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

Abstract

SummaryBy 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.

Resolving intramolecular-distortion changes induced by the partial fluorination of pentacene adsorbed on Cu(111)

“…mild fluorination, the backbone curvature that renders slightly inequivalent adsorption sites in the case of PEN [9,10,26] can still be expected, as deduced from the aforementioned shoulder. The precise assignment of the different inequivalent carbon components C(1-5) within the backbone is a difficult task, not exempt from controversy, which ideally would require theoretical input [10,24,28,29]. In our case, the core-level fitting [17] was done in parallel with the XSW analysis, and the structural information obtained from each component was used as a guideline for the peak assignment.…”

“…On the other hand, the characteristic line shape of the backbone component, with the pronounced shoulder accompanying the main peak, can be explained by the effect of the substrate on the chemical environment of the different carbon-core atoms, which, depending on the position relative to the copper atoms underneath, undergo different BE shifts. Such an effect has been used to explain the core-level-peak splitting of PEN on different copper (among others [10,24]) surfaces [18,[25][26][27]. In the case of F4PEN, whose hydrogen atoms at the short molecular edges are substituted by fluorine, the C(6) component (C-F) is shifted toward higher BE due to the strong electronegativity of fluorine, thus turning the double peak seen for PEN on Cu(111) [18] into a shoulder.…”

“…They usually involve functional groups with heteroatoms that act as the main channel whereby the electronic and/or chemical coupling with the surface atoms occurs [3][4][5][6]. However, the distortion of a hydrocarbon core has not been experimentally probed with the same success [7,8] and, in most cases, it has only been accessible through state-of-the-art density-functionaltheory (DFT) calculations [8][9][10]. In this work, we directly quantify, using the x-ray standing wave (XSW) technique [11][12][13], the distortion of the hydrocarbon backbone of a partially fluorinated pentacene (PEN) derivative, namely 2,3,9,10tetrafluoropentacene (F4PEN, C 22 F 4 H 10 ) [14][15][16], vacuumsublimated on Cu(111).…”

Ultrafast electron injection into photo-excited organic molecules

“…To compare computational results with the experiment, we focus on the LUMO* case, with an added valence electron as eventually attracted from the substrate to screen the perturbation. [23][24][25][26][27] This corresponds to a fully relaxed electronic configuration after the molecule is ionized. The attractive potential introduced by the core hole lowers the energy of the molecular orbitals with respect to the ground state.…”

Chemisorption of Pentacene on Pt(111) with a Little Molecular Distortion

“…Structural and morphological studies of thin Pc films have been reported for most of the coinage metal surfaces, where a large variety of different phases have been observed, according to the degree of molecule to substrate interaction. [18][19][20][21] In the case of gold and silver, Pc displays a weak interaction coupling with the substrate, whereas the degree of intermolecular interaction, as tailored by the molecular coverage, leads to the formation of different phases during the growth of the first two layers. 20,[22][23][24][25] Only in the specific case of the reconstructed (1x2)-Au(110) surface, the substrate anisotropy effectively drives a more complex phase diagram for a few layers thickness.…”