Scripta METALLURGICA Vol. 20, pp. 181-184, 1986 Pergamon Press Ltd. Printed in the U.S.A. All rights reserved INVESTIGATION OF SOLID ARGON BUBBLES IN NICKEL BY GLANCING ANGLE X-RAY DIFFRACTION Rita Khanna, A.K. Tyagi, R.V. Nandedkar and G.V.N. Rao Materials Science Laboratory, Reactor Research Centre, Kalpakkam 603 102, India (Received September 17, 1985) (Revised November 18, 1985) INTRODUCTION Recent exciting observations of precipitation of implanted inert gases into solid bubbles (1,2,3) in metals at room temperature have provided direct evidence of extremely high pressures existing in such small bubbles. Using transmission electron microscopy, Evans and Mazey (3) observed three dimensional solid precipitates of solid krypton in copper, nickel and gold. In another TEM study, Templier et al (2) have reported solid xenon bubbles in aluminium, vom Fe,lde et al (i) observed solid Xenon and argon bubbles in aluminium but noticed the failure of neon to solidify at room temperature. These observations were made on the basis of electron energy loss spectra and diffraction pattern of aluminium films. Because of the limited momentum transfer range avail- able (0.07 to 0.36 nm), in the energy loss spectrometer only (iii) reflection of solidified gas bubbles was observed and higher order reflections could not be seen. Such limited diffraction data seriously constrains structure determination of a new phase and can also lead to ambiguous results. In this paper we report the complete x-ray diffraction study of solid argon bubbles in nickel for the first time. As conventional x-ray methods are not suitable for studying low energy ion implanted metals where the damage and the implanted species are confined to near-surface region and may not be uniformly distributed, we have used glancing angle (1/2 ° - 2 °) x-ray diffraction method (5) for studying argon bubbles in nickel. The penetration depth X (Fig.l) for 99% absorption on x-ray beam is given by in(100.0) X = ~'[Cosec~ +-Cosec (28 -4 )] (i) where ~0 is the mass absorption coefficient. ~ and @ are respectively the angles of incidence and diffraction. For a given material, the value of X can be continuously altered either by changing ~ or by using x-rays of different wavelengths. For example, CrK< and CuK~ incident at 1 ° probe 0.3 ~m and 1 ~n depths respectively, in nickel In this investigation, nickel foils were irradiated with i00 keY argon ions. The damage and the precipitated argon bubbles are con- fined to the near-surface region, typically few tens of nm. Diffraction pattern from the damaged region was investigated for the change in lattice parameter of nickel and for additional diffrac- tion peaks from solid argon. EXPERIMENTAL Nickel specimens (99.99%, Atomergic Chemicals Corporation, USA)_~n the form of 3 mm diameter disks (i ram thick) were annealed at 1320 K for 4 hours under i0 Pa vacuum. Annealed specimens were given a fine metallographic polish using a i0 ~m alumina abrasive to ensure a flat surface. Irradiations were carried out at room temperature in a vacuum of better than 10-4 Pa, with i00 keY argon ions using a Sames J-150 keV ion accelerator. The ion beam was inciden~ normal to the specimen surface _a~d the ion current density was kept constant at about 200 mAm ( -~ 1.2 x i0-v ions m-- sec -±) . The beam area was defined by a circular aperture of 3 mm diameter and the entire sample s~face was u~formly i~radiated. Samples were irradiated to various doses in the range of i x i0 to 1 x l0 ~ ions m ~. The projected range of i00 keV argon ions in nickel is about 45 nm (4). The sputtering yield of argon being very high, the local atomic concentration of implanted argon is not expected to exceed few atomic percent. Glancing angle x-ray diffraction measurements were made using a Huber flat plate Laue camera. The specimen, fixed on a perspex disc, was mounted atop the goniometer head. The sample surface was first aligned parallel to the x-ray beam with the help of a telescopic arrangement. The desired angle of incidence was then set by rotating the goniometer about an axis in the sample plane which was perpendicular to the x-ray beam. Because of limited penetration of x-ray beam,a 181 0036-9748/86 $3.00 + .00 Copyright (c) 1986 Pergamon Press Ltd.