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  • 1.
    Bouhafs, Chamseddine
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Zakharov, A. A.
    Lund University, Sweden.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Giannazzo, F.
    CNR IMM, Italy.
    Eriksson, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, Faculty of Science & Engineering.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kuhne, Philipp
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Hofmann, Tino
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. University of Nebraska Lincoln, NE 68588 USA.
    Schubert, Mathias
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. University of Nebraska Lincoln, NE 68588 USA.
    Roccaforte, F.
    CNR IMM, Italy.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Multi-scale investigation of interface properties, stacking order and decoupling of few layer graphene on C-face 4H-SiC2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 116, p. 722-732Article in journal (Refereed)
    Abstract [en]

    In this work, we report a multi-scale investigation using several nano-, micro and macro-scale techniques of few layer graphene (FLG) sample consisting of large monolayer (ML) and bilayer (BL) areas grown on C-face 4H-SiC (000-1) by high-temperature sublimation. Single 1 x 1 diffraction patterns are observed by micro-low-energy electron diffraction for ML, BL and trilayer graphene with no indication of out-of-plane rotational disorder. A SiOx layer is identified between graphene and SiC by X-ray photoelectron emission spectroscopy and reflectance measurements. The chemical composition of the interface layer changes towards SiO2 and its thickness increases with aging in normal ambient conditions. The formation mechanism of the interface layer is discussed. It is shown by torsion resonance conductive atomic force microscopy that the interface layer causes the formation of non-ideal Schottky contact between ML graphene and SiC. This is attributed to the presence of a large density of interface states. Mid-infrared optical Hall effect measurements revealed Landau-level transitions in FLG that have a square-root dependence on magnetic field, which evidences a stack of decoupled graphene sheets. Contrary to previous works on decoupled C-face graphene, our BL and FLG are composed of ordered decoupled graphene layers without out-of-plane rotation. (C) 2017 Elsevier Ltd. All rights reserved.

  • 2.
    Chua, Cassandra
    et al.
    University of Cambridge, England.
    Lartsev, Arseniy
    Chalmers, Sweden.
    Sui, Jinggao
    University of Cambridge, England.
    Panchal, Vishal
    National Phys Lab, England.
    Puddy, Reuben
    University of Cambridge, England.
    Richardson, Carly
    University of Cambridge, England.
    Smith, Charles G.
    University of Cambridge, England.
    Janssen, T. J. B. M.
    National Phys Lab, England.
    Tzalenchuk, Alexander
    National Phys Lab, England; Royal Holloway University of London, England.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kubatkin, Sergey
    Chalmers, Sweden.
    Connolly, Malcolm R.
    University of Cambridge, England.
    Observation of Coulomb blockade in nanostructured epitaxial bilayer graphene on SiC2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 119, p. 426-430Article in journal (Refereed)
    Abstract [en]

    We study electron transport in nanostructures patterned in bilayer graphene patches grown epitaxially on SiC as a function of doping, magnetic field, and temperature. Away from charge neutrality transport is only weakly modulated by changes in carrier concentration induced by a local side-gate. At low n-type doping close to charge neutrality, electron transport resembles that in exfoliated graphene nanoribbons and is well described by tunnelling of single electrons through a network of Coulomb-blockaded islands. Under the influence of an external magnetic field, Coulomb blockade resonances fluctuate around an average energy and the gap shrinks as a function of magnetic field. At charge neutrality, however, conduction is less insensitive to external magnetic fields. In this regime we also observe a stronger suppression of the conductance below T*, which we interpret as a sign of broken interlayer symmetry or strong fluctuations in the edge/potential disorder. (C) 2017 Elsevier Ltd. All rights reserved.

  • 3.
    Ferreira da Cunha, Wiliam
    et al.
    University of Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering. University of Brasilia, Brazil.
    Luciano de Almeida Fonseca, Antonio
    University of Brasilia, Brazil.
    Gargano, Ricardo
    University of Brasilia, Brazil; University of Florida, FL 32611 USA; University of Florida, FL 32611 USA.
    Magela e Silva, Geraldo
    University of Brasilia, Brazil.
    Impurity effects on polaron dynamics in graphene nanoribbons2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 91, p. 171-177Article in journal (Refereed)
    Abstract [en]

    The impurity effects on the dynamics of polarons in armchair graphene nanoribbons are numerically investigated in the scope of a two-dimensional tight-binding approach with lattice relaxation. The results show that the presence of an impurity changes significantly the net charge distribution associated to the polaron structure. Moreover, the interplay between external electric field and the local impurities plays the role of drastically modifying the polaron dynamics. Interestingly, nanoribbons containing mobile polarons are noted to take place even when considering high impurity levels, which is associated with the highly conductive character of the graphene nanoribbons. This investigation may enlighten the understanding of the charge transport mechanism in carbon-based nanomaterials. (C) 2015 Elsevier Ltd. All rights reserved.

