In situ and ex situ FTIR characterization of a cyanate adlayer on Cu(1 1 1)

Abstract

Cyanate adlayers were investigated with in situ and ex situ infrared reflection absorption spectroscopy (IRRAS) on a Cu(1 1 1)-electrode. The cyanate layers were adsorbed in 5 mM KOCN + 0.5 mM H 2SO 4 solution and measured in cyanate-free as well as in cyanate-containing sulphuric acid. The in situ IR spectra exhibit an absorption band near 2270 cm −1 of N-bound cyanate that partly appears bipolar and also shows a potential dependent frequency shift between 30 and 80 cm −1 V −1 depending on the surrounding electrolyte and the immersion potential. Further analysis of the frequency and intensity of the band as a function of the electrode potential during the IR measurements points to cyanate desorption below 0.1 V and a rearrangement of the remaining molecules from on top positions at high surface coverages to bridge or hollow adsorption sites at lower coverages. Simultaneously parts of the remaining adsorbate lie down flat on the surface as the potential and therewith the coverage decreases. Two additional absorption bands at 2169 and 2220 cm −1 are detected which are assigned to solved cyanate and a copper complex in the thin layer solution. After transfer into UHV, the system was studied by means of ex situ IRRAS and Auger electron spectroscopy (AES). The ex situ IR spectra display a similar band at around 2250 cm −1 as the in situ spectra with a clear dependence on the emersion potential. This indicates the successful transfer of the electrochemical double layer including the potential dependent occupation of different adsorption sites. AES data show that K + ions are replaced by H + when rinsing the cyanate-covered surface with dilute sulphuric acid in the electrochemical cell.