Tm on W(110): A Growth Study by Scanning Tunneling Microscopy

Exploring bottom-up procedures to achieve island and particles with a defined size can open opportunities in many applications. This contribution focuses on the growth of epitaxial Tm islands, below the monolayer range, on the W(110) surface by studying in situ the diffusion process at high temperature, between 700 and 1200 K, by means of scanning tunnel microscopy (STM) to determine the topography of the Tm deposits as a function of the coverage and thermal treatments of an initial room temperature deposit. Samples subject to a prolonged heating process, spending several hours at temperatures below 700 K, show that the average Tm islands size remains constant at higher temperatures, in contrast with samples subject to a faster heating. It is observed that the presence of carbon strongly limits the diffusion of Tm, thus leading to the formation of pseudomorphic nanometric islands instead of a full monolayer

On-surface synthesis of functional organic nanostructures

The improvement of electronic device efficiency is currently based on the miniaturization of existing electronic devices. The manufacturing costs of reducing the size of semiconductor based circuits below 10 nm is unfeasible for companies. To overcome this limitation, other materials are currently being developed to fabricate equivalent electronic circuits with smaller dimensions. In this context, on-surface synthesis (OSS) is a bottom-up manufacturing technique based on the reaction of molecules to achieve a well-defined organic structure. The atomic precision of OSS allows to create functional organic molecules for molecular electronic devices. Scanning probe microscopy techniques are the most common microscopy techniques used to analyze on-surface synthesized structures. In this thesis, we present the synthesis by OSS and characterization by scanning tunneling microscopy (STM) and spectroscopy (STS) techniques of functional nanostructures. The synthesized manganese phthalocyanine (MnPc) includes in the phthalocyanine ring four diarylethylene moieties (DAE). The DAE moiety is an optically active group. This organo-metallic complex with optically active groups and the Mn in its structure could work as a magneto-optical transducer. We have successfully induced reversible switches with the STM tip between the assigned open and closed configurations of the DAE moiety. The other organic structures synthesized by OSS studied in this thesis are chiral graphene nanoribbons (ch-GNRs) on Ag(001). Combining STM and STS techniques we have studied the evolution of the electronic structure of ch-GNRs depending on their width and length. Furthermore, when the ch-GNRs are relocated on top of MgO monoloayers grown on the same Ag(001) substrate by means of atomic manipulation, a combination of charge transfer and electronic localization gives rise to a critical discretization of the extended edge states. This causes unprecedented long life times of the ribbon’s electronic states and spin splitting of the frontier orbitals ascribed to electron-electron correlations. Finally, we have evaluated the suitability of the ch-GNR/MgO monolayer/Ag(001) system as a molecular spin polarized transistor.<br /

Manipulation of the surface density of states of Ag(111) by means of resonators. Experiment and theory.

We show that the density of surface Shockley states of Ag(111) probed by the differential conductance G(V ) = d I /d V by a scanning-tunneling microscope (STM) can be enhanced significantly at certain energies and positions introducing simple arrays of Co or Ag atoms on the surface, in contrast to other noble-metal surfaces. Specifically we have studied resonators consisting of two parallel walls of five atoms deposited on the clean Ag(111) surface. A simple model in which the effect of the adatoms is taken into account by an attractive local potential and a small hybridization between surface and bulk at the position of the adatoms explains the main features of the observed G(V ) and allows us to extract the proportion of surface and bulk states sensed by the STM tip. These results might be relevant to engineer the surface spectral density of states, to study the effects of surface states on the Kondo effect, and to separate bulk and surface contributions in STM studies of topological surface states