  • 4.
    Giusca, Cristina E.
    et al.
    National Phys Lab, England .
    Spencer, Steve J.
    National Phys Lab, England .
    Shard, Alex G.
    National Phys Lab, England .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kazakova, Olga
    National Phys Lab, England .
    Exploring graphene formation on the C-terminated face of SiC by structural, chemical and electrical methods2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 69, p. 221-229Article in journal (Refereed)
    Abstract [en]

    The properties of epitaxial graphene on the C-face of SiC are investigated using comprehensive structural, chemical and electrical analyses. By matching similar nanoscale features on the surface potential and Raman spectroscopy maps, individual domains have been assigned to graphene patches of 1-5 monolayers thick, as well as bare SiC substrate. Furthermore, these studies revealed that the growth proceeds in an island-like fashion, consistent with the Volmer-Weber growth mode, illustrating also the presence of nucleation sites for graphene domain growth. Raman spectroscopy data shows evidence of large area crystallites (up to 620 nm) and high quality graphene on the C-face of SiC. A comprehensive chemical analysis of the sample has been provided by X-ray photoelectron spectroscopy investigations, further supporting surface potential mapping observations on the thickness of graphene layers. It is shown that for the growth conditions used in this study, 5 monolayer thick graphene does not form a continuous layer, so such thickness is not sufficient to completely cover the substrate.

  • 5.
    Hellgren, Niklas
    et al.
    Messiah Coll, PA 17055 USA.
    Haasch, Richard T.
    University of Illinois, IL 61801 USA.
    Schmidt, Susann
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, IL 61801 USA.
    Interpretation of X-ray photoelectron spectra of carbon-nitride thin films: New insights from in situ XPS2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 108, p. 242-252Article in journal (Refereed)
    Abstract [en]

    We report on angular-resolved x-ray photoelectron spectroscopy (XPS) studies of magnetron sputtered CNx thin films, first in situ (without air exposure), then after air exposure (for time periods ranging from minutes to several years), and finally after Ar ion etching using ion energies ranging from 500 eV to 4 keV. The as-deposited films typically exhibit two strong N1s peaks corresponding to pyridine-like, and graphite-like, at similar to 398.2 eV and similar to 400.7 eV, respectively. Comparison between in situ and air-exposed samples suggests that the peak component at similar to 402-403 eV is due only to quaternary nitrogen and not oxidized nitrogen. Furthermore, peak components in the similar to 399-400 eV range cannot only be ascribed to nitriles or pyrrolic nitrogen as is commonly done. We propose that it can also be due to a polarization shift in pyridinic N, induced by surface water or hydroxides. Argon ion etching readily removes surface oxygen, but results also in a strong preferential sputtering of nitrogen and can cause amorphization of the film surface. The best methods for evaluating and interpreting the CNx film structure and composition with ex-situ XPS are discussed. (C) 2016 Elsevier Ltd. All rights reserved.

  • 6.
    Hens, Philip
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology. University of Marburg, Germany.
    Zakharov, Alexei A.
    Lund University, Sweden.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Large area buffer-free graphene on non-polar (001) cubic silicon carbide2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 80, p. 823-829Article in journal (Refereed)
    Abstract [en]

    Graphene is, due to its extraordinary properties, a promising material for future electronic applications. A common process for the production of large area epitaxial graphene is a high temperature annealing process of atomically flat surfaces from hexagonal silicon carbide. This procedure is very promising but has the drawback of the formation of a buffer layer consisting of a graphene-like sheet, which is covalently bound to the substrate. This buffer layer degenerates the properties of the graphene above and needs to be avoided. We are presenting the combination of a high temperature process for the graphene production with a newly developed substrate of (0 0 1)-oriented cubic silicon carbide. This combination is a promising candidate to be able to supply large area homogenous epitaxial graphene on silicon carbide without a buffer layer. We are presenting the new substrate and first samples of epitaxial graphene on them. Results are shown using low energy electron microscopy and diffraction, photoelectron angular distribution and X-ray photoemission spectroscopy. All these measurements indicate the successful growth of a buffer free few layer graphene on a cubic silicon carbide surface. On our large area samples also the epitaxial relationship between the cubic substrate and the hexagonal graphene could be clarified.

  • 7.
    Hill-Pearce, R. E.
    et al.
    National Phys Lab, England.
    Eless, V.
    National Phys Lab, England.
    Lartsev, A.
    Chalmers, Sweden.
    Martin, N. A.
    National Phys Lab, England.
    Barker Snook, I. L.
    National Phys Lab, England.
    Helmore, J. J.
    National Phys Lab, England.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Gallop, J. C.
    National Phys Lab, England.
    Hao, L.
    National Phys Lab, England.
    The effect of bilayer regions on the response of epitaxial graphene devices to environmental gating2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 93, p. 896-902Article in journal (Refereed)
    Abstract [en]

    The effect of a bilayer area on the electronic response to environmental gating of a monolayer graphene Hall bar device is investigated using room temperature magnetotransport and scanning Kelvin probe microscopy measurements in a controlled environment. The device is tuned through the charge neutrality point with n-p-n-junctions formed. Scanning Kelvin probe measurements show that the work function of the monolayer graphene decreases more than that of the bilayer area however magnetotransport measurements show a larger change in carrier concentration for bilayer graphene with environmental gating. Interface scattering at the boundary between the monolayer and bilayer regions also affects device response with field-dependent suppression of the conductivity observed near the charge neutrality point. Simultaneous electronic and environmental scanning Kelvin probe measurements are used to build nano-scale maps of the work function of the device surface revealing the areas of greatest work function change with environmental gating. Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.

