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  • 1.
    Aakash, ?
    et al.
    Department of Electronics and Communication Engg., Birla Institute of Technology.
    Nordblad, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Mohan, Rajendra
    Department of Physics, National Institute of Technology Patna.
    Mukherjee, Samrat
    Department of Physics, National Institute of Technology Patna.
    Structural, magnetic and hyperfine characterizations of nanocrystalline Zn-Cd doped nickel ferrites2017Inngår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 441, 710-717 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In our present work, we have synthesized a series of Cd-Zn doped nickel ferrite ((Cd-0.5 Zn-x(x)) Ni0(.5)Fe(2)O(4); x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) through standard chemical co-precipitation method to study the influence of diamagnetic ions (Cd, Zn) on the magnetic properties of ferrites. XRD and Raman spectroscopy were employed for the structural characterizations. The refinement of the X-ray diffractogram data augmented by the Williamson-Hall plots showed the presence of Cd2+ vacancies and a strained crystal structure. The vibrational spectroscopy indicated the presence of lower space-group symmetry and a distorted crystal structure. Magnetic measurements showed the samples possessed low magnetic anisotropy along with a canted spin structure. The Mossbauer measurements confirmed the cation distribution and gave evidence of super transferred hyperfine interactions arising due to canted spin structure of the system.

  • 2.
    Abdalla, Hassan
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Komplexa material och system. Linköpings universitet, Tekniska fakulteten.
    Fabiano, Simone
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska fakulteten.
    Kemerink, Martijn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Komplexa material och system. Linköpings universitet, Tekniska fakulteten.
    Investigation of the dimensionality of charge transport in organic field effect transistors2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 8, 85301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ever since the first experimental investigations of organic field effect transistors (OFETs) the dimensionality of charge transport has alternately been described as two dimensional (2D) and three dimensional (3D). More recently, researchers have turned to an analytical analysis of the temperature-dependent transfer characteristics to classify the dimensionality as either 2D or 3D as well as to determine the disorder of the system, thereby greatly simplifying dimensionality investigations. We applied said analytical analysis to the experimental results of our OFETs comprising molecularly well-defined polymeric layers as the active material as well as to results obtained from kinetic Monte Carlo simulations and found that it was not able to correctly distinguish between 2D and 3D transports or give meaningful values for the disorder and should only be used for quasiquantitative and comparative analysis. We conclude to show that the dimensionality of charge transport in OFETs is a function of the interplay between transistor physics and morphology of the organic material.

  • 3. Aberg, D
    et al.
    Hallberg, T
    Svensson, B G
    Lindstrom, J L
    Linnarsson, M K
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Ultra-shallow thermal donor formation in oxygen-containing ambient1998Inngår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 210, 527-532 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Czochralski-grown phosphorus-doped (approximate to 2 x 10(14) cm(-3)) silicon wafers have been annealed in nitrogen, wet nitrogen, argon, oxygen, and vacuum ambients at 470 degrees C for times up to 500 h. Sample characterization was made with capacitance-voltage, four-point probe, DLTS, thermally stimulated capacitance, admittance spectroscopy, secondary ion-mass spectrometry, and Fourier transform infrared spectroscopy. This study finds a strong relation between the previously reported ultra-shallow thermal donors (USTDs) and shallow thermal donors (STDs), and it is shown that the net concentration of thermally formed donors is independent on annealing ambient within the experimental accuracy. It was found that the majority of formed donors for long anneals consisted of either STDs or USTDs, however, it was found that oxygen-containing ambient is indispensable for forming USTDs.

  • 4. Aberg, D
    et al.
    Linnarsson, M K
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Svensson, B G
    Hallberg, T
    Lindstrom, J L
    Ultrashallow thermal donor formation in silicon by annealing in ambient oxygen1999Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 85, 8054-8059 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Czochralski-grown silicon wafers doped with phosphorus (similar to 10(14) cm(-3)) have been annealed in nitrogen, wet nitrogen, oxygen, argon, and vacuum ambients at 470 degrees C for times up to 500 h. Sample characterization was made using predominantly electrical techniques such as admittance spectroscopy and thermally stimulated capacitance measurements but also secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy were employed. In all samples, an increasing concentration of free carrier electrons is observed with increasing annealing time, reaching a maximum of similar to 10(16) cm(-3) at 100 h. For durations in excess of 100 h gradual decrease of the free electron concentration takes place except for the samples treated in wet nitrogen and oxygen atmospheres, which display donors stable even after 200 h. These stable centers are found to have shallower donor level positions in the energy band gap (similar to 25 meV below the conduction band edge E-c) than those of the centers formed in vacuum, argon, and nitrogen atmospheres (similar to 35 meV below E-c). The latter centers are associated with the well-established shallow thermal donors (STDs) while the origin of the former ones, which are labeled ultrashallow thermal donors (USTDs) is less known. However, on the basis of a wealth of experimental results we show that the USTDs are most likely perturbated STDs modified through interaction with fast-in diffusing oxygen species, possibly oxygen dimers. Further, comparison between the electrical data and the SIMS measurements reveals unambiguously that neither the STD nor the USTD centers involve nitrogen, in contrast to recent suggestions in the literature. (C) 1999 American Institute of Physics. [S0021-8979(99)06512-3].

  • 5.
    Abergel, David
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Mucha-Kruczynski, Marcin
    Infrared absorption of closely aligned heterostructures of monolayer and bilayer graphene with hexagonal boron nitride2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 11, 115430Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We model optical absorption of monolayer and bilayer graphene on hexagonal boron nitride for the case of closely aligned crystal lattices. We show that perturbations with different spatial symmetry can lead to similar absorption spectra. We suggest that a study of the absorption spectra as a function of the doping for an almost completely full first miniband is necessary to extract meaningful information about the moire characteristics from optical absorption measurements and to distinguish between various theoretical proposals for the physically realistic interaction. Also, for bilayer graphene, the ability to compare spectra for the opposite signs of electric-field-induced interlayer asymmetry might provide additional information about the moire parameters.

  • 6. Abou-Hamad, E.
    et al.
    Babaa, M. -R
    Bouhrara, M.
    Kim, Y.
    Saih, Y.
    Dennler, S.
    Mauri, F.
    Basset, J. -M
    Goze-Bac, C.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Structural properties of carbon nanotubes derived from (13)C NMR2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 16, 165417- s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a detailed experimental and theoretical study on how structural properties of carbon nanotubes can be derived from 13C NMR investigations. Magic angle spinning solid state NMR experiments have been performed on single-and multiwalled carbon nanotubes with diameters in the range from 0.7 to 100 nm and with number of walls from 1 to 90. We provide models on how diameter and the number of nanotube walls influence NMR linewidth and line position. Both models are supported by theoretical calculations. Increasing the diameter D, from the smallest investigated nanotube, which in our study corresponds to the inner nanotube of a double-walled tube to the largest studied diameter, corresponding to large multiwalled nanotubes, leads to a 23.5 ppm diamagnetic shift of the isotropic NMR line position d. We show that the isotropic line follows the relation d = 18.3/D + 102.5 ppm, where D is the diameter of the tube and NMR line position d is relative to tetramethylsilane. The relation asymptotically tends to approach the line position expected in graphene. A characteristic broadening of the line shape is observed with the increasing number of walls. This feature can be rationalized by an isotropic shift distribution originating from different diamagnetic shielding of the encapsulated nanotubes together with a heterogeneity of the samples. Based on our results, NMR is shown to be a nondestructive spectroscopic method that can be used as a complementary method to, for example, transmission electron microscopy to obtain structural information for carbon nanotubes, especially bulk samples.

  • 7. Abou-Hamad, E.
    et al.
    Kim, Y.
    Bouhrara, M.
    Saih, Y.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Luzzi, D. E.
    Goze-Bac, C.
    NMR strategies to study the local magnetic properties of carbon nanotubes2012Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, Vol. 407, nr 4, 740-742 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The local magnetic properties of the one dimensional inner space of the nanotubes are investigated using C-13 nuclear magnetic resonance spectroscopy of encapsulated fullerene molecules inside single walled carbon nanotubes. Isotope engineering and magnetically purified nanotubes have been advantageously used on our study to discriminate between the different diamagnetic and paramagnetic shifts of the resonances. Ring currents originating from the pi electrons circulating on the nanotube, are found to actively screen the applied magnetic field by -36.9 ppm. Defects and holes in the nanotube walls cancel this screening locally. What is interesting, that at high magnetic fields, the modifications of the NMR resonances of the molecules from free to encapsulated can be exploited to determine some structural characteristics of the surrounding nanotubes, never observed experimentally. (C) 2011 Elsevier B.V. All rights reserved.

