Interaction of nanostructured metal overlayers with oxide surfaces

There are many two-dimensional superconductors, but only now have monolayers of metallic atoms shown superconductivity. Grown on silicon substrates, epitaxial films of lead and indium represent the thinnest superconductors possible.

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Superconductivity in one-atomic-layer metal films grown on Si(111)

Oxygen plasma treatment of indium tin oxide (ITO) results in a change in work function and electron affinity by ∼0.5 eV. This change correlates with the measured increase in injected current in simple “hole-only” organic devices with O-plasma treated ITO electrodes. Neither addition nor removal of surface hydroxyl functionality accounts for the observed work function and electron affinity changes. X-ray and ultraviolet photoelectron spectroscopies show a new type of oxygen species is formed. Oxidation of surface Sn-OH to surface Sn-O• units is proposed to account for the observed changes in O-plasma treated ITO; this proposal can explain a wide variety of previously described ITO surface activation results.

/pdf/surface-oxidation-activates-indium-tin-oxide-for-hole-4ql2x5ope2.pdf

Surface oxidation activates indium tin oxide for hole injection

http://fizz.phys.dal.ca/~ihill/Publications_files/Goteborg.pdf

Organic semiconductor interfaces: electronic structure and transport properties

Hydrogen interaction with clean and modified silicon surfaces

The complete phase diagram of In-induced surface reconstructions on Si(111) surfaces has been mapped by scanning tunneling microscopy (STM) and spectroscopy (STS) The spectroscopy results illustrate the transition from low-coverage semiconducting reconstructions via semimetallic phases to the metallic surfaces at monolayer coverages Electronic effects in the STM imaging process preclude a straightforward interpretation of the STM data in terms of structure models for the surfaces at intermediate coverages, but for the higher-coverage metallic phases a topographic STM analysis is possible and detailed structure models are presented The In-Si(111) monolayer surfaces are interpreted in terms of regular adlayer structures above the first Si double layer, but discommensurate phases are observed in the presence of an external stress field, introduced by an external perturbation

Surface reconstructions of In on Si(111)

The structure of the indium-Si(111) ( 7 × 3) monolayer surface

The evolution of core-level photoemission spectra has been studied during the initial stages of Cs and In overlayer growth on thin ${\mathrm{SiO}}_{2}$ layers on Si(111) substrates to probe the influence of the metal-${\mathrm{SiO}}_{2}$ interaction on the charge state of the resulting structure. The Si 2p soft-x-ray photoelectron spectra on the ${\mathrm{SiO}}_{2}$ and the Si substrate, which have been recorded simultaneously, show substantially different shifts to higher binding energy for the two components of the structure for Cs adsorption on the ${\mathrm{SiO}}_{2}$ surface, but only small uniform shifts for In overlayers. The Si 2p core-level spectra have been analyzed by simulating the spectra with a model that separates the Cs-covered ${\mathrm{SiO}}_{2}$ structure into thin layers with a constant dipole field gradient applied across them. Accordingly, the metal-induced Si 2p core-level shifts of the Si substrate are interpreted in terms of Si band-bending changes as a result of charge transport from the metal layer to the ${\mathrm{SiO}}_{2}$/Si interface. The differential Si 2p shifts, which lead to a larger separation of substrate and oxide peaks on cesiated ${\mathrm{SiO}}_{2}$/Si than on the pristine ${\mathrm{SiO}}_{2}$/Si structure, are discussed in terms of a Cs-induced dipole field across the ${\mathrm{SiO}}_{2}$ layer. It is proposed that the different behavior of Cs and In overlayers may be related to the different electronegativity and, consequently, to the different adsorbate dipoles of the two metals.

J. Kraft

Papers

Surface reconstructions of In on Si(111)

The structure of the indium-Si(111) ( 7 × 3) monolayer surface

Metal-overlayer-induced charge-transfer effects in thin SiO 2 -Si structures

Electronic structure and morphology of In-oxide-Si(111) interfaces

Strain relief, close-packed overlayer formation and discommensurate phases: In on Si(111)