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Stabilizing ordered assemblies of molecules represents the first step towards the construction of molecular devices featuring hybrid (organic-inorganic) interfaces where molecules can be easily functionalized in view of specific applications. Molecular layers of planar metal-tetraphenylporphyrins (MTPP) grown on an ultrathin iron oxide [namely Fe(001)- p (1 × 1)O] show indeed a high degree of structural order. The generality of such a picture is tested by exploiting non-planar porphyrins, such as vanadyl-TPP (VOTPP). These molecules feature a VO 2+ ion in their center, with the O atom protruding out of the plane of the porphyrin ring. In this work, by employing diffraction, photoemission and X-ray absorption, we prove that non-planar VOTPP can nevertheless form a square and ordered superstructure, where porphyrin molecules lie flat with respect to the underlying substrate. Ab initio density functional theory simulations are used to elucidate the VO bond orientation with respect to the iron substrate.

Hybrid sp-sp 2 structures can be efficiently obtained on metal substrates via on-surface synthesis. The choice of both the precursor and the substrate impacts on the effectiveness of the process and the stability of the formed structures. Here we demonstrate that using anthracene-based precursor molecules on Au(111) the formation of polymers hosting sp carbon chains is affected by the steric hindrance between aromatic groups. In particular, by scanning tunneling microscopy experiments and density functional theory simulations we show that the de-metalation of organometallic structures induces a lateral separation of adjacent polymers that prevents the formation of ordered domains. This study contributes to the understanding of the mechanisms driving the on-surface synthesis processes, a fundamental step toward the realization of novel carbon-based nanostructures with perspective applications in nanocatalysis, photoconversion, and nano-electronics.

We present a joint experimental and theoretical characterization of the magnetic properties of coordination clusters with an antiferromagnetic core of four magnetic ions. Two different compounds are analyzed, with Co and Mn ions in the core. While both molecules are antiferromagnetic, they display different sensitivities to external magnetic field, according to the different atomic magnetic moments and strength of the intra-molecular magnetic couplings. In particular, the dependence of the magnetization versus field of the two molecules switches with temperature: at low temperature the magnetization is smaller in {Mn 4 } than in Co 4 , while the opposite happens at high temperature. Through a detailed analysis of the electronic and magnetic properties of the two compounds we identify a stronger magnetic interaction between the magnetic ions in {Mn 4 } with respect to {Co 4 }. Moreover {Co 4 } displays not negligible spin-orbit related effects that could affect the spin lifetime in future antiferromagnetic spintronic applications. We highlight the necessity to account for these spin-orbit effects together with electronic correlation effects for a reliable description of these compounds.

We analyse the spinterface formed by a C 60 molecular layer on a Fe(001) surface covered by a two-dimensional Cr 4 O 5 layer. We consider different geometries, by combining the high symmetry adsorption sites of the surface with three possible orientations of the molecules in a fully relaxed Density Functional Theory calculation. We show that the local hybridization between the electronic states of the Cr 4 O 5 layer and those of the organic molecules is able to modify the magnetic coupling of the Cr atoms. Both the intra-layer and the inter-layer magnetic interaction is indeed driven by O atoms of the two-dimensional oxide. We demonstrate that the C 60 adsorption on the energetically most stable site turns the ferromagnetic intra-layer coupling into an antiferromagnetic one, and that antiferromagnetic to ferromagnetic switching and spin patterning of the substrate could be possible by adsorption on other sites.

The structure and electronic properties of carbon atom chains Cn in contact with Ag electrodes are investigated in detail with first principles means. The ideal Ag(100) surface is used as a model for binding, and electron transport through the chains is studied as a function of their length, applied bias voltage, presence of capping atoms (Si, S) and adsorption site. It is found that the metal-molecule bond largely influences electronic coupling to the leads. Without capping atoms the quality of the electric contact improves when increasing the carbon atom coordination number to the metal (1, 2 and 4 for adsorption on a top, bridge and hollow position, respectively) and this finding translates almost unchanged in more realistic tip-like contacts which present one, two or four metal atoms at the contact. Current-voltage characteristics show Ohmic behaviour over a wide range of bias voltages and the resulting conductances change only weakly when increasing the wire length. The effect of a capping species is typically drastic, and either largely reduces (S) or largely increases (Si) the coupling of the wire to the electrodes. Comparison of our findings with recent experimental results highlights the limits of the adopted approach, which can be traced back to the known gap problem of density-functional-theory.

The electronic and transport properties of graphene ribbons sandwiched between hydrogen dimer lines, of the kind recently realized by Nilsson et al., Carbon, 2012, 50, 2052, are investigated with the help of first principles methods. It is found that such lines of hydrogen atoms block conduction between neighboring channels and effectively allow the confinement of graphene charge carriers, thereby opening the possibility of imprinting nano-circuits in graphene by controlled hydrogenation.