Reactividad química del para-aminofenol en superficies metálicas: nuevos mecanismos de síntesis sobre superficies

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 30-10-202

Few-layer antimonene electrical properties

Antimonene -a single layer of antimony atoms- and its few layer forms are among the latest additions to the 2D mono-elemental materials family. Numerous predictions and experimental evidence of its remarkable properties including (opto)electronic, energetic or biomedical, among others, together with its robustness under ambient conditions, have attracted the attention of the scientific community. However, experimental evidence of its electrical properties is still lacking. Here, we characterized the electronic properties of mechanically exfoliated flakes of few-layer (FL) antimonene of different thicknesses (∼ 2–40 nm) through photoemission electron microscopy, kelvin probe force microscopy and transport measurements, which allows us to estimate a sheet resistance of ∼ 1200 Ω sq−1 and a mobility of ∼ 150 cm2V−1s−1 in ambient conditions, independent of the flake thickness. Alternatively, our theoretical calculations indicate that topologically protected surface states (TPSS) should play a key role in the electronic properties of FL antimonene, which supports our experimental findings. We anticipate our work will trigger further experimental studies on TPSS in FL antimonene thanks to its simple structure and significant stability in ambient environmentsWe acknowledge financial support through the “Maríade Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M), the Spanish MINECO through projects PCI2018-093081, FIS2016-80434-P, PID2019-109539GB-C43, PID2019- 106268GB-C31 and -C32, MAT2016-77608-C3-1-P and -3-P, MAT2013-46753-C2-2-P and MAT2017-85089-C2-1R, the EU Graphene Flagship funding (Graphene Flagship Core3 881603 and JTC2017/2D-Sb&Ge), the EU via the ERC-Synergy Program (GrantERC-2013-SYG-610256 NANOCOSMOS), the Comunidad Autónoma de Madrid through MAD2D-CM, S2018/NMT-4321 (NanomagCOST-CM) and the European StructuralFunds via FotoArt CM project (S2018/NMT-4367), and the Fundación Ramón Areces. S.P. acknowledges financial support by the VILLUM FONDEN via the Centre of Excellence for Dirac Materials (Grant No. 11744

On-surface synthesis of metal–organic frameworks: the critical role of the reaction conditions

[EN] Two different metal–organic frameworks with either a honeycomb or Kagome structure were grown on Cu(111) using para-aminophenol molecules and native surface adatoms. Although both frameworks are made up from the same chemical species, they are structurally differ- ent emphasizing the critical role being played by the reaction condi- tions during their growth. This work highlights the importance of the balance between thermodynamics and kinetics in the final structure of surface-supported metal–organic networks.This work was supported by the FotoArt-CM (S2018/NMT- 4367) and FotoSurf-CM (Proyectos Sin ́ergicos I+D, Y2020/NMT- 6469) projects funded by the ‘‘Comunidad de Madrid’’ and co-financed by European Structural Funds, and by grants PID2020-113142RB-C21,funded by MCIN/AEI/10.13039/501100011033,and PLEC2021-007906 and TED2021-129999B-C31, funded by MCIN/AEI/10.13039/501100011033 and the ‘‘European Union NextGenerationEU/PRTR’’. CSS acknowledges grant RYC2018-024364-I funded by MCIN/AEI/10.13039/501100011033 and by ‘‘ESF Investing in your future’’ and NRdA the Spanish MINECO for support from the FPI program (BES-2015-072642). We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe

On surface synthesis of new 2D nanostructures based on 4-aminophenol on Cu(110)

Trabajo presentado en la IX edición de GEFES, celebrada en Cuenca del 13 al 15 de enero de 2016.On-surface chemistry has recently emerged as a research field where the catalytic properties of surfaces are essential tools to synthesize new materials sometimes not accessible with other techniques [1]. This new approach has high potential for technological applications and can be a platform for discovering new low dimensional molecular networks [1-3]. In the present work we employ on-surface chemistry techniques to synthesize a new 2D material following a bottom-up strategy. We study the thermally activated chemical reaction of 4-aminophenol (4-AP) induced by the Cu(110) surface in a UHV environment. 4-AP is a good candidate to be used as building blocks for on-surface chemistry due to the presence of functional groups (-NH2, -OH), each with wide specific chemistry. At room temperature the adsorbed 4-AP molecules form mainly an ordered monolayer (Fig.1a) on the Cu(110) surface. The annealing of this monolayer up to 493K induces new chemical reactions that lead to the formation of polymeric-like structures of 4-AP building blocks (Fig.1b). The use of different surface techniques such as STM, LEED, NEXAFS and XPS allows us to obtain structural information of both systems as well as to provide information on the chemical environment of the atoms. It is confirmed that the use of a combination of surface techniques is an optimal strategy to gain insight into on-surface chemical reactions for developing new routes of synthesis for novel materials.N