  • 8.
    Abou-Hamad, Edy
    et al.
    Universite Montpellier II.
    Kim, Y
    University of Pennsylvania.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Goze-Bac, Christophe
    Universite Montpellier II.
    Luzzi, David
    University of Pennsylvania.
    Rubio, Angelo
    University of Basque Country.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Hydrogenation of C-60 in Peapods: Physical Chemistry in Nano Vessels2009Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, Vol. 113, nr 20, 8583-8587 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogenation of C-60 molecules inside SWNT was achieved by direct reaction with hydrogen gas at elevated pressure and temperature. Evidence for the C-60 hydrogenation in peapods is provided by isotopic engineering with specific enrichment of encapsulated species and high resolution C-13 and H-1 NMR spectroscopy with the observation of characteristic diamagnetic and paramagnetic shifts of the NMR lines and the appearance of sp(3) carbon resonances. We estimate that approximately 78% of the C-60 molecules inside SWNTs are hydrogenated to an average degree of 14 hydrogen atoms per C-60 molecule. As a consequence, the rotational dynamics of the encapsulated C60Hx molecules is clearly hindered. Our successful hydrogenation experiments open completely new roads to understand and control confined chemical reactions at the nano scale

  • 9.
    Abou-Hamad, Edy
    et al.
    Universite Montpellier 2, France.
    Kim, Y.
    University of Pennsylvania, Philadelphia.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boesch, D.
    University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Aloni, S.
    University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Zettl, Alex
    University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Rubio, Angelo
    Universidad del Pas Vasco UPV/EHU.
    Luzzi, David E.
    University of Pennsylvania, Philadelphia.
    Goze-Bac, Christophe
    CNRS Universit Montpellier 2.
    Molecular dynamics and phase transition in one-dimensional crystal of C60 encapsulated inside single wall carbon nanotubes2009Inngår i: ACS Nano, ISSN 1936-0851, Vol. 3, nr 12, 3878-3883 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One-dimensional crystals of 25% 13C-enriched C60 encapsulated inside highly magnetically purified SWNTs were investigated by following the temperature dependence of the 13C NMR line shapes and the relaxation rates from 300 K down to 5 K. High-resolution MAS techniques reveal that 32% of the encapsulated molecules, so-called the C60α, are blocked at room temperature and 68%, labeled C60β, are shown to reversly undergo molecular reorientational dynamics. Contrary to previous NMR studies, spin−lattice relaxation time reveals a phase transition at 100 K associated with the changes in the nature of the C60β dynamics. Above the transition, the C60β exhibits continuous rotational diffusion; below the transition, C60β executes uniaxial hindered rotations most likely along the nanotubes axis and freeze out below 25 K. The associated activation energies of these two dynamical regimes are measured to be 6 times lower than in fcc-C60, suggesting a quiet smooth orientational dependence of the interaction between C60β molecules and the inner surface of the nanotubes.

  • 10.
    Abou-Ras, Daniel
    et al.
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Hahn Meitner Pl 1, D-14109 Berlin, Germany..
    Wagner, Sigurd
    Princeton Univ, Dept Elect Engn, Princeton, NJ 08544 USA..
    Stanbery, Bill J.
    Siva Power, 5102 Calle Sol, Santa Clara, CA 95054 USA..
    Schock, Hans-Werner
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Hahn Meitner Pl 1, D-14109 Berlin, Germany..
    Scheer, Roland
    Martin Luther Univ Halle Wittenberg, Inst Phys, Photovolta Grp, D-06120 Halle, Saale, Germany..
    Stolt, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik. Solibro Res AB, Sweden.
    Siebentritt, Susanne
    Univ Luxembourg, Phys & Mat Sci Res Unit, Lab Photovolta, Belvaux, Luxembourg..
    Lincot, Daniel
    CNRS EDF Chim Paristech PSL, Inst Photovolta Ile France IPVF, IRDEP, 6 Quai Watier, F-78401 Chatou, France..
    Eberspacher, Chris
    Solopower Syst Inc, Corp & Mfg Headquarters, 6308 North Marine Dr, Portland, OR 97203 USA..
    Kushiya, Katsumi
    Solar Frontier KK, 123-1 Shimo Kawairi, Atsugi, Kanagawa, Japan..
    Tiwari, Ayodhya N.
    Empa Swiss Fed Labs Mat Sci & Technol, Lab Thin Films & Photovolta, Ueberlandstr 129, CH-8600 Dubendorf, Switzerland..
    Innovation highway: Breakthrough milestones and key developments in chalcopyrite photovoltaics from a retrospective viewpoint2017Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 633, 2-12 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present contribution is a summary of an event that was organized as a special evening session in Symposium V "Chalcogenide Thin-Film Solar Cells" at the E-MRS 2016 Spring Meeting, Lille, France. The presentations in this session were given by the coauthors of this paper. These authors present retrospectives of key developments in the field of Cu(In,Ga)(S,Se)(2) solar cells as they themselves had witnessed in their laboratories or companies. Also, anecdotes are brought up, which captured interesting circumstances in that evolutionary phase of the field. Because the focus was on historical perspectives rather than a comprehensive review of the field, recent developments intentionally were not addressed.

  • 11. Abrikosov, I. A.
    et al.
    Olsson, Pär
    Department of Materials and Mechanics of Components, EDF RandD, les Renardières, Moret-sur-Loing, France.
    Ponomareva, A. V.
    Correlation between electronic structure, magnetism and physical properties of Fe-Cr alloys: Ab initio modeling2008Inngår i: MATERIALS ISSUES FOR GENERATION IV SYSTEMS: STATUS, OPEN QUESTIONS AND CHALLENGES, 2008, 153-168 s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We review recent developments in the field of ab initio electronic structure theory and its application for studies of phase stability of alloy systems. Basic ideas behind state-of-the-art techniques for first-principles theoretical simulations of the phase stabilities and properties of intermetallic compounds and alloys based on the density functional theory are outlined. We concentrate on methods that allow for an efficient treatment of disorder effects, and illustrate their predictive power for the case of Fe-Cr system. We show that in the ferromagnetic alloys there are peculiarities of the mixing enthalpy in the low-Cr region in the bee phase. Thus the stability of the Cr containing steels stems from the negative mixing enthalpy at low concentrations of chromium. We explain the effect by the strong concentration dependence of the interatomic interactions in Fe-Cr system.

  • 12.
    Abrikosov, Igor A.
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Steneteg, Peter
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Hultberg, Lasse
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska fakulteten.
    Hellman, Olle
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Yu Mosyagin, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Department of Theoretical Physics and Quantum Technologies, National Research, Technological University MISiS, Moscow, Russia.
    Lugovskoy, Andrey V.
    Department of Theoretical Physics and Quantum Technologies, National Research, Technological University MISiS, Russia.
    Barannikova, Svetlana A.
    Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Science, Tomsk, Russia / Department of Physics and Engineering, Tomsk State University, Tomsk, Russia.
    Finite Temperature, Magnetic, and Many-Body Effects in Ab Initio Simulations of Alloy Thermodynamics2013Inngår i: TMS2013 Supplemental Proceedings, John Wiley & Sons, 2013, 617-626 s.Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Ab initio electronic structure theory is known as a useful tool for prediction of materials properties. However, majority of simulations still deal with calculations in the framework of density functional theory with local or semi-local functionals carried out at zero temperature. We present new methodological solution.s, which go beyond this approach and explicitly take finite temperature, magnetic, and many-body effects into account. Considering Ti-based alloys, we discuss !imitations of the quasiharmonic approximation for the treatment of lattice vibrations, and present an accurate and easily extendable method to calculate free ,energies of strongly anharmonic solids. We underline the necessity to going beyond the state-of-the-art techniques for the determination of effective cluster interactions in systems exhibiting mctal-to-insulator transition, and describe a unified cluster expansion approach developed for this class of materials. Finally, we outline a first-principles method, disordered local moments molecular dynamics, for calculations of thermodynamic properties of magnetic alloys, like Cr1-x,.AlxN, in their high-temperature paramagnetic state. Our results unambiguously demonstrate importance of finite temperature effects in theoretical calculations ofthermodynamic properties ofmaterials.

