Site switching and restructuring of oxygen adlayers induced by high coverage NO on Co{101̄0} at 100 K

Abstract

We have employed reflection–absorption IR spectroscopy (RAIRS) as the principal technique as well as low energy electron diffraction (LEED) and temperature programmed desorption (TPD) as diagnostic tools to study the adsorption and reaction of nitric oxide (NO) on oxygen precovered Co{101̄0} surfaces at 100 K. The presence of oxygen adatoms greatly attenuates the occupation of two-fold sites in favor of atop sites, but O adatoms do not show any significant blocking effect for NO adsorption, and the NO coverage is close to 0.5 ML, as found on the clean surface. Beyond a critical coverage of NO, whatever the initial O coverage, a new IR band appears at ∼1876 cm−1 which is indicative of a strong NO–O interaction. The coadsorption of NO with various precoverages of oxygen (0.15–1.0 ML) including three ordered oxygen overlayers, c(2×4) (θO≈0.5 ML), p(2×1) (θO≈0.5 ML), and p(2×1)-g (θO≈1.0 ML), reveals an NO-induced surface restructuring process, in which O adatoms are driven from overlayer to underlayer sites at high NO coverages. This restructuring process increases the O effective diameter to up to ∼10 Å, this being the range over which the NO–O interaction is strong, producing the 1870 cm−1 N–O band.