Nicolás Lorente

Self-consistent LDA calculation in ion neutralization at metal surfaces

Abstract The neutralization of He + scattered off aluminum is calculated via a self-consistent LDA where the metal surface is modeled by an LDA jellium surface, and its structure factor is consistently calculated. This approach includes Auger and plasmon-assisted neutralization channels of He + to the He ground state in front of aluminum. We analyze these neutralization channels, which leads us to a revision of the usual calculations of ion neutralization on surfaces depending on the transferred energy lying below, near, or above the metal plasma frequency. The results of this calculation are compared with those of other methods, namely usual unscreened calculations, calculations which extrapolate bulk results, calculations performed for a step potential surface, and surface calculations in the long-distance limit.

Imaging the dynamics of individually adsorbed molecules

Although noise is observed in many experiments, it is rarely used as a source of information. However, valuable information can be extracted from noisy signals. The motion of particles on a surface induced, for example, by thermal activation or by the interaction with the tip of a scanning tunnelling microscope may lead to fluctuations or switching of the tunnelling current. The analysis of these processes gives insight into dynamics on a single atomic or molecular level. Unfortunately, scanning tunnelling microscopy (STM) is not a useful tool to study dynamics in detail, as it is an intrinsically slow technique. Here, we show that this problem can be solved by providing a full real-time characterization of random telegraph noise in the current signal. The hopping rate, the noise amplitude and the relative occupation of the involved states are measured as a function of the tunnelling parameters, providing spatially resolved maps. In contrast to standard STM, our technique gives access to transiently populated states revealing an electron-driven hindered rotation between the equilibrium and two metastable positions of an individually adsorbed molecule. The new approach yields a complete characterization of copper phthalocyanine molecules on Cu(111), ranging from dynamical processes on surfaces to the underlying electronic structure on the single-molecule level.

Size effects in surface-reconstructed⟨100⟩and⟨110⟩silicon nanowires

The geometrical and electronic structure properties of

Charge transfer of slow light ions interacting with surfaces

and

On-Surface Engineering of a Magnetic Organometallic Nanowire.

silicon nanowires in the absence of surface passivation are studied by means of density-functional calculations. As we have shown in a recent publication [R. Rurali and N. Lorente, Phys. Rev. Lett. {\bf 94}, 026805 (2005)] the reconstruction of facets can give rise to surface metallic states. In this work, we analyze the dependence of geometric and electronic structure features on the size of the wire and on the growth direction.

Efficient Spin-Flip Excitation of a Nickelocene Molecule

Metallocene (MCp2) wires have recently attracted considerable interest in relation to molecular spintronics due to predictions concerning their half-metallic nature. This exciting prospect is however hampered by the little and often-contradictory knowledge we have concerning the metallocene self-assembly and interaction with a metal. Here, we elucidate these aspects by focusing on the adsorption of ferrocene on Cu(111) and Cu(100). Combining low-temperature scanning tunneling microscopy and density functional theory calculations, we demonstrate that the two-dimensional molecular arrangement consists of vertical- and horizontal-lying molecules. The noncovalent T-shaped interactions between Cp rings of vertical and horizontal molecules are essential for the stability of the physisorbed molecular layer. These results provide a fresh insight into ferrocene adsorption on surfaces and may serve as an archetypal reference for future work with this important variety of organometallic molecules.

Correlation-Mediated Processes for Electron-Induced Switching between Neel States of Fe Antiferromagnetic Chains

Abstract The charge transfer of slow atoms colliding with a surface is studied by means of a LCAO-method supplemented with a LD many-body contribution. Atomic levels and the parameters controlling the atom-surface interaction are obtained for H and He on Al(100). The method is well suited for analyzing short ion-surface distances, where the strong coupling promotes molecular orbitals. Charge transfer processes are finally calculated by solving Keldysh-Green function equations that describe the full quantum process associated with the ion-surface interactions. These equations give a specific prescription for calculating velocity and three-dimensional crystal effects, taking into account the two-dimensional surface periodicity. Calculations for some specific cases are presented.

Magnetic transitions induced by tunnelling electrons in individual adsorbed M-Phthalocyanine molecules (M

Abstract Negative ion formation is enhanced in low energy ion-surface collisions at grazing incidence. As the parallel velocity of the ion increases, there is an effective broadening of the solids surface density of states as seen from the moving ion. In the present work, we analyze negative ion formation at grazing incidence for a gapless solid (Al), a small gap (1.1 eV) solid (Si) and a large gap (8.9 eV) solid (LiF). The electronic features of the different solids lead us to a formulation of resonant charge transfer theory which takes into account the periodicity of the surface band structure and its gaps, leaving aside the common parabolic-band and jellium-like description of solids.