Real space manifestations of coherent screening in atomic scale Kondo lattices

The interaction among magnetic moments screened by conduction electrons drives quantum phase transitions between magnetically ordered and heavy-fermion ground states. Here, starting from isolated magnetic impurities in the Kondo regime, we investigate the formation of the finite size analogue of a heavy Fermi liquid. We build regularly-spaced chains of Co adatoms on a metallic surface by atomic manipulation. Scanning tunneling spectroscopy is used to obtain maps of the Kondo resonance intensity with sub-atomic resolution. For sufficiently small interatomic separation, the spatial distribution of Kondo screening does not coincide with the position of the adatoms. It also develops enhancements at both edges of the chains. Since we can rule out any other interaction between Kondo impurities, this is explained in terms of the indirect hybridization of the Kondo orbitals mediated by a coherent electron gas, the mechanism that causes the emergence of heavy quasiparticles in the thermodynamic limit.Financial support was provided by the Spanish Plan Nacional de I+ D+ i (grants MAT 2013-46593-C6-3-P, MAT2016-78293-C6-6-R, MAT2015-66888-C3-2-R, and FIS2015-64886-C5-3-P), Charles University (programme PRIMUS/Sci/09) and the European Union through programmes Interreg-POCTEFA (grant TNSI/EFA194/16) and H2020-EINFRA-5-2015 MaX Center of Excellence (grant no. 676598). M. M.-L., M. P., and D. S. acknowledge the use of SAI at Universidad de Zaragoza. R. R. acknowledges The Severo Ochoa Centers of Excellence Program (grant no. SEV-2017-0706) and Generalitat de Catalunya (grant no. 2017SGR1506 and the CERCA Programme)

Reversible magnetic switching of high-spin molecules on a giant Rashba surface

The quantum mechanical screening of a spin via conduction electrons depends sensitively on the environment seen by the magnetic impurity. A high degree of responsiveness can be obtained with metal complexes, as the embedding of a metal ion into an organic molecule prevents intercalation or alloying and allows for a good control by an appropriate choice of the ligands. There are therefore hopes to reach an "on demand" control of the spin state of single molecules adsorbed on substrates. Hitherto one route was to rely on "switchable" molecules with intrinsic bistabilities triggered by external stimuli, such as temperature or light, or on the controlled dosing of chemicals to form reversible bonds. However, these methods constrain the functionality to switchable molecules or depend on access to atoms or molecules. Here, we present a way to induce bistability also in a planar molecule by making use of the environment. We found that the particular "habitat" offered by an antiphase boundary of the Rashba system BiAg$_2$ stabilizes a second structure for manganese phthalocyanine molecules, in which the central Mn ion moves out of the molecular plane. This corresponds to the formation of a large magnetic moment and a concomitant change of the ground state with respect to the conventional adsorption site. The reversible spin switch found here shows how we can not only rearrange electronic levels or lift orbital degeneracies via the substrate, but even sway the effects of many-body interactions in single molecules by acting on their surrounding.Comment: Main text, 7 pages, 6 figures. Supplementary material available at https://www.nature.com/articles/s41535-018-0126-

Knowledge pills skills as a resource of learning in Blended Learning

[EN] The advent of new technologies together with a society characterized by immediacy, volatility and constant change has transformed the education scene in the last few years. These changes have to consider the policy framework in higher education recent reforms. Thus, that forces us to reconsider our methodologies, pedagogical processes and educational contents, in an attempt to guarantee the access to knowledge in a systematic way and give the maximum effect to Learning-knowledge processes. One of the latest training practises inside the field of high education, is the Blended Learning, which makes use of technology resources whether on a face-to-face or on-line lessons, in order to facilitate the learning process. In response to the student’s role as the main agent in learning process, we focus on one of the tools that gives us the answer to the request of lifelong learning and allowing us to adapt to new demands of the new time-space scenery of learning, the knowledge pills

Antiferromagnetic spin coupling between rare earthadatoms and iron islands probed by spin-polarized tunneling

High-density magnetic storage or quantum computing could be achieved using small magnets with large magnetic anisotropy, a requirement that rare-earth iron alloys fulfill in bulk. This compelling property demands a thorough investigation of the magnetism in low dimensional rare-earth iron structures. Here, we report on the magnetic coupling between 4f single atoms and a 3d magnetic nanoisland. Thulium and lutetium adatoms deposited on iron monolayer islands pseudomorphically grown on W(110) have been investigated at low temperature with scanning tunneling microscopy and spectroscopy. The spin-polarized current indicates that both kind of adatoms have in-plane magnetic moments, which couple antiferromagnetically with their underlying iron islands. Our first-principles calculations explain the observed behavior, predicting an antiparallel coupling of the induced 5d electrons magnetic moment of the lanthanides with the 3d magnetic moment of iron, as well as their in-plane orientation, and pointing to a non-contribution of 4f electrons to the spin-polarized tunneling processes in rare earths.This work was supported by the Spanish MINECO (Grants MAT2010-15659 and MAT2012-31309), Gobierno de Aragón (Grant E81), University of Zaragoza (JIUZ-2013-CIE-12) and Fondo Social Europeo.Peer Reviewe

