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Craig (1993)–tilted, calculation

Polarization and angle-resolved NEXAFS of benzene adsorbed on oriented single-domain Si(100)-2x1 surface, N. Witkowski(France), F. Hennies, A. Pietzsch, S. Mattsson, A. Fohlisch, and W. Wurth (Germany) M. Nagasono(Kyoto U., Japan), M. N. Piancastelli(Italy),

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Craig (1993)–tilted, calculation

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  1. Polarization and angle-resolved NEXAFS of benzene adsorbed on oriented single-domain Si(100)-2x1 surface, N. Witkowski(France), F. Hennies, A. Pietzsch, S. Mattsson, A. Fohlisch, and W. Wurth (Germany) M. Nagasono(Kyoto U., Japan), M. N. Piancastelli(Italy), Phys. Rev. B 68, 115408 (2003).

  2. Taguchi (1991)–butterfly or tilted, ~1 benzene/ 2 dimers (TDS, AES, HREELS) Craig (1993)–tilted, calculation Jeong (1995)–Pedestal, Semiempirical calculation Birkenheuer (1998)–butterfly, First princlple, density functional calculation Gokhale (1998)–butterfly, TDS, UPS

  3. Lopinski (JVST,1998)–butterfly -> pedestal, STM, FTIR Borovsky (PRB,1998)–butterfly -> tilt, STM,

  4. Kong (SS,1998) – butterfly -> tilt, (NEXAFS,TDS,IR) Molecular benzene Physisorbed benzene Chemisorbed benzene No peak at 288.8 eV -> Breaking of conjugated benzene ring At RT, benzene is chemisorbed like (a) then, is transformed into (c) after a long time.

  5. Experiment At MAX-Lab BL I511 (providing linearly polarized light) Endstation - Prep. + Analysis chamber(XPS, NEXAFS, XES) Sample - 5o-off vicinal Si(100) -8.5 dimers per terrace - two SD-samples 90o-rotated each other Sample cleaning & preparation - Xe-sputtering at RT(800K) & annealing (1250K) cycles - 10L of benzene exposure at RT ~ saturation coverage NEXAFS measurements - scanning photon energies while monitoring CFS (KLL carbon Auger peak) - Emission angle = 55o,

  6. 10L benzene/Si(100) at RT • 284.8 eV – C 1s -> π* • 286.9 eV – C 1s -> σC-H* • Still, C=C double bond is preserved at RT. • ---- > Pedestal can be excluded !!!!

  7. Overall decrease of the peak at 248.8 eV compared with Fig. 2 • -> molecule is close to in-plane (but, not parallel to the surface) • Apparent difference between Fig. 3 and Fig. 4 • -> π* resonance has an in-plane component normal to the dimers • No asymmetric shape (contrary to the previous NEXAFS results (Tong, SS 1998)) • -> Not a metastable species ! (Also, no change after further annealing) • σC-H*resonance appears all in Fig. 2-4. • -> C-H is tilted away from in-plane or out-of plane • No 289 eV peak (due to conjugated benzene ring) -> aromatic ring is broken. • ---- > Butterfly rather than tilted geometry !!!!

  8. From Fig. 5, adsorbed benzene has a mirror plane perpendicular to the dimer. • From Fig. 6, adsorbed benzene has a mirror plane parallel to the dimer. • Small difference in the CH* resonance -> a slight distortion on each side • -> step edge effect(?)

  9. Summary • Major conclusions that can be drawn from the above results are, • Still, π-bond is preserved. (OK) • No other bonding structure other than “butterfly” is observe (?) • - in conflict with previous STM, NEXAFS results • From Fig. 3-4, butterfly rather than tilted ----- ? • butterfly still comply with the results of Fig. 5-6.

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