He-diffraction studies of hydrogen chemisorption on rhodium (311)

The (311) surfaces of fcc materials are of special interest as they offer, due to the existence of (111) and (100) microfacets, a large variety of differently coordinated adsorption sites. He atom beam diffraction experiments were performed on Rh(311) in order to investigate the formation of ordered chemisorption structures of hydrogen. The observation of c(1 × 3), p(1 × 1) and p(1 × 1) _REC phases is in agreement with previous LEED studies. However, before the formation of the c(1 × 3), a c(1 × 1) phase was identified with He diffraction, which requires a coverage of 1 ML. Therefore, the initial sticking coefficient of hydrogen is practically unity and the saturation H-coverage reached in the p(1 × 1) _REC phase is 2-3 ML, much larger than anticipated.