Amorphization of Zr/Ni Bilayers by Ion-Beam-Mixing
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AMORPHIZATION OF Zr/Ni BILAYERS BY ION-BEAM-MIXING L. THOME# AND M. KOPCEWICZ* JACEK *InstituteJAGIELSKI*, of Electronic Materials Technology, W61czyfiska 133, 01-919 Warsaw, Poland #Centre de Spectrom6trie Nucl6aire et de Spectrom6trie de Masse, Bit. 108, 91405 Orsay, France ABSTRACT
The amorphization process induced by ion-beam-mixing was studied for the Zr/Ni bilayer system by means of the RBS/channelling and CEMS techniques. The number of atoms mixed per one incident atom was found to be the same for -100 K and 300 K irradiations, whereas it was increased by the factor of 2.5 for 500 K irradiation what indicates, that the change in the mixing mechanism occurred above room temperature. The results show that amorphization of the Zr/Ni system is controlled by the number of mixed atoms and depends on the irradiation temperature. A change in CEMS spectra was observed at -770 K what suggests that recrystallization of the amorphous phase occurs at this temperature. INTRODUCTION
The amorphization process of metallic systems has been studied in detail in the case of ion implantation and ion irradiation experiments [1,2]. It was established that the amorphization results from combination of two effects: damage production and disorder stabilisation, and thus strongly depends on the bombardment procedure [3]. In the case of ion implantation the surface layer of the metal may be amorphized when a sufficiently high concentration of foreign atoms able to stabilise the structural disorder is reached. The required impurity concentration is usually of the order of several atomic per cent what corresponds to the doses of the order of 1017 at/cm 2 . The damage produced during implantation of such a high dose may reach several hundreds of displacements per atom (dpa), it is thus evident that the formation of the amorphous phase is directly related to the stabilisation and not to the creation of structural disorder. The opposite is true in the case of the irradiation experiment where a crystalline compound having an amorphous counterpart is bombarded with chemically inert ions. The crystalline-to-amorphous transformation is completed for doses of the order of 1013-1014 at/cm 2 (what corresponds to less than 1 dpa). In consequence, in the case of the ion irradiation experiment the amorphization process is controlled directly by the creation of radiation damage. The third ion beam technique which may lead to the formation of the amorphous phase is ion beam mixing. The method consists in irradiating a multilayer structure composed of different elements deposited on a substrate. In general the energy of ions is chosen so as to obtain their projected range greater than the total thickness of the deposited films [4-7]. The amorphization process induced by ion-beam-mixing has been less extensively studied than it is the case of ion implantation and ion irradiation experiments [1]. Recently some preliminary results concerning the quantitative correlation between mixing and amorphization in the bilayer metal systems were published [8,9]. H
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