Surface combinatorial studies of IR properties of nanostructured Ru film electrodes using CO as probe molecule

Abstract

An individually addressable array of Pt microelectrodes was designed and prepared. Ru film of different nanostructures was prepared electrochemically on platinum microelectrodes of the array under cyclic voltammetric conditions. The electrochemical behavior and surface structure of the Ru film were investigated, respectively, using cyclic voltammetry and scanning tunneling microscopy. In combining the individually addressable array with an in situ microscope FTIR reflection spectroscopy (MFTIRS), surface combinatorial studies of IR properties of different nanostructured Ru films have been conveniently carried out. In situ microscope FTIR spectral library of CO adsorbed on different nanostructured Ru films and at different electrode potentials was acquired rapidly. Particular IR properties of nanostructured Ru film were revealed. IR absorption of both bridge-bonded CO (CO B, around 1800 cm −1) and linearly bonded CO (CO L, near 2000 cm −1) was significantly enhanced, and an enhancement factor of IR absorption has been determined to be varied between 11.8 and 15.5 along with the variation of nanostructure of Ru film on the array. Following consecutive increase in thickness of Ru film and in size of Ru islands that form the film, CO B species yielded always a broad band appearing in anti-absorption direction, while CO L species produced an IR band that was transformed from a bipolar shape to monopolar shape of anti-absorption direction. Together with the shift of IR band center, the large increase in IR bandwidth and in Stark tuning rate, the particular IR properties were illustrated as a change from Fano-like asymmetric spectral characteristics to abnormal IR features, and attributed to the consecutive variation of nanostructure of Ru film on the individually addressable array.