A. Stenborg

The adsorption of Sm on a Mo(110) surface

The adsorption of Sm on a Mo(110) surface at room temperature is studied as a function of coverage up to several monolayers with AES, LEED, work function change measurements, thermal desorption spectroscopy and low energy electron loss spectroscopy with the goal to determine the evolution of the structure and of structure-related properties with the dimensionality of the system. Although many similarities are found to other rare earth adsorbates on Mo(110) and W(110) such as Eu, Gd, Tb, Yb also features specific to Sm are noted such as a particularly pronounced tendency to island formation. The relation between structure and electronic structure is also discussed.

Coverage dependent core level shifts for electropositive metals adsorbed on metals; Yb on Mo(110)

Abstract The coverage dependent 4f binding energy shifts of Yb adsorbed on Mo(110) were studied by photoemission. The measurements were performed at the TGM beam line at the MAX synchrotron radiation facility in Lund, Sweden. The measured 4f binding energy undergoes a continuous shift from 1.65 eV at a coverage of θ a = 0.01 to 0.88 eV at the complete monolayer. The slope of the shift curve changes drastically at the transition from an n × 2 LEED pattern to a hexagonal one. The results are discussed in terms of a total energy interpretation of the shifts and are compared to the behaviour of other electropositive metal overlayer systems.

Ordered structures of Yb and Sm on a Mo(110) surface

Ordered structures of thin layers of Yb and Sm on a Mo(110) surface have been studied. The discussions are based on results from low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), work function change (Δσ) measurements and thermal desorption spectroscopy (TDS). The main features in LEED, Δσ and thermal desorption spectra upon increasing adsorbate density show many similarities, at least up to a coverage of one monolayer. The first ordered phase is, for instance, of an (n×2) type and starts to grow in islands, and a continuous one-dimensional compression is present at higher coverages in both cases. There are also significant differences between the elements, such as the coverage at which the island formation starts. The coverage of the closely packed monolayer and the behaviour above the monolayer point also differ. The results are discussed with respect to differences in electronic structure and form bases for further investigations relating to the question of the intermediate valence of surface Sm.

Two-dimensional intermetallic Yb-Ni compounds

Abstract Two-dimensional (2D) Yb-Ni intermetallic compounds formed by co-depositing Yb and Ni on a Mo(110) surface have been studied with high resolution core level photoemission and LEED. Two 2D intermetallic compound phases, Yb 2 Ni and YbNi 2 , were found to develop. The Yb 2 Ni compound is characterized by a 7 × 2 LEED pattern and an Yb 4f 7 2 binding energy of 1.0 eV, the YbNi 2 by a 3 × 2 LEED pattern and a 4f 7 2 binding energy of 0.6 eV. Models for these phases are proposed from the LEED patterns and are shown to be consistent with the Yb core level binding energies. A phase diagram of the Yb-Ni on Mo(110) 2D system is proposed based on separation into Yb 2 Ni, YbNi 2 and pure Yb and Ni layers. This phase diagram is discussed in terms of a competition between the 2D compound heat of formation and the lowering of the Mo(110) surface energy by adsorbed Yb.