R. Larciprete

New England Complex Systems Institute, RMG, Georgia, United States

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Publications (153)534.1 Total impact

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    ABSTRACT: The possibility to intercalate noble gas atoms below epitaxial graphene monolayers coupled with the instability at high temperature of graphene on the surface of certain metals has been exploited to produce Ar filled graphene nanosized blisters evenly distributed on the bare Ni(111) surface. We have followed in real time the self assembling of the nanoblisters during the thermal annealing of the Gr/Ni(111) interface loaded with Ar and characterized their morphology and structure at the atomic scale. The nanoblisters contain Ar aggregates compressed at high pressure arranged below the graphene monolayer skin which is decoupled from the Ni substrate and sealed only at the periphery through stable C-Ni bonds. Their in-plane truncated triangular shapes are driven by the crystallographic directions of the Ni surface. The nonuniform strain revealed along the blister profile is explained by the inhomogeneous expansion of the flexible graphene lattice which adjusts to envelop the Ar atom stacks.
    No preview · Article · Feb 2016 · Nano Letters
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    ABSTRACT: Carbon nanoparticles in laminar premixed flames are broadly divided into two classes based on the bimodal shape of the particle size distribution and on the different chemical and physical properties that these particles present depending on the combustion conditions, such as residence time, equivalence ratio, and fuel chemical composition. The chemical and structural characteristics of carbon nanoparticles have been the subject of numerous works because these properties might be of relevance for particle reactivity and optical properties. Few information are available on their hydrophilic properties although these are of relevance for the human health, the climate change, in addition to the technological implementation of condensation nuclei particle counters in aerosol science, water scrubbers and electrostatic precipitators. The aim of this work is to investigate the hydrophilic/hydrophobic behavior of carbon nanoparticles formed in different flame conditions. Static contact angle measurements in addition to chemical and physical characterization of the carbon nanoparticles have been implemented. Results show that nanoparticles formed in richer flame conditions, are the most hydrophobic, whereas nanoparticles of organic carbon, formed in relatively leaner flame condition, appeared to be the most hydrophilic.The reason for a different water affinity of particles, and especially of the smaller organic carbon nanoparticles, has been discussed by analyzing the different material in terms of their chemical/structural composition and in terms of surface functionalities. While no significant differences have been found by Raman spectroscopy in terms of their carbon structure, the different hydrophilicity is explained in terms of the different amount of surface oxygen detected by X-ray photoelectron spectroscopy (XPS). Combustion conditions are therefore very important in outlining the hydrophilic/hydrophobic tendency of the carbon particles.
    No preview · Article · Sep 2015 · Experimental Thermal and Fluid Science
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    ABSTRACT: The detailed study of the secondary electron yield (SEY) of technical surfaces for very low electron landing energies (from 0 to 20 eV) is a very important parameter in many fields of research. Some of the devices used in all those fields of research base some of their essential functionalities on the number of electrons produced by a surface when hit by other electrons, namely, its SEY and, in most cases, its very-low-energy behavior SEY (LE-SEY). Despite such interest, the very low electron landing energy part of an SEY curve has been rarely addressed due to the intrinsic experimental complexity to control and detect very low energy electrons. Furthermore, several results published in the past have been recently questioned to suffer from experimental systematic errors. In this paper, we critically review the experimental method used to study LE-SEY and define more precisely the energy region, in which the experimental data can be considered valid. By analyzing the significantly different behavior of LE-SEY in atomically clean polycrystalline Cu and in its as-received technical counterpart, we solve most, if not all, of the apparent controversy present in the literature, producing important inputs for better understanding the devices performances related to their LE-SEY.
    No preview · Article · Sep 2015 · IEEE Transactions on Plasma Science
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    ABSTRACT: We achieve a controllable chemical gating of epitaxial graphene grown on metal substrates by exploiting the electrostatic polarization of ultrathin SiO2 layers synthesized below it. Intercalated oxygen diffusing through the SiO2 layer modifies the metal-oxide work function hole doping graphene. The graphene|oxide|metal heterostructure behaves as a gated plane capacitor with the in-situ grown SiO2 layer acting as a homogeneous dielectric spacer, whose high capacity allows the Fermi level of graphene to be shifted by a few hundreds meV when the oxygen coverage at the metal substrate is of the order of 0.5 monolayer. The hole doping can be finely tuned by controlling the amount of the interfacial oxygen, as well as by adjusting the thickness of the oxide layer. After complete thermal desorption of oxygen the intrinsic doping of SiO2 supported graphene is evaluated in the absence of contaminants and adventitious adsorbates. The demonstration that the charge state of graphene can be changed by chemically modifying the buried oxide/metal interface hints at the possibility of tuning level and sign of doping by the use of other intercalants capable to diffuse through the ultrathin porous dielectric and reach the interface with the metal.