  • 8.
    Ivanov, Ivan Gueorguiev
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ul Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Zakharov, Alexei A.
    Lund University, Sweden .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Layer-number determination in graphene on SiC by reflectance mapping2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 77, p. 492-500Article in journal (Refereed)
    Abstract [en]

    We report a simple, handy and affordable optical approach for precise number-of-layers determination of graphene on SiC based on monitoring the power of the laser beam reflected from the sample (reflectance mapping) in a slightly modified micro-Raman setup. Reflectance mapping is compatible with simultaneous Raman mapping. We find experimentally that the reflectance of graphene on SiC normalized to the reflectivity of bare substrate (the contrast) increases linearly with similar to 1.7% per layer for up to 12 layers, in agreement with theory The wavelength dependence of the contrast in the visible is investigated using the concept of ideal fermions and compared with existing experimental data for the optical constants of graphene. We argue also that the observed contrast is insensitive to the doping condition of the sample, as well as to the type of sample (graphene on C- or Si-face of 4H or 6H SiC, hydrogen-intercalated graphene). The possibility to extend the precise layer counting to similar to 50 layers makes reflectivity mapping superior to low-energy electron microscopy (limited to similar to 10 layers) in quantitative evaluation of graphene on the C-face of SiC. The method is applicable for graphene on other insulating or semiconducting substrates.

  • 9.
    Karlsson, Linda
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Mockuté, Aurelija
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Sigurdur Ingason, Arni
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ta, Huy Q.
    Polish Academic Science, Poland; Sungkyunkwan University, South Korea; Soochow University, Peoples R China; Soochow University, Peoples R China.
    Rummeli, Mark H.
    Polish Academic Science, Poland; Soochow University, Peoples R China; Soochow University, Peoples R China; IFW Dresden, Germany.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O. Å.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Residue reduction and intersurface interaction on single graphene sheets2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 100, p. 345-350Article in journal (Refereed)
    Abstract [en]

    Large regions of pristine graphene are essential to applications which rely on the ideal graphene properties. Common methods for transferring chemical vapour deposition grown graphene to suitable substrates leaves metal oxide particles and poly(methyl methacrylate) (PMMA) residues on opposing surfaces, which degrade the properties. A common method to reduce the residues include annealing in vacuum or in argon, however, residues remain on the graphene sheet. The present investigation reports on the metal oxide particle ripening and PMMA decomposition on a single graphene sheet during in-situ annealing up to 1300 degrees C in a transmission electron microscope. It is shown that the PMMA residues are increasingly reduced at elevated temperatures although the reduction is strongly correlated to the metal oxide particle coverage on the opposing graphene surface. This is shown to occur as a consequence of an electrostatic interaction between the residues and that this prevents the establishment of large clean areas. (C) 2016 Elsevier Ltd. All rights reserved.

  • 10.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Shtepliuk, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Tsiaoussis, I.
    Aristotle University of Thessaloniki, Thessaloniki, Greece.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Light emission enhancement from ZnO nanostructured films grown on Gr/SiC substrates2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 99, p. 295-301Article in journal (Refereed)
    Abstract [en]

    We report on the application of a single layer graphene substrates for the growth of polycrystalline ZnO films with advanced light emission properties. Unusually high ultraviolet (UV) and visible (VIS) photoluminesce was observed from the ZnO/Gr/SiC structures in comparison to identical samples without graphene. The photoluminescence intensity depends non-monotonically on the films thickness, reaching its maximum for 150 nm thick films. The phenomena observed is explained as due to the dual graphene role: i) the dangling bond free substrate, providing growth of relaxed thin ZnO layers ii) a back reflector active mirror of the Fabry-Perot cavity that is formed. The reported results demonstrate the potential of two-dimensional carbon materials integration with light emitting wide band gap semiconductors and can be of practical importance for the design of future optoelectronic devices.

  • 11.
    Majee, S.
    et al.
    Uppsala University, Sweden.
    Banerjee, D.
    Uppsala University, Sweden.
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Zhang, S. -L.
    Uppsala University, Sweden.
    Zhang, Z. -B.
    Uppsala University, Sweden.
    Efficient and thermally stable iodine doping of printed graphene nano-platelets2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 117, p. 240-245Article in journal (Refereed)
    Abstract [en]

    We report on an efficient and highly thermally stable doping with iodine on ink-jet printed graphene films. The films consist of pristine few-layer graphene nano-platelates (p-GNPs) that are randomly stacked. With iodine doping simply by soaking in aqueous iodine solution, the printed p-GNPs films are enhanced in electrical conductivity by up to around 2 times. The doping effect exhibits excellent thermal stability up to 500 degrees C under high vacuum condition (10(-6) mBar) evidenced by electrical and spectroscopic means. Furthermore, the doping of iodine leads to a slight increment of work function by 0.07 eV. Using depth profile measurements, it is found that iodine species diffuse deeply into the films and likely intercalate between two adjacent p-GNPs which interpret the aforementioned efficient enhancement and thermal stability of the doping effect. The reported doping scheme offers a viable low-temperature optimization method for conductive electrodes with p-GNPs in the application of printed devices. (C) 2017 Elsevier Ltd. All rights reserved.

