Using ab initio calculations, we have studied the modification of the electronic structure of the MoS2(0001) surface by several point defects: a surface S vacancy and different transition metal atoms substituting a S atom (Pd, Au, Fe, and V). With a S vacancy, a gap state appears with weight mostly on the Mo and S atoms surrounding the vacancy. The substitutional atoms of complete d band (Pd and Au) do not present magnetic polarization and slightly modify the DOS near the Fermi energy. On the other hand, the incomplete d band atoms (Fe and V) present spin polarization and modify significantly the states near the band edges. From calculated STM images and STS curves, we show that this chemical signature can be measured and used to characterize the surface defects of the substrate which are suitable nucleation centers for nanocluster growth.

The adsorption and self-assembling properties of terephthalic acid (TPA) molecules deposited on Cu(001) at room temperature have been systematically studied with both experimental and theoretical tools. The system forms two phases at room temperature: the metastable β-phase and the stable (3 × 3) one. In the case of the β phase, low-energy electron diffraction and scanning tunneling microscopy (STM) results indicate that it has a (9√2 × 2√2) R45° unit cell with exactly the same molecular coverage as the (3 × 3) phase. In addition, the high-resolution X-ray photoelectron-spectroscopy spectra of the O 1s core level indicate that the irreversible β → (3 × 3) transition involves the following two processes: (i) deprotonation of the complete carboxyl groups remaining in the metastable phase and (ii) eventual rearrangement of the molecules into the 3 × 3 configuration. We explored possible molecular configurations for the β phase with different degree of deprotonation (including structures with Cu adatoms) by means of density functional theory calculations. Our theoretical results indicate the formation of strong bonds between the O atoms in carboxylates and the Cu atoms of the surface, which causes a bending of the molecules and a buckling of the first Cu layer. In the (3 × 3) phases, we show that the bending produces observable effects in the molecular STM images. Moreover, the strong interaction between the carboxylates and the Cu atoms at the step edges drives the reorientation of the surface steps along the ⟨100⟩ crystallographic directions.

A combination of Scanning Tunnelling Microscopy and Density Functional Theory simulations highlights the role of van der Waals interactions in the self-assembly of an aminohelicene on Cu(100) and Au(111).

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We present measurements of the anisotropic magnetoresistance (AMR) of La(0.75)Sr(0.25)MnO(3) films deposited on (001) SrTiO(3) substrates, and a model that describes the experimental results. The model, based on the electronic structure of manganites plus the spin-orbit coupling, correctly accounts for the dependence of the AMR on the direction of the current to the crystalline axes. We measure an AMR of the order of 10(-3) for the current I parallel to the [100] axis of the crystal and vanishing AMR for I , in agreement with the model predictions. Further, we calculate the planar Hall effect and show its connection to AMR.

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The recent observation of a pressure-induced insulator to metal (I-M) transition in pure LaMnO3 [I. Loa, Phys. Rev. Lett. 87, 125501 (2001).10.1103/PhysRevLett.87.125501], opens the way to a study of the role of the orbital degrees of freedom on the electronic structure in a stoichiometric material and its interaction with lattice distortion. To obtain the energy of the system, we resort to a slave boson description for the electronic part and add an elastic term associated to the Jahn-Teller distortion. We obtain the evolution of the electronic structure and the Jahn-Teller distortion with pressure. We find that the Jahn-Teller distortion does not vanish before entering the metallic phase, that the gap closes with pressure in a way similar to that indicated by the temperature dependence of the conductivity, and that both Coulomb and Jahn-Teller interactions are necessary to describe appropriately the phase transition in LaMnO3.