The geometric and electronic structure of two structurally similar metal–organic networks grown on the Au(111) surface is investigated by scanning tunnelling microscopy (STM) and spectroscopy (STS) combined with density functional theory (DFT) calculations. The networks are composed of (i) F4TCNQ (C12F4N4, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquino–dimethane) molecules and Au adatoms segregated from the pristine metal surface, and (ii) TCNQ (C12H4N4, 7,7,8,8-tetracyanoquinodimethane) and codeposited Mn atoms. In both cases, the strong electron acceptor character of the molecules results in metal–to-ligand charge transfer to the lowest unoccupied molecular orbital (LUMO). The amount of electrons donated from the 4-fold coordinated Mn atoms to TCNQ is higher compared to the 2-fold coordinated Au adatoms to F4TCNQ. This behavior is reflected in the appearance of distinct spectral features in STS data in the energy region close to the Fermi level resulting from the intricate interplay between surface states, adatom states, and molecular orbitals. These observations are consistent with a picture in which the LUMO of the TCNQ acceptor molecule hybridizes with Mn and Au substrate metal states becoming practically filled, while the LUMO of F4TCNQ is only partially filled despite being the stronger electron acceptor. Our results reveal the importance of the type of bonding between the strong acceptor and the metal center (Au or Mn) as well as its coordination in the determination of the charge transfer to the adlayer, which is important for its electronic properties.

Inelastic electron tunneling spectroscopy (IETS) within the junction of a scanning tunneling microscope (STM) uses current-driven spin-flip excitations for an all-electrical characterization of the spin state of a single object. Usually decoupling layers between the single object, atom or molecule, and the supporting surface are needed to observe these excitations. Here we study the surface magnetism of a sandwich nickelocene molecule (Nc) adsorbed directly on Cu(100) by means of X-ray magnetic circular dichroism (XMCD) and density functional theory (DFT) calculations and show with IETS that it exhibits an exceptionally efficient spin-flip excitation. The molecule preserves its magnetic moment and magnetic anisotropy not only on Cu(100), but also in different metallic environments including the tip apex. By taking advantage of this robusteness, we are able to functionalize the microscope tip with a Nc, which can be employed as a portable source of inelastic excitations as exemplified by a double spin-flip excitation process.

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We present a study of the electron dynamics in the layered compound 2H -NbSe 2 . First-principles calculations are used to obtain the band structure employed in the evaluation of the loss function with inclusion of local-field (LF) effects. Two different symmetry directions [(100) and (010)] were explored in the hexagonal basal plane. In both cases, a low-energy charge-carrier plasmon (CCP) at ∼1 eV presenting a negative dispersion over a wide momentum transfer range is found, in agreement with recent experimental results [Wezel et al., Phys. Rev. Lett. 107, 176404 (2011)]. On the contrary, in the (001) perpendicular direction, the CCP has negative dispersion at small momenta only, presenting strong positive dispersion at larger momenta. Our calculations reveal that this behavior can be explained without invoking many-body effects, as long as band structure effects are properly included in the evaluation of the excitation spectra. In addition to this CCP mode, we find another one with an arclike oscillating dispersion along the perpendicular direction, as well as the appearance of a CCP replica at high momenta due to LF effects.

To whom correspondence should be addressed 1 Magnetization curves of two rectangular metal-organic coordination networks formed by the organic ligand TCNQ (7,7,8,8-tetracyanoquinodimethane) and two different (Mn and Ni) 3d transition metal atoms [M(3d)] show marked differences that are explained using first principles density functional theory and model calculations. We find that the existence of a weakly dispersive hybrid band with M(3d) and TCNQ character crossing the Fermi level is determinant for the appearance of ferromagnetic coupling between metal centers, as it is the case of the metallic system Ni-TCNQ but not of the insulating system Mn-TCNQ. The spin magnetic moment localized at the Ni atoms induces a significant spin polarization in the organic molecule; the corresponding spin density being delocalized along the whole system. The exchange interaction between localized spins at Ni centers and the itinerant spin density is ferromagnetic. Based on two different model Hamiltonians, we estimate the strength of exchange couplings between magnetic atoms for both Ni-and Mn-TCNQ networks that results in weak ferromagnetic and very weak antiferromagnetic correlations for Ni-and Mn-TCNQ networks, respectively.

Electron emission coming from the valence band of metal surfaces due to grazing incidence of highfrequency ultrashort laser pulses is studied. We introduce a distorted-wave method, named impulsive jelliumVolkov ͑IJV͒ approximation, in which the surface is represented by the jellium model while the interaction with the laser field is described by means of the Volkov phase. With the purpose of examining the proposed approach, we compare IJV results with values derived from the numerical solution of the corresponding time-dependent Schrödinger equation ͑TDSE͒. For Al͑111͒ surfaces, double and single differential probability spectra are calculated considering different durations of the laser pulse. Very good agreement between IJV and TDSE results was found. The total probability dependence on the intensity and carrier-envelope phase of the pulse is also investigated.

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Electron emission from the conduction band of metal surfaces is studied under grazing scattering conditions. We investigate this process making use of the quantum-mechanical (QM) model to represent the electronic interactions within the binary collisional formalism. The QM approach is based on the use of the model potential and allows us to describe the main features of the metal surface. It provides a precise description of both one-electron states and surface induced potential. In this work, the approximation is employed to evaluate electron distributions for 100 keV protons impinging grazingly on the Al͑111͒ surface. We have found that the realistic representation of the surface included in the QM model introduces substantial changes in the valence emission at low electron energies and intermediate ejection angles. The influence of the surface wake potential on the valence emission probability is also addressed. In order to compare with experiments, we add the contribution coming from atomic inner shells calculated with the field-distorted-wave approximation. Total theoretical results obtained with the QM model are in fairly good agreement with the available experimental data.