  • 12.
    Mikoushkin, V. M.
    et al.
    Ioffe Institute, Russia.
    Shnitov, V. V.
    Ioffe Institute, Russia.
    Lebedev, A. A.
    Ioffe Institute, Russia; University of ITMO, Russia.
    Lebedev, S. P.
    Ioffe Institute, Russia; University of ITMO, Russia.
    Nikonov, S. Yu.
    Ioffe Institute, Russia.
    Vilkou, O. Yu.
    Technical University of Dresden, Germany; St Petersburg State University, Russia.
    Iakimou, T.
    Ioffe Institute, 194021 St. Petersburg, Russia.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Size confinement effect in graphene grown on 6H-SiC (0001) substrate2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 86, p. 139-145Article in journal (Refereed)
    Abstract [en]

    We have observed the energy structure in the density of occupied states of graphene grown on n-type 6H-SiC (0001). The structure revealed with photoelectron spectroscopy is described by creation of the quantum well states whose number and the energy position (E-1 = 0.3 eV, E-2 = 1.2 eV, E-3 = 2.6 eV) coincide with the calculated ones for deep (V = 2.9 eV) and narrow (d = 2.15 angstrom) quantum well formed by potential relief of the valence bands in the structure graphene/n-SiC. We believe that the quantum well states should be formed also in graphene on dielectric and in suspended graphene. (C) 2015 Elsevier Ltd. All rights reserved.

  • 13.
    Neidhardt, Jörg
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Czigany, Z
    Correlated high resolution transmission electron microscopy and X-ray photoelectron spectroscopy studies of structured CNx (0 < x < 0.25) thin solid films2004In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 42, no Dec-13, p. 2729-2734Article in journal (Refereed)
    Abstract [en]

    Structured carbon nitride (CNx), thin solid films, also known as fullerene-like, consist of, upon nitrogen substitution, bent and cross-linked graphene planes. They were synthesized by unbalanced reactive magnetron sputtering and analyzed by high-resolution transmission electron microscopy (HRTEM) in combination with X-ray photoelectron spectroscopy (XPS). The microstructure evolution in terms of plane alignment, extension and cross-linking can be controlled by adjusting the synthesis conditions, such as growth temperature, N-2 fraction in the discharge gas and ion energy. HRTEM on plan-view samples was used to examine the structural changes depending on growth temperature and N-2 fraction. The problem of projection artifacts for imaging the structural features was partially overcome by selected area electron diffraction analysis, where it is shown that diffraction corresponding to 3.5 Angstrom is associated with the formation of structured CNx. The incorporation of N is crucial for the evolution of heavily bent and frequently cross-linked basal planes, since it triggers pentagon formation and cross-linking at much lower energies compared to pure carbon films. Therefore, the two spectral features in the nitrogen Is core electron spectra as examined by XPS were correlated to the microstructure evolution. (C) 2004 Elsevier Ltd. All rights reserved.

  • 14.
    Pakornchote, T.
    et al.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Ektarawong, Annop
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Inst Eisenforsch GmbH, Germany.
    Pinsook, U.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Tancharakorn, S.
    Synchrotron Light Res Inst Publ Org, Thailand.
    Busayaporn, W.
    Synchrotron Light Res Inst Publ Org, Thailand.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Phase stabilities and vibrational analysis of hydrogenated diamondized bilayer graphenes: A first principles investigation2019In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 146, p. 468-475Article in journal (Refereed)
    Abstract [en]

    The phase stabilities as well as some intrinsic properties of hydrogenated diamondized bilayer graphenes, 2-dimensional materials adopting the crystal structure of diamond and of lonsdaleite, are investigated using a first-principles approach. Our simulations demonstrate that hydrogenated diamondized bilayer graphenes are thermodynamically stable with respect to bilayer graphene and hydrogen molecule even at 0 GPa, and additionally they are found to withstand the physical change in structure up to at least 1000 K, ensuring their dynamical and thermal stabilities. The studied hydrogenated diamondized bilayer graphenes are predicted not only to behave as direct and wide band gap semiconductors, but also to have a remarkably high resistance to in-plane plastic deformation induced by indentation as implied by their high in-plane elastic constants comparable to those of diamond and of lonsdaleite. The mechanical stability of the materials is confirmed though the fulfilment of the Born stability criteria. Detailed analysis of phonon vibrational frequencies of hydrogenated diamondized bilayer graphenes reveals possible Raman active and IR active modes, which are found to be distinctly different from those of hydrogenated diamond-like amorphous carbon and defective graphene and thus could be used as a fingerprint for future experimental characterization of the materials. (c) 2019 Elsevier Ltd. All rights reserved.

