Interface configuration and metal adhesion in Au-polycarbonate bilayer structure: Influence of 27Al+ ion mixing

Abstract

Structural modification at the Au-polycarbonate (PC) interface upon 100 keV Al+27 ion implantation at a dose and beam current density 5×1016 ions cm−2 and 30–50 nA cm−2, respectively, was studied through x-ray photoelectron spectroscopy (XPS) with a Au thickness of 28.2 nm. XPS depth profiling with 3 keV Ar+ ion sputtering at 1 μA revealed the interface to be sharp covering a few monolayers. A substantial Au atomic concentration of ∼5% in the bulk PC indicated the Ar+ ion assisted diffusion of the metal into the bulk. Existence of weak Au→C charge transfer interactions with Au as the electron injector distributing a net charge density at the C=O bond as the primary interaction site was deduced from the appearance of the 282.4 eV C1s feature [H. A. Mizes, K. G. Loh, R. J. D. Miller, S. K. Ahuja, and E. F. Grabowski, Appl. Phys. Lett. 59, 2901 (1991)]. Al+ ion implantation induced interfacial mixing of the substrate C with the Au film in the bilayer target was observed with the evolution of a broad interface of ∼50 nm thickness, accompanied by the formation of Au–Al, Al–O, and Al–O–C bonds along with dominant graphitization of the polymer. Free carbon transport into and through the Au film to the surface resulted in a diffused interface with an abnormally low oxygen concentration throughout. Au–Al bonding was identified in the Au-rich region, and shifted to Al–O bonding in the C-rich region of the polymer, with the Al atomic concentration reaching a maximum of 1.8%. After ion-beam mixing and surface modification by ion bombardment, force curve measurements performed through atomic force microscopy showed a drastic reduction in the interface adhesion values.