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)

Molecular tilting and columnar stacking of Fe phthalocyanine thin films on Au(111)

Scanning tunneling microscopy and x-ray absorption spectroscopic results at the Fe K edge of Fe phthalocyanine (FePc) thin films grown on Au substrates, together with theoretical calculations, allow us to refine the structure of the film. In particular, we show that the columnar stacking of the FePc molecules is different from that found in bulk ¿ and ß phases. Moreover, the molecules do not lay parallel to the surface of the substrate. These structural findings are relevant to understand magnetism of FePc films.The financial support of the Spanish financial agency MINECO MAT2011-2379 and MAT2014-53921-R, Aragonese DGA-IMANA E34 (co-funded by European Social Fund), as well as European Union FEDER funds is acknowledged. The sample preparation and initial structural characterization were supported by the Office of Basic Energy Science, U.S. Department of Energy, BES-DMS funded by the Department of Energy’s Office of Basic Energy Science, DMR under Grant No. DE FG03 87ER-45332 and NSF DMR 0847552.Peer Reviewe

Publisher Correction : Real space manifestations of coherent screening in atomic scale Kondo lattices

Aquesta és una correcció a l'article 10.1038/s41467-019-10103-

Tuning the magnetic moment of high density FePc/Ag(110) phases by oxygen dosing

Resumen del trabajo presentado a la 64th Annual Conference on Magnetism and Magnetic Materials (MMM), celebrada en Las Vegas (USA) del 4 al 8 de noviembre de 2019.Peer reviewe

Schaltbare Moleküle auf metallischen Oberflächen untersucht mittels röntgenspektroskopischer Methoden