  • 15.
    Prudkovskiy, V. S.
    et al.
    University of Crete, Greece; Research Institute Dev Science and Educ Potential Youth, Russia.
    Katin, K. P.
    National Research Nucl University of MEPhI, Russia; Research Institute Dev Science and Educ Potential Youth, Russia.
    Maslov, M. M.
    National Research Nucl University of MEPhI, Russia; Research Institute Dev Science and Educ Potential Youth, Russia.
    Puech, P.
    University of Toulouse, France.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Deligeorgis, G.
    FORTH, Greece.
    Efficient cleaning of graphene from residual lithographic polymers by ozone treatment2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 109, p. 221-226Article in journal (Refereed)
    Abstract [en]

    We present an experimental study of time dependent ozone treatment on post-process epitaxial graphene using both electron transport measurements and resonant micro-Raman spectroscopy. We focus on a systematic analysis of residual polymer decomposition on the epitaxial graphene on SiC substrate. It was found that graphene could be effectively cleaned by ultraviolet (UV)/ozone treatment after nano fabrication from residual lithographic polymers. This procedure improves the charge carrier mobility, almost by a factor of two for strongly contaminated samples, decreases the doping level and does not introduce defect inside the graphene lattice. It was found that epitaxial SiC graphene is extremely stable when exposed to radical oxygen atoms. We ascribe this effect to the substrate topography, which significantly affects the graphene stability under UV/ozone treatment. Our calculations reveal that surface roughness of the SiC substrate can change the energy gain from epoxy group adsorption by a few tenths of electron volts. (C) 2016 Elsevier Ltd. All rights reserved.

  • 16.
    Rohringer, Philip
    et al.
    University of Vienna, Austria .
    Shi, Lei
    University of Vienna, Austria .
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Yanagi, Kazuhiro
    Tokyo Metropolitan University, Japan .
    Pichler, Thomas
    University of Vienna, Austria .
    Purification, separation and extraction of inner tubes from double-walled carbon nanotubes by tailoring density gradient ultracentrifugation using optical probes2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 74, p. 282-290Article in journal (Refereed)
    Abstract [en]

    We studied the effect of varying sonication and centrifugation parameters on double-walled carbon nanotubes (DWCNT) by measuring optical absorption and photoluminescence (PL) of the samples. We found that by using a low sonication intensity before applying density gradient ultracentrifugation (DGU), only inner tube species with a diameter less than= 0.8 nm can be identified in absorption measurements. This is in stark contrast to the result after sonicating at higher intensities, where also bigger inner tubes can be found. Furthermore, by comparing PL properties of samples centrifugated either with or without a gradient medium, we found that applying DGU greatly enhances the PL intensity, whereas centrifugation at even higher speeds but without a gradient medium results in lower intensities. This can be explained by extraction of inner tubes from their host outer tubes in a two-stage process: the different shearing forces from the sonication treatments result in some DWCNT to be opened, whereas others stay uncut. A subsequent application of DGU leads to the extraction of the inner tubes or not if the host nanotube stayed uncut or no gradient medium was used. This work shows a pathway to avoid this phenomenon to unravel the intrinsic PL from inner tubes of DWCNT.

  • 17.
    Saidi, Wissam A.
    et al.
    University of Pittsburgh, PA 15261 USA .
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Probing single-walled carbon nanotube defect chemistry using resonance Raman spectroscopy2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 67, p. 17-26Article in journal (Refereed)
    Abstract [en]

    Using state-of-the-art time-dependent density functional theory and employing the complex polarization propagator theory, we compute the UV-vis absorption and resonance Raman (RR) spectra of pristine and H- and F-decorated single-walled carbon nanotubes (SWCNTs). We find that H- and F-functionalization brightens a low energy exciton that couples the SWCNT local-defect chemistry to its extended pi network. Surprisingly, the energy of the strongly light absorbing pi-pi* excitation (S-11(S) ) and the Raman shift of the radial breathing mode (RBM) are not very sensitive to the presence of the defects, and to a lesser degree their type. In contrast, the RR intensities of the RBM resonance profile are reduced by two orders of magnitude upon functionalization due to changes in the dynamic polarizabilities. Additionally, the resonance profile shows sensitivity to the defect chemistry where the H-functionalized CNTs have a factor approximate to 4 larger intensities than F-functionalized CNTs in the near resonance region. Despite the differences in the nature of the local defects, our findings are in good agreement with recent experiments on individual SWCNTs with well controlled topological defects. The study shows that photoluminescence is not sensitive to low concentrations of defects, but RR spectroscopy provides a powerful ultra-sensitive tool to identify and categorize CNT defects.

