Making use of the inherent surface anisotropy of different high index surface planes vicinal to the low index Au(111) orientation, one-dimensional polymers have been synthesized following established procedures from two different precursor molecules. The successful polymerization of both 4,4″-dibromo-p-terphenyl and 5,5′-dibromo-salophenato-Co(II) precursors into poly(p-phenylene) and poly-[salophenato-Co(II)], respectively, has been confirmed by scanning tunneling microscopy and low energy electron diffraction. Angle-resolved photoemission spectroscopy data reveal a highly dispersive band in the case of poly(p-phenylene) while no significant dispersion is resolved for poly[salophenato-Co(II)]. On the basis of density functional theory calculations, we explain this observation as a result of a high conjugation along the aromatic phenyl groups in poly(p-phenylene) that is absent in the case of poly[salophenato-Co(II)], where intramolecular conjugation is interrupted in the salophenato-Co(II) unit. Furthermore, we make use of multicenter and delocalization indexes to characterize the electron mobility (corresponding to a high band dispersion) along different paths associated with individual molecular orbitals.

Nanometer-thick epitaxial Co films intercalated between graphene (Gr) and a heavy metal (HM) substrate are promising systems for the development of spin–orbitronic devices due to their large perpendicular magnetic anisotropy (PMA). A combination of theoretical modeling and experiments reveals the origin of the PMA and explains its behavior as a function of the Co thickness. High quality epitaxial Gr/Co n /HM­(111) (HM = Pt,Ir) heterostructures are grown by intercalation below graphene, which acts as a surfactant that kinetically stabilizes the pseudomorphic growth of highly perfect Co face-centered tetragonal (fct) films, with a reduced number of stacking faults as the only structural defect observable by high-resolution scanning transmission electron microscopy (STEM). Magneto-optic Kerr effect (MOKE) measurements show that such heterostructures present PMA up to large Co critical thicknesses of about 4 nm (20 ML) and 2 nm (10 ML) for Pt and Ir substrates, respectively. X-ray magnetic circular dichroism (XMCD) measurements show an inverse power law of the anisotropy of the orbital moment with Co thickness, reflecting its interfacial nature, that changes sign at about the same critical values. First principles calculations show that, regardless of the presence of graphene, ideal Co fct films on HM buffers do not sustain PMAs beyond around 6 mLs due to the in-plane contribution of the inner bulk-like Co layers. The large experimental critical thicknesses sustaining PMA can only be retrieved by the inclusion of structural defects that promote a local hcp stacking such as twin boundaries or stacking faults. Remarkably, a layer resolved analysis of the orbital momentum anisotropy reproduces its interfacial nature, and reveals that the Gr/Co interface contribution is comparable to that of the Co/Pt­(Ir).

The catalytic oxidation of CO on transition metals, such as Pt, is commonly viewed as asharp transition from the CO-inhibited surface to the active metal, covered with O. However,w ef ind that minor amounts of Oa re present in the CO-poisoned layer that explain why,surprisingly,COdesorbs at stepped and flat Pt crystal planes at once,r egardless of the reaction conditions.Using near-ambient pressure X-ray photoemission and ac urved Pt(111) crystal we probe the chemical composition at surfaces with variable step density during the CO oxidation reaction. Analysis of Cand Ocore levels across the curved crystal reveals that, right before light-off,subsurface Ob uilds up within (111) terraces.T his is key to trigger the simultaneous ignition of the catalytic reaction at different Pt surfaces:aCO-Pt-O complex is formed that equals the CO chemisorption energy at terraces and steps,l eading to the abrupt desorption of poisoning CO from all crystal facets at the same temperature.

First-principles calculations are performed to characterize the NO adsorption on large carbonaceous clusters modeling the surface of soot. Adsorption on the face and on the edges of perfect and defective clusters is considered in the calculations. It is shown that the first situation corresponds to physisorption and requires taking into account long-range dispersion interactions in the calculations. In contrast, interaction of NO with the unsaturated edge of a defective cluster leads preferentially to a C-N rather than to a C-O chemical binding. This indicates that soot may be an efficient sink for NO in the troposphere only if it contains a high number of unsaturated carbon atoms. From a more fundamental point of view, this study also clearly evidences that quantum calculations have to be carefully conducted when considering the interaction between radical species and carbonaceous surfaces. Problems encountered with the choice of the functional used in density functional theory approaches as well as with the size of the basis set, spin multiplicity, and spin contamination have to be systematically addressed before any relevant conclusion can be drawn.