Mass density of glassy Pd 80 Si 20 during low-temperature light ion irradiation
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Changes in mass density of amorphous Pd80Si20 were monitored in situ during irradiation with He2+ and H+ ions at temperatures below 100 K and during subsequent thermal treatment. The mass density decreased with increasing ion fluence and exponentially approached a saturation value of −1.2%, corresponding to a recombination volume of 190 atomic volumes. The initial swelling rate was 2.3 atomic volumes/displaced atom. The mass density of the irradiated material increased during subsequent thermal treatment, and the irradiation-induced decrease of the mass density recovered completely at room temperature. I. INTRODUCTION
Amorphous materials, as well as others that can undergo amorphization, are being considered for applications in microelectronic devices as well as for radioactive waste storage. Such applications require a basic understanding of changes produced by irradiation. Irradiation effects have been most intensively investigated for amorphous Pd80Si20. Electrical resistance changes have been measured during low-temperature irradiation with electrons,1 ions,2–5 and neutrons.6,7 Electron irradiation1 resulted in the increase of the electrical resistivity toward a fractional change of 3%. Fast neutron irradiation6 resulted in a saturation of the increase at about 5%. The increases produced by irradiation are about 1 order of magnitude larger and have opposite sign than the changes in electrical resistivity produced during thermal treatment of nonirradiated material below the kinetic glass transition temperature.8 Thermal treatments also increase the mass density of amorphous Pd80Si20 by about 0.5%.9 Hence, irradiation of amorphous Pd80Si20 may also cause a large decrease in the mass density. Since the mass density severely affects the mechanical properties of amorphous alloys, an accurate determination of irradiation-induced density change is desirable. Changes in mass density after lowtemperature irradiation of glassy Pd80Si20 with ions of very high energy (>1 MeV/amu)5 have been measured. However, these density measurements were performed at room temperature, where at least part of the damage
a)
Present address: Hahn-Meitner-Institut, Berlin, Germany.
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http://journals.cambridge.org
is expected to anneal.1,2,6,7 Additionally, the density measurements reported in Ref. 5 have an appreciable uncertainty. The present contribution describes in situ density measurements on amorphous Pd80Si20. The measurements were performed at low temperatures during ion irradiation and after thermal treatment of the irradiated material. Amorphous Pd80Si20 was chosen for the present investigations because it is one of the most intensively studied alloys with respect to radiation damage. This allows one to compare the results of the present work with results reported in the literature. II. EXPERIMENTAL
A melt-quenched ribbon (30 m × 0.8 mm) of amorphous Pd80Si20, supplied by Vacuumschmelze Hanau, was cold-rolled and mechanically polished to a thickness of 4 to 10 m and heat treated at 523 K for 3600 s in an argon atmospher
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