    No preview · Article · Jun 2015 · Nanoscale
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    ABSTRACT: Functionalization of graphene by substitution of carbon with nitrogen atoms is a promising way to tailor its electronic properties, but a good control over the heteroatomic configuration in the graphene network is most often a difficult task. In this paper, the synthesis of N-doped graphene by nitrogen plasma treatment of graphene/Ir(111) is presented. The formation of substitutional, pyrrolic and pyridinic nitrogen is analyzed by means of X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffraction (XPD). The graphene–Ir interaction is suggested to control the variation in the relative concentration of the nitrogen species. Annealing of the sample also leads to modifications of the nitrogen species incorporated in the graphene layer. Furthermore, the connection of the substitutional nitrogen arrangement with its corresponding spectroscopic fingerprint is unequivocally confirmed by XPD measurements, which give also a direct insight on the local geometry of the nitrogen atoms incorporated in the carbon network.
    No preview · Article · Jun 2015 · Surface Science
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    ABSTRACT: The detailed study of the low energy secondary electron yield (LE-SEY) of technical Cu for low electron energies (from 0 to 20 eV) is very important for electron cloud build up in high intensity accelerators and in many other fields of research. Different devices base their functionalities on the number of electrons produced by a surface when hit by other electrons, namely its SEY, and, in most cases, on its very low energy behavior. However, LE-SEY has been rarely addressed due to the intrinsic experimental complexity to control very low energy electrons. Furthermore, several results published in the past have been recently questioned, allegedly suffering from experimental systematics. Here, we critically review the experimental method used to study LE-SEY and precisely define the energy region in which the experimental data can be considered valid. By analyzing the significantly different behavior of LE-SEY in clean polycrystalline Cu (going toward zero at zero impinging energies) and in its as received technical counterpart (maintaining a significant value in the entire region), we solve most, if not all, of the apparent controversy present in the literature, producing important inputs for better understanding the device performances related to their LE-SEY. Simulations are then performed to address the impact of such results on electron cloud predictions in the LHC.
    No preview · Article · May 2015 · Physical Review Special Topics - Accelerators and Beams
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    ABSTRACT: The relation between the atomic hybridization and the secondary electron emission yield (SEY) in carbon materials has been investigated during the thermal graphitization of thin amorphous carbon layers deposited by magnetron sputtering on Cu substrates. C1s core level, valence band and Raman spectroscopy were used to follow the sp3→sp2 structural reorganization while the SEY curves as a function of the kinetic energy of the incident electron beam were measured in parallel. We found that an amorphous C layer with a thickness of a few tens of nanometers is capable to modify the secondary emission properties of the clean copper surface, reducing the maximum yield from 1.4 to 1.2. A further SEY decrease observed with the progressive conversion of sp3 hybrids into six-fold aromatic domains was related to the electronic structure close to the Fermi level of the C-films. We found that a moderate structural quality of the C layer is sufficient to notably decrease the SEY as aromatic clusters of limited size approach the secondary emission properties of graphite.
    No preview · Article · Feb 2015 · Applied Surface Science
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    ABSTRACT: We propose the implementation of graphene-based field effect transistor (FET) as radiation sensor. In the proposed detector, graphene obtained via chemical vapor deposition is integrated into a Si-based field effect device as the gate readout electrode, able to sense any change in the field distribution induced by ionization in the underneath absorber, because of the strong variation in the graphene conductivity close to the charge neutrality point. Different 2-dimensional layered materials can be envisaged in this kind of device.
    No preview · Article · Jan 2015
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    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.
    No preview · Article · Nov 2014 · ACS Nano