Spatial variation of the active phases during the catalytic oxidation of CO measured on a curved Pd(111) surface

Resumen del póster presentado al 5th Annual Ambient Pressure X-ray Photoelectron Spectroscopy Workshop, celebrado en Berlin (Alemania) del 11 al 14 de diciembre de 2018.For decades, the study of chemical reactions on single metal surfaces has been aimed at identifying those active sites and crystal planes that feature nanoparticles. However, nanocrystal facets coexist in a reduced space, and are expected to simultaneously undergo chemical and structural transformations during catalytic reactions. In ALBA we explore chemical-structural interplays among crystal planes using curved crystals and near-ambient X-ray photoemission (XPS) at CIRCE. As a test case for the approach, we recently used a curved Pd(111) surface, on which we freeze the CO oxidation reaction at the ignition temperature. By scanning the photon beam across the curved surface, we observe a smooth spatial variation of chemisorbed phases, demonstrating a different reaction stage at each crystallographic plane. As shown in the Figure, the XPS signal from chemisorbed CO reveals the linearly decreasing fraction of CO-poisoned areas, from the (111) direction up to a 10º critical angle, and at various temperatures around light-off. This behavior is explained as a collective structural response of the surface at the reaction onset, consisting in the weighted segregation of less-active (111) phase and highly-active (223) and (332) facets in A-type and B-type vicinal planes, respectively.We acknowledge financial support from the Spanish Ministry of Economy (Grant MAT2013-46593-C6-4-P) and Basque Govemment (Grant IT621-13).Peer Reviewe

Transforming C60 into graphene: growth, structural and electronic characterization

Trabajo presentado en GraphITA, celebrado en Bolonia (Italia) del 14 al 18 de septiemnbre de 2015.The production of high-quality graphene inexpensively and in bulk is an absolutely necessary first step for the material to ever live up to its promise in commercial applications. Among the different reported growth methods, chemical vapor deposition (CVD) and its variants with transition metal substrates has proven its ability to produce large-scale, one-atom thick graphene sheets [1-2]. Particularly attractive is the use of low carbon solubility Cu substrates for CVD graphene growth, owing to its inexpensiveness and the possibility of post-growth graphene transfer on arbitrary substrates [3]. In this work we present the growth of graphene layers by chemical vapor deposition under ultra-high vacuum conditions on polycrystalline oxygen-free Cu foils. As a carbon source, a C60 evaporator maintained at 500 C has been used. Prior to carbon evaporation the Cu foils have been treated by Ar-sputtering and thermal annealing cycles in order to clean them and promote the growth of well oriented large Cu terraces, especially suitable for LEED analysis (figure 1). C60 deposition has taken place while controlling the Cu foil temperature with an optical pyrometer. After growth is complete, sample analysis is performed with different techniques to characterize the graphene layer. In-situ LEED images show well defined Cu 111 and 100 reflections and rings corresponding to graphene in various orientations with respect to the Cu grains (figure 1). Ex- situ Atomic Force Microscopy (AFM) and Raman spectroscopy are employed to gather information on sample morphology and quality (figure 1). In order to determine the electronic band structure, angle resolved photoelectron emission measurements have been done in synchrotron facility where linear behavior of electrons near Dirac point has been observed (figure 1). We are currently optimizing graphene transfer from our samples to insulating oxide substrates with aim to determining its bandgap and macroscopic and local magnetotransport properties.N

On-surface synthesis of metal-organic frameworks: the critical role of the reaction conditions

Two different metal-organic frameworks with either a honeycomb or Kagome structure were grown on Cu(111) using para-aminophenol molecules and native surface adatoms. Although both frameworks are made up from the same chemical species, they are structurally different emphasizing the critical role being played by the reaction conditions during their growth. This work highlights the importance of the balance between thermodynamics and kinetics in the final structure of surface-supported metal-organic networks.Fil: Ruiz del Árbol, Nerea. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Sánchez Sánchez, Carlos. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Martínez, José I.. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Rodriguez, Luis Miguel. Instituto de Ciencia de Materiales de Madrid; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Serrate, David. Universidad de Zaragoza; EspañaFil: Verdini, Alberto. No especifíca;Fil: Floreano, Luca. No especifíca;Fil: Jacobson, Peter. University of Graz; AustriaFil: Grill, Leonhard. University of Graz; AustriaFil: Martín Gago, José Ángel. Instituto de Ciencia de Materiales de Madrid; EspañaFil: López, María F.. Instituto de Ciencia de Materiales de Madrid; Españ

