ELSEVIER Surface and Coatings Technology 83 (1996) 88-92 Radiation-induced redistribution of implanted impurities in Al D.C. Kothari a, V.N. Kulkarni b, A. Miotello ‘, L. Guzman ‘, G. Linker d, B. Strehlau d a Depwtment of Physics, University of Bombay, Vidyanagari, Bombay 400 098, In&n b Department of Physics, Indian Institute of Technology?, Knnpw 208 016, India ’ Dipaytimento di Fisicn, Univewita degli Stzidi di Trento, I-38050 Povo, Twnto, ItnlJ * Kelrlfoischungszent~~~~l Kadsruhe, Institutfiir Festkrperphysik, POB 3640, D-7500 Ktwlsrd~e, Gerwwy Abstract Ion-beam-induced migration of an implanted impurity is studied using a phenomenological model involving diffusion of the impurity, vacancies and coupling between their motion. Redistribution of implanted Mn, Fe and Ni in Al is experimentally observed using the RBS technique and analyzed using the phenomenological model. Implantations are carried out at 200 key, to a dose of 1 x 1Ol6 ions cm-’ and at temperatures ranging from 77 K to 473 K. Coupled continuity equations for implanted atom and vacancy fluxes are solved to obtain theoretical fits to the experimental concentration vs. depth profiles. An effective diffusion coefficient describing radiation-induced thermal and athermal processes is obtained from the theoretical fits and is found to have a value a few orders of magnitude higher than the normal diffusion coefficients. K~JWO~~S: Sputtering; Recoil implantation; Displacement mixing; Radiation-induced redistribution of atoms 1. Introduction Depth distribution profiles of implanted impurities can be predicted using the LSS theory [I]. The predict- ability is advantageously used to introduce any impurity at required positions in the near-surface region of any substrate. However, any radiation-induced effects modify the depth profiles and the predictability is lost. In the present work we study the effect of radiation-induced redistribution of atoms (RIRA) on the depth profiles of implanted Mn, Ni and Fe in polycrystalline Al. RIRA is mainly caused by two types of process; namely, thermal and athermal. Athermal processes are ballistic in nature and are prompt, i.e. they take place within 1 ps after a collision event. Three main processes in this category are (i) sputtering (SP), (ii) recoil implant- ation (RI), and (iii) displacement mixing (DM). SP causes surface erosion and composition modification of the first few atomic layers near the surface, in case there is preferential sputtering (PS) of a particular atomic species. RI causes light atoms to be dragged along the beam direction. DM causes randomization of atoms within the collision cascade. Thermal process are delayed, i.e. they occur after a picosecond and are activated by temperature. Three main processes in this category are (i) Gibbsian adsorp- tion (GA), (ii) radiation-enhanced diffusion (RED), and 0257-8972/96/$15.00 0 1996 Elsevier Science S.A. All rights reserved CCDF lY7s-l 8937105\n1Qn-l 1 (iii) radiation-induced segregation IRIS). GA modifies the first two atomic layers near the surface. RED causes enhanced diffusion of impurities because of a large number of mobile point defects present in the radiation environment. RIS causes either depletion or enrichment of a particular atomic species at sinks such as the surface and extended defects, depending on its coupling with the point-defect fluxes. The model presented in this work takes into account the relevant processes from the above, in an effective way in describing the motion of the implanted impurity. Al is used as a substrate material because it is known to have high mobility for various impurities in a radia- tion environment [a]. Mn, Fe and Ni are chosen to be implanted in Al because they are expected to behave differently in the presence of a vacancy flux. It is pro- posed that the fast-diffusing impurity atom moves oppo- site to the vacancy flux, and the slow diffuser moves in the same direction as that of the vacancy flux [3]. Mn and Ni are fast diffusers (compared to Al self-diffusion) therefore would be depleted at the sinks and the surface, as they move opposite to the vacancy flux. Fe would instead be segregated at the sinks and the surface. Again the behavior would be different at different temperatures. Thus Mn, Ni and Fe were chosen to be implanted at different temperatures to understand their atomic trans- port behavior in radiation environment. Implantations