  • 18.
    Shi, Yuchen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Zakharov, Alexei A.
    MAXIV Laboratory, Lund, Sweden.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza Reza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sun, Jianwu
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)2018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 140, p. 533-542Article in journal (Refereed)
    Abstract [en]

    Multilayer graphene has exhibited distinct electronic properties such as the tunable bandgap for optoelectronic applications. Among all graphene growth techniques, thermal decomposition of SiC is regarded as a promising method for production of device-quality graphene. However, it is still very challenging to grow uniform graphene over a large-area, especially multilayer graphene. One of the main obstacles is the occurrence of step bunching on the SiC surface, which significantly influences the formation process and the uniformity of the multilayer graphene. In this work, we have systematically studied the growth of monolayer and multilayer graphene on off-axis 3CSiC(111). Taking advantage of the synergistic effect of periodic SiC step edges as graphene nucleation sites and the unique thermal decomposition energy of 3CSiC steps, we demonstrate that the step bunching can be fully eliminated during graphene growth and large-area monolayer, bilayer, and four-layer graphene can be controllably obtained on high-quality off-axis 3CSiC(111) surface. The low energy electron microscopy results demonstrate that a uniform four-layer graphene has been grown over areas of tens of square micrometers, which opens the possibility to tune the bandgap for optoelectronic devices. Furthermore, a model for graphene growth along with the step bunching elimination is proposed.

    The full text will be freely available from 2020-08-24 11:11
  • 19.
    Torop, Janno
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, The Institute of Technology.
    Aabloo, Alvo
    University of Tartu, Estonia.
    Jager, Edwin
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, The Institute of Technology.
    Novel actuators based on polypyrrole/carbide-derived carbon hybrid materials2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 80, p. 387-395Article in journal (Refereed)
    Abstract [en]

    Polypyrrole (PPy) hybrid films incorporated with porous carbide-derived carbon (CDC) particles are synthesized through a novel one-step electrochemical synthesis process that provides a simple and efficient alternative for current tape-casting and inkjet printing technologies to make conducting polymer-CDC-based electroactive composites. The resulting porous, robust and electrically conductive hybrid layer was used to fabricate electroactive polymer actuators both as perpendicularly expanding actuators and as bending trilayer actuators. Raman and FTIR spectroscopy confirm successful incorporation of CDC in the PPy matrix. Cyclic voltammograms confirm slightly higher charging/discharging currents of the PPyCDC hybrid. This indicates the successful coupling of CDC in order to increase electric double-layer capacitance in the hybrid films. The maximum steady state electromechanical diametrical strain is 13% for hybrid material which is in the same order of magnitude as for PPy and 10x more than previously reported CDC films made with non-conducting polymer binders. Furthermore, the expanding actuators made from hybrid material are more efficient than non-modified PPy actuators, having doubled the amount of swelling per injected charge. This improvement is very important since the low energy efficiency is a major shortcoming for ionic electroactive polymers. The high pseudocapacitance makes these new hybrid materials also interesting for energy storage applications.

  • 20.
    Trong Dinh, Nghia
    et al.
    Technical University of Chemnitz, Germany.
    Sowade, Enrico
    Technical University of Chemnitz, Germany.
    Blaudeck, Thomas
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Hermann, Sascha
    Technical University of Chemnitz, Germany.
    Rodriguez, Raul D.
    Technical University of Chemnitz, Germany.
    Zahn, Dietrich R. T.
    Technical University of Chemnitz, Germany.
    Schulz, Stefan E.
    Technical University of Chemnitz, Germany; Fraunhofer Institute Elect Nano Syst ENAS, Germany.
    Baumann, Reinhard R.
    Technical University of Chemnitz, Germany; Fraunhofer Institute Elect Nano Syst ENAS, Germany.
    Kanoun, Olfa
    Technical University of Chemnitz, Germany.
    High-resolution inkjet printing of conductive carbon nanotube twin lines utilizing evaporation-driven self-assembly2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 96, p. 382-393Article in journal (Refereed)
    Abstract [en]

    We report about the inkjet printing of multi-walled carbon nanotubes (MWCNTs) for conductive tracks. The MWCNTs were grown by chemical vapor deposition allowing a defined length and diameter. An inkjet-printable ink formulation was prepared by dispersing the MWCNTs in water. Inkjet-printed high resolution patterns were obtained by printing the prepared ink formulation on silicon wafers utilizing evaporation-driven self-assembly processes. After the deposition of the ink, the solvent evaporation induces material flows within the liquid moving the MWCNTs preferably to the edges of the printed patterns as well as to the print starting position where they assemble. Atomic force microscopy (AFM) reveals a preferential orientation of the deposited MWCNTs. The resulting deposit pattern is well-known as coffee-ring effect which is used here to enable high resolution printing and self-ordering of the MWCNTs. Depending on different print parameters such as drop spacing or substrate temperature, conductive track widths in the range of 5-15 mu m were achieved with a electrical resistivity of about 3.9.10(-3) to 5.6.10(-3) Omega.m measured by current-sensitive AFM. (C) 2015 Elsevier Ltd. All rights reserved.

