Thin molecular films under model conditions are often exploited as benchmarks and case studies to investigate the electronic and structural changes occurring on the surface of metallic electrodes. Here we show that the modification of a metallic surface induced by oxygen adsorption allows the preservation of the geometry of a molecular adlayer, giving access to the determination of molecular orbital symmetries by means of near-edge Xray absorption fine structure spectroscopy, NEXAFS. As a prototypical example, we exploited nickel tetraphenylporphyrin molecules deposited on a bare and on an oxygen pre-covered Cu(1 0 0) surface. We find that adsorbed atomic oxygen quenches the charge transfer at the metal-organic interface but, in contrast to a thin film sample, maintains the ordered adsorption geometry of the organic molecules. In this way, it is possible to disentangle π* and σ* symmetry orbitals, hence estimate the relative oscillator strength of core level transitions directly from the experimental data, as well as to evaluate and localize the degree of charge transfer in a coupled system. In particular, we neatly single out the σ* contribution associated with the N 1s transition to the mixed N 2px,y-Ni 3dx2-y2 orbital, which falls close to the leading π*-symmetry LUMO resonance.

Evaluation of molecular orbital symmetry via oxygen-induced charge transfer quenching at a metal-organic interface

Cojocariu I.;Zamborlini G.
;
Cossaro A.;Verdini A.;Stredansky M.;Vesselli E.;Jugovac M.;
2020-01-01

Abstract

Thin molecular films under model conditions are often exploited as benchmarks and case studies to investigate the electronic and structural changes occurring on the surface of metallic electrodes. Here we show that the modification of a metallic surface induced by oxygen adsorption allows the preservation of the geometry of a molecular adlayer, giving access to the determination of molecular orbital symmetries by means of near-edge Xray absorption fine structure spectroscopy, NEXAFS. As a prototypical example, we exploited nickel tetraphenylporphyrin molecules deposited on a bare and on an oxygen pre-covered Cu(1 0 0) surface. We find that adsorbed atomic oxygen quenches the charge transfer at the metal-organic interface but, in contrast to a thin film sample, maintains the ordered adsorption geometry of the organic molecules. In this way, it is possible to disentangle π* and σ* symmetry orbitals, hence estimate the relative oscillator strength of core level transitions directly from the experimental data, as well as to evaluate and localize the degree of charge transfer in a coupled system. In particular, we neatly single out the σ* contribution associated with the N 1s transition to the mixed N 2px,y-Ni 3dx2-y2 orbital, which falls close to the leading π*-symmetry LUMO resonance.
2020
Pubblicato
https://www.sciencedirect.com/science/article/pii/S0169433219331599
File in questo prodotto:
File Dimensione Formato  
P76 ApplSurfSci504(2020)144343.pdf

Accesso chiuso

Tipologia: Documento in Versione Editoriale
Licenza: Copyright Editore
Dimensione 475.84 kB
Formato Adobe PDF
475.84 kB Adobe PDF   Visualizza/Apri   Richiedi una copia
Pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11368/2954529
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 17
  • ???jsp.display-item.citation.isi??? 15
social impact