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An FT-IR attenuated total reflection (ATR) method is described for quantitative in situ analysis of the adsorption and rinsing-removal of surfactants from silicon surfaces. Spectral bands at wavenumbers below 1550 cm-1 are nearly inaccessible when single-crystal silicon
ATR internal reflection elements (IREs) are used. A new ATR technique was attempted in order to overcome this limitation. The silicon was sputtered as a thin film onto a thin Al2O3 buffer layer, which had been previously sputtered onto a ZnSe IRE to improve adhesion of
the silicon layer. The method allowed observation of species at the silicon/aqueous solution interface below 1550 cm-1, to 1100 cm-1. Absorption bands due to adsorbed octylphenol polyethylene oxide (OPEO) and dodecyl trimethyl ammonium bromide (DTAB) surfactants were
observed in the 1550-1100 cm-1 spectral region, which were assigned to benzene-ring modes and the aliphatic stretching vibrations for OPEO and to the aliphatic stretching vibrations for DTAB. A mathematical method to calculate adsorption density for stratified ATR IRE systems having
more than three phases (i.e., ZnSe/Al2O3/Si/aqueous solution) was developed and applied to the determination of the adsorption density of DTAB and OPEO surfactants on silicon, in situ. The method was confirmed through spectra obtained with a single-crystal Si IRE
and the previous three-phase calculation method. The agreement indicates that the two surfaces have very similar physisorption chemistry. In addition, this method allows direct, in situ observations of the oxidation-induced growth of a SiO-Si band near 1150 cm-1 and its removal
by dilute HF solutions.
Department of Chemistry, University of Arizona, Tucson, Arizona 85721 2:
Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721
Publication date: August 1, 1995
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The Society publishes the internationally recognized, peer reviewed journal, Applied Spectroscopy, which is available both in print and online. Subscriptions are included with membership or can be purchased by institutional or corporate organizations. Abstracts may be viewed free of charge. Previously published as Bulletin (Society for Applied Spectroscopy)