C Wigren

The surface core-level shift of the Pd(100) single-crystal surface

The surface core-level shift of the Pd(100) single-crystal surface has been measured from high-resolution Pd 3d core-level spectra. The surface atoms are found to have 0.44+or-0.03 eV lower binding energy than the bulk atoms. The result is compared with theoretical estimates.

Epitaxial silicide formation in the Mg/Si(111) system

Abstract The silicide formation has been studied in the Mg/Si(111) system by low energy electron diffraction (LEED) and photoelectron spectroscopy. It has been found that an epitaxial Mg 2 Si silicide is responsible for the ( 2 3 √3 × 2 3 √3)R30° reconstru system. The thickness of the silicide is limited due to the very low formation temperature for this silicide. The Fermi level is positioned 0.59 ± 0.06 eV above the valence band maximum in the Si substrate and the valence band maximum in the epitaxial silicide is positioned 0.3 ± 0.1 eV below the Fermi level.

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.

Etching and a disordered overlayer on the Ge(100)-S surface

High resolution core level photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM) have been used to study the adsorption and desorption of S on and off the Ge(100) surface. The pr ...

GROWTH AND EPITAXY OF YB SILICIDES ON SI(111)

Yb silicides have been grown epitaxially on the Si(111) surface using solid-state epitaxy with annealing to 400-degrees-C. The amount of deposited Yb was varied from parts of a monolayer to films b ...

Iodine reaction and passivation of the Ge(111) surface

Abstract The Ge(111)-I surface has been studied at different I coverages ranging from 0.05 ML up to saturation, and different annealing temperatures, using photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM). At saturation the surface is covered with I in the top site and GeI2 species in the bridge site, coexisting with small islands/clusters comprising GeI2, giving a total coverage of I in GeIx species of 1.15 ML. The chemically induced shifts in the Ge 3d core level are 0.39 eV per attached I atom. The coverage determined from the I 4d core level is higher than 1.15 ML, which we explain by the presence of I not bound to Ge. Annealing at 200°C decreases the iodine coverage, whereas the I 4d and Ge 3d line profiles are practically unchanged. Further heating desorbs the iodide species and restores the virgin c(2 × 8) structure.

Formation of Sm silicides on Si(111) : composition and epitaxy

The formation of Sm silicides on Si(111) by means of solid phase epitaxy has been studied with low energy electron diffraction, Auger electron spectroscopy and photoelectron spectroscopy of the Sm 4f level and Si 2p level. A limited reaction is found to occur already at room temperature whereas at higher temperatures a strongly intermixed Sm/Si layer showing some long range order is formed. The Sm atoms of this intermixed phase are found to be completely trivalent in accordance with expectations. The intermixed layer consists of two silicides with different compositions, one of them being SmSi2-x, the other being tentatively ascribed to SmSi.

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.

Measurement of metal-metal adhesion and interface segregation energies by core-level photoelectron spectroscopy: Al and Si on Mo(110)

Quantitative information about adhesion and segregation energies in metallic systems can be obtained by means of the binding energy shifts between different layers observed in core-level photoelectron spectroscopy. Layer-dependent Al2p core-level spectra for Al deposited on Mo(110) are presented. The difference in adhesion energy of Al and Si on Mo is found to be 0.24 eV per atom, with the Si-Mo bonding being the stronger one. It is found that the energetics favour a segregation of Si impurities in the Al layer to the Al/Mo interface. These results are shown to be in good agreement with calculations based on Miedemas scheme.

Surface related core level shifts for the Si(111)√3×√3: Al system

The Si(111)√3×√3:Al reconstruction has been studied by surface sensitive high resolution core level spectroscopy. It is shown that three components are needed to fit the Si 2p spectra. The Al 2p emission is found to consist of more than one component and it is argued that this is related to defects in the overlayer.