Synchrotron radiation photoemission study on growth of gadolinium film over Ni(110) surface

The growth of Gd film on Ni(110) surface was studied by synchrotron radiati on photoemission spectroscopy and XPS techniques. It is revealed that in th e coverage range of 0-0. 22 nm Gd4f core level showed a single-peak structu re, therefore Gd film grows over Ni(110) in the layer-by-layer mode. Howeve r, when Gd coverage was larger than 0.22 nm the Gd4f peak turned gradually into double-peak and a double-peak structure with 2.3 eV separation was for med at 1.51 nm, meanwhile similar phenomenon was observed in the Gd4d XPS s pectra. It is suggested that the double-peak structure of Gd4f was derived from the growth of Gd film in cluster mode and the Gd atomic clusters may e xhibit different electronic states from Gd metal owing to their special str uctures. The Gd4f double-peak evolved into a single-peak on annealing at 60 0 K, implying that Gd clusters are thermodynamically unstable.