Quantum size effects in the electronic structure of low dimensional metallic systems

By angle resolved photoemission the electronic structure of quantum films of Mg, Ag, and Au has been compared on W 110 and Mo 110 substrates which are structurally and electronically very similar but differ in atomic number. In all cases, substrate induced states with characteristic dispersions are observed in the region of a bulk band gap of the substrate. Based on the comparison between Mo and W, we can exclude that previously observed Mg states are spin orbit split but observe a spin orbit splitting in Ag and Au monolayers. This splitting is mainly caused by the substrate because it does not differ much between Ag and Au overlayers despite the large difference in atomic numbe

Structural Stability of Stepped Nickel Surfaces

The structural stability of stepped Ni 755 and Ni 771 surfaces in the temperature range 20 500 degrees C and during adsorption of oxygen and different forms of carbon has been studied using scanning tunneling microscopy and low energy electron diffraction. A phase transition from the structure with double steps at room temperature to the structure with single steps at a temperature above 350 degrees C has been observed on the clean Ni 755 surface. This transition disappears after oxygen adsorption at a temperature above 350 degrees C. In this case, the structure on the Ni 755 surface with single steps is stabilized in contrast to Ni 771 , which tends to faceting during oxygen adsorption. It has been shown that fullerenes C 60 form an array of one dimensional chains at the upper boundaries of steps of the substrate, when they are adsorbed on the Ni 755 surfac

XPS and NEXAFS investigation of electronic energy structure of Ti Ni and TiNi Cu alloys

The electronic energy structure of Ti-Ni and TiNi-Cu alloys has been studied experimentally by XPS and NEXAFS and theoretically by the full-potential local-orbital minimum-basis code. The study has revealed formation in the valence band of the Ti50Ni50 alloy of a common d-band through hybridization of the d-states of Ti with those of Ni, which is localized within a narrow binding-energy interval. This brings about an intra-atomic redistribution of Ti electron density in the Ti50Ni50 alloy compared to the pure metal: decrease of the occupancy of the Ti d-shell is countered by an increase in the number of Ti p-electrons. The occupancy of the Ti d-shell in the TiNi-Cu alloys, where Ni atoms are partially substituted by Cu, and in the Ti-Ni alloys with an excess of the Ni is more than in the equiatomic Ti50Ni50 alloy. The occupancy of the Ni and Cu d-shells in the Ti-Ni and TiNi-Cu alloys is independent of the atomic composition. The Ti d-shell sensitivity to variation of the nearest atomic environment is apparently due to their relatively itinerant behavior in the studied alloys. The results obtained suggest that the increase of the stiffness of an interatomic bond in the TiNi-Cu alloys with increasing Cu content and in the Ti-Ni alloys with increasing Ni content is possibly associated with the filling of Ti bonding d-states.</jats:p