Ion Mixing Kinetics of Thin Layered Films in the Fe-Al System
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ION MIXING KINETICS OF THIN LAYERED FILMS IN THE Fe-Al SYSTEM J. GRILHE, J.P. RIVIERE, J. DELAFOND, C. JAOUEN Laboratoire de M~tallurgie Physique, L.A. 131 du C.N.R.S. 40, avenue du Recteur Pineau 86022 Poitiers (France) ABSTRACT Evaporated bilayers and multilayers of Fe and Al have been studied during ion beam mixing with Xe ions using in-situ electrical resistivity measurements.Experiments have been performed in the composition range 40 58 at.% Al and at both temperatures 77 K and 300 K. A semi-empirical model is proposed to explain the observed kinetics. At low doses, a square root dependence of the mixed volume fraction on dose is found at 77 K but not at 300 K. The results are discussed by comparison with the different models proposed for ion beam mixing. INTRODUCTION Presently, surface alloys are readily produced by the technique of ion mixing (1,2,3). Fundamental studies have been carried out in order to understand the basic mechanisms of ion mixing. Up to now, most of the experimental results have been obtained using Rutherford backscattering spectrometry analysis. The models may be divided into two general classes : ballistic and thermally activated models. However, the basic mechanisms proposed for both models are not yet well understood. It appears that a precise kinetic study able to point out the fundamental mechanisms of ion mixing must be done with a technique allowing at the same time a very sensitive and continuous measure while the mixing proceeds. Electrical resistivity measurements are well suited to the preceding requirements. They are an easily measured bulk quantity capable of giving continuous measurement, and their extreme sensitivity to radiation damage has been demonstrated in irradiation studies in metals. It is interesting to apply this experimental technique to study ion mixing kinetics (4) especially in the case of multilayers, where it is not possible to measure kinetics by R.B.S. In the present paper, we give the results of a study performed in the Fe-Al system for both bilayer and multilayer thin film structures. Since the temperature of the film is a fundamental parameter for the different mechanisms of ion mixing, the experiments have been performed at room tenmerature and 77 K. EXPERIMENTAL RESULTS The experimental procedure as well as the general behavior of the resistivity variations as a function of dose have been previously described (5). At low doses typically U-)
in
A
E
0
100 A
20A
U)
m77
200
300
A3 A
FLUENCE
(10141orne. cm-2)
250 Q::
FIG.2. Electrical resistivity increase at 77K and 300K during ion mixing of a multilayer (final composition Fe-)8 at.% Al).
lm77K 150 400
0
100
120
,"'
Xe30Kev in Fe-Al 58Oat
A
LLJ
860
±,300K
1.4
FLUENCE
(1014ions. cm-2)
1.4A N.
vj 0.
2.8B-
Xe 290K.V in Fo~l 77K
0o 4.20 -4 LE.C 0.8 L LOG (FLUENCE)
1.8 3.5 (10-*14c,,-2)
5.4
FIG.3. Variations at 77K of the mixed volume fraction C of a bilayer Fe-40 at.% Al. Mixing dominates in the fluence 2 5 range 5 1I03 - 5 I0O cmand data are fitted with a straight line (sl
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