Evidence of possible band symmetry effects in STM studies of Gd overlayers

The thinner Gd films form a rectangular structure on both W(1 1 2) (1–2 ML (monolayers)) and Mo(1 1 2) (3–10 ML), with crystallite domains exhibiting a large in-plane aspect ratio along the 〈1̄ 1̄ 1〉 surface direction versus the 〈1 1̄ 0〉 direction. At slightly higher coverages on W(1 1 2) (and much higher coverages on Mo(1 1 2)), the Gd overlayer adopts an hexagonal packing consistent with that expected of the hcp crystal structure of Gd(0 0 0 1). The band symmetries are expected to differ substantially with structure, based on angle-resolved photoemission studies of Gd on Mo(1 1 2). With changes in the overlayer structure, the changes in the band symmetries, as well as occupied density of states, are believed to influence the tunneling current and hence the apparent corrugation observed in STM for Gd on W(1 1 2). Changes in the unoccupied states do not result in significant changes in the observed STM corrugation.