Abstract i Kurzfassung iii 1 Introduction 1 2 Core-level spectroscopies 5 2.1 Photoemission . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1 Primary XPS peaks . . . . . . . . . . . . . . . . . . . . . 9 2.1.2 XPS satellites . . . . . . . . . . . . . . . . . . . . . . . . 11 2.1.3 Photoelectron cross section . . . . . . . . . . . . . . . . . 13 2.2 Near edge X-ray absorption fine structure . . . . . . . . . . . . 17 2.2.1 Spectral structure . . . . . . . . . . . . . . . . . . . . . . 17 2.2.2 Angle dependence . . . . . . . . . . . . . . . . . . . . . . 20 2.2.3 Data acquisition . . . . . . . . . . . . . . . . . . . . . . . 22 2.3 X-ray sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.3.1 X-ray gun . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.3.2 Synchrotron radiation . . . . . . . . . . . . . . . . . . . 24 3 Simulation of NEXAFS 27 3.1 Molecular states . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.2 Quantum-chemical methods . . . . . . . . . . . . . . . . . . . . 29 3.2.1 Born-Oppenheimer approximation . . . . . . . . . . . . . 29 3.2.2 Hartree-Fock approximation . . . . . . . . . . . . . . . . 30 3.2.3 Density functional theory . . . . . . . . . . . . . . . . . 32 3.2.4 Molecular orbital representation . . . . . . . . . . . . . . 34 3.3 Simulated NEXAFS . . . . . . . . . . . . . . . . . . . . . . . . 35 3.3.1 Ionization potentials . . . . . . . . . . . . . . . . . . . . 36 3.3.2 Transition energies . . . . . . . . . . . . . . . . . . . . . 36 3.3.3 Transition intensities . . . . . . . . . . . . . . . . . . . . 37 4 Azobenzene on noble metal surfaces 39 4.1 Photoisomerization of azobenzene . . . . . . . . . . . . . . . . . 40 4.2 Azobenzene derivatives . . . . . . . . . . . . . . . . . . . . . . . 45 4.2.1 Dimetacyano azobenzene . . . . . . . . . . . . . . . . . . 47 4.2.2 Carboxymethylester azobenzene . . . . . . . . . . . . . . 56 4.3 Adsorption on metallic surfaces . . . . . . . . . . . . . . . . . . 61 4.3.1 Adsorption on Au(111) . . . . . . . . . . . . . . . . . . . 62 4.3.1.1 Adsorption rate . . . . . . . . . . . . . . . . . . 62 4.3.1.2 Adsorption state . . . . . . . . . . . . . . . . . 63 4.3.2 Adsorption on Cu(001) . . . . . . . . . . . . . . . . . . . 72 4.3.2.1 Adsorption rate . . . . . . . . . . . . . . . . . . 72 4.3.2.2 Temperature-dependent adsorption . . . . . . . 73 4.3.2.3 Thickness-dependent adsorption . . . . . . . . . 77 4.3.2.4 Adsorption at low coverages . . . . . . . . . . . 82 4.3.2.5 Adsorption mechanism . . . . . . . . . . . . . . 86 4.3.2.6 Molecular orientation . . . . . . . . . . . . . . . 91 4.3.2.7 Adsorption at high coverages . . . . . . . . . . 94 4.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 5 Ring-opening reaction of spiropyran 101 5.1 Isomerization process . . . . . . . . . . . . . . . . . . . . . . . . 103 5.2 Multilayer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 5.2.1 Growth mode . . . . . . . . . . . . . . . . . . . . . . . . 107 5.2.2 Electronic properties of spiropyran . . . . . . . . . . . . 109 5.2.3 Switching properties . . . . . . . . . . . . . . . . . . . . 112 5.3 Adsorption on Au(111) . . . . . . . . . . . . . . . . . . . . . . . 117 5.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Conclusions 125 Bibliography 128The scope of this work is the investigation of the interactions that appear in molecular switches on noble metal surfaces. The adsorption of two different types of switching molecules is studied by means of near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS). Samples of molecular powders and evaporated molecular multilayers are used as references in which the molecules are decoupled from the surface. The interpretation of the measured data is supported by quantum-chemical calculations based on density-functional theory (DFT), resulting in a deep understanding of the interaction mechanisms. In the first part of this work dimetacyano azobenzene and dimetacarboxymethylester azobenzene are chosen as simple model systems representing the class of conformal switches. These two compounds exhibit the same adsorption behavior and provide complementary information about the adsorption state. Au(111) and Cu(001) are used as substrates with different surface reactivities. On Au(111) at room temperature, azobenzene physisorbs flat in its trans configuration up to a saturation coverage of one monolayer, while the electronic structure of the adsorbate resembles the one calculated for the free molecule. In contrast, on Cu(001) we find that the substrate temperature and the molecule coverage have an influence on the adsorption state. Below half a monolayer evaporated on Cu(001) at 150 K, the majority of azobenzene molecules are found to be in the same physisorbed state as on Au(111). After annealing the substrate above 250 K most of the molecules chemisorb via their azobenzene center, where the frontier orbitals at the azo bridge rehybridize with the substrate orbitals. This