Atomic-resolution scanning tunneling microscopy and infrared spectroscopy as combined in situ probes of electrochemical adlayer structure: carbon monoxide on rhodium (111)

Abstract

Abstract : In-situ scanning tunneling microscopy (STM) has been combined with infrared reflection-absorption spectroscopy (IRRAS) to yield detailed atomic- level adlayer structures for saturated coverages of CO on ordered Rh(111) in aqueous solutions. Two distinctly different structures were obtained in CO- containing 0.1 M NaC104, depending on the electrode potential. At higher potentials, ca -0.1 to 0.3 V vs SCE, atomic-resolution STM images were obtained that indicated the presence of a (2 x 2)-3CO unit cell, having a CO coverage in agreement with electrochemical and IRRAS measurements. The corresponding in-situ infrared spectra indicate the presence of two atop (or near-atop) and one twofold bridging CO in the unit cell. A real-space structure is suggested that is related to the corresponding (2 x 2)-3CO adlattice on Rh(111) in uhv as deduced previously by low-energy electron diffraction and vibrational spectroscopy.