A study was made, of clean and oxidized (100) samples, grown from aluminum melts, by performing Auger, LEED, evaporation and work function measurements on well-defined surfaces. The clean surface showed no La enrichment when initially heated to as high as 1700C. The LEED pattern was 1 x 1; indicating no surface reconstruction. Langmuir evaporation studies at up to 1700C revealed only La and B, evaporating non-congruently, and LaO. The activation energy for B evaporation was abot 5.5eV; very close to that from elemental B. Rare-earth activation energies varied, being highest for the rare-earth whose pure metal vapor pressure was lowest. Oxidation was carried out at room temperature using O2 pressures of up to 10-7Torr and at 1000C using O2 pressures up to 10-4Torr. At room temperature, oxygen adsorption proceeded up to a saturation value indicated, by the LEED behavior, to be about one monolayer. It produced a monotonic work-function increase, which also saturated (at 1.40V); varying linearly with the oxygen uptake. Oxidation at 1000C was much more extensive than at room temperature; involving at least several monolayers, and resulted in a work function increase of 2.42V. The results were explained in terms of a terminal plane composed of La atoms, and adsorbed oxygen which, when given sufficient mobility, preferred bonding to La atoms at sites atop the B octahedra.

Characterization of Clean and Oxidized (100)LaB6. Goldstein, B., Szostak, D.J.: Surface Science, 1978, 74[2], 461-78