On-surface synthesis and characterization of polyaniline oligomers

Resumen del póster presentado a la Conferencia bienal Fuerzas y Túnel, celebrada en Jaca (España) del 27 al 29 de junio de 2018.Polyaniline (PANI) has been studied since 1835 because of its interest as inherently conducting polymer due to its wide range of potential applications that range from batteries to biosensors. The interest of PANI lies on its capability to express different properties depending on its nitrogen oxidation state: leucoemeraldine (the fully reduced form), emeraldine (the half-oxidized form), and pernigraniline (the fully oxidized form). There are two conventional synthesis methods, electrochemical processing and chemical oxidative polymerization of aniline in a wet environment. Although doped emeraldine structure present good conductivity, it has been shown that the size, the preparation method and the existence of a metal-polymer interface, influence the physical properties of the final PANI. Here, we present a new route to synthesize 1D oligomers of PANI based on a specific on-surface synthesis process. The synthesis was carried out using p-aminophenol (p-Ap) molecules as building blocks on a Pt(111) single-crystal in a UHV environment. At 200°C p-Ap molecules are activated inducing a shift base reaction resulting in oligomer chains with pernigraniline structure. The mechanism of the chemical reaction was followed by XPS, LT-STM/STS and nc-AFM and confronted with theoretical calculations. XPS show that oxygen is removed from the p-AP molecule resulting in a coupling of the precursors via the nitrogen. STM and nc-AFM reveals that oligomers are formed by ca. 10 molecular precursors. STS shows the presence of two broad unoccupied electronic states around 200 mV and 650 mV above the Fermi level that we are able to resolve spatially. Finally, DFT calculations show that the atomic structure is influenced by the substrate crystallography.Peer Reviewe

Characterization of 2D-assembled overlayers based on p-aminophenol on Cu(110)

Trabajo presentado en el International Workshop On-surface Synthesis, celebrado en San Sebastián del 27 al 30 de junio de 2016.On-surface chemistry has emerged as an important research field leading to unconventional self-assembled nanoarchitectures with tunable properties [1,2]. The development of surfacesensitive spectroscopies has provided a powerful set of tools for a detailed characterization of the structure, composition, and physicochemical properties of the molecular structures obtained by this methodology. We have evaporated p-aminophenol (p-AP) on Cu(110) at 493 K and followed a bottom-up azocoupling reaction, leading to dimer formation: 4,4'-azobis(phenol). We have characterized the on-surface synthesized self-assembled structure by different techniques. Thus, by using a combination of STM/AFM, LEED, XPS and NEXAFS as well as DFT calculations, we are able to unveil the structural and chemical characteristics of the process and outcome. The structural analysis reveals that p-AP molecules have coupled forming new molecular species that self-organize on the surface. They lay in a flat geometry preserving the in-plane ¿- conjugated benzene units as depicted by NEXAFS. LEED pattern analysis shows that the molecular layer exhibit a long-range order with a [(5,1),(-1,2)] symmetry, forming chains rotated 20º with respect to the [001] direction of the Cu surface, as deduced by the STM/AFM images. (Fig 1). Finally, the XPS N1s spectra reveal an oxidation reaction from amine to imine while XPS O1s data suggests that oxygen atoms are covalently bound to the substrate. In summary, all the information obtained by following this multitechnique study, allow us to figure out a model of the structure promoted by the catalytic properties of substrate in a thermal activated process.N

On-Surface Driven Formal Michael AdditionProduces m-PolyanilineOligomers on Pt (111)

[EN] On-surface synthesis is emerging as a highly rational bottom-up methodology for the synthesis of molecular structures that are unattainable or complex to obtain by wet chemistry. Here, oligomers of meta-polyaniline, a known ferromagnetic polymer, were synthesized from para-aminophenol building-blocks via an unexpected and highly specific on-surface formal 1, 4 Michael-type addition at the meta position, driven by the reduction of the aminophenol molecule. We rationalize this dehydrogenation and coupling reaction mechanism with a combination of in situ scanning tunneling and non-contact atomic force microscopies, high-resolution synchrotron-based X-ray photoemission spectroscopy and first-principles calculations. This study demonstrates the capability of surfaces to selectively modify local molecular conditions to redirect well-established synthetic routes, such as Michael coupling, towards the rational synthesis of new covalent nanostructures.Spanish MINECO(MAT2017-85089-C2-1-R, RYC-2015–17730), European Research Council (ERC) under contract (ERC-2013-SYG-610256 NANOCOSMOS), Comunidad de Madrid via Programa de InvestigaciónTecnologías 2018 (FOTOART-CMS2018/NMT-4367), and the innovation program under grantagreements 785219 and 881603 (GrapheneCore2 and Gra-pheneCore3-Graphene-based disruptive technologies,re-spectively). CSS acknowledges MCIU for the “RamnyCajal” contract (RYC2018-024364-I). NRdA is grateful tothe Spanish MINECO for support from the FPI program(BES-2015–072642)Peer reviewe