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Surface-umklapp in ARPES at an organic-metal interface

We show that angle-resolved photoemission performed using low-energy photons on an organic-metal interface allows to clearly distinguish genuine interface states from features of substrate photoelectrons diffracted by the molecular lattice. As a model system an ordered monolayer of Zn-phthalocyanine is used as a diffraction lattice to probe the electronic band structure of a Ag(110) substrate. Photoemission close to normal emission geometry reveals strongly dispersive features absent in the pristine substrate spectra. Density functional theory modeling helped identifying these as bulk sp direct transitions undergoing surface-umklapp processes. The present results establish the important role of final-state diffraction effects in photoemission experiments at organic-inorganic interfaces. Moreover, this phenomenon is illustrated through a series of examples of noble-metal single-crystal surfaces covered by monolayers of large π-conjugated organic molecules.

Retrieve articles Final-state diffraction effects in angle-resolved photoemission at an organic-metal interface F.C. Bocquet, L. Giovanelli, P. Amsalem, L. Petaccia, D. Topwal, S. Gorovikov, M. Abel, N. Koch, L. Porte, A. Goldoni, J.-M. Themlin, Phys. Rev. B 84, 241407(R) (2011). doi: 10.1103/PhysRevB.84.241407 Interpretation of valence band photoemission spectra at organic-metal interfaces L. Giovanelli, F.C. Bocquet, P. Amsalem, H.-L. Lee, M. Abel, S. Clair, M. Koudia, T. Faury, L. Petaccia, D. Topwal, E. Salomon, T. Angot, A.A. Cafolla, N. Koch, L. Porte, A. Goldoni, J.-M. Themlin, Phys. Rev. B 87, 035413 (2013). doi: 10.1103/PhysRevB.87.035413