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The Fermi surface of ErSi1.7(0001) thin films grown epitaxially on Si(111) has been measured by angular photoemission intensity distribution maps at different photon energies using synchrotron radiation. Valence-band spectra at different collection angles along the main symmetry directions of the surface Brillouin zone (SBZ) have been measured, and they have allowed us to find that the Fermi surface is characterized by hole and electron pockets at particular high-symmetry points of the SBZ. The shape of the experimental Fermi surface for different photon energies is similar, indicating a bidimensional electronic character, in contrary to the expectation based upon band-structure calculations and the crystallographic structure. Moreover, Si 2p core-level photoemission spectra taken at surface-sensitive conditions reveal only one chemical state for the Si atoms at the surface layer.

The structure and electronic properties of the interfaces formed by Re evaporation on clean Si(111)-7 × 7 and subsequent annealing were investigated by low energy electron diffraction (LEED), Photoelectron spectroscopy (XPS/XAES, UPS) and work function (WF) measurements. Rhenium was deposited from submonolayer up to 50 ML coverages and gradually annealed up to 1100 K. Deposition causes rapid disappearance of the 7 × 7 reconstruction and the substrate UPS features, a gradual increase in the WF from 4.5 to 5.1 eV and negligible chemical shift in the XPS/XAES peaks. The interface remained abrupt with no intermixing, as metallic Re grew in a simultaneous multilayers fashion above 0.8 ML coverage. Annealing of 50 ML of Re causes a Si enrichment of the overlayer above 600 K and the formation at around 950 K of a continuous layer of silicide which remains stable up to 1100 K, whereas annealing of Re layers close to 1 ML creates ReSi 2 islands on the substrate surface.

ErSi2−x silicides, bulk and epitaxially grown on Si(111), are investigated by X-ray absorption spectroscopy at Er L edges in order to determine the effects of the relaxation due to the silicon vacancies on the local environment of erbium in those materials. The value of the shortest Er-Si bond length derived from the L1 edge data is found to be 2.95 ± 0.03 A, in agreement with previous neutron diffraction data giving an orthorhombic-hexagonal deformation of the AlB2 structure where the Si vacancies are ordered. The same bond length is deduced from L3 edge data recorded from epitaxial film. This result is consistent with a simple model for the relaxation due to the vacancies in these epitaxial films, where the hexagonal symmetry is preserved. The effect of the strain due to the mismatch to the Si substrate is also evidenced from EXAFS. Preliminary results on a two-dimensional erbium silicide layer are given, showing the strong anisotropy of Er environment for one monolayer Er coverage.

The formation of erbium silicide ErSi1.7 interface and thin films on plane and stepped Si(100) surfaces have been investigated by low-energy electron diffraction (LEED), photoelectron spectroscopy (XPS and UPS) and Auger electron spectroscopy (AES). For the interfaces, approximately 0.3–2 ML of Er was evaporated on the substrate and subsequently annealed at 400–600°C. For the thin films the co-evaporation method was used. On stepped Si(100) the surface state disappears less rapidly than on a plane one, suggesting a preferential clustering of the silicide along the steps. Upon annealing of the deposits (~ 50 to 100 A) a diffuse (2 × 2) LEED pattern is observed at 600–800°C. This pattern corresponds to a (2 × 1)ErSi 1.7 (10 1 2) . The valence bands show two main peaks at 1.3 and 2.8 eV and no dispersion in the surface plane, confirming the poor crystallinity of the film. The results are discussed with those obtained for ErSi 1.7 Si (111) .

The electronic structure of erbium silicide ultra-thin films epitaxially grown on Si(111) has been studied by means of angle-resolved ultra-violet photoemission spectroscopy (ARUPS) in the coverage range 0.2–4 monolayers (ML). Some peaks probably related to the silicide surface atomic structure are observed at any coverage. Features that appear at normal emission in connection with an R3 superstructure are ascribed to vacancy-induced states in the silicon surface plane. No true interface states could be identified in this study.