  • 13.
    ABUDULIMU, ABASI
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Effectof Growth Time, Growth Temperature and Light  on Growth Mechanism of C60 nanorods2013Independent thesis Advanced level (degree of Master (Two Years)), 10 poäng / 15 hpOppgave
    Abstract [en]

    In this thesis work C60 nanorods were produced by Liquid-Liquid Interfacial Precipitation method (LLIP) assisted with 10 s of weak sonication. Ethanol and m-dichlorobenzene were used as poor and good solvents of C60, respectively. Five different temperatures, 4, 10, 20, 30, 40 and 50                         , were chosen as growth temperatures of different samples to investigate the effect of temperature on the grown structures. Different samples were prepared in the dark and under the light with various growth time to determine the effect of light and growth time on growth of C60 nanorods. The characterization of the grown C60 nanorods were conducted by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The result of characterization indicated that the sonication introduced smaller C60 nanostructures; light irradiation and temperature increase (till 40 C0) during the growth time resulted in nanorods with smaller diameter, whereas the long growth time lead to the increase of the diameter of C60 nanorods. The as-grown C60 nanorods synthesized at different conditions possess an hcp crystal structure.    

  • 14. Achtziger, N
    et al.
    Grillenberger, J
    Witthuhn, W
    Linnarsson, M K
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Janson, M S
    Svensson, B G
    Hydrogen passivation of silicon carbide by low-energy ion implantation1998Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 73, 945-947 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    implantation of deuterium is performed to investigate the mobility and passivating effect of hydrogen in epitaxial alpha-SiC (polytypes 4H and 6H). To avoid excessive damage and the resulting trapping of hydrogen, the implantation is performed with low energy (600 eV H-2(2)+). The H-2 depth profile is analyzed by secondary ion mass spectrometry. Electrical properties are measured by capacitance-voltage profiling and admittance spectroscopy. In p-type SIG, hydrogen diffuses on a mu m scale even at room temperature and effectively passivates accepters. In n-type SiC, the incorporation of H is suppressed and no passivation is detected. (C) 1998 American Institute of Physics.

  • 15. Achtziger, N
    et al.
    Hulsen, C
    Janson, M
    Linnarsson, M K
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Svensson, B G
    Witthuhn, W
    Formation of passivated layers in p-type SiC by low energy ion implantation of hydrogen2000Inngår i: SILICON CARBIDE AND RELATED MATERIALS - 1999 PTS, 1 & 2, 2000, Vol. 338-3, 933-936 s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The mobility of hydrogen and its passivating effect on accepters in p-type SiC is investigated. Hydrogen (isotope H-1 or H-2 alternatively) is implanted at temperatures between 300 K and 680 K with low energy (300 eV per atom) in order to minimize implantation damage. The depth profiles of 2H and of passivated accepters correspond closely. Up to 500 K, a fully passivated layer with a well defined thickness is formed. Its depth ton the order of 1 micrometer) is investigated as a function of doping level and hydrogen fluence. At higher temperatures, the incorporation drastically increases, but the electrical passivation is partial only. Qualitative explanations are given.

  • 16. Achtziger, N
    et al.
    Hulsen, C
    Witthuhn, W
    Linnarsson, M K
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Janson, M
    Svensson, B G
    Mobility passivating effect and thermal stability of hydrogen in silicon carbide1998Inngår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 210, 395-399 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The diffusion and passivating effect of hydrogen (isotope H-2) in epitaxial p-type SiC is studied by secondary ion mass spectrometry and capacitance-voltage profiling on Schottky diodes. The incorporation of hydrogen is achieved by low-energy ion implantation. The influence of implantation energy, temperature and subsequent annealing is presented. Annealing experiments with an electric field applied reveal a reactivation of passivated accepters and a H+ ion drift at a surprisingly low temperature of 530 K.

  • 17. Adeyev, V.M.
    et al.
    Vasylyev, M.O.
    Pogorelov, Ye.
    Features of auger-investigations of ultrathin periodic metallic film structures2006Inngår i: Metallofizika i novejsie tehnologii, ISSN 1024-1809, Vol. 28, nr 2, 193-200 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the presented work the applicability of Auger Electron Spectroscopy for studying layered metal film structures Fe/(Au, Cu)/Tb on Si substrate with thickness of layers up to 30 Å was shown. It was ascertained that Fe layer is interacting with Si substrate and as a result Fe-silicide is formed. The thickness of buffer layers aimed to protect Fe layer appeared to be insufficient for complete suppression of silicide formation

  • 18.
    Agnarsson, Björn
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Surface studies on α–sapphire for potential use in GaN epitaxial growth2009Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This Licentiate thesis summarizes the work carried out by the author the years 2004 to 2008 at the University of Iceland and the Royal Institute of Technology (KTH) in Sweden. The aim of the project was to investigate the structure of sapphire (alpha-Al2O3) surfaces, both for pure scientific reasons and also for potential use as substrate for GaN-growth by molecular beam epitaxy.

    More generally the thesis describes some surface science methods used for investigating the substrates; the general physical back ground, the experi- mental implementation and what information they can give. The described techniques are used for surface analysis on sapphire substrates which have been treated variously in order to optimize them for use as templates for epi- taxial growth of GaN or related III-V compounds.

    The thesis is based on three published papers.

    The first paper focuses on the formation a thin AlN layer on sapphire, which may act as a buffer layer for potential epitaxial growth of GaN or any related III-V materials. Two types of sapphire substrates (reconstructed and non- reconstructed) were exposed to ammonia resulting in the formation of AlN on the surface. The efficiency of the AlN formation (nitridation efficiency) for the two surfaces was then compared as a function of substrate temperature through photoelectron spectroscopy and low electron energy diffraction. The reconstructed surface showed a much higher nitridation efficiency than the non-reconstructed surface.

    In the second paper, the affect of different annealing processes on the sapphire morphology, and thus its capability to act as a template for GaN growth, was studied. Atomic force microscopy, X-ray diffraction analysis together with ellipsometry measurements showed that annealing in H2 ambient and subse- quent annealing at 1300 °C in O2 for 11 hours resulted in high quality and atomically flat sapphire surface suitable for III-V epitaxial growth.

    The third paper describes the effect of argon sputtering on cleaning GaN surfaces and the possibility of using indium as surfactant for establishing a clean and stoichiometric GaN surface, after such sputtering. Soft sputtering, followed by deposition of 2 ML of indium and subsequent annealing at around 500 °C resulted in a well ordered and clean GaN surface while hard sputtering introduced defects and incorporated both metallic gallium and indium in the surface.

  • 19.
    Agnarsson, Björn
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Olafsson, S.
    Gislason, H. P.
    Karlsson, Ulf O.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Influence of initial surface reconstruction on nitridation of Al2O3 (0001) using low pressure ammonia2007Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, nr 1, 013519- s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of this study is to investigate the effect of initial surface reconstruction on the nitridation process of Al2O3 (0001). This was done by exposing differently reconstructed sapphire substrates at different temperatures to low pressure ammonia (NH3). Structural and chemical analysis were carried out using low-electron energy diffraction and x-ray photoelectron spectroscopy. The experiments revealed that using low pressure ammonia (P-NH3 < 1 X 10(-5) Torr), no nitridation takes place on (1x1) unreconstructed surfaces. However, when the unreconstructed surface starts to change to a (root 31 x root 31) R +/- 9 degrees reconstructed surface, with increasing substrate temperature, the nitridation becomes successful. When using the initially reconstructed surface, the nitridation is successful even from the lowest temperature used. These results suggest that the initial surface reconstruction has a major effect on the nitridation process. This kinetic behavior has not been reported before, with most nitridation studies mainly focusing on the effect of surface temperature on the resulting surface morphology, rather than the actual kinetics of the process itself.

  • 20. Agterberg, Daniel F.
    et al.
    Garaud, Julien
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Checkerboard order in vortex cores from pair-density-wave superconductivity2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 10, 104512Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider competing pair-density-wave (PDW) and d-wave superconducting states in a magnetic field. We show that PDW order appears in the cores of d-wave vortices, driving checkerboard charge-density-wave (CDW) order in the vortex cores, which is consistent with experimental observations. Furthermore, we find an additional CDW order that appears on a ring outside the vortex cores. This CDW order varies with a period that is twice that of the checkerboard CDW and it only appears where both PDW and d-wave order coexist. The observation of this additional CDW order would provide strong evidence for PDW order in the pseudogap phase of the cuprates. We further argue that the CDW seen by nuclear magnetic resonance at high fields is due to a PDW state that emerges when a magnetic field is applied.

