Chemisorption of CO on Co(0001). Structure and electronic properties

Abstract

Angle-resolved photoemission with synchrotron radiation, low-energy electron diffraction, and x-ray photoelectron spectroscopy have been combined to study the behavior of chemisorbed CO on the hexagonal Co(0001) surface as a function of coverage, temperature, and CO partial pressure. The band structure was measured for the $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ (coverage $\ensuremath{\bigominus}=\frac{1}{3}$ monolayer) and the $(2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ ($\ensuremath{\bigominus}=\frac{7}{12}$ monolayer) phases. The results are compared to tight-binding calculations and show that hybridization effects for the $5\ensuremath{\sigma}$ and $1\ensuremath{\pi}$ bands and orbital mixing are important. The photoemission cross sections (shape resonances) are found to be significantly different for the high- and low-temperature phases.