Investigation of the La-Rh(100) surface alloy

In the present work surface alloy formation when La on Rh(1 0 0) is anneale d to 1350 K is investigated by photoelectron spectroscopy, low energy elect ron diffraction (LEED), and temperature programmed desorption (TPD). When a sub-monolayer of La deposited on Rh(1 0 0) is annealed, a LEED pattern wit h streaked fractional order spots appears. By increasing the La coverage a modified c(2 X 2) structure is formed. In this case split fractional order spots indicative of anti-phase domain effects are observed in LEED. Analyse s of the photoemission spectra of the Rh 3d(5/2) and La 5p core levels show that an ordering takes place in going from the as-deposited to the anneale d system, which results in a Rh terminated surface, TPD experiments of CO a dsorbed on the annealed La/Rh(1 0 0) system show CO desorption peaks at sig nificantly 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 thes e results it is concluded that a true, ordered surface alloy is formed with new electronic states. (C) 2001 Elsevier Science B.V. All rights reserved.