  • 21.
    Ahlberg, Martina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Critical Phenomena and Exchange Coupling in Magnetic Heterostructures2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The continuous phase transition in thin magnetic films and superlattices has been studied using the magneto-optical Kerr effect (MOKE) and polarized neutron scattering (PNR).  It has been shown that the critical behavior of amorphous thin films belonging to the 2D XY universality class can be described within the same theory as crystalline sample. This means that quenched disorder only serves as a marginal perturbation in systems with this symmetry.

    The connection between interlayer exchange coupling and the observed critical behavior in Fe/V superlattices was explored. The results prove that the origin of unusually high values of the exponent β can be traced to a position dependence of the magnetization at elevated temperatures. The magnetization of the outermost layers within the superlattice shows a more pronounced decrease at lower temperatures, compared to the inner layers, which in turn have a more abrupt decrease in the vicinity of the critical temperature. This translates to a high exponent, especially when the layers are probed by a technique where more weight is given to the layers close to the surface, e.g.MOKE.  The interlayer exchange coupling as a function of spacer thickness and temperature was also studied in its own right. The data was compared to the literature, and a dependence on the thickness of the magnetic layers was concluded.

    The phase transition in amorphous FeZr/CoZr multilayers, where the magnetization emanates from ferromagnetic proximity effects, was investigated. Even though the determined exponents of the zero-field magnetization, the susceptibility and the critical isotherm did not correspond to any universality class, scaling plots displayed an excellent data collapse.

    Samples consisting of Fe δ-layers (0.3-1.4 monolayers) embedded in Pd were studied using element-specific resonant x-ray magnetic scattering. The magnetization of the two constituents showed distinctly different temperature dependences.

  • 22.
    Ahlberg, Martina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Andersson, Gabriella
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Two-dimensional XY-like amorphous Co68Fe24Zr8/Al70Zr30 multilayers2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 22, 224404- s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present an experimental realization of a magnetic two-dimensional XY system using amorphous materials. The classification of the dimensionality is based on the critical behavior of amorphous Co68Fe24Zr8(d)/Al70O30 (20 angstrom) multilayers, where d = 11 - 16 angstrom. Analysis of the remanent magnetization, the magnetic isotherms, the initial susceptibility, and the magnetic correlation length shows that the magnetic phase transition can be described by the 2D XY model. The samples are not paramagnetic above the critical temperature but are characterized by local magnetic order manifested in the field and temperature dependence of the magnetization. Furthermore, an average spin-spin interaction length of 8.1 angstrom was estimated using the thickness dependence of the Curie temperature.

  • 23.
    Ahlberg, Martina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Korelis, Panagiotis
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Andersson, Gabriella
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Effect of ferromagnetic proximity on critical behavior2012Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 85, nr 22, 224425-1-224425-6 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the magnetic phase transition in amorphous Fe93Zr7(x angstrom)/Co95Zr5(1 angstrom) multilayers, where x = 25, 50, and 75. The extremely thin CoZr layer induces magnetic order at temperatures well above the inherent ordering temperature of Fe93Zr7. The changes in the critical exponent beta, associated with the temperature dependence of the magnetization, imply a crossover from two-to three-dimensional behavior as the FeZr thickness is reduced, consistent with a substantial magnetic induction in the FeZr layers. In addition we determined the exponents delta and gamma, of the critical isotherm and the susceptibility, respectively, and their values confirm the nonuniversal character of the phase transition. Scaling of the results yields an excellent data collapse and is found to hold in the crossover regime where the universality hypothesis is not applicable. 

  • 24.
    Ahlberg, Martina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Papaioannou,, Evangelos Th
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Temperature dependence of magnetic properties in weakly exchange coupled Fe/V superlattices2013Inngår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, Vol. 341, 142-147 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use Fe(3)/V(x)Fe(3)/V(x) superlattices, x = 16-27 monolayers (ML) to explore the interlayer exchange coupling (IEC) as a function of both spacer layer thickness and temperature. Fe/V is a common model system for studies addressing the IEC, but the behavior in the weakly exchange coupled regime, complemented with the temperature dependence of the magnetic properties, have remained unexplored. We observe clear regions with ferro- and antiferromagnetic coupling, which is manifested in oscillations in the saturation field, the remanence and the critical temperature. The oscillation in the interlayer coupling (J') has a period of 5.8(1) ML. This is approximate to 0.8 ML smaller than observed for Fe(7)/V(x) superlattices which illustrates the influence of the magnetic layer thickness on the interlayer coupling. The temperature dependence of the remanent magnetization was proven to be significantly affected by the strength of the ferromagnetic coupling, leading to high values of the effective critical exponent beta(eff).

  • 25.
    Ahmad, Mohammed Metwally Gomaa
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten. National Research Centre, Egypt.
    Yazdi, Gholamreza
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Schmidt, Susann
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Boshta, M.
    National Research Centre, Egypt.
    Khranovskyy, Volodymyr
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Eriksson, Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Farag, B. S.
    National Research Centre, Egypt.
    Osman, M. B. S.
    Ain Shams University, Egypt.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Effect of precursor solutions on the structural and optical properties of sprayed NiO thin films2017Inngår i: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 64, 32-38 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nickel oxide thin films were deposited by a simple and low-cost spray pyrolysis technique using three different precursors: nickel nitrate, nickel chloride, and nickel acetate on corning glass substrates. X-ray diffraction show that the NiO films are polycrystalline and have a cubic crystal structure, although predominantly with a preferred 111-orientation in the growth direction and a random in-plane orientation. The deconvolution of the Ni 2p and O 1s core level X-ray photoelectron-spectra of nickel oxides produced by using different precursors indicates a shift of the binding energies. The sprayed NiO deposited from nickel nitrate has an optical transmittance in the range of 60-65% in the visible region. The optical band gap energies of the sprayed NiO films deposited from nickel nitrate, nickel chloride and nickel acetate are 3.5, 3.2 and 3.43 eV respectively. Also, the extinction coefficient and refractive index of NiO films have been calculated from transmittance and reflectance measurements. The average value of refractive index for sprayed films by nickel nitrate, nickel chloride and nickel acetate are 2.1, 1.6 and 1.85 respectively. It is revealed that the band gap and refractive index of NiO films by using nickel nitrate corresponds to the commonly reported values. We attribute the observed behavior in the optical band gap and optical constants as due to the change of the Ni/O ratio.

    Fulltekst tilgjengelig fra 2019-03-16 17:22
  • 26.
    Ahmadi, Sareh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Structure-dependent charge transfer at the interafce between organic thin films, and metals and metal oxides2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The purpose of the research work, presented in this thesis is to offer a detailed atomic level study of interfaces created by adsorption of organic molecules on metals and metal oxides to point out significant impact of substrate, dye structure as well as different mediators on the charge transfer at these interfaces, which is proven to influence the device performance to a great extent.

    Adsorption of organic photosensitive molecules on metals and metal-oxides is the main focus of this thesis. Phthalocyanines which are organic semiconductors offer a broad range of properties, such as thermal and chemical stability, high charge mobility and strong absorption coefficient in the visible and near-IR regions, which make them very attractive to be applied in various systems and devices. Fuel cells, organic field-effect transistors (OFETs), organic light emitting diodes (OLEDs) and solar cells are examples of phthalocyanine’s applications. The main focus of this work is to characterize the interfaces of Dye Sensitized Solar Cells (DSSCs).

    DSSC was invented by Michael Grätzel and Brian O’Regan in 1988. At the heart of this cell there is an oxide which is coated by a photosensitive dye. Under illumination, an electron is excited from HOMO to LUMO of the molecule, which can be further transferred to the conduction band of the oxide by a proper energy level alignment. The original state of the dye is regenerated by electron donation via the electrolyte, which usually is an organic solvent containing a redox couple e.g., iodide/triiodide. The iodide is regenerated by reduction of triiodide at the counter electrode. To improve the functionality of the cell, different additives can be added to the electrolyte.

