Investigation of the La–Rh(1 0 0) surface alloy

In the present work surface alloy formation when La on Rh(1 0 0) is annealed to 1350 K is investigated by photoelectron spectroscopy, low energy electron diffraction (LEED), and temperature programmed desorption (TPD). When a sub-monolayer of La deposited on Rh(1 0 0) is annealed, a LEED pattern with streaked fractional order spots appears. By increasing the La coverage a modified c(2×2) structure is formed. In this case split fractional order spots indicative of anti-phase domain effects are observed in LEED. Analyses of the photoemission spectra of the Rh 3d5/2 and La 5p core levels show that an ordering takes place in going from the as-deposited to the annealed system, which results in a Rh terminated surface. TPD experiments of CO adsorbed on the annealed La/Rh(1 0 0) system show CO desorption peaks at significantly lower temperature than CO on the as-deposited La/Rh(1 0 0), but still higher than the desorption peaks found for CO on Rh(1 0 0). From these results it is concluded that a true, ordered surface alloy is formed with new electronic states.