SURFACE-STRUCTURE OF RARE-EARTH-METALS

We have performed LEED, angle-resolved UV photoemission (ARUPS) and inverse photoemission (IPE) measurements on a representative set of hcp rare earth surfaces in order to obtain basic structural information. LEED patterns from the (0001) surfaces show six-fold symmetry due to the two equally probable bulk terminations. ARUPS data show a large non-dispersing peak at approximately 10 eV binding energy, with intensity extremely sensitive to surface order, which is not reproduced in one-electron calculations. Suggestions that this many-body feature is due to an unoccupied surface state are supported by our IPE data, which appear to show such a state just above the Fermi level. LEED patterns from the (1120BAR) surfaces of Y, Ho and Er also show six-fold symmetry, with no visible substrate spots, implying that these relatively open surfaces have collapsed to a (7 x 1) close-packed structure many layers deep. ARUPS data from the reconstructed (1120BAR) surface of Ho are virtually indistinguishable from those obtained from Ho(0001). This suggests that the two structures are identical within the probing depth of this technique.