    To mimic the interfaces of this cell, molecular layers of MPc (M: Fe, Zn, Mg) are adsorbed on both metallic surfaces, Au(111) and Pt(111), and rutile TiO2(110). Layers of iodine were inserted between metallic substrates and dyes to investigate the electronic properties and charge transfer at these multi-interface systems. 4-tert-butyl pyridine is a significant additive to the electrolyte and has proven to enhance the cell’s performance. This molecule was also adsorbed on Pt(111) and TiO2(110). Phthalocyanines were deposited by organic molecular beam deposition and 4TBP was evaporated at room temperature. Surface structures and reconstructions were confirmed by LEED measurements. Surface sensitive synchrotron radiation based spectroscopy methods, XPS and NEXAFS were applied to characterize these surfaces and interfaces. STM images directly give a topographical and electronic map over the surface. All measurements were carried out in UHV condition.

    When MPc was adsorbed on Au(111) and TiO2(110), charge transfer from molecule to substrate is suggested, while the opposite holds for MPc adsorbed on Pt(111). Moreover, stronger interaction between MPc and Pt(111) and TiO2(110) compared to Au(111) also demonstrates the effect of substrate on the charge transfer at the interface. The stronger interaction observed for these two substrates disturbed the smooth growth of a monolayer; it also resulted in bending of the molecular plane. Interaction of MPc with metallic surfaces was modified by inserting iodine at the interface. Another substrate-related effect was observed when MgPc was adsorbed on TiO2(110);  and -cross linked surfaces, where the surface reconstruction directly affect the molecular configuration as well as electronic structure at the interface. Besides, it is shown that the d-orbital filling of the central metal atom in MPc plays an important role for the properties of the molecular layer as well as charge transfer at the interface.

    Upon adsorption of 4TBP on Pt(111), C-H bond is dissociatively broken and molecules is adsorbed with N atoms down. Modification of surface by iodine, prevent this dissociation. In the low coverage of iodine, there is a competition between 4TBP and iodine to directly bind to Pt(111). Investigation on the adsorption of 4TBP on TiO2(110) illustrated that these molecules in low coverage regime, prefer the oxygen vacancy sites and their adsorption on these sites, results in a downward band bending at the substrate’s surface. 

  • 27.
    Ahmadi, Sareh
    et al.
    Materialfusik,KTH-Electrum.
    Shariati, Masumeh-Nina
    Yu, Shun
    Göthelid, Mats
    Charge transfer and chemical interaction of ZnPc and FePc with Au(111)Manuskript (preprint) (Annet vitenskapelig)
  • 28.
    Ahmed, Rizwan
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Abbas, Shahid
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Electrical and Optical Characteristics of InP Nanowires based p-i-n Photodetectors2010Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    Photodetectors are a kind of semiconductor devices that convert incoming light to an electrical signal. Photodetectors are classified based on their different structure, fabrication technology, applications and different sensitivity. Infrared photodetectors are widely used in many applications such as night vision, thermal cameras, remote temperature sensing, and medical diagnosis etc.

     

    All detectors have material inside that is sensitive to incoming light. It will absorb the photons and, if the incoming photons have enough energy, electrons will be excited to higher energy levels and if these electrons are free to move, under the effect of an external electric field, a photocurrent is generated.

     

    In this project Fourier Transform Infrared (FT-IR) Spectroscopy is used to investigate a new kind of photodiodes that are based on self-assembled semiconductor nanowires (NWs) which are grown directly on the substrate without any epi-layer. The spectrally resolved photocurrent (at different applied biases) and IV curves (in darkness and illumination) for different temperatures have been studied respectively. Polarization effects (at low and high Temperatures) have been investigated.  The experiments are conducted for different samples with high concentration of NWs as well as with lower concentration of NWs in the temperature range from 78 K (-195ºC) to 300 (27ºC). These photodiodes are designed to work in near infrared (NIR) spectral range.

     

    The results show that the NW photodetectors indeed are promising devices with fairly high break down voltage, change of photocurrent spectra with polarized light, low and constant reverse saturation current (Is). The impact of different polarized light on photocurrent spectra has been investigated and an attempt has been made to clarify the observed double peak of InP photocurrent spectrum. Our investigations also include a comparison to a conventional planar InP p-i-n photodetector.

     

  • 29. Ahola-Tuomi, M.
    et al.
    Punkkinen, Marko Patrick John
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Laukkanen, P.
    Kuzmin, M.
    Lang, J.
    Schulte, K.
    Pietzsch, A.
    Perala, R. E.
    Rasanen, N.
    Vayrynen, I. J.
    Properties of self-assembled Bi nanolines on InAs(100) studied by core-level and valence-band photoemission, and first-principles calculations2011Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 24, 245401- s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied self-assembled bismuth (Bi) nanolines on the Bi-terminated InAs(100) surface by core-level and valence-band photoelectron spectroscopy, and ab initio first-principles calculations. A structural model for this intriguing surface is suggested based on the comparison of the measured and calculated core-level shifts. Also, the atomic origins for the core-level shifts are proposed based on the calculations. A clear peak related to this surface was observed in the valence band 0.34 eV below the Fermi level, which can be used as a "fingerprint" of a well-ordered Bi/InAs(100) nanoline surface.

  • 30.
    Aijaz, Asim
    et al.
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden.;Uppsala Univ, Dept Engn Sci, Angstrom Lab, POB 534, SE-75121 Uppsala, Sweden..
    Louring, Sascha
    Aarhus Univ, Interdisciplinary Nanosci Ctr iNANO, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.;Danish Technol Inst, Tribol Ctr, Teknol Pk,Kongsvang Alle 29, DK-8000 Aarhus C, Denmark..
    Lundin, Daniel
    Univ Paris Saclay, Univ Paris Sud, LPGP, CNRS,UMR 8578, F-91405 Orsay, France..
    Kubart, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Jensen, Jens
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Sarakinos, Kostas
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Helmersson, Ulf
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Synthesis of hydrogenated diamondlike carbon thin films using neon-acetylene based high power impulse magnetron sputtering discharges2016Inngår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 34, nr 6, 061504Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogenated diamondlike carbon (DLC:H) thin films exhibit many interesting properties that can be tailored by controlling the composition and energy of the vapor fluxes used for their synthesis. This control can be facilitated by high electron density and/or high electron temperature plasmas that allow one to effectively tune the gas and surface chemistry during film growth, as well as the degree of ionization of the film forming species. The authors have recently demonstrated by adding Ne in an Ar-C high power impulse magnetron sputtering (HiPIMS) discharge that electron temperatures can be effectively increased to substantially ionize C species [Aijaz et al., Diamond Relat. Mater. 23, 1 (2012)]. The authors also developed an Ar-C2H2 HiPIMS process in which the high electron densities provided by the HiPIMS operation mode enhance gas phase dissociation reactions enabling control of the plasma and growth chemistry [Aijaz et al., Diamond Relat. Mater. 44, 117 (2014)]. Seeking to further enhance electron temperature and thereby promote electron impact induced interactions, control plasma chemical reaction pathways, and tune the resulting film properties, in this work, the authors synthesize DLC: H thin films by admixing Ne in a HiPIMS based Ar/C2H2 discharge. The authors investigate the plasma properties and discharge characteristics by measuring electron energy distributions as well as by studying discharge current characteristics showing an electron temperature enhancement in C2H2 based discharges and the role of ionic contribution to the film growth. These discharge conditions allow for the growth of thick (>1 mu m) DLC: H thin films exhibiting low compressive stresses (similar to 0.5 GPa), high hardness (similar to 25 GPa), low H content (similar to 11%), and density in the order of 2.2 g/cm(3). The authors also show that film densification and change of mechanical properties are related to H removal by ion bombardment rather than subplantation.

