THE ELECTRONIC-STRUCTURE OF GADOLINIUM GROWN ON MO(112)

The electronic structure of strained ultra-thin and thin films of Gd g rown on a corrugated Mo(112) surface are described. Gadolinium overlay ers order at a coverage of 2/3 monolayers forming a p(3 x 2) LEED patt ern. At this coverage an interface state of b(1) symmetry (d(xz), p(x) ) is formed at a binding energy of similar to 0.3 eV at the surface Br illouin zone centre (<(Gamma)over bar>). The effective mass of this in terface state was determined to be (2.7 +/- 0.2) m(e), in both orthogo nal directions along the nearly square reduced Brillouin zone. For thi cker Gd films of approximately 3 to 10 ML thickness, the corresponding gadolinium state switches symmetry to the a(1) representation (Gd 5d( z2-r2) or 6s character) and has a much larger effective mass. The over layer forms a rectangular surface Brillouin zone resembling the hcp (< 10(1)under bar 2>) surface. Gadolinium films thicker than approximatel y 10 ML form strained hexagonal ordered films also with substantial mi sfit dislocations. The strain of the thin hexagonal ordered Gd films i s reflected by a reduced Brillouin zone size along <(Gamma Sigma M)ove r bar> by approximately 4% with respect to the less strained Gd overla yers on W(110) and Gd(0001) single crystals. The induced strain severe ly alters the band structure of the Gd 5d/6s bulk bands, which dispers e in the opposite direction relative to the corresponding bands of the relaxed Gd(0001) structure. The surface of the strained hexagonal fcc (111) or hcp (0001) Gd films forms a localized state of a(1) symmetry (Gd 5d(z2-r2) or 6s character) at approximately 0.7 eV binding energy . There is little observed strain relief within the Gd films up to app roximately 150 Angstrom film thickness.