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SMALL Kick-off meeting , Madrid| Jan 2011

Electron spectroscopy James N. O’Shea School of Physics & Astronomy Nottingham Nanoscience and Nanotechnology Centre University of Nottingham. SMALL Kick-off meeting , Madrid| Jan 2011. Outline Something to study: Dye molecules Chemical information: XPS Molecular orbitals: PES & XAS

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SMALL Kick-off meeting , Madrid| Jan 2011

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  1. Electron spectroscopyJames N. O’SheaSchool of Physics & AstronomyNottingham Nanoscience and Nanotechnology CentreUniversity of Nottingham SMALL Kick-off meeting , Madrid| Jan 2011

  2. Outline Something to study: Dye molecules Chemical information: XPS Molecular orbitals: PES & XAS Adsorption geometry: XAS Charge transfer dynamics: RPES SMALL Kick-off meeting , Madrid| Jan 2011

  3. Dye molecules on surfaces

  4. Charge injection interface How is the molecule bonded to the surface? What can we say about the electronic coupling? LUMO HOMO

  5. A model dye-sensitised system LUMO HOMO

  6. Vacuum level KE hv BE L. Patthey et al, J. Chem. Phys. 110, 5913 (1999) Core-level photoemission LUMO HOMO Core level

  7. Intensity (arb. Units) Ethyl-trifluoroacetate K. Siegbahn et al Chemical shift (eV) Chemical information with x-ray photoelectron spectroscopy (XPS) Although the core-level electrons are not directly involved in the formation of bonds, a change in the valence electrons (chemical state) will change the potential a core-electron feels and therefore modify the binding energy.

  8. Vacuum level KE hv BE Core-level photoemission LUMO HOMO Core level L. C Mayor et al, J. Chem. Phys. 129, 114701 (2008)

  9. Electron spectroscopy is surface sensitive We all know that x-rays themselves can penetrate deep into most matter… …but the electrons coming out can only travel through a couple of layers without banging into something along the way.

  10. Surface sensitivity of XPS

  11. KE hv BE Occupied states: valence photoelectron spectroscopy Vacuum level

  12. BEres BEcore hv Unoccupied states: x-ray absorption spectroscopy (XAS) Vacuum level

  13. Molecular orientation & XAS J. Ben Taylor et al, J. Chem. Phys. 127, 134707 (2007)

  14. Vacuum level hv RPES: Participator decay Participator electrons leave the atom in a final state just like valence photoemission. They track with constant binding energy. LUMO HOMO N1s

  15. Vacuum level hv RPES: Spectator decay Spectator electrons leave the atom in a final state just like Auger decay with an extra electron in an unoccupied state. They track with constant kinetic energy…like Auger electrons but shifted up. LUMO HOMO N1s

  16. Vacuum level hv RPES: Auger decay Charge transfer of the originally excited electron leaves Auger decay as the only non-radiative core-hole decay option. They track with constant kinetic energy. LUMO HOMO N1s

  17. LUMO LUMO+1 LUMO+2 Participator J. Schnadt et al, Nature 418, 621 (2002) J. Schnadt et al, Nature 418, 621 (2002) Bi-isonicotinic acid on rutile TiO2(110)

  18. The benchmark The sensitivity of RPES compared to XAS intensity is assessed for the decoupled molecule (multilayer) where no charge transfer is expected for any unoccupied state. A state-dependent ratio that we call C is generated for the case of an isolated molecule (in this case, C=⅓). J. Schnadt et al, Nature 418, 621 (2002)

  19. Pulling out charge transfer timescales

  20. Conclusions Chemical information: XPS Molecular orbitals: PES & XAS Adsorption geometry: XAS Charge transfer dynamics: RPES SMALL Kick-off meeting , Madrid| Jan 2011

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