  • 21.
    ul-Hassan, Jawad
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Winters, M.
    Chalmers, Sweden.
    Gueorguiev Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Habibpour, O.
    Chalmers, Sweden.
    Zirath, H.
    Chalmers, Sweden.
    Rorsman, N.
    Chalmers, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Quasi-free-standing monolayer and bilayer graphene growth on homoepitaxial on-axis 4H-SiC(0001) layers2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 82, p. 12-23Article in journal (Refereed)
    Abstract [en]

    Quasi-free-standing monolayer and bilayer graphene is grown on homoepitaxial layers of 4H-SiC. The SiC epilayers themselves are grown on the Si-face of nominally on-axis semi-insulating substrates using a conventional SiC hot-wall chemical vapor deposition reactor. The epilayers were confirmed to consist entirely of the 4H polytype by low temperature photoluminescence. The doping of the SiC epilayers may be modified allowing for graphene to be grown on a conducing substrate. Graphene growth was performed via thermal decomposition of the surface of the SiC epilayers under Si background pressure in order to achieve control on thickness uniformity over large area. Monolayer and bilayer samples were prepared through the conversion of a carbon buffer layer and monolayer graphene respectively using hydrogen intercalation process. Micro-Raman and reflectance mappings confirmed predominantly quasi-free-standing monolayer and bilayer graphene on samples grown under optimized growth conditions. Measurements of the Hall properties of Van der Pauw structures fabricated on these layers show high charge carrier mobility (greater than 2000 cm(2)/Vs) and low carrier density (less than0.9 x 10(13) cm(-2)) in quasi-free-standing bilayer samples relative to monolayer samples. Also, bilayers on homoepitaxial layers are found to be superior in quality compared to bilayers grown directly on SI substrates.

  • 22.
    Vinicius Da Costa Medeiros, Paulo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Bonding, charge rearrangement and interface dipoles of benzene, graphene, and PAH molecules on Au(111) and Cu(111)2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 81, p. 620-628Article in journal (Refereed)
    Abstract [en]

    We perform a theoretical study of the electronic properties of polyaromatic hydrocarbon (PAH) molecules, as well as benzene and graphene, adsorbed on copper and gold. The PAH molecules studied are coronene (C24H12), circumcoronene (C54H18) and circumcircumcoronene (C96H24), which we consider as gradual approximations to an infinite graphene layer. In order to understand how the size of the adsorbed PAH molecules influences the adsorbate-metal interactions, we generalize the approach used in our earlier study [Phys Rev B, 85 (2012), p. 205423] to decompose the binding energies and net charge transfers into separate contributions from specific groups of atoms, and we then show that the zigzag edges of the PAH molecules interact stronger with the metal surfaces than the armchair ones. We discuss the nature of binding in our model systems as well as the formation of interface dipoles. We show that for all model systems studied here, the charge rearrangement contribution to the interface dipoles can be expressed as the product of the charge involved in the formation of the dipole and the distance between well-defined centers of charge for electron accumulation and depletion. This distance is only marginally dependent on the specific PAH molecules, decreasing slowly with their size.

  • 23.
    Wang, Xin
    et al.
    Shanghai Univ, Peoples R China.
    Fei, Siming
    Shanghai Univ, Peoples R China.
    Huang, Shoushuang
    Shanghai Univ, Peoples R China.
    Wu, Chenghao
    Shanghai Univ, Peoples R China.
    Zhao, Junru
    Shanghai Univ, Peoples R China.
    Chen, Zhiwen
    Shanghai Univ, Peoples R China.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Hu, Zhang-Jun
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering. Shanghai Univ, Peoples R China.
    MoS2 nanosheets inlaid in 3D fibrous N-doped carbon spheres for lithium-ion batteries and electrocatalytic hydrogen evolution reaction2019In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 150, p. 363-370Article in journal (Refereed)
    Abstract [en]

    Molybdenum disulfide (MoS2) has received considerable interests in rechargeable lithium-ion batteries (LIBs) and hydrogen evolution reaction (HER). To overcome the instinct limitations of pristine MoS2, such as low conductivity, poor cyclic stability and rate performance, hybrid carbon-MoS2 composites are often practically applied to improve the electrochemical properties. Herein, a facile, scalable, and durable synthesis method is innovated to inlay MoS2 nanosheets into three-dimensional (3D) fibrous nitrogen-doped carbon spheres (FNCs) for achieving 3D FNC-MoS2 composites. The free-standing 3D FNC-MoS2 nanocomposites can be used as the anode for LIBs. It exhibits a high reversible capacity of similar to 700 mA h g(-1), and nearly no fading of the capacity nearly after 400 cycles at a current density of 1.2 A g(-1). Meanwhile, FNC-MoS2 exhibits superior HER activity accompanied by a small overpotential of around 194 mV in 0.5 M H2SO4. Tafel slopes are estimated to be 54 mV dec(-1), and the current density of FNC-MoS2 decreases very slightly compared to the initial one after 1000 cycles. We are convinced that the enhanced Li+ storage performance and HER activity are attributed to the synergistic effects and structural advantages, such as higher specific surface, larger pore volume, radical fibrous structure, and chemical/mechanical stability, achieved from the unique architectures of the title material. (C) 2019 Elsevier Ltd. All rights reserved.