  • 31.
    Aikebaier, Faluke
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Effects of electron-electron interaction in pristine and doped graphene2014Independent thesis Advanced level (degree of Master (Two Years)), 30 poäng / 45 hpOppgave
    Abstract [en]

    The goal of this master thesis is to investigate the eect of electron-electron interaction on electronic properties of graphene that can be measured experimentally. A tight-binding model, which includes up to next-nearest-neighbor hopping, with parameters tted to density functional theory calculations, has been used to describe the electronic structure of graphene. The electron-electron interaction is described by the Hubbard model using a mean- eld approximation. Based on the analysis of dierent tight-binding models available in the literature, we conclude that a next-nearest-neighbor tight-binding model is in better agreement with density functional theory calculations, especially for the linear dispersion around the Dirac point. The Fermi velocity in this case is very close to the experimental value, which was measured by using a variety of techniques. Interaction-induced modi cations of the linear dispersion around the Dirac point have been obtained. Unlike the non-local Hartree-Fock calculations, which take into account the long-range electron-electron interaction and yield logarithmic corrections, in agreement with experiment, we found only linear modi cations of the Fermi velocity. The reasons why one cannot obtain logarithmic corrections using the mean- eld Hubbard model have been discussed in detail. The remaining part of the thesis is focused on calculations of the local density of states around a single substitutional impurity in graphene. This quantity can be directly compared to the results of the scanning tunneling microscopy in doped graphene. We compare explicitly non-interacting and interacting cases. In the latter case, we performed self-consistent calculations, and found that electron-electron interaction has a signi cant eect on the local density of states. Furthermore, the band gap at high-symmetry points of the Brillouin zone of a supercell, triggered by the impurity, is modi ed by interactions. We use a perturbative model to explain this eect and quantitative agreement with numerical results. In conclusion, it is expected that the long-range electron-electron nteraction is extremely strong and important in graphene. However, as this thesis has shown, interactions at the level of the Hubbard model and mean- eld approximation also introduce corrections to the electronic properties of graphene.

     

  • 32.
    Aikebaier, Faluke
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Pertsova, Anna
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Canali, Carlo M.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Effects of short-range electron-electron interactions in doped graphene2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 15, 155420Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study theoretically the effects of short-range electron-electron interactions on the electronic structure of graphene, in the presence of substitutional impurities. Our computational approach is based on the π orbital tight-binding model for graphene, with the electron-electron interactions treated self-consistently at the level of the mean-field Hubbard model. The finite impurity concentration is modeled using the supercell approach. We compare explicitly noninteracting and interacting cases with varying interaction strength and impurity potential strength. We focus in particular on the interaction-induced modifications in the local density of states around the impurity, which is a quantity that can be directly probed by scanning tunneling spectroscopy of doped graphene. We find that the resonant character of the impurity states near the Fermi level is enhanced by the interactions. Furthermore, the size of the energy gap, which opens up at high-symmetry points of the Brillouin zone of the supercell upon doping, is significantly affected by the interactions. The details of this effect depend subtly on the supercell geometry. We use a perturbative model to explain these features and find quantitative agreement with numerical results.

  • 33. Airiskallio, E.
    et al.
    Nurmi, E.
    Heinonen, M. H.
    Vayrynen, I. J.
    Kokko, K.
    Ropo, M.
    Punkkinen, M. P. J.
    Pitkanen, H.
    Alatalo, M.
    Kollar, J.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Third element effect in the surface zone of Fe-Cr-Al alloys2010Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The third element effect to improve the high temperature corrosion resistance of the low-Al Fe-Cr-Al alloys is suggested to involve a mechanism that boosts the recovering of the Al concentration to the required level in the Al-depleted zone beneath the oxide layer. We propose that the key factor in this mechanism is the coexistent Cr depletion that helps to maintain a sufficient Al content in the depleted zone. Several previous experiments related to our study support that conditions for such a mechanism to be functional prevail in real oxidation processes of Fe-Cr-Al alloys.

  • 34. Ajuria, Jon
    et al.
    Arnaiz, Maria
    Botas, Cristina
    Carriazo, Daniel
    Mysyk, Roman
    Rojo, Teofilo
    Talyzin, Alexandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Goikolea, Eider
    Graphene-based lithium ion capacitor with high gravimetric energy and power densities2017Inngår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 363, 422-427 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hybrid capacitor configurations are now of increasing interest to overcome the current energy limitations of supercapacitors. In this work, we report a lithium ion capacitor (LIC) entirely based on graphene. On the one hand, the negative-battery-type- electrode consists of a self-standing, binder-free 3D macroporous foam formed by reduced graphene oxide and decorated with tin oxide nanoparticles (SnO2-rGO). On the other hand, the positive-capacitor-type- electrode is based on a thermally expanded and physically activated reduced graphene oxide (a-TEGO). For comparison purposes, a symmetric electrical double layer capacitor (EDLC) using the same activated graphene in 1.5 M Et4NBE4/ACN electrolyte is also assembled. Built in 1 M LiPF6 EC:DMC, the graphene-based LIC shows an outstanding, 10-fold increase in energy density with respect to its EDLC counterpart at low discharge rates (up to 200 Wh kg(-1)). Furthermore, it is still capable to deliver double the energy in the high power region, within a discharge time of few seconds.

  • 35.
    Akhtar, Sultan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Rubino, Stefano
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Leifer, Klaus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    A simple TEM method for fast thickness characterization of suspendedgraphene flakesManuskript (preprint) (Annet vitenskapelig)
  • 36. Akhter, Shahida
    et al.
    Paul, D. P.
    Hoque, S. M.
    Hakim, M. A.
    Hudl, Matthias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Mathieu, Roland
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Nordblad, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Magnetic and magnetocaloric properties of Cu1-xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites2014Inngår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, Vol. 367, 75-80 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of Zn substitution on the magnetic and magnetocaloric properties of Cu1-xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites over a wide temperature range has been investigated. The polycrystalline samples were synthesized using the solid-state reaction at sintering temperature 1050 degrees C (1323 K) for 2 h and has been characterized by SQUID magnetometry. Magnetization versus temperature showed that all samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature T-c is found to decrease from 373 K for x=0.6 to 140 K for x=0.8 as well as the saturation magnetization Ms which shifts from 100 to 44 emu/gm. The magnetocaloric effect was obtained by measuring a family of M-I1 curves at set temperature intervals and calculating the entropy change, LIS for this system using the Maxwell relation. The AS of all samples increased with increasing applied field and showed a maximum around their respective 'Fe. The entropy change (Delta S) decreased with increasing Zn content, whereas the relative cooling power (RCP) slightly increased. The large RCP and Delta S found in Zn substitution Cu-Zn ferrites will be interesting for magnetic refrigeration near room temperature.

  • 37. Aksenova, N.A.
    et al.
    Isakina, A.P.
    Prokhvatilov, A.I.
    Strzhemechny, M.A.
    Soldatov, Alexander V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Structure studies of C60 polymerized at low pressures1997Inngår i: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, vol. 5, Pennington, NJ: The Electrochemical Society , 1997, 687-694 s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The structure and lattice properties of a polymerized C60 sample were investigated by X-ray powder diffraction over the range from liquid-nitrogen to room temperature. The aim of these studies was to establish the effect of low-pressure compression (up to 1.1 GPa) on the phase composition of the sample, to determine the structure of the phases involved, to obtain the variation of the lattice parameters with temperature, to observe eventual phase transformation in polymerized C60, and to elucidate the evolution of the orientational order with varying temperature. Analysis of the room-temperature diffraction patterns indicates that the sample contained at least two major phases, namely rhombohedral and and tetragonal with the polymerization array close to two-dimensional. Our data obtained on samples annealed at 300 C in the air allow us to conclude that polymerized C60 converts to a mixture of the fcc structure plus a new phase, presumably C60O.

  • 38.
    Albrecht, Steffen
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Sigma-delta based techniques for future multi-standard wireless radios2005Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Improvements in process technology and design innovations have resulted in compact and cost effective digital baseband solutions. The radio part, however, has remained a bottleneck in terms of chip area and power consumption as the feature size of analog devices does not directly benefit from scaling. With the addition of yet more standards into emerging products, the requirements of future radios will extend over characteristic performance features into demands of programmable and reconfigurable hardware for radios covering multiple frequency bands. Hence, a guideline in the design of such radios is a large degree of hardware sharing.

    The thesis investigates the application of sigma-delta modulation to arising multistandard wireless radios. First, it reviews principles in wireless radios, such as selected modulation and access techniques. It also examines several communication standards of personal wireless radios as well as common receiver architectures for their implementation. This is followed by general considerations and background information about sigma-delta modulators. In the third and fourth chapter, implementations to two blocks of a wireless radio receiver system are suggested: An architecture for a frequency synthesizer and an implementation of an analog-to-digital converter.

