Abstract

A metal overlayer FT-IR-ATR technique that is found to substantially enhance the signal-to-noise ratio of monolayer and submonolayer film spectra is described. Experimental evidence of the enhancement is given for, as examples, a deposited poly(vinyl acetate) film of 0.5 or 5 nm and a thin film of adsorbed protein human serum albumin, estimated to be of the order of 5 nm. The evidence is supported by simulations showing the expected trends in Δ<i>R</i> as a function of thickness of the air gap between the film sample and the metal overlayer, the thickness of the film sample itself, and electric field diagrams illustrating that polarization dependence and enhancement effects can result from a correct choice of optical configuration. The metals investigated include gold and aluminum. The practical aspects and limitations of this technique are also discussed.

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