R. Larciprete

Sapienza University of Rome, Roma, Latium, Italy

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Publications (136)433.72 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the structure of epitaxially grown hexagonal boron nitride (h-BN) on Ir(111) by chemical vapor deposition of borazine. Using photoelectron diffraction spectroscopy, we unambiguously show that a single-domain h-BN monolayer can be synthesized by cyclic dose of high-purity borazine onto the metal substrate at room temperature followed by annealing at T = 1270 K, this method giving rise to a diffraction pattern with three-fold symmetry. In contrast, high-temperature borazine deposition (T = 1070 K) results in a h-BN monolayer formed by domains with opposite orientation and characterized by a six-fold symmetric diffraction pattern. We identify the thermal energy and the energy difference between fcc and hcp seeds as key parameters in controlling the alignment of the h-BN clusters during the first stage of the growth, and we further propose structural models for the h-BN monolayer on the Ir(111) surface.
    ACS Nano 11/2014; · 12.03 Impact Factor
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    ABSTRACT: The production of high-quality graphene-oxide interfaces is normally achieved by graphene growth via chemical vapour deposition on a metallic surface, followed by transfer of the C layer onto the oxide, by atomic layer and physical vapour deposition of the oxide on graphene or by carbon deposition on top of oxide surfaces. These methods, however, come with a series of issues: they are complex, costly and can easily result in damage to the carbon network, with detrimental effects on the carrier mobility. Here we show that the growth of a graphene layer on a bimetallic Ni3Al alloy and its subsequent exposure to oxygen at 520 K result in the formation of a 1.5 nm thick alumina nanosheet underneath graphene. This new, simple and low-cost strategy based on the use of alloys opens a promising route to the direct synthesis of a wide range of interfaces formed by graphene and high-κ dielectrics.
    Nature Communications 01/2014; 5:5062. · 10.74 Impact Factor
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    ABSTRACT: We show that bimetallic surface alloying provides a viable route for governing the interaction between graphene and metal through the selective choice of the elemental composition of the surface alloy. This concept is illustrated by an experimental and theoretical characterization of the properties of graphene on a model PtRu surface alloy on Ru(0001), with a concentration of Pt atoms in the first layer between 0 and 50%. The progressive increase of the Pt content determines the gradual detachment of graphene from the substrate, which results from the modification of the carbon orbital hybridization promoted by Pt. Alloying is also found to affect the morphology of graphene, which is strongly corrugated on bare Ru, but becomes flat at a Pt coverage of 50%. The method here proposed can be readily extended to several supports, thus opening the way to the conformal growth of graphene on metals and to a full tunability of the graphene-substrate interaction.
    Scientific Reports 08/2013; 3:2430. · 5.08 Impact Factor
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    ABSTRACT: The secondary emission yield (SEY) properties of colaminated Cu samples for LHC beam screens are correlated to the surface chemical composition determined by X-ray photoelectron spectroscopy. The surface of the "as received" samples is characterized by the presence of significant quantities of contaminating adsorbates and by the maximum of the SEY curve (dmax) being as high as 2.2. After extended electron scrubbing at kinetic energy of 10 and 500 eV, the dmax value drops to the ultimate values of 1.35 and 1.1, respectively. In both cases the surface oxidized phases are significantly reduced, whereas only in the sample scrubbed at 500 eV the formation of a graphitic-like C layer is observed. We find that the electron scrubbing of technical Cu surfaces can be described as occurring in two steps, where the first step consists in the electron induced desorption of weakly bound contaminants that occurs indifferently at 10 and at 500 eV and corresponds to a partial decrease of dmax, and the second step, activated by more energetic electrons and becoming evident at high doses, which increases the number of graphitic-like C-C bonds via the dissociation of adsorbates already contaminating the "as received" surface or accumulating on this surface during irradiation. Our results demonstrate how the kinetic energy of impinging electrons is a crucial parameter when conditioning technical surfaces of Cu and other metals by means of electron induced chemical processing.
