HYDROGEN ADSORPTION ON GD(0001)

The electronic structure of hydrogen adsorbate-induced states on Gd(00 01) was investigated by means of photoelectron spectroscopy with linea rly polarized radiation. The E Vector of the incoming photon beam is r otatable. Clean and well-ordered rare-earth (0001) surfaces exhibit a highly localized surface state near the Fermi edge. After the adsorpti on of hydrogen, the surface state disappears and an additional sharp f eature at about 4 eV binding energy is observed. For this latter d(z)2 -like state, the ratio of the radial matrix elements as well as the re lative phase shifts were determined to be R=R-p/R-f=2.4+/-0.3 and delt a(f)-delta(p)=310+/-10 degrees, respectively. The removal of the Gd su rface state by hydrogen adsorption was investigated by means of scanni ng tunneling microscopy (STM) and spectroscopy (STS). The removal of t he surface state exhibits domain-like behavior, with surface steps act ing as domain boundaries. The tunneling spectra reveal that hydrogen a dsorption causes a dramatic reduction in the differential conductivity near the Fermi level. (C) 1998 Elsevier Science B.V. All rights reser ved.