Swift heavy ion irradiation eects in Pt/C and Ni/C multilayers Ajay Gupta a, * , Suneel Pandita b , D.K. Avasthi c , G.S. Lodha d , R.V. Nandedkar d a Inter-University Consortium for DAE Facilities, University Campus, Khandwa Road, Indore 452001, India b School of Physics, Devi Ahilya University, Khandwa Road, Indore 452001, India c Nuclear Science Centre, Aruna Asaf Ali Road, New Delhi, India d Centre for Advanced Technology, P.O. CAT, Indore, India Abstract Irradiation eects of 100 MeV Ag ion irradiation on Ni/C and Pt/C multilayers have been studied using X-ray re- ¯ectivity measurements. Modi®cations are observed in both the multilayers at (dE/dx) e values much below the threshold values for Ni and Pt. This eect is attributed to the discontinuous nature of the metal layers. In both the multilayers interfacial roughness increases with irradiation dose. While Ni/C multilayers exhibit large ion-beam induced intermixing, no observable intermixing is observed in the case of Pt/C multilayer. This dierence in the behavior of the two systems suggests a signi®cant role for chemically guided defect motion in the mixing process associated with swift heavy ion irradiation. Ó 1997 Elsevier Science B.V. All rights reserved. 1. Introduction Swift heavy ions lose their energy in the target mainly via inelastic collisions leading to the exci- tation of the target electrons. The electronic energy loss has been found to create various modi®cations in the target material which include creation of point defects, latent track formation, sputtering and intermixing at the interfaces [1±9]. While the material modi®cation in insulators using swift heavy ion irradiation has been studied quite ex- tensively [1±3], it is only in recent years that such eects have been observed also in metals [4±9]. In metals damage creation occurs when the electronic energy loss, (dE/dx) e , exceeds a certain threshold value which may vary from metal to metal [10,11]. While in case of iron this threshold (dE/dx) e is 5 keV/  A [10], in Ni and Pt the threshold is expected to be higher than 6.7 and 9.0 keV/  A, respectively [11]. There are only a limited number of studies in which swift heavy ion induced intermixing at the interfaces has been studied [7±9]. Dufour et al., studied the mixing induced by 650 MeV U ions in Fe/Si multilayers [7]. A complete mixing was ob- served for ¯uence as low as 10 13 ions/cm 2 . In an- other experiment Leguay et al., observed electronic excitation induced interdiusion in Ni/Ti bilayers as a result of irradiation with 0.89 GeV Ta ions [8]. Teillet et al., have studied swift heavy ion irradi- ation eects in Fe/Tb multilayers [9]. It has been found that with increasing irradiation dose, ini- tially a small demixing eect is observed at the Nuclear Instruments and Methods in Physics Research B 146 (1998) 265±270 * Corresponding author. Tel.: +91 731 472200; fax: +91 731 462294; e-mail: ag@iuc.cat.ernet.in 0168-583X/98/$ ± see front matter Ó 1997 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 0 4 3 3 - 9