    08/2013;
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    ABSTRACT: In this study we have investigated the relation between the secondary electron yield (SEY) and the surface chemical state for technical Al alloy samples cut from the inner walls of the Petra III storage ring. SEY curves measured after prolonged electron beam irradiation at 500 eV showed maximum values (δmax⁡) between 1.8 and 1.5. By combining x-ray photoelectron spectroscopy with SEY measurements, we have been able to relate the surface chemical composition to the δmax⁡ values for the “as-received” surface (δmax⁡=2.7), for the electron beam conditioned sample (δmax⁡=1.8-1.5), and after substantially removing the surface contaminating layer by means of Ar+ ion sputtering (δmax⁡=1.3). Our detailed chemical analysis shows that the SEY strongly increases in the presence of the thin surface oxide film which unavoidably forms on the clean Al alloy sample under electron beam irradiation even in ultrahigh vacuum conditions, and suggests that the high reactivity of pure Al and Al alloys to oxygen could be the cause of the difference among the SEY values measured in different ultrahigh vacuum environments.
    Physical Review Special Topics - Accelerators and Beams 05/2013; 16:051003. · 1.57 Impact Factor
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    ABSTRACT: Combined fast X-ray photoelectron spectroscopy and density functional theory calculations reveal the presence of two types of hydrogen adsorbate structures at the graphene/Ir(111) interface, namely graphane-like islands and hydrogen dimer structures. While the former give rise to a periodic pattern, dimers tend to destroy the periodicity. Our data reveal distinctive growth rates and stability of both types of structures, thereby allowing to obtain well defined patterns of hydrogen clusters. The ability to control and manipulate the formation and size of hydrogen structures on graphene facilitates tailoring of its properties for a wide range of applications by means of covalent functionalization.
    ACS Nano 04/2013; · 12.03 Impact Factor
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    ABSTRACT: The charge transfer rates of a localized excited electron to graphene monolayers with variable substrate coupling have been investigated by the core hole clock method with adsorbed argon. Expressed as charge transfer times, we find strong variations between ~ 3 fs (on graphene "valleys" on Ru(0001)) to ~ 16 fs (quasi-free graphene on SiC, O/Ru(0001), or SiO2/Ru). The values for the "hills" on Gr/Ru, and on Gr/Pt(111) are in between, with the ratio 1.7 between the charge transfer times measured on "hills" and "valleys" of Gr/Ru. We discuss the results for Gr on metals in terms of hybridized Ru-C orbitals which change with the relative Gr-Ru alignment and distance. The charge transfer on the decoupled graphene layers must represent the intrinsic coupling to the graphene empty π(*) states and charge spreading in two dimensions. Its low rate may be influenced by dynamical Coulomb blockade and/or scattering processes.
    ACS Nano 04/2013; · 12.03 Impact Factor
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    ABSTRACT: Iron-phthalocyanine molecules self-assemble on the moiré pattern of graphene/Ir(111) as a flat and weakly interacting layer, as determined by core-level photoemission and absorption spectroscopy. The graphene buffer layer decouples the FePc two-dimensional structure from the underlying metal; the electronic structure of the FePc molecular macrocycles is preserved; and the Fe-L2,3 edges present narrower and slightly modified resonances at the FePc single-layer coverage with respect to a thin film. The FePc layer induces a slight electron doping to the Ir-supported graphene resulting in the Dirac cone position expected for an ideal free-standing-like graphene layer with the standard Fermi velocity.
    The Journal of Physical Chemistry C 02/2013; 117(6):3019. · 4.84 Impact Factor
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    ABSTRACT: 10.1103/PhysRevSTAB.16.011002
    Physical Review Special Topics - Accelerators and Beams 01/2013; 16:011002. · 1.57 Impact Factor
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    ABSTRACT: Using photoemission spectroscopy techniques, we show that oxygen intercalation is achieved on an extended layer of epitaxial graphene on Ir(111), which results in the "lifting" of the graphene layer and in its decoupling from the metal substrate. The oxygen adsorption below graphene proceeds as on clean Ir(111), giving only a slightly higher oxygen coverage. Upon lifting, the C 1s signal shows a downshift in binding energy, due to the charge transfer to graphene from the oxygen-covered metal surface. Moreover, the characteristic spectral signatures of the graphene-substrate interaction in the valence band are removed, and the spectrum of strongly hole-doped, quasi free-standing graphene with a single Dirac cone around the K̅ point is observed. The oxygen can be deintercalated by annealing, and this process takes place at around T = 600 K, in a rather abrupt way. A small amount of carbon atoms is lost, implying that graphene has been etched. After deintercalation graphene restores its interaction with the Ir(111) substrate. Additional intercalation/deintercalation cycles readily occur at lower oxygen doses and temperatures, consistently with an increasingly defective lattice. Our findings demonstrate that oxygen intercalation is an efficient method for fully decoupling an extended layer of graphene from a metal substrate, such as Ir(111). They pave the way for the fundamental research on graphene, where extended, ordered layers of free-standing graphene are important and, due to the stability of the intercalated system in a wide temperature range, also for the advancement of next-generation graphene-based electronics.
