Core-level spectra and molecular deformation in adsorption: V-shaped pentacene on Al(001)

• Published in: Beilstein journal of nanotechnology Vol. 6; no. 1; pp. 2242 - 2251
• Main Authors: Baby, Anu, Lin, He, Brivio, Gian Paolo, Floreano, Luca, Fratesi, Guido
• Format: Journal Article
• Language: English
• Published: Germany Beilstein-Institut zur Föerderung der Chemischen Wissenschaften 2015; Beilstein-Institut
• Subjects: Adsorption; aluminum; Carbon; Chemical bonds; Covalent bonds; Deformation effects; density functional theory (DFT); Destabilization; Dichroism; Electron density; Fine structure; First principles; Full Research Paper; Mapping; Molecular orbitals; Molecular structure; Nanoscience; Nanotechnology; near-edge X-ray absorption fine structure (NEXAFS); pentacene; Photoelectrons; Spectra; X ray absorption; X ray photoelectron spectroscopy; X-ray photoelectron spectroscopy (XPS); density functional theory (DFT); near-edge X-ray absorption fine structure (NEXAFS); pentacene; aluminum; X-ray photoelectron spectroscopy (XPS)
• ISSN: 2190-4286; 2190-4286
• DOI: 10.3762/bjnano.6.230

By first-principle simulations we study the effects of molecular deformation on the electronic and spectroscopic properties as it occurs for pentacene adsorbed on the most stable site of Al(001). The rationale for the particular V-shaped deformed structure is discussed and understood. The molecule-surface bond is made evident by mapping the charge redistribution. Upon X-ray photoelectron spectroscopy (XPS) from the molecule, the bond with the surface is destabilized by the electron density rearrangement to screen the core hole. This destabilization depends on the ionized carbon atom, inducing a narrowing of the XPS spectrum with respect to the molecules adsorbed hypothetically undistorted, in full agreement to experiments. When looking instead at the near-edge X-ray absorption fine structure (NEXAFS) spectra, individual contributions from the non-equivalent C atoms provide evidence of the molecular orbital filling, hybridization, and interchange induced by distortion. The alteration of the C-C bond lengths due to the V-shaped bending decreases by a factor of two the azimuthal dichroism of NEXAFS spectra, i.e., the energy splitting of the sigma resonances measured along the two in-plane molecular axes.