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The structure of VOPc on Cu(111): Does V=O point up, or down, or both?

DOI: 10.1021/acs.jpcc.8b07530 DOI Help

Authors: P. J. Blowey (Diamond Light Source; University of Warwick) , R. J. Maurer (University of Warwick) , L. A. Rochford (University of Warwick; University of Birmingham) , D. A. Duncan (Diamond Light Source; University of Birmingham) , Jie Hun Kang (Kookmin University) , D. A. Warr (University of Warwick) , A. J. Ramadan (University of Oxford) , T.-l. Lee (Diamond Light Source) , P. K. Thakur (Diamond Light Source) , G. Costantini (University of Warwick) , K. Reuter (Technische Universität München) , D. P. Woodruff (University of Warwick)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: The Journal Of Physical Chemistry C

State: Published (Approved)
Published: October 2018
Diamond Proposal Number(s): 9459 , 14524 , 15899

Abstract: The local structure of the non-planar phthalocyanine, vanadyl phthalocyanine (VOPc), adsorbed on Cu(111) at a coverage of approximately one half of a saturated molecular layer, has been investigated by a combination of normal-incidence X-ray standing waves (NIXSW), scanned-energy mode photoelectron diffraction (PhD) and density-functional theory (DFT), complemented by scanning tunnelling microscopy (STM). Qualitative assessment of the NIXSW data clearly shows that both ‘up’ and ‘down’ orientations of the molecule (with V=O pointing out of, and into, the surface) must coexist on the surface. O 1s PhD proves to be inconclusive regarding the molecular orientation. DFT calculations, using two different dispersion correction schemes, show good quantitative agreement with the NIXSW structural results for equal co-occupation of the two different molecular orientations and clearly favour the Many Body Dispersion (MBD) method to deal with long-range dispersion forces. The calculated relative adsorption energies of the differently-oriented molecules at the lowest coverage show a strong preference for the ‘up’ orientation, but at higher local coverages, this energetic difference decreases and mixed orientation phases are almost energetically equivalent to pure ‘up’ oriented phases. DFT-based Tersoff-Hamann simulations of STM topographs for the two orientations cast some light on the extent to which such images provide a reliable guide to molecular orientation.

Subject Areas: Chemistry


Instruments: I09-Surface and Interface Structural Analysis