    ACS Nano 10/2012; · 12.03 Impact Factor
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    ABSTRACT: We performed a combined secondary electron yield (SEY) and x-ray photoelectron spectroscopy study as a function of the electron dose and energy on a Cu technical surface representative of the LHC accelerator walls. The electron bombardment is accompanied by a clear chemical modification, indicating an increased graphitization as the SEY decreases. The decrease in the SEY is also found to depend significantly on the kinetic energy of the primary electrons. When low-energy primary electrons are employed (E 20 eV), the reduction of the SEY is slower and smaller in magnitude than when higher-energy electrons are used. Consequences of this observation are discussed mainly for their relevance on the commissioning scenario for the LHC in operation at CERN (Geneva), but are expected to be of interest for other research fields. An extremely vast range of research spanning from detectors, photon or electron multipliers, high power microwave tubes, systems for satellite applications [1], and radio frequency cavities [2] to optics for extreme ultraviolet lithography [3] base some of their essential functionalities on the number of electrons produced by a surface when hit by other electrons. This quantity, called secondary electron yield (SEY), is defined as the ratio of the number of emitted electrons (also called secondary electrons) to the number of incident electrons (also called primary electrons) [4], and is commonly denoted by . Its value, its time stability and its dependence on primary-electron dose and energy are indeed a crucial issue and an essential ingredient in the design of many devices. In particular, for particle accelerators with intense and positively charged beams and/or vacuum chambers of small transverse dimensions, electrons can be produced either by the synchrotron radiation hitting the accelerator walls [5,6] or by direct ionization of residual gases. Once the primary electrons are produced, they are accelerated by the electric field of the bunch in the direction perpendicular to the beam direction, creating secondary electrons at the accelerator walls. If the bunch charge and the bunch spac-ing satisfy certain conditions, a resonance phenomenon called multipacting can be established. When the effective SEY at the chamber is larger than unity, the electron population grows rapidly in time with successive bunch passages. This can lead to a high electron density, and, hence, to detrimental effects such as a rapid vacuum pres-sure rise resulting in beam loss. This phenomenon is called electron cloud (EC) buildup, and has been identified as source of limitations of accelerator performances in the positron rings at the B (Beauty) factories PEP-II and KEKB [7–11]. It is now clear that the best performance of present and future accelerators can be achieved if EC effects are understood, predicted, and finally mitigated. The only way to control and overcome such effects is to ensure a low SEY. At the Large Hadron Collider (LHC), SEY reduction (scrubbing or conditioning) is expected to occur during commissioning and is considered necessary to reach nominal operation [7–9,12]. In this Letter, we present the results of SEY and x-ray photoelectron spectroscopy (XPS) measurements of a Cu prototype of the beam screen adopted for the LHC, which is presently under commissioning at CERN. The target surfaces have been conditioned by electron bombardment (scrubbing). We have studied the variation of the SEY versus both the dose of the impinging electrons as well as their energy. Particular attention has been paid to low-energy primary electrons (E < 20 eV) which have been shown to have peculiar behavior in terms of reflectivity [13,14] and have been suggested to be the dominant species in the ring [15]. The experiment has been performed at the Material Science INFN-LNF Laboratory of Frascati (RM), with a dedicated experimental apparatus which is described else-where [5]. Briefly, the UHV system includes a -metal chamber (background pressure below 10 À10 mbar), with less than a 5 mG residual magnetic field at the sample position, dedicated to XPS analysis and a second chamber for in situ sample preparation. Photoemission spectra have been acquired with an Omicron EAC125 electron analyzer. Nonmonochromatic Mg K radiation (h ¼ 1253:6 eV) has been used to induce photoemission. The samples
    Physical Review Letters 08/2012; 109:064801. · 7.73 Impact Factor
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    ABSTRACT: High-quality, large-area epitaxial graphene can be grown on metal surfaces, but its transport properties cannot be exploited because the electrical conduction is dominated by the substrate. Here we insulate epitaxial graphene on Ru(0001) by a stepwise intercalation of silicon and oxygen, and the eventual formation of a SiO(2) layer between the graphene and the metal. We follow the reaction steps by X-ray photoemission spectroscopy and demonstrate the electrical insulation using a nanoscale multipoint probe technique.