Er metal has been evaporated on clean Si(111)(7 × 7) substrates at room temperature and the ErSi interaction at the interface studied by low energy electron diffraction (LEED). X-ray photoemission spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES). The use of the low and high energy X-ray lines given by the Zr anode (Zr Mξ and Lα) have allowed us to detect respectively the surface sensitive Si2p core-level and the chemical state sensitive Si KLL Auger transition, and hence, to evidence the inter-diffusion and to determine the nature of the reacted phase(s). A three-step mechanism has been found: formation of a chemisorbed layer until a critical coverage θ c ≈ 0.8 ML (monolayer) is attained, inter-mixing reaction in the ∼ 0.8–2.5 ML range giving a silicide-like layer, and growth of a nearly pure Er upper layer.

The electronic properties of erbium silicide thin films epitaxially grown on Si(111) have been investigated by X-ray and UV photoemission. The crystalline quality has been checked by low-energy electron diffraction. XPS indicates very weak charge transfer and metallic bonding in the silicide phase. The Si 2p core-level and the Auger transition Si KLL present double structures revealing two types of Si sites, the first one attributed to Si atoms in normal sites in the silicide and the second one to Si atoms in the vicinity of the vacancies and (or) the Si substrate portions seen through the holes of the film. The UPS valence band of about 4 eV width and formed of Er(6s5d)-Si(3s3p) hybridized states disperses weakly in the direction perpendicular to the surface and strongly in the surface plane. This valence band is compared to the ones already measured on YSi −1.7 and GdSi −1.7 and to the calculations made for YSi 2

We report UPS, AES and WF measurements on the interaction of K and O 2 on thin semiconducting epitaxial layers of β-FeSi 2 on Si(111). Oxygen was adsorbed on clean and K-covered β-FeSi 2 at 300 K and the system was heated up to 900 K with the suicide remaining stable. A correlation of the experimental results indicates that at RT on clean β-FeSi 2 oxygen chemisorbs dissociatively on silicon sites and does not interact with iron. In the presence of K oxygen chemisorbs on iron and on silicon sites with an increased sticking coefficient. No potassium oxide was formed. Upon heating up to 800 K SiO 2 is formed on the suicide film under conditions in which the suicide remains stable.

The unoccupied electronic states of the interfaces formed by the heavy refractory metals (W, Mo, Ta and Nb) with a silicon substrate have been investigated by inverse photoemission in the UV range. Emission from metals dominates the IPE spectra. In the submonolayer range the four metals give alike unoccupied densities of states, consisting of a broad structure centered at about 2–3 eV above the Fermi level, which is attributed to the antibonding states of the chemisorbed metal atoms. At higher surface coverage θ, two types of spectrum evolution are observed. For Mo and W on the one hand, which form abrupt interfaces with Si, the IPE spectra tend rapidly towards the metal ones, already attained at θ ⩾ 3 ML. For Nb and Ta on the other hand, which form “surface disilicide” thin layers and diffuse interfaces, the metal spectra develop at much higher θ. The conduction bands of the “surface disilicides” are different from bulk silicide ones, indicating a lack of long range order.

Electron energy loss spectroscopy (EELS) has been applied to investigate the Co/Si(111) interface formation at room temperature. The results allow to conclude that at very low coverage θ ⩽ 2 − 3 monolayers a CoSi 2 -like phase is already formed. With higher coverages the topmost layer displays an average composition richer in Co and finally for θ ⩾ 10 monolayers a film of almost pure Co is growing on top of the interface. During the interface development, an interface plasmon coupling effect has also been evidenced by the EELS technique.

The interfaces formed by Si evaporated onto a Ni(100) surface have been studied by ultraviolet photoemission and inverse photoemission spectroscopy in the VUV range. It is found that at room temperature the first stage of compound formation corresponds to a “Ni 2 Si” type silicide; as more and more silicon is deposited on the clean Ni surface, a NiSi-like phase is obtained and then finally amorphous silicon is observed for high coverage.