interaction forces the molecule to a butterfly-like bent molecular geometry in which the outer aromatic groups are tilted out of the surface plane. In this conformation the lone-pair electrons can participate in the chemical binding, leading to a higher stabilization of the bent structure. The structural reorientation is accompanied by the deoccupation of the bonding and the occupation of the antibonding molecular π orbital, which is described by the Dewar-Chatt- Duncanson model. At higher coverages the increased intermolecular interaction provokes a larger tilt, which increases the stronger lone-pair – surface interactions and finally leads to the dissociation at the central N–N azo bond. The second part examines the adsorption of nitro-spiropyran (SP) as a member of the class of ring-opening/ring-closing switches in multi- and monolayers on Au(111). In multilayered films, the SP molecules order in a crystalline structure. UV irradiation causes half of the amount of molecules to undergo the ring-opening reaction. The resulting merocyanine (MC) is stabilized in the crystalline confinement such that a back reaction is not possible. For monolayer coverages, the molecule adsorbs on the substrate at 150 K with its nitro moiety flat on the surface. Annealing the substrate to 330 K provokes the ring-opening reaction. The resulting planar merocyanine molecule lies flat on the surface arranged in dimers that are liked by hydrogen bonds. The latter stabilize the ring-opened form and prevent the back reaction.Ziel dieser Arbeit ist es, die Wechselwirkungen molekularer Schalter auf und mit verschiedenen Edelmetalloberflächen zu untersuchen. Zu diesem Zweck wird das unterschiedliche Adsorptionsverhalten von zwei Typen schaltbarer Moleküle mit Hilfe von Röntgen-Nahkanten-Absorptionsspektroskopie (NEXAFS) und Röntgen- Photoelektronenspektroskopie (XPS) charakterisiert. Proben der Moleküle in Pulverform und adsorbiert in Multilagen dienen als Referenz zu den an die Oberfläche gekoppelten Adsorbaten. Quantenchemische Berechnungen auf Basis von Dichtefunktionaltheorie (DFT) ermöglich dabei eine Interpretation der experimentellen Daten in Hinsicht auf ein grundlegendes Verständnis der auftretenden Wechselwirkungen. Im ersten Teil der Arbeit werden Dimetacyano- and Dimetacarboxymethylesterazobenzol als prototypische Vertreter der Klasse konformeller Schalter untersucht. Beide Verbindingen zeigen dasselbe Adsorptionsverhalten und liefern dennoch unterschiedliche, sich ergänzende Informationen über ihren chemischen Zustand auf der Oberfläche. Au(111) und Cu(001) dienen als Oberflächen mit unterschiedlicher Reaktivität. Die Azobenzole physisorbieren auf Au(111) bei Raumtemperatur, wobei die Moleküle in ihrer planaren trans-Form parallel zur Oberfläche ausgerichtet sind. Im Gegensatz dazu ist ein Teil der Moleküle auf Cu(001) für Bedeckungen unterhalb einer halben Monolage schon bei Temperaturen von 150 K chemisorbiert. Oberhalb von 250 K ist die Chemisorption der gesamten Submonolage annähernd vollständig abgeschlossen. In diesem Zustand rehybridisieren die π- Orbitale der Azo- Brücke mit denen des Substrats. Diese Wechselwirkung verursacht eine leichte Deformation der planaren Struktur des trans-Azobenzols, bei der sich die äußeren aromatischen Einheiten von der Oberfläche wegbiegen. In dieser Geometrie können sich die freien Elektronenpaare der Stickstoffatome an der Bindung zum Substrat beteiligen, was zu einer erhöhten Stabilität der Struktur führt. Die Ausbildung der Bindungen zur Oberfläche wird begleitet von einer teilweisen Entvölkerung des bindenden π- Orbitals und einer teilweisen Besetzung des antibindenden π- Orbitals, so wie es im Rahmen des Dewar-Chatt- Duncanson-Modells beschrieben wird. Für höhere Bedeckungen nahe einer Monolage nehmen die zwischenmolekularen Wechselwirkungen an Bedeutung zu und bewirken eine noch stärkere Verbiegung der adsorbierten Moleküle. Dies führt zu einer teilweisen Dissoziation der Adsorbatmoleküle. Der zweite Teil der Arbeit behandelt die Adsorption von Nitro-Spiropyran (SP), einem Mitglied der Klasse der Ringöffnungs-/Ringschlussschalter, in Multi- und Monolagen auf Au(111). In Multilagen ordnen sich die SP-Moleküle zu einkristallinen Strukturen. Die Beleuchtung dieser Ensembles führt bei etwa der Hälfte der Moleküle zur Ringöffnung. Das entstandene Merocyanin ist so in den Kristall eingebunden, dass eine Rückreaktion nicht möglich ist. Auch hier kann ein temperaturabhängiges Verhalten beobachtet werden. Nach der Adsorption auf einer Au(111)-Oberfläche bei 150 K ist die Nitrogruppe des Moleküls parallel zur Oberfläche orientiert. Durch Erhöhung der Substrattemperatur auf 330 K öffnet sich der Pyranring und das resultierende planare Merocyanin adsorbiert flach auf der Oberfläche. Dabei formen sich Dimere, die durch Wasserstoffbrücken stabilisiert sind. Letzteres ist unter anderem verantwortlich für die Unterdrückung der entgegengesetzten Ringschlussreaktion