  • 24.
    Winters, M.
    et al.
    Chalmers, Sweden.
    Habibpour, O.
    Chalmers, Sweden.
    Gueorguiev Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Zirath, H.
    Chalmers, Sweden.
    Rorsman, N.
    Chalmers, Sweden.
    Assessment of H-intercalated graphene for microwave FETs through material characterization and electron transport studies2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 81, p. 96-104Article in journal (Refereed)
    Abstract [en]

    Epitaxial graphene is grown on semi-insulating (SI) 4H-SiC in a hot wall CVD reactor by graphitization and in-situ intercalation with (H)ydrogen. A holistic material characterization is performed in order to ascertain the number of layers, layer uniformity, and electron transport properties of the epi-layers via electronic test structures and Raman spectroscopy. Bilayer graphene field effect transistors (GFETs) are fabricated using a full electron beam lithography (EBL) process which is optimized for low contact resistances of r(c) less than 0.2 Omega mm. Mobilities of order 2500 cm(2)/V s are achieved on bilayer samples after fabrication. The devices demonstrate high transconductance g(m) = 400 mS/mm and high current density I-ds = 1.8 A/mm. The output conductance at the bias of maximum transconductance is g(ds) = 300 mS/mm. The GFETs demonstrate an extrinsic f(t)(ext) and f(max)(ext) of 20 and 13 GHz, respectively and show 6 dB power gain at 1 GHz in a 50 Omega system, which is the highest reported to date.

  • 25.
    Xia, Chao
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Johansson, Leif I.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Niu, Yuran
    MAX-lab, Lund University, Sweden .
    Zakharov, Alexei A.
    MAX-lab, Lund University, Sweden .
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Virojanadara, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    High thermal stability quasi-free-standing bilayer graphene formed on 4H-SiC(0 0 0 1) via platinum intercalation2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 79, p. 631-635Article in journal (Refereed)
    Abstract [en]

    Influences on electronic structure induced by platinum (Pt) deposited on monolayer graphene grown on SiC(0 0 0 1) are investigated by photoelectron spectroscopy (PES), selected area low energy electron diffraction (μ-LEED) and angle resolved photoelectron spectroscopy (ARPES) techniques at the MAX Laboratory. Stable monolayer graphene electronic properties are observed after Pt deposition and after annealing at temperatures below 600 °C. At ⩾600 °C platinum silicide forms at the graphene/SiC interface. Annealing at 900 °C results in an efficient decoupling of the carbon buffer layer from the SiC substrate and transformation into a second graphene layer. At this stage a quasi-free standing bi-layer graphene sample is obtained. The new superstructure spots then appearing in μ-LEED pattern suggest formation of an ordered platinum silicide at the interface. This silicide is found to be stable even after annealing at temperature up to 1200 °C.

  • 26.
    Yager, Tom
    et al.
    Chalmers, Sweden.
    Lartsev, Arseniy
    Chalmers, Sweden.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lara-Avila, Samuel
    Chalmers, Sweden.
    Kubatkin, Sergey
    Chalmers, Sweden.
    Wafer-scale homogeneity of transport properties in epitaxial graphene on SiC2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 87, p. 409-414Article in journal (Refereed)
    Abstract [en]

    Magnetotransport measurements on Hall bar devices fabricated on purely monolayer epitaxial graphene on silicon carbide (SiC/G) show a very tight spread in carrier concentration and mobility across wafer-size dimensions. In contrast, SiC/G devices containing bilayer graphene domains display variations in their electronic properties linked to the amount of bilayer content. The spread in properties among devices patterned on the same SiC/G wafer can thus be understood by considering the inhomogeneous number of layers often grown on the surface of epitaxial graphene on SiC. (C) 2015 Elsevier Ltd. All rights reserved.

  • 27.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Vasiliauskas, Remigijus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Zakharov, Alexei
    Lund University, Sweden .
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Growth of large area monolayer graphene on 3C-SiC and a comparison with other SiC polytypes2013In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 57, p. 477-484Article in journal (Refereed)
    Abstract [en]

    Epitaxial graphene growth was performed on the Si-terminated face of 4H-, 6H-, and 3C-SiC substrates by silicon sublimation from SiC in argon atmosphere at a temperature of 2000 degrees C. Graphene surface morphology, thickness and band structure have been assessed by using atomic force microscopy, low-energy electron microscopy, and angle-resolved photoemission spectroscopy, respectively. Differences in the morphology of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. The uniformity of silicon sublimation is a decisive factor for obtaining large area homogenous graphene. It is also shown that a lower substrate surface roughness results in more uniform step bunching with a lower distribution of step heights and consequently better quality of the grown graphene. Large homogeneous areas of graphene monolayers (over 50 x 50 mu m(2)) have been grown on 3C-SiC (1 1 1) substrates. The comparison with the other polytypes suggests a similarity in the surface behaviour of 3C- and 6H-SiC.

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