Aluminium metallisation of argon and oxygen plasma-modified polycarbonate thin film surfaces

The influence of plasma treatment on the metallisation of polycarbonate sur faces was studied using X-ray absorption spectroscopy (XAFS) and core level X-ray photoelectron spectroscopy (XPS). Thin films of two different molecu les were chosen: bis-phenol-A polycarbonate with phenol endgroups (P-PC) pr epared ex situ by the spin-coating technique onto MoTe2{0001}surfaces, and the model compound bis-phenol-A polycarbonate (n = 1) with tert-butyl pheny l endgroups (tBP-PC) evaporated in situ in UHV onto Cu{110}, Ag{100} and Ag {111} surfaces with film thicknesses of up to several monolayers. Surfaces of untreated samples and of samples which were pre-treated with either an i nert argon or a reactive oxygen microwave plasma were metallised with Al (e vaporated by electron beam heating) at film thicknesses ranging from the su b-monolayer region up to several monolayers. For the untreated surface, XAF S and XPS spectra suggest that the Al reacts with the carbonate groups lead ing to a breaking of the C=O double bonds (and/or a reduction in bond order ) as well as formation of Al oxide, Al hydroxide and Al-O-C linkages. A stu dy of the time-dependent oxidation of the evaporated Al leads to the conclu sion that Al slowly diffuses to the reactive sites in the first few subsurf ace levers of the polymer. Argon plasma treatment of samples leads to a red uction in the number of carbonyl groups in the near surface region. After m etal deposition a higher ratio of metallic, non-reacted, Al was observed co vering the polycarbonate surface and the diffusion rate into the polymer bu lk seems to be higher than in the case of the untreated surface. Oxygen pla sma treatment leads to the creation of additional C=O containing species wh ich also react with the Al in the subsequent metallisation process, Here, t he ratio of oxidised Al on the polymer surface is higher than observed for untreated and argon plasma pre-treated polymer surfaces. (C) 1998 Published by Elsevier Science B.V. All rights reserved.