    Nano Letters 08/2012; 12(9):4503-7. · 13.03 Impact Factor
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    ABSTRACT: Further insight into the dissociative adsorption of NH3 on Si(001) has been obtained using a combined computational and experimental approach. A novel route leading to the dissociation of the chemisorbed NH3 is proposed, based on H-bonding interactions between the gas phase and the chemisorbed NH3 molecules. Our model, complemented by synchrotron radiation photoelectron spectroscopy measurements, demonstrates that the low temperature dissociation of molecular chemisorbed NH3 is driven by the continuous flux of ammonia molecules from the gas phase.
    Physical Review Letters 07/2012; 109(3):036102. · 7.73 Impact Factor
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    ABSTRACT: The chemical and physical properties of nanoclusters largely depend on their sizes and shapes. This is partly due to finite size effects influencing the local electronic structure of the nanocluster atoms which are located on the nanofacets and on their edges. Here we present a thorough study on graphene-supported Rh nanocluster assemblies and their geometry-dependent electronic structure obtained by combining high-energy resolution core level photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory. We demonstrate the possibility to finely control the morphology and the degree of structural order of Rh clusters grown in register with the template surface of graphene/Ir(111). By comparing measured and calculated core electron binding energies, we identify edge, facet, and bulk atoms of the nanoclusters. We describe how small interatomic distance changes occur while varying the nanocluster size, substantially modifying the properties of surface atoms. The properties of under-coordinated Rh atoms are discussed in view of their importance in heterogeneous catalysis and magnetism.
    ACS Nano 03/2012; 6(4):3034-43. · 12.03 Impact Factor
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    ABSTRACT: We exploit the capabilities of photoelectron diffraction (PED) to provide quantitative information on the local structure of the first layers of clean and adsorbate-covered surface systems. Selected studies of low-energy PED are presented, highlighting the advantages of the angle-scanning approach. In the first experiment, we evaluate the clean Rh(110) surface layer relaxation by employing the PED of the Rh 3d5/2 surface component. The resulting relaxation is in good accord with previous low energy electron diffraction data. In the second experiment, a system lacking long-range order is examined, namely the saturation layer formed by nitrogen monoxide on Rh(100) at 123 K. Preliminary results confirm the bridge adsorption geometry model. The last example is a chemical shift PED study of the c(4 × 2) phase of carbon monoxide on Pt(111). In this system, CO molecules are coadsorbed at two different adsorption sites, the energy separation of the respective C1s components being 0.7 eV. Structural determination has been achieved by an independent analysis of the diffraction yield originated by the two chemically shifted C1s components. The structure of Pt(111) + c(4 × 2)-2CO has been refined with an automated search of the best parameters using a modified version of MSCD (multiple scattering calculation of diffraction) code.
    Surface Review and Letters 01/2012; 09(02). · 0.28 Impact Factor
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    ABSTRACT: We followed in real time the thermal reaction of fullerene molecules with the Si(111) surface by means of fast photoemission spectroscopy. The formation of SiC via C60 fragmentation on Si(111) is used as a key example of the capability of fast photoemission, associated with a fine temperature control, in determining the nature of thermally induced chemical reactions. By monitoring every 13 s the evolution of the C1s core level photoemission spectrum, as a function of temperature and as a function of time at fixed temperature, we were able to identify several steps in the interaction of C60 with Si(111). A model describing the thermal evolution of this interaction, in agreement with these and other experimental observations, considers the initial chemisorption of C60 in mainly metastable configurations, the evolution toward more stable configurations, allowed by molecular rotations and breaking of Si–Si bonds, the cage deformation to further increase the number of C–Si bonds, the final cage fragmentation and SiC formation only above 1050 ± 10 K.
    Surface Review and Letters 01/2012; 09(02). · 0.28 Impact Factor
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    ABSTRACT: The chemisorption of O atoms on graphite and the thermal reduction of the oxidized surface were studied by means of high energy resolution photoelectron spectroscopy with synchrotron radiation. The C 1s and O 1s core levels and the valence band spectra were used to identify the different oxidizing surface species and to evaluate the extension of the sp2 conjugation as a function of oxidation time and annealing temperature. We found that epoxy groups are the dominant species only at the low oxidation stage, and ethers and semiquinones form as oxidation proceeds. The evolution of the ether/epoxy ratio with increasing oxygen coverage provides evidence for the occurrence of C–C bond unzipping. Epoxy groups are the functionalities with the lowest thermal stability and start to desorb around 370 K, strongly affecting the desorption temperature of other functional groups. The ratio between ethers and epoxy groups determines the balance between epoxy–epoxy and epoxy–ether reactions, the latter promoting the removal of C atoms from the C backbone. Adsorbate spectroscopy during thermal annealing definitely proves the catalytic effect of the basal plane oxygen atoms on the desorption reactions.
