Insitucharacterization of thenhyphen;Si/acetonitrile interface by electromodulated infrared internalhyphen;reflection spectroscopy

摘要

We present a systematic experimental investigation on the infrared (IR) vibrational absorption spectroscopy of thenhyphen;Si/acetonitrile interface utilizing the attenuated total internalhyphen;reflection geometry in the nearhyphen;infrared (1.1ndash;5 mgr;m) spectral region. The IR absorption of the interface has been isolated selectively by electromodulation, and studied as a function of modulation potential. The electrochemical behavior of the interface has been checked by current/voltage and impedance measurements. The IR spectra are composed of a broad background and various sharp vibrational peaks. The background can be analyzed as the sum of two contributions: (i) absorption by surface states at shorter wavelengths (2 mgr;m), (ii) freehyphen;carrier absorption at longer wavelengths. The freehyphen;carrier contribution is itself composed of a Drudehyphen;like component (proportional to lgr;3/2) and an interband component. The vibrational peaks can be ascribed to the Cequiv;N, Cndash;H, Sindash;H, and (Sindash;)Ondash;H chemical bonds. The shapes and magnitudes of the Cequiv;N and Cndash;H peaks can be quantitatively understood in terms of displaced ions and acetonitrile molecules near the surface upon the electrode potential modulation. The shape of the Cequiv;N peak also gives an indication of a weak interaction of the acetonitrile molecules with the electrode surface. The Sindash;H and (Sindash;)Ondash;H peaks can be interpreted in terms of Stark effect modulation of the infrared absorption of these species. The shape of the Ondash;H peak indicates the presence of nonequivalent sites at the interface. Upon the electrode aging and oxidation the magnitude of the Sindash;H peak decreases and the (Sindash;)Ondash;H peak increases and correspondingly the surfacehyphen;state density increases which provides a directinsituphysicochemical information regarding the slow oxidation of the electrode surface.