Core-level Components Research Articles

High-resolution photoemission study of Co/Si(111) interface formation.

We have examined the formation of the Co/Si(111) interface at room temperature using high-resolution core-level photoemission spectroscopy. Two chemically shifted Si 2p core-level components have been identified. The evolution of these components with Co coverage makes it possible to model the development of this interface. Heterogeneous ${\mathrm{CoSi}}_{2}$-like cluster formation is observed for nominal Co coverages of less than \ensuremath{\approxeq}4 A\r{}. Continued reaction to form ${\mathrm{CoSi}}_{2}$ becomes diffusion limited when the clusters coalesce, and a solid solution forms with Si atoms in a Co matrix. For Co coverages of more than 8--10 A\r{}, the interfacial region is buried by a metallic Co film.

Transition metals on GaAs(110): A case for extrinsic surface states

The interactions of transition metal overlayers with the GaAs(110) cleaved surface have been investigated using core level photoemission spectroscopy. The appearance of chemically shifted core level components for coverages of a fraction of a monolayer indicate that both Mn and V overlayers interact strongly with the cleaved surface. At higher coverages there is evidence for the outdiffusion of both Ga and As into the metal overlayer. Valence band spectra for the V overlayer exhibit strong emission in the semiconductor band gap associated with d-electron states of the transition metal atoms. The onset of this emission coincides with the position of the surface Fermi level, which suggests that these states are responsible for Fermi level pinning. Photoemission core level studies suggest that the origin of the interface states is associated with an exchange reaction of the metal and the gallium. The notion that a transition metal impurity state is responsible for the pinning of the Fermi level at the interface is formulated and supported by the experimental results. Fermi level shifts for both n- and p-type crystals were investigated over a broad coverage range. The pinning position in the band gap was found to be identical for both n- and p-type crystals, however the final barrier heights varied for the different transition metals. Schottky barrier heights of 0.75 (0.68)±0.05 eV for V and 0.84 (0.59)±0.05 eV for Mn were measured for n- and p-type substrates.

Angle resolved photoemission studies of the band structures of semiconductors: PbI 2

Angle resolved photoemission data is presented for single crystals of the layered semiconductor PbI 2. The geometric form of the valence electron energy bands has been mapped using a simple approximation and the possible electronic origins of these bands are discussed. Such band dispersion effects in angle resolved measurements are contrasted with HeII excited data for the localised Pb 5 d 5 2 core level component, where “flat” band behaviour and only weak residual final state scattering effects may be discerned. Finally we comment on the role of the incoming photon in such experiments.