Study of Surface-Enhanced IR Absorption Spectroscopy over Evaporated Au Films in an Ultrahigh Vacuum System

Abstract

IR transmission spectra were measured in an ultrahigh vacuum system for Fe(CO)₅, n-decane, and NH₃ adsorbed at <150 K on transparent Au films evaporated on a sapphire plate. The spectra of Fe(CO)₅ show ∼10-fold enhancement as compared to those observed on an SiO₂ lm coated on a sapphire plate, which has been reported as surface-enhanced IR-absorption (SEIRA). The enhancement is reduced when the coverage of adsorbate exceeds a mono-layer or other molecules present on the surface prior to adsorption, indicating that SEIRA is effective only in the close vicinity of the surface. The SEIRA effect is also reduced when film is heated in a vacuum, probably because of sintering of the Au particles forming the film. In addition, the heat treatment of the film results in blue shifts of bands, accompanied by some band distortion. With the use of SEIRAS, the surface photochemistry of Fe(CO)₅ has been investigated.