Copper electroless deposition on NiTi shape memory alloy: an XPS study of Sn-Pd-Cu growth

XPS analysis of electroless deposition of successive Sn, Pd and Cu films on NiTi(O) surface has been done in order to explain their nucleation and gro wth. Chemical interaction of Sn sensitisation element. with NiTi(O) surface is shown to be associated with the growth of Sn(O) interfacial oxide which can be formed after the reaction of Sn atoms with Ni2O3 nickel oxide. The dissociation of this non-stable oxide leads to the formation of Sn oxide fi lm and to the migration of free metallic nickel atoms at the free surface o f the electroless Sn(O) film Pd chemisorption on Sn(O) surface is associate d with the formation of strong Sn-O-Pd interfacial bonds. Further on, 2D an d 3D growth of pure metallic palladium occurs, leading to the formation of nanometric Pd clusters. The interaction of copper atoms with that palladium surface leads to the formation of interfacial Pd-Cu intermetallic and cons equently to strong interfacial adhesion. (C) 2000 Elsevier Science B.V. All rights reserved.