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    ABSTRACT: The assembly and the orientation of functionalized pentacene at the interface with inorganics strongly influence both the electric contact and the charge transport in organic electronic devices. In this study electronic spectroscopies and theoretical modeling are combined to investigate the properties of the bis(triisopropylsilylethynyl)pentacene (TIPS-Pc)/Au(111) interface as a function of the molecular coverage to compare the molecular state in the gas phase and in the adsorbed phase and to determine the thermal stability of TIPS-Pc in contact with gold. Our results show that in the free molecule only the acene atoms directly bonded to the ligands are affected by the functionalization. Adsorption on Au(111) leads to a weak coupling which causes only modest binding energy shifts in the TIPS-Pc and substrate core level spectra. In the first monolayer the acene plane form an angle of 33 +/- 2 degrees with the Au(111) surface at variance with the vertical geometry reported for thicker solution-processed or evaporated films, whereas the presence of configurational disorder was observed in the multilayer. The thermal annealing of the TIPS-Pc/Au(111) interface reveals the ligand desorption at similar to 470 K, which leaves the backbone of the decomposed molecule flat-lying on the metal surface as in the case of the unmodified pentacene. The weak interaction with the metal substrate causes the molecular dissociation to occur 60 K below the thermal decomposition taking place in thick drop-cast films.
    No preview · Article · Oct 2014 · The Journal of Physical Chemistry C
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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.
    No preview · Article · Sep 2014 · Nature Communications
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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.
    No preview · Article · Aug 2013 · Scientific Reports
  • Source
    R. Larciprete · D. R. Grosso · M. Commisso · R. Flammini · R. Cimino
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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.
    Full-text · Article · Aug 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.
    Full-text · Article · May 2013 · Physical Review Special Topics - Accelerators and Beams
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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.
    No preview · Article · Apr 2013 · ACS Nano
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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.
    No preview · Article · Apr 2013 · ACS Nano
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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.
    No preview · Article · Feb 2013 · The Journal of Physical Chemistry C
  • Source
    R. Larciprete · D. R. Grosso · M. Commisso · R. Flammini · R. Cimino
    [Show abstract] [Hide abstract]
    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 (${$\delta${}}_{\mathrm{max}}$) being as high as 2.1. After extended electron scrubbing at kinetic energy of 10 and 500 eV, the ${$\delta${}}_{\mathrm{max}}$ 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: 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 ${$\delta${}}_{\mathrm{max}}$; the second step, activated by more energetic electrons and becoming evident at high doses, 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 the surfaces of Cu and other metals by means of electron-induced chemical processing.
    Full-text · Article · Jan 2013 · Physical Review Special Topics - Accelerators and Beams
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    ABSTRACT: Ferromagnetic metal nanocrystals in semiconducting hosts are currently investigated for their potential applications in nanotechnology. Still, the controlled growth of the nanocrystals along particular directions or planes is not yet achievable in most nanocomposites like Co/TiO2, where preferential localizations are generally accompanied by a distribution of nanoclusters over the whole overlayer. Here we present planar arrays of cobalt nanoparticles embedded in TiO2 layers prepared by pulsed laser deposition on amorphous Si3N4 membranes. High resolution transmission electron microscopy reveals the presence of Co nanocrystals arranged in bidimensional arrays at the film–substrate interface within the rutile TiO2 matrix. X-ray absorption spectra at the Ti L-, O K-, and Co L-edges carried out in surface sensitive and bulk sensitive modalities confirm the rutile phase of the titania matrix and the metallic state of Co atoms and indicate only negligible concentration of Co in the near-surface layers. Based on these results, a route for the synthesis of bidimensional arrays of Co nanoparticles within the rutile TiO2 matrix is proposed.
    Full-text · Article · Dec 2012 · The Journal of Physical Chemistry C
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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.
    Full-text · Article · Oct 2012 · ACS Nano

Publication Stats

2k Citations
534.10 Total Impact Points

Institutions

  • 2012-2015
    • New England Complex Systems Institute
      RMG, Georgia, United States
  • 2009-2015
    • INO - Istituto Nazionale di Ottica
      Florens, Tuscany, Italy
  • 2010-2013
    • University of Rome Tor Vergata
      Roma, Latium, Italy
  • 2011
    • National Institute of Geophysics and Volcanology
      Roma, Latium, Italy
  • 2001-2009
    • Sincrotrone Trieste S.C.p.A.
      Trst, Friuli Venezia Giulia, Italy
  • 2002
    • AREA Science Park
      Trst, Friuli Venezia Giulia, Italy
  • 1985-2002
    • ENEA
      • Applied Physics Division
      Roma, Latium, Italy
  • 2000
    • TS Corporation
      Taviano, Apulia, Italy
    • Università degli Studi di Modena e Reggio Emilia
      Modène, Emilia-Romagna, Italy
  • 1986-1987
    • Max Planck Institute for Biophysical Chemistry
      Göttingen, Lower Saxony, Germany