, an example will be given for a new CEMS-based method for determining
magnetic spin textures in thin iron films (MOMS=Magnetic Orientation
Mössbauer Spectroscopy) before and after ion irradiation. It is
unambiguously proven by CEMS results that ion irradiation can induce a
perfect uni-axial spin texture in these iron films. The method and the
results are explained and compared with magneto-optical Kerr effect (MOKE)
measurements.