R. Rieger

Publications (9)14.79 Total impact

• Article: Electronic structure of large disc-type donors and acceptors.

  K Medjanik, D Kutnyakhov, S A Nepijko, G Schönhense, S Naghavi, V Alijani, C Felser, N Koch, R Rieger, M Baumgarten, K Müllen
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  ABSTRACT: Searching for new pi-conjugated charge-transfer systems, the electronic structure of a new acceptor-donor pair derived from coronene (C(24)H(12)) was investigated by ultraviolet photoelectron spectroscopy (UPS). The acceptor coronene-hexaone (C(24)H(6)O(6), in the following abbreviated as COHON) and the donor hexamethoxycoronene (C(30)H(24)O(6), abbreviated as HMC) were adsorbed as pure and mixed phases on gold substrates. At low coverage, COHON adsorption leads to the appearance of a charge-transfer induced interface state 1.75 eV below the Fermi energy. At multilayer coverage the photoemission intensity of the interface state drops and the valence spectrum of neutral COHON appears. The sample work function decreases from 5.3 eV (clean Au) to 4.8 eV (monolayer) followed by an increase to 5.6 eV (multilayer). The formation of a significant interface dipole due to charge-transfer at the metal-organic interface is possibly accompanied by a change in molecular orientation. HMC on Au exhibits no interface state and the sample work function decreases monotonically to ca. 4.8 eV (multilayer). The UPS spectra of individual donor and acceptor multilayers show good agreement with density functional theory modeling. In donor/acceptor mixed films the photoemission signal of the donor (acceptor) shifts to higher (lower) binding energy. This trend is predicted by the calculation and is anticipated when charge is transferred from donor to acceptor. We propose that mixed films of COHON and HMC constitute a weak charge-transfer system.
  Physical Chemistry Chemical Physics 07/2010; 12(26):7184-93. · 3.57 Impact Factor
• Source

  Available from: Jürgen P Rabe

  Article: Density-dependent reorientation and rehybridization of chemisorbed conjugated molecules for controlling interface electronic structure.

  B Bröker, O T Hofmann, G M Rangger, P Frank, R-P Blum, R Rieger, L Venema, A Vollmer, K Müllen, J P Rabe, A Winkler, P Rudolf, E Zojer, N Koch
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  ABSTRACT: The adsorption of the molecular acceptor hexaazatriphenylene-hexacarbonitrile on Ag(111) was investigated as function of layer density. We find that the orientation of the first molecular layer changes from a face-on to an edge-on conformation depending on layer density, facilitated through specific interactions of the peripheral molecular cyano groups with the metal. This is accompanied by a rehybridization of molecular and metal electronic states, which significantly modifies the interface and surface electronic properties, as rationalized by theoretical modeling.
  Physical Review Letters 06/2010; 104(24):246805. · 7.37 Impact Factor
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  Available from: Jürgen P Rabe

  Article: Gold work function reduction by 2.2 eV with an air-stable molecular donor layer

  B. Bröker, R.-P. Blum, J. Frisch, A. Vollmer, O. T. Hofmann, R. Rieger, K. Müllen, J. P. Rabe, E. Zojer, N. Koch
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  ABSTRACT: Ultraviolet photoelectron spectroscopy was used to investigate neutral methyl viologen (1,1′-dimethyl-1H,1′H-[4,4′]bipyridinylidene, MV0) deposited on Au(111). As a result of molecule-to-metal electron transfer, the work function of Au(111) was decreased from 5.50 to 3.30 eV. The energy levels of electron transport layers deposited on top of modified Au surfaces were shifted to higher binding energies compared to layers on pristine Au, and the electron injection barrier was reduced by 0.80 eV for tris(8-hydroxyquinoline)aluminum (Alq3) and by 0.65 eV for C60. The air-stable donor MV0 can thus be used to facilitate electron injection into organic semiconductors even from high work function metals.
  Applied Physics Letters 12/2008; 93(24):243303-243303-3. · 3.84 Impact Factor
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  Available from: Jürgen P Rabe

