Orbital tomography: Deconvoluting photoemission spectra of organic molecules

Abstract

We study the interface of an organic monolayer with a metallic surface, i.e., PTCDA (3,4,9,10-perylenetetracarboxylic-dianhydride) on Ag(110), by means of angle-resolved photoemission spectroscopy (ARPES) and ab initio electronic structure calculations. We present a tomographic method that uses the energy and momentum dependence of ARPES data to deconvolute spectra into individual orbital contributions beyond the limits of energy resolution. This provides an orbital-by-orbital characterization of large adsorbate systems without the need to invoke a sophisticated theory of photoemission, allowing us to directly estimate the effects of bonding on individual orbitals. Moreover, these experimental data serve as a most stringent test necessary for the further development of ab initio electronic structure theory.

Substrate-mediated band-dispersion of adsorbate molecular states

“…The energy dispersion thus displays the Bloch-character of the PTCDA LUMO, while the angledependent intensity distribution ( Supplementary Fig. S1) shows its molecular origin 27,28,31 .…”

“…3 for molecular structure and arrangement in the brickwall layer) 29,30 . For panel (a), the measurements were performed along the substrate (1 10) direction, that is, from the centre of the Brillouin zone to the intensity maximum of the LUMO 27,28,31 (see Supplementary Fig. S1 and Supplementary Note 1), while the data in Fig.…”

“…1b were recorded in a direction rotated by 47°against the (1 10) direction. Owing to the strong orbital-specific intensity variations 27,28,31 the data were normalized as specified in Supplementary Note 2 and Supplementary Fig. S2.…”

“…For the model systems 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) adsorbed on Ag(110) surfaces the lowest unoccupied molecular orbital (LUMO), which hybridizes with substrate states and is occupied by charge transfer from the metal [26][27][28] , shows a dispersion of 230 meV and 180 meV, respectively, along the surface in angle-resolved photoelectron spectroscopy (ARPES). Density functional theory (DFT) calculations quantitatively confirm the experimentally observed dispersion and reveal its origin as being primarily due to molecule-metal hybridization.…”

Energy level alignment at molecule-metal interfaces from an optimally tuned range-separated hybrid functional

“…In addition, since it is based on GKS and includes a fraction of short-range Fock exchange, it can also yield improved relative orbital spacing, as shown in the examples of AntSe/Au(111) and NTCDA/Ag(111), as well as improved orbital ordering, as was demonstrated previously for other systems. 58,85,92,[145][146][147] In spite of its success, we also would like to point out that the method proposed here is not a panacea. In particular, we focused here on the level alignment and PDOS of the molecule and did not discuss how the choice of α, β, and γ may affect specifics in the electronic structure of the metal substrate.…”