The magnetization orientation of Fe ultrathin layers in contact with graphene

In this paper, we study the magnetic and chemical properties of Fe/graphene vertically stacked ultrathin films by means of X-ray magnetic circular dichroism and X-ray photoelectron spectroscopy. We compare two systems: an iron layer deposited directly on top of the Pt(111) surface, and an intercalated Fe film sandwiched between graphene and Pt(111). The system composed of a submonolayer Fe deposited directly on Pt(111) maintains an out-of-plane easy magnetization axis, even if it has been covered by graphene that quenches effectively the magnetic orbital moment of Fe. However, when the Fe coverage is increased above 1 ML the easy magnetization axis flips in the in-plane direction

A synchrotron-based spectroscopic study of the electronic structure of N-doped HOPG and PdY/N-doped HOPG

N-doped Highly Oriented Pyrolytic Graphite (HOPG) (obtained by ion implantation) was used as a model system for mimicking the effect of N-doping in sp2 hybridized carbon based supports. The electronic structure of such system has been careful characterized by means of spectroscopic techniques adopting synchrotron radiation. We demonstrate that it is possible to tailor different functional groups simply by tuning the annealing temperature after ion implantation. On such chemical modified HOPG, PdY catalyst nanoparticles have been deposited under strictly controlled conditions in ultra-high-vacuum (UHV) and the nanoparticle/support interactions studied by photoemission. The formation of the Pd3Y alloy is evidenced by core level shift in Y 3d and Pd 3d states due to charge transfer

In-Situ Carbon Doping of TiO2 Nanotubes Via Anodization in Graphene Oxide Quantum Dot Containing Electrolyte and Carburization to TiOxCy Nanotubes

Anodic production of self-organized titania nanotubes (TNTs) in an electrolyte enriched with graphene oxide quantum dots (GOQDs) is reported. The TNT-GOQD composites grown under these conditions show in-situ carbon doping, leading to the formation of anatase TiO2 domains and to the reduction to substoichiometric oxide (TiOx) and TiC. Surface science and electrochemical techniques are used in synergy to reveal that graphitic carbon is incorporated into TiO2 upon anodic nanotube growth promoting the formation of oxygen vacancies and thus TiO2 reduction. Upon annealing in ultrahigh vacuum, titanium oxycarbide (TiOxCy) is formed at temperatures 400 degrees C, where the material changes from a semiconductor to a semimetal. At the solid/liquid interface, the apparent electron donor density increases from as-grown TNTs to as-grown TNT-GOQD composites due to the carbon doping, and the conductivity increases further with annealing temperature due to the increasing concentration of coordinatively unsaturated C atoms, crystallinity, and TiO2 reduction. The materials synthesized and characterized in this study find application in different areas ranging from visible light photocatalysis and photo-electrochemistry to use as Li-ion battery anodes and electrocatalyst supports, because it is possible to gradually tune the density of states below the Fermi level, which can be referred to as band-gap engineering

TiO2/graphene nanocomposites from the direct reduction of graphene oxide by metal evaporation

We demonstrate that graphene oxide can be efficiently reduced by evaporating metal Titanium in high vacuum. A detailed description of this reaction is provided by combining in situ photoemission spectroscopy measurements and DFT calculations: the titanium atoms readily react with the oxygenated groups of graphene oxide, disrupting the C\u2013O bonds, with the consequent formation of titania and the recovery of the sp2 hybridized carbon atoms. When all surface oxygen is consumed, titanium can react with the carbon substrate and form carbidic species. Resonant photoemission spectroscopy measurements allow identifying the presence and exact energy position in the valence band of the Ti\u2013C and Ti\u2013O\u2013C states, which are supposed to control the electron and energy transfer across the TiO2/graphene interface. Therefore with this study we provide a versatile method and the rationale for controlling, at the atomic level, the nature of the interface of graphene/metal oxide nano composites

Fast One-Pot Synthesis of MoS2/Crumpled Graphene p-n Nanonjunctions for Enhanced Photoelectrochemical Hydrogen Production

none12NEXUSrestrictedCarraro, Francesco; Calvillo, Laura; Cattelan, Mattia; Favaro, Marco; Righetto, Marcello; Nappini, Silvia; Píš, Igor; Celorrio, Verónica; Fermín, David J.; Martucci, Alessandro; Agnoli, Stefano; Granozzi, GaetanoCarraro, Francesco; CALVILLO LAMANA, Laura; Cattelan, Mattia; Favaro, Marco; Righetto, Marcello; Nappini, Silvia; Píš, Igor; Celorrio, Verónica; Fermín, David J.; Martucci, Alessandro; Agnoli, Stefano; Granozzi, Gaetan

Carbon Doping: In‐Situ Carbon Doping of TiO2 Nanotubes Via Anodization in Graphene Oxide Quantum Dot Containing Electrolyte and Carburization to TiOxCy Nanotubes (Adv. Mater. Interfaces 5/2015)

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Surface-Confined Polymerization of Halogenated Polyacenes: The Case of Dibromotetracene on Ag(110)

On-surface synthesis of thin organic and organometallic films in a bottom-up fashion has become a promising approach for the development of new nanotechnologies. In this work we studied 5,11-dibromotetracene (C18H10Br2) as a prototypical case of rodlike polyaromatic molecules functionalized with two bromine atoms on the sides. The adsorption and temperature-stimulated transformations of dibromotetracene assemblies on Ag(110) have been investigated by a combination of synchrotron radiation X-ray photoemission spectroscopy (XPS), near-edge X-ray absorption spectroscopy (NEXAFS), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. Upon the contact with the Ag substrate, the Br-C bonds are promptly cleaved at room temperature, and Ag-coordinated protopolymers are formed along the [001] substrate direction. The organometallic dimers and trimers remain on the surface up to 523 K. The stabilization of the protopolymers is driven by the substrate anisotropy and weak interactions with nearby Br atoms. The short oligomers formed at elevated temperatures are weakly bounded to the substrate and desorb before covalent structures can be formed

Synthesis of graphene nanoribbons with a defined mixed edge-site sequence by surface assisted polymerization of (1,6)-dibromopyrene on Ag(110)

By a combination of scanning tunneling microscopy, X-ray spectroscopic techniques and density functional theory calculations, we prove the formation of extended patterns of parallel, graphene nanoribbons with alternate zig-zag and armchair edges and selected width by surface-assisted Ullmann coupling polymerization and dehydrogenation of 1,6-dibromopyrene (C16H8Br2). Besides the relevance of these nanostructures for their possible application in nanodevices, we demonstrate the peculiarity of halogenated pyrene derivatives for the formation of nanoribbons, in particular on Ag(110). These results open the possibility of tuning the shape and dimension of nanoribbons (and hence the correlated electronic properties) by choosing suitably tailored or on-purpose designed molecular precursors