    In the first contribution, the thesis develops a novel concept for frequency synthesis that is more suitable for multi-band, multi-standard radio architectures, achieving a large amount of hardware sharing among different wireless standards. As a second pillar, the thesis contributes with the design of a dual-standard sigma-delta modulator for data conversion within a radio receiver. Parts of the work concerning the dual-standard modulator are embodied in a granted swedish patent.

  • 39. Aleksandrovskii, A. N.
    et al.
    Dolbin, A.V.
    Esel'son, V.B.
    Gavrilko, V.G.
    Manzhelii, V.G.
    Udovidchenko, B.G.
    Bakai, A.S.
    Gadd, G.E.
    Moricca, S.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Low-temperature thermal expansion of pure and inert gas-doped fullerite C602003Inngår i: Fizika Nizkikh Temperatur (Kharkov), ISSN 0132-6414 (Print) 1816-0328 (On-line), Vol. 29, nr 4, 432-442 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The low temperature (2–24 K) thermal expansion of pure (single-crystal and polycrystalline) C60 and polycrystalline C60 intercalated with He, Ne, Ar, and Kr has been investigated using the high-resolution capacitance dilatometer. The investigation of the time dependence of the sample length variations deltaL(t) on heating by deltaT shows that the thermal expansion is determined by the sum of positive and negative contributions, which have different relaxation times. The negative thermal expansion usually prevails at helium temperatures. The positive expansion is connected with the phonon thermalization of the system. The negative expansion is caused by reorientation of the C60 molecules. It is assumed that the reorientation is of a quantum character. The inert gas impurities affect the reorientation of the C60 molecules very strongly, especially at liquid helium temperatures. A temperature hysteresis of the thermal expansion coefficient of Kr– and He–C60 solutions has been revealed. The hysteresis is attributed to orientational polyamorphous transformation in these systems.

  • 40. Aleksandrovskii, A. N.
    et al.
    Esel'son, V.B.
    Manzhelii, Vadim Grigorovich
    Udovidchenko, B.G.
    Soldatov, Alexander
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Negative thermal expansion of fullerite C60 at helium temperatures1997Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, Vol. 23, nr 11, 943-946 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal expansion of fullerite C60 has been measured in the temperature range 2–9 K. A compacted fullerite sample with a diameter of about 6 mm and height of 2.4 mm was used. It was found that at temperatures below ~ 3.4 K the linear thermal expansion coefficient becomes negative. At temperatures above 5 K our results are in good agreement with the available literature data. A qualitative explanation of the results is proposed

  • 41. Aleksandrovskii, A. N.
    et al.
    Esel'son, V.B.
    Manzhelii, V.G.
    Udovidchenko, B.G.
    Soldatov, Alexander
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal expansion of single-crystal fullerite C60 at helium temperatures2000Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, Vol. 26, nr 1, 75-80 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal expansion of single-crystal fullerite C60 has been studied in the range of liquid-helium temperatures (2–10 K). At temperatures below ~4.5 K the thermal expansion of fullerite C60 becomes negative, in agreement with the previous results on polycrystalline materials. A qualitative explanation of the results is proposed.

  • 42. Aleksandrovskii, A. N.
    et al.
    Gavrilko, V.G.
    Esel'son, V.B.
    Manzhelii, V. G.
    Udovidchenko, B.G.
    Maletskiy, V.P.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Effect of argon on the thermal expansion of fullerite C60 at helium temperatures2001Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, Vol. 27, nr 3, 245-246 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The linear thermal expansion of compacted Ar-doped fullerite C60(ArxC60) is investigated at 2–12 K using a dilatometric method. The thermal expansion of ArxC60 is also studied after partial desaturation of argon from fullerite. It is revealed that argon doping resulted in a considerable change of the temperature dependence of the thermal expansion of fullerite. An explanation of the observed effects is proposed.

  • 43. Aleksandrovskii, A.N.
    et al.
    Bakai, A.S.
    Cassidy, D.
    Dolbin, A.V.
    Esel'son, V.B.
    Gadd, G.E.
    Gavrilko, V.G.
    Manzhelii, V.G.
    Moricca, S.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    On the polyamorphism of fullerite-based orientational glasses.2005Inngår i: Low Temperature Physics, ISSN 1063-777X, Vol. 31, nr 5, 429-444 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dilatometric investigation in the temperature range of 2–28 K shows that a first-order

    polyamorphous transition occurs in the orientational glasses based on C60 doped with H2, D2 and

    Xe. A polyamorphous transition was also detected in C60 doped with Kr and He. It is observed that

    the hysteresis of thermal expansion caused by the polyamorphous transition (and, hence, the transition

    temperature) is essentially dependent on the type of doping gas. Both positive and negative

    contributions to the thermal expansion were observed in the low-temperature phase of the glasses.

    The relaxation time of the negative contribution occurs to be much longer than that of the positive

    contribution. The positive contribution is found to be due to phonon and libron modes, whilst the

    negative contribution is attributed to tunneling states of the C60 molecules. The characteristic

    time of the phase transformation from the low-T phase to the high-T phase has been found for the

    C60–H2 system at 12 K. A theoretical model is proposed to interpret these observed phenomena.

    The theoretical model proposed, includes a consideration of the nature of polyamorphism in

    glasses, as well as the thermodynamics and kinetics of the transition. A model of noninteracting

    tunneling states is used to explain the negative contribution to the thermal expansion. The experimental

    data obtained is considered within the framework of the theoretical model. From the theoretical

    model the order of magnitude of the polyamorphous transition temperature has been estimated.

    It is found that the late stage of the polyamorphous transformation is described well by the

    Kolmogorov law with an exponent of n = 1. At this stage of the transformation, the two-dimensional

    phase boundary moves along the normal, and the nucleation is not important.

  • 44. Aleksandrovskii, A.N.
    et al.
    Gavrilko, V.G.
    Esel'son, V.B.
    Manzhelii, V. G.
    Udovidchenko, B.G.
    Maletskiy, V.P.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Thermal expansion of fullerite C60 alloyed with argon and neon2001Inngår i: Low temperature physics (Woodbury, N.Y., Print), ISSN 1063-777X, Vol. 27, nr 12, 1033-1036 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The linear thermal expansion of compacted fullerite C60 alloyed with argon (ArxC60) and neon (NexC60) are investigated by a dilatometric method. The experimental temperature is 2–12 K. In the same temperature interval the thermal expansion of ArxC60 and NexC60 are examined after partial desaturation of the gases from fullerite. It is found that Ar and Ne alloying affects the temperature dependence of the thermal expansion coefficient of C60 quite appreciably. The libration and translation contributions to the thermal expansion of pure C60 are separated. The experimental results on the thermal expansion are used to obtain the Debye temperature of pure C60. The effects observed are tentatively interpreted.

  • 45.
    Alexander-Webber, J. A.
    et al.
    University of Oxford, England; University of Cambridge, England.
    Huang, J.
    University of Oxford, England.
    Maude, D. K.
    CNRS UGA UPS INSA, France.
    Janssen, T. J. B. M.
    National Phys Lab, England.
    Tzalenchuk, A.
    National Phys Lab, England; Royal Holloway University of London, England.
    Antonov, V.
    Royal Holloway University of London, England.
    Yager, T.
    Chalmers, Sweden.
    Lara-Avila, S.
    Chalmers, Sweden.
    Kubatkin, S.
    Chalmers, Sweden.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Nicholas, R. J.
    University of Oxford, England.
    Giant quantum Hall plateaus generated by charge transfer in epitaxial graphene2016Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, nr 30296Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Epitaxial graphene has proven itself to be the best candidate for quantum electrical resistance standards due to its wide quantum Hall plateaus with exceptionally high breakdown currents. However one key underlying mechanism, a magnetic field dependent charge transfer process, is yet to be fully understood. Here we report measurements of the quantum Hall effect in epitaxial graphene showing the widest quantum Hall plateau observed to date extending over 50 T, attributed to an almost linear increase in carrier density with magnetic field. This behaviour is strong evidence for field dependent charge transfer from charge reservoirs with exceptionally high densities of states in close proximity to the graphene. Using a realistic framework of broadened Landau levels we model the densities of donor states and predict the field dependence of charge transfer in excellent agreement with experimental results, thus providing a guide towards engineering epitaxial graphene for applications such as quantum metrology.