Ferroelectricidad en la escala atómica basada en aislantes iónicos tipos salroca

Ferroelectricity at atomic scale has been recently shown in ultrathin layers of NaCl on Cu2N/Cu(001). The origin was suppossed to be the strain of NaCl. In this thesis, the two rocksalt compounds KBr and LiCl were investigated with respect to their growth behaviour on Cu(001) and the polar insulator Cu2N/Cu(001). Furthermore the electronic structure and the ferroelectric behaviour of KBr is described. In gap-states due to the hybridisation with Cu(001) were found at KBr/Cu(001), which are suppressed due to the adding of Cu2N. Surprisingly, also without a strain, ultrathin layers of KBr on Cu2N/Cu(001)shows ferroelectrism. In this thesis we applied the following experimental techniques: Scanning Tunneling Microscopy(STM), Scanning Tunneling Spectroscopy(STS), Atomic Force Microscopy(AFM), Kelvin-Probe-Spectroscopy and Low Energy Electron Refraction(LEED). LiCl was investigated at ultra high vacuum and room temperature, KBr at ultra high vacuum and 4K

Nanofiltration with polyamide thin film composite membrane with ZIF-93/SWCNT intermediate layers on polyimide support

Among current separation processes, nanofiltration (NF), besides its easy scalability, exhibits low energy consumption, environmental impact and footprint, being widely used for water treatment and solvent recovery. The development of membranes for NF involves perfecting the skin selective layer, the sublayers and the support. In this work, a multilayer structure membrane is presented where a selective layer of polyamide (PA, thickness 40–60 nm) was interfacially polymerized on a sub-layer of MOF ZIF-93 (thickness ∼ 50 nm) grown on another sub-layer of single-walled carbon nanotubes (SWCNT, thickness ∼ 400 nm) vacuum filtrated on an asymmetric polyimide P84® support (thickness ∼ 200 μm). The membrane with structure PA/ZIF-93/SWCNT/P84 showed excellent results in water NF and methanol organic solvent NF of different dyes (with the highest values of water and methanol permeances of up to 57.6 and 84.5 L·m−2·h−1·bar−1, respectively, with rejections usually greater than 99%). By means of a wide range of characterization techniques (contact angle, AFM, XRD, ATR-FTIR and FIB-SEM) the role of every component in the membrane was elucidated. In fact, the presence of the sublayer of ZIF-93 increased the roughness and hydrophilicity as well as decreased the thickness of the PA layer. These effects are related to the fact that the sublayers subordinate the interfacial polymerization as well as influence the properties of the PA film and therefore its NF performance, even showing chlorine resistance as well as ten-day cross-flow NF stability

Manganese phthalocyanine derivatives synthesized by on-surface cyclotetramerization

et al.We report a two-step on-surface synthesis of Mn phthalocyanine molecules from four tetracyanobenzene (TCNB) monomers through coordinative bonding with manganese adatoms. In the first step, the coevaporation of TCNB and Mn atoms leads to a metal-organic network stabilized by a combination of coordination and hydrogen (H) bonds. In the second step, annealing the coordination networks above room temperature results in individual Mn phthalocyanine molecules. The results shown here demonstrate the viability of an on-surface chemical synthesis strategy involving the reduction of the organic reagents by metal ions to produce metal-organic molecules. © 2014 American Chemical Society.Financial support by the Spanish Ministry of Science through Plan Nacional de I+D+i grant MAT2010-19236, University of Zaragoza (JIUZ-2013-CIE-12), and the German Academic Exchange Program (DAAD) is acknowledged.Peer Reviewe

Tuning the magnetic moment of Fe-Phtalocyanine on Ag(110) by oxygen dosing

Resumen del trabajo presentado a la 20th International Conference on Solid Compounds of Transition Elements, celebrada del 11 al 15 de abril de 2016 en Zaragoza (España).Molecular overlayers on ordered substrates have a broad field of application in catalysis, sensing, molecular electronics, light-to-energy conversion, etc. In particular, bio-inspired oxygen-binding metalated macrocycles, such as iron-phtalocyanines (FePc), are being investigated as viable substitutes for precious metals in catalysis of the Oxygen Reduction Reaction (ORR) in low-temperature fuel cells. Recent studies of FePc on Ag(110) have shown that sub-monolayer (sub-ML) phases are catalitically active; remarkably, in oxygen-dosed phases O2 intercalates between the molecules and the surface thereby substantially changing the Fe magnetic moment. Reversible switching of the Fe magnetic moment in some low-density (LD) FePc phases upon an oxygenation (OD) - annealing (ANN) cycle has been demonstrated. In this contribution we report on the structural and magnetic changes along a catalytic cycle of a new “quasi-squared” FePc sub-ML phase (R3) evaporated on Ag(110), Fig. a. Structural changes were monitored by Scanning Tunneling Microscopy (STM) and Low Energy Electron Diffraction (LEED). X-ray absortion spectroscopy (XAS), x-ray lineal polarized absortion (XLPA) and x-ray magnetic circular dichroism (XMCD) experiments at the Fe L2,3 edge were performed on four samples: the as-evaporated phase (R3), two differently oxygenated samples (OX1 and OX2) and the annealed phase (R3ANN). XLPA and XMCD (Fig. b) analysis evidence the new R3 phase is catalitically active, however, oxygenation / deoxydation is less effective than previously characterised LD phase: only partial oxygenation is achieved (about 20%, 50% for OX1 and OX2, respectively), and the pristine phase is not fully recovered after annealing. Sum rule analysis allowed us to determine the effective spin (ms eff) and orbital (mL) magnetic moments as a function of the incidence angle (Fig. c). It is concluded that all characterised phases display planar anisotropy, and the values of ms eff are about one order of magnitude larger than mL. By oxydation the isotropic moment undergoes an increase from 7.2x10-2 μB/hole to 1.8x10-1 μB/hole, which is about a factor of 2 smaller than the increase achieved for LD phase. Our spectroscopic results are in agreement with a combined study of STM and non-contact tuning fork AFM microscopies showing that oxydation of FePc on Ag(110) requires a rotation and displacement of the FePc molecule, which is more difficult to fulfill in denser phasesPeer reviewe