Temperature Dependence of Ion Mixing Of Markers in Zr
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TEMPERATURE DEPENDENCE OF ION MIXING OF MARKERS IN Zr S.-J. KIM-, M-A. NICOLET*, AND R. S. AVERBACK**# * California Institute of Technology, Department of Electrical Engineering, Pasadena, CA 91125 ** Argonne National Laboratory, Material Science Division, Argonne, IL 60439 # Present Address: Department of Materials Science, University of Illinois Urbana-Champaign, Urbana, IL 61801 ABSTRACT Iq mixing of thin markers in Zr was investigated by irradiating with 660 ions at temperatures between 300 to 423 K. Very thin films of vacuum keV Kr evaporated Ti, Cr, Fe, Co, Ni, Cu- Hf, W, and Au served as markers. The samples were analyzed by 2 MeV He backscattering spectrometry. The marker elements that are likely to dissolve interstitially in Zr have higher mixing efficiencies at elevated irradiation temperature than the markers that are likely to dissolve substitutionally. The results are explained by radiation-enhanced diffusion theory. INTRODUCTION There have been numerous studies of ion mixing at low temperature and two main mechanism have been identified: collisional displacements [i] and intermixing by thermal spikes [2]. Especially the thermal spike mechanism is known to contribute significantly to ion mixing. During a thermal spike, the chemical as well as the physical properties of target atoms influence the mixing [3,4] which, in particular, has been found to correlate with the thermally activated diffusion by vacancy mechanism [2,4]. At high ambient temperature, radiation-enhanced diffusion (RED) is known to contribute significantly to the atomic intermixing. The basic theories are well developed [5,6] and the existence of RED is established through many experiments [7]. However, experimental results on impurity diffusion by RED mechanisms are few [7]. We have undertaken a systematic investigation of this kind and report its results in this paper. We investigate ion mixing of markers in a Zr matrix. In Zr, some impurities are known to diffuse thermally by an interstitial mechanism, others by a vacancy mechanism. We have selected marker impurities of either type and compare the amount of intermixing observed for each after irradiation. It has been suggested L8] recently that during RED, the vacancy mechanism dominates the atomic transport process. If that suggestion is correct, marker species that thermally diffuse vacancy-wise in Zr should mix more than the marker species that thermally diffuse by a interstitial mechanism if the mechanisms of intermixing by ion irradiation and thermal activation are simply related to each other. The experimental results reported here enable these suggestions to be critically tested on the basis of RED theory. EXPERIMENTAL PROCEDURE The marker samples were prepared on organically clean SiO 2 substrates by sequential e-guy evaporations of Zr and of the marker elements at a vacuum torr. The markers had nominal thicknesses of -IO A and were better than 10 located at mid-plane of a "'800 A thick Zr film. A cover layer of Si about 30 A thick was deposited on top of all the samples to m
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