  • 46.
    Alfredsson, Svante
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Högberg, Jia Li
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    A closed-form solution to statically indeterminate adhesive joint problems — exemplified on ELS-specimens2008Inngår i: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 28, nr 7, 350-361 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A beam/adhesive-layer model is developed. For this model a closed-form solution method applicable to arbitrary boundary conditions is presented. This enables the solution of a large number of practical problems which may be statically indeterminate. The stress state in the adhesive layer and the adherends of the beam/adhesive-layer model is also scrutinized. The method is exemplified in an analysis of the end-loaded split (ELS) specimen, commonly used to determine fracture energies of adhesive layers. The effect of the flexibility of the adhesive layer on the energy release rate and the critical crack length for stable crack growth is examined. Both symmetric and unsymmetric ELS-specimens are studied.

  • 47.
    Al-Hayali, Asifa
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Characterization of ion-irradiation-induced defects in graphite by Raman and Atomic Force Microscopy2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Graphite is an interesting prototype material for ion implantation studies because of the anisotropy in its physical and structural properties; In particular, due to the layered nature of the graphite lattice, the processes of amorphization and recrystallization (graphitization) of the implanted region are conceptually different from that observed in commonly studied materials. Since ion implantation provides a controlled method for the introduction of lattice defects which can be subsequently annealed, this technique provides fundamental information on the unique crystalline regrowth (graphitization)process of this highly anisotropic material. The structure of ion‐irradiated HOPG has also been studied, and drawing inspiration from this, the crystallite size is fundamental in these novel properties in carbon. The bombarded graphite (with H+ and He ions), diamagnetic graphite, were performed using a Renishaw Raman microscope with a 514.5 nm Ar‐ion laser. The work includes the following parts:

    1. Raman spectroscopy (measurements, spectra treatment with Origin and LabFit program, interpretation based on available literature).

    2. Atomic force microscopy, interpretation with the SPIP software.

    3. TRIM software simulation ion tracks in the sample.

  • 48.
    Ali, M.
    et al.
    Helsinki University of Technology (TKK), Micronova, Department of Micro and Nanosciences, P.O. Box 3500, FIN-02015 TKK, Finland.
    Svensk, Olle
    Helsinki University of Technology (TKK), Micronova, Department of Micro and Nanosciences, P.O. Box 3500, FIN-02015 TKK, Finland.
    Zhen, Z.
    Helsinki University of Technology (TKK), Micronova, Department of Micro and Nanosciences, P.O. Box 3500, FIN-02015 TKK, Finland.
    Suihkonen, S.
    Helsinki University of Technology (TKK), Micronova, Department of Micro and Nanosciences, P.O. Box 3500, FIN-02015 TKK, Finland.
    Törmä, P.T.
    Helsinki University of Technology (TKK), Micronova, Department of Micro and Nanosciences, P.O. Box 3500, FIN-02015 TKK, Finland.
    Lipsanen, H.
    Helsinki University of Technology (TKK), Micronova, Department of Micro and Nanosciences, P.O. Box 3500, FIN-02015 TKK, Finland.
    Sopanen, M.
    Helsinki University of Technology (TKK), Micronova, Department of Micro and Nanosciences, P.O. Box 3500, FIN-02015 TKK, Finland.
    Hjort, Klas
    Department of Engineering Sciences, Uppsala University, P.O. Box 534, SE-75121 Uppsala, Sweden.
    Jensen, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Reduced photoluminescence from InGaN/GaN multiple quantum well structures following 40 MeV iodine ion irradiation2009Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, ISSN 0921-4526, Vol. 404, nr 23-24, 4925-4928 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects following ion irradiation of GaN-based devices are still limited. Here we present data on the photoluminescence (PL) emitted from InGaN/GaN multiple quantum well (MQW) structures, which have been exposed to 40 MeV I ion irradiation. The PL is reduced as a function of applied ion fluence, with essentially no PL signal left above 1011 ions/cm2. It is observed that even the ion fluences in the 109 ions/cm2 range have a pronounced effect on the photoluminescence properties of the MQW structures. This may have consequences concerning application of InGaN/GaN MQW’s in radiation-rich environments, in addition to defect build-up during ion beam analysis.

  • 49.
    Alippi, Paola
    et al.
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Lanzilotto, Valeria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik. CNR IOM, Lab Nazl TASC, C Area Sci Pk SS14 Km 163-5, I-34129 Trieste, Italy.;Univ Trieste, Dept Phys, Via Valerio 2, I-34127 Trieste, Italy..
    Paoletti, Anna Maria
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Mattioli, Giuseppe
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Zanotti, Gloria
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Pennesi, Giovanna
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Filippone, Francesco
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Cossaro, Albano
    CNR IOM, Lab Nazl TASC, C Area Sci Pk SS14 Km 163-5, I-34129 Trieste, Italy..
    Verdini, Alberto
    CNR IOM, Lab Nazl TASC, C Area Sci Pk SS14 Km 163-5, I-34129 Trieste, Italy..
    Morgante, Alberto
    CNR IOM, Lab Nazl TASC, C Area Sci Pk SS14 Km 163-5, I-34129 Trieste, Italy.;Univ Trieste, Dept Phys, Via Valerio 2, I-34127 Trieste, Italy..
    Bonapasta, Aldo Amore
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    A Ru-Ru pair housed in ruthenium phthalocyanine: the role of a "cage" architecture in the molecule coupling with the Ag(111) surface2017Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 2, 1449-1457 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A number of studies have investigated the properties of monomeric and double-decker phthalocyanines (Pcs) adsorbed on metal surfaces, in view of applications in spintronics devices. In a combined experimental and theoretical study, we consider here a different member of the Pcs family, the (RuPc)(2) dimer, whose structure is characterized by two paired up magnetic centers embedded in a double-decker architecture. For (RuPc)(2) on Ag(111), we show that this architecture works as a preserving cage by shielding the Ru-Ru pair from a direct interaction with the surface atoms. In fact, while noticeable surface-to-molecule charge transfer occurs with the ensuing quenching of the molecular magnetic moment, such phenomena occur here in the absence of a direct Ru-Ag coupling or structural rearrangement, at variance with other Pcs and thanks to the above shielding effect. These unique properties of the (RuPc)(2) architecture are expected to permit an easy control of the surface-to-molecule charge-transfer process as well as of the molecular magnetic properties, thus making the (RuPc)(2) dimer a significant paradigm for innovative "cage" structures as well as a promising candidate for applications in spintronics nano or single-molecule devices.

  • 50.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Configurational and Magnetic Interactions in Multicomponent Systems2010Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is a theoretical study of configurational and magnetic interactions in multicomponent solids. These interactions are the projections onto the configurational and magnetic degrees of freedom of the underlying electronic quantum mechanical system, and can be used to model, explain and predict the properties of materials. For example, the interactions govern temperature induced configurational and magnetic order-disorder transitions in Heusler alloys and ternary nitrides.

    In particular three perspectives are studied. The first is how the interactions can be derived from first-principles calculations at relevant physical conditions. The second is their consequences, like the critical temperatures for disordering, obtained with e.g. Monte Carlo simulations. The third is their origin in terms of the underlying electronic structure of the materials.

    Intrinsic defects in the half-Heusler system NiMnSb are studied and it is found that low-energy defects do not destroy the important half-metallic property at low concentrations. Deliberate doping of NiMnSb with 3d-metals is considered and it is found that replacing some Ni with extra Mn or Cr creates new strong magnetic interactions which could be beneficial for applications at elevated temperature. A self-consistent scheme to include the effects of thermal expansion and one-electron excitations in the calculation of the magnetic critical temperature is introduced and applied to a study of Ni1−xCuxMnSb.

    A supercell implementation of the disordered local moments approach is suggested and benchmarked for the treatment of paramagnetic CrN as a disordered magnetic phase. It is found that the orthorhombic-to-cubic phase transition in this nitride can be understood as a first-order magnetic order-disorder transition. The ferromagnetism in Ti1−xCrxN solid solutions, an unusual property in nitrides, is explained in terms of a charge transfer induced change in the Cr-Cr magnetic interactions.

    Cubic Ti1−xAlxN solid solutions displays a complex and concentration dependent phase separation tendency. A unified cluster expansion method is presented that can be used to simulate the configurational thermodynamics of this system. It is shown that short range clustering do influence the free energy of mixing but only slightly change the isostructural phase diagram as compared to mean-field estimates.

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