Benzene Adsorption on Rh(111): A New Perspective on Intermolecular Interactions and Molecular Ordering

Abstract

The adsorption of benzene on the Rh(111) substrate was investigated through scanning tunneling microscopy (STM) imaging and density functional theory (DFT) calculations. Experiments were carried out at various surface coverages, with the amount of benzene adsorbed determined to influence the molecular adsorption site, the intermolecular interactions, and the interaction between the molecule and the substrate. At a sub-monolayer coverage of the surface, the molecules are disordered and kept apart by a strong inter-adsorbate repulsion, with a preference for the molecule to adsorb on a three-fold hcp hollow site. At high coverage, the preferred adsorption site becomes the two-fold symmetric bridge site, whether as part of the two dense ordered structures that form at high coverage ((2√3×3)rect or Page 1 of 48 ACS Paragon Plus Environment The Journal of Physical Chemistry (√19×√19)R23.4°) or as part of the disordered array of benzene molecules, which are arranged in formations which resemble the "building blocks" of the ordered overlayers. Despite the adsorption energy for benzene within both dense structures being similar, the (√19×√19)R23.4° overlayer is only observed if the substrate is annealed to 363 K during or after deposition, indicating that the formation of the (√19×√19)R23.4° ordering is inhibited by an activation barrier at lower temperatures and can only be overcome by increasing the temperature of the Rh(111) support.

Adsorption of Monocyclic Aromatics on Transition Metal Surfaces: Insight into Variation of Binding Strength from First-Principles

“…The only exception is Cu(111) where the physiosorbed BZ is unaffected resulting in identical brightness for six equivalent phenyl C atoms. For validity, we note here that the features of our simulated STM images show excellent match with those of low-coverage adsorbed BZ observed in previous experiments/simulations . For comparison, the brighter spot can be identified as the O atom of adsorbed phenol on metal surfaces, suggesting that the negatively charged O atom with the intrinsically rich electron density around O nucleus is competitive with those of binding C atoms of the phenyl ring, regardless of the metals (Figure S6).…”

“…STM , is a highly sensitive technique for probing both electronic and geometric structures of a surface, providing information on atom-resolved structures of the surface (or interface) and adsorbate geometry. , For π-conjugated aromatic molecules adsorbed on metal surfaces, numerous STM studies have been reported over the years including BZ adsorbed on Rh(111), , Pt(111), Ni(110) and Cu(110), , and Si(100) . Our DFT-simulated STM images of BZ adsorbed on eight close-packed metal surfaces studied are displayed in Figure .…”

“…The monocyclic aromatic compounds adsorb on metal surfaces, most likely across the two threefold hollow sites (fcc and hcp), in a bridge position (bri30), with the phenyl ring parallel to rather than perpendicular to the surface (Figure B). In particular, methyl (−CH 3 ) is at the σ-position, whereas hydroxyl (−OH) is at the π-position, following the nomenclature of Réocreux et al Such an adsorption configuration has been observed to be the most stable for BZ and phenolic compounds (e.g., guaiacol, anisole, cresol, and phenol) on close-packed metal surfaces including Ni(111), ,, Fe(110), ,, Fe(100), Pt(111), ,,,,− Pd(111), ,, Rh(111), and Ru(0001). , Thereafter, all calculated results in this study are based on such a bri30 adsorption configuration, providing an additional benefit of eliminating the influence of alternative adsorption configurations on varied metal surfaces. ,, …”

“…For validity, we note here that the features of our simulated STM images show excellent match with those of low-coverage adsorbed BZ observed in previous experiments/ simulations. 72 For comparison, the brighter spot can be identified as the O atom of adsorbed phenol on metal surfaces, suggesting that the negatively charged O atom with the intrinsically rich electron density around O nucleus is competitive with those of binding C atoms of the phenyl ring, regardless of the metals (Figure S6). Still, the only exception is the STM image of phenol adsorbed on Cu(111), which reflects its physisorption nature.…”

Lignin Intermediates on Palladium: Insights into Keto‐Enol Tautomerization from Theoretical Modelling

“…As in previous studies, the bridge 30°site was found to be the most favourable. However, the most stable adsorption site for aromatic rings on metallic surfaces is still under debate as demonstrated by the recent work of Treanor et al [34] who found the hollow hcp site to be (slightly) favourable on Rh(111). Lower row: The labelling schemes we use in this study.…”