Antiferromagnetic Spin Coupling between Rare Earth Adatoms and Iron Islands Probed by Spin-Polarized Tunneling

High-density magnetic storage or quantum computing could be achieved using small magnets with large magnetic anisotropy, a requirement that rare-earth iron alloys fulfill in bulk. This compelling property demands a thorough investigation of the magnetism in low dimensional rare-earth iron structures. Here, we report on the magnetic coupling between 4f single atoms and a 3d magnetic nanoisland. Thulium and lutetium adatoms deposited on iron monolayer islands pseudomorphically grown on W(110) have been investigated at low temperature with scanning tunneling microscopy and spectroscopy. The spin-polarized current indicates that both kind of adatoms have in-plane magnetic moments, which couple antiferromagnetically with their underlying iron islands. Our first-principles calculations explain the observed behavior, predicting an antiparallel coupling of the induced 5d electrons magnetic moment of the lanthanides with the 3d magnetic moment of iron, as well as their in-plane orientation, and pointing to a non-contribution of 4f electrons to the spin-polarized tunneling processes in rare earths

Estudio teórico de la generación de calor por nanopartículas magnéticas utilizando liposomas como membranas celulares modelo

En la actualidad, las nanopartículas magnéticas (MNPs, por sus siglas en inglés) son ampliamente estudiadas en el campo de la biomedicina por sus interesantes características. Sus aplicaciones van desde su uso como agentes de contraste en resonancia magnética de imagen (RMI), la fabricación de biosensores, la liberación controlada de fármacos o incluso los tratamientos tumorales mediante hipertermia magnética. El presente trabajo de final de máster ha sido impulsado por una aplicación menos común de la hipertermia magnética, concretamente su uso para modular las propiedades biofísicas de membranas celulares modelo (liposomas) mediante un calentamiento localizado y controlado. El trabajo se ha centrado en el estudio teórico de la capacidad de generar calor de MNPs de distintos tamaños bajo la aplicación de campos magnéticos alternos. Para lograr este objetivo, se han empleado métodos computacionales para simular un modelo teórico que contempla MNPs con un diámetro comprendido entre los 6 y 18 nm. Estas MNPs se han simulado variando su anisotropía y las condiciones del campo magnético aplicado. Modificar dichos parámetros ha sido crucial para evaluar su efecto en la capacidad de disipación de calor de las MNPs. Previamente a este estudio, en el grupo BioNanosurf se han sintetizado y caracterizado las MNPs de forma experimental. Los resultados obtenidos en el laboratorio han sido comparados con las simulaciones realizadas en el presente trabajo. Esta comparación ha permitido entender mejor los resultados experimentales y determinar cuáles son las condiciones que favorecen una mayor generación de calor en la aplicación propuesta. El trabajo realizado asienta las bases para continuar investigando el efecto de otras variables como puede ser la interacción entre nanopartículas, algo que ocurriría en aplicaciones in vitro e in vivo. <br /

Evolución estructural con la temperatura de cadenas zigzag mediante derivados de terfenilos

Este trabajo trata de la preparación de polímeros metal-orgánicos y covalentes en forma de anillos y de cadenas zigzag mediante el método de síntesis en superficie (on-surface synthesis,OSS). Dicho método es una aproximación de crecimiento de abajo-arriba (bottom-up approach) para sintetizar nanoestructuras a partir de precursores moleculares simples. Estudiamos el papel de la temperatura y del sustrato sobre los productos obtenidos por síntesis en condiciones de ultra-alto-vacío (UHV). Las estructuras obtenidas se caracterizan mediante un Microscopio de Efecto Túnel (STM) a 4K sobre Ag y Au terminados en el plano (111). Se concluye que la sínteis funciona en ambos sustratos, aunque las estructuras que se forman y la temperatura a la que lo hacen dependen de éste. Así mismo se encuentran intermedios metal-orgánicos en el sustrato de Ag(111).<br /