    The Journal of Physical Chemistry C 01/2012; 116:9900. · 4.84 Impact Factor
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    ABSTRACT: The formation of a hexagonal boron nitride (h-BN) layer through dissociation of borazine (B3N3H6) molecules on Ir(111) has been investigated by a combination of X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, temperature-programmed desorption, and low-energy electron diffraction. At low temperature (T = 170 K), molecular borazine adsorption occurs with the plane of the benzene-like ring parallel to the substrate. Dehydrogenation is observed at temperatures higher than 250 K and extends up to 900 K, with a maximum H2 desorption rate around 300 K. Besides dehydrogenation, room temperature adsorption of borazine leads to the formation of atomic and molecular fragments due to the break-up of part of the BN bonds. The epitaxial growth of h-BN starts at temperature higher than 1000 K where an extended and long-range ordered layer is obtained. The presence of a corrugation in the h-BN layer with moiré periodicity of (13 × 13)/(12 × 12) BN/Ir unit cell is reflected in the double component structure of the B 1s and N 1s core level spectra.
    The Journal of Physical Chemistry C. 12/2011; 116(1):157–164.
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    ABSTRACT: Iron-phthalocyanine (FePc) molecules have been adsorbed on a graphene sheet prepared on the Ir(111) surface. The FePc molecules are flatlying on graphene, as determined by near-edge X-ray absorption fine-structure, constituting a sub-nanometer thick molecular array at the single-layer coverage. The flat FePc single-layer presents a weak interaction of the organic macrocycle with the graphene surface and Ir subsurface substrate. Further FePc deposition on top of the first flat single-layer determines a threedimensional island growth with varying molecular orientation. © Springer Science+Business Media B.V. 2011.
    Journal of Nanoparticle Research 11/2011; 13:6013-6020. · 2.18 Impact Factor
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    ABSTRACT: Graphene is easily produced by thermally reducing graphene oxide. However, defect formation in the C network during deoxygenation compromises the charge carrier mobility in the reduced material. Understanding the mechanisms of the thermal reactions is essential for defining alternative routes able to limit the density of defects generated by carbon evolution. Here, we identify a dual path mechanism in the thermal reduction of graphene oxide driven by the oxygen coverage: at low surface density, the O atoms adsorbed as epoxy groups evolve as O(2) leaving the C network unmodified. At higher coverage, the formation of other O-containing species opens competing reaction channels, which consume the C backbone. We combined spectroscopic tools and ab initio calculations to probe the species residing on the surface and those released in the gas phase during heating and to identify reaction pathways and rate-limiting steps. Our results illuminate the current puzzling scenario of the low temperature gasification of graphene oxide.
    Journal of the American Chemical Society 08/2011; 133(43):17315-21. · 10.68 Impact Factor

Publication Stats

556 Citations
433.72 Total Impact Points

Institutions

  • 2012
    • Sapienza University of Rome
      • Department of Chemistry
      Roma, Latium, Italy
  • 2011
    • National Research Council
      Roma, Latium, Italy
  • 2001–2010
    • Sincrotrone Trieste S.C.p.A.
      Trst, Friuli Venezia Giulia, Italy
  • 2005
    • Università degli Studi di Trieste
      • Department of Physics
      Trieste, Friuli Venezia Giulia, Italy
  • 2004
    • Università degli Studi della Basilicata
      Potenza, Basilicate, Italy
  • 2003
    • Università della Calabria
      • Department of Physics
      Rende, Calabria, Italy
  • 2002
    • The University of Manchester
      Manchester, England, United Kingdom
    • AREA Science Park
      Trst, Friuli Venezia Giulia, Italy
  • 1988–2001
    • ENEA
      • Applied Physics Division
      Roma, Latium, Italy
  • 2000
    • TS Corporation
      Taviano, Apulia, Italy
  • 1986–1987
    • Max Planck Institute for Biophysical Chemistry
      Göttingen, Lower Saxony, Germany