Surface-enhanced infrared absorption (SEIRA) and its use in analysis of plasma-modified surface

A thin film (<10 nm) of fine metal clusters (silver or gold) with an island form was deposited on a CaF2 salt plate by slow vacuum thermal evaporation . Molecular layers of stearic acid, p-nitrobenzoic acid, and m-nitrobenzoic acid (p- and m-NBA) were prepared on the thin metal film. The system was t hen examined by infrared spectroscopy attenuated total reflection (IR-ATR). It was found that through the interaction between the metal islands film a nd the electric field of the incident IR beam the infrared absorption of th e molecule layers adsorbed on the islands was enhanced by a factor of 17. T he surface-enhanced IR absorption (SEIRA) also presents a selection rule. T his method was then used to study the surface modification with O-2 and NH3 plasma and the plasma polymerization of allylamine. This is the first time that SEIRA has been used in plasma investigations. A model is provided to explain the interactions between the metal islands film and the electric fi eld of the incident IR beam in the SEIRA. The in-plasma-built functional gr oups can be further used to graft biofunctional molecules for the biomedica l industry. (C) 1999 John Wiley & Sons, Inc.