  Article: Tuning hole-injection barriers at organic/metal interfaces exploiting the orientation of a molecular acceptor interlayer

  J. Niederhausen, P. Amsalem, J. Frisch, A. Wilke, A. Vollmer, R. Rieger, K. Müllen, J. P. Rabe, N. Koch
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  ABSTRACT: Ultraviolet photoelectron spectroscopy was used to demonstrate organic/metal-contact charge injection barrier tuning by exploiting the orientation-dependent work function ϕ of a molecular acceptor [hexaazatriphenylene-hexanitrile (HATCN)] interlayer on Ag(111). The work function ϕ of a flat-lying HATCN monolayer on Ag was 4.6 eV (similar to a pristine Ag electrode), whereas a layer of edge-on HATCN on Ag exhibited ϕ of 5.5 eV (comparable to a pristine Au electrode). The hole-injection barriers (HIBs) between HATCN-modified electrodes and the organic semiconductors tris(8-hydroxyquinoline)aluminum (Alq3) and N,N′-bis(1-naphtyhl)-N,N′-diphenyl-1,1′-biphenyl-4.4′-diamine (α-NPD) were reduced by more than 1 eV compared to pristine Ag and Au electrodes. Noteworthy, the HIBs determined with the flat-lying HATCN interlayer were lower than those obtained for pristine Ag substrates (ϕ of both electrodes is 4.6 eV), and the HIBs with the edge-on HATCN on Ag were lower than those found for pristine Au (ϕ of both electrodes ca. 5.4 eV). This shows that acceptor interlayers are beneficial for charge injection in electronic devices even when the molecularly modified electrode ϕ is comparable to that of a pristine metal surface. It is argued that the molecularly modified electrodes are electronically more rigid than their pristine metal counterparts, i.e., the electron spill-out at the organic-terminated surface is less pronounced compared to Ag and Au surfaces.
  Phys. Rev. B. 84(16).
• Source

  Available from: Jürgen P Rabe

  Article: Density-Dependent Reorientation and Rehybridization of Chemisorbed Conjugated Molecules for Controlling Interface Electronic Structure

  B. Bröker, O. T. Hofmann, G. M. Rangger, P. Frank, R. P. Blum, R. Rieger, L Venema, A Vollmer, Klaus Müllen, J.P. Rabe, A Winkler, P Rudolf, E Zojer, N. Koch
  Physical Review Letters, v.104 (2010).
• Source

  Available from: Jürgen P Rabe

  Article: Density Dependent Reorientation and Rehybridization of Chemisorbed Conjugated Molecules for Controlling Interface Electronic Structure

  B Broker, OT Hofmann, GM Rangger, P. Frank, RP Blum, R. Rieger, L Venema, A Vollmer, K Mullen, JP Rabe, A Winkler, P Rudolf, E Zojer, N. Koch
• Article: Layer Growth, Thermal Stability, and Desorption Behavior of Hexaaza-triphenylene-hexacarbonitrile on Ag(111)

  P. Frank, T. Djuric, M. Koini, I. Salzmann, R. Rieger, K Müllen, R. Resel, N. Koch, A Winkler
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  ABSTRACT: Journal article
  J. Phys. Chem. C 114(2010),6650.
• Article: Layer Growth, Thermal Stability, and Desorption Behavior of Hexaaza-triphenylene-hexacarbonitrile on Ag(111)

  P. Frank, T. Djuric, M. Koini, I. Salzmann, R. Rieger, Klaus Müllen, R. Resel, N. Koch, A Winkler
  Journal of Physical Chemistry C, v.114, 6650-6657 (2010).
• Article: Electronic structure of large disc-type donors and acceptors

  K. Medjanik, D. Kutnyakhov, S A Nepijko, G. Schönhense, S. Naghavi, V. Alijani, C. Felser, N. Koch, R. Rieger, Martin Baumgarten, Klaus Müllen
  Physical Chemistry Chemical Physics, v.12, 7184-7193 (2010).