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  • 101.
    Goss, J.P.
    et al.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Eberlein, T.A.G.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Pinho, N.
    School of Physics, University of Exeter.
    Blumenau, A.T.
    Theoretische Physik, Universität Paderborn.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Electrical and optical properties of rod-like defects in silicon2004In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, no 20, p. 4633-4635Article in journal (Refereed)
    Abstract [en]

    Self-interstitials in silicon can aggregate to form rod-like defects (RLDs) having both electrical and optical activity. We carry out local density functional calculations for both {113} and {111} RLDs to determine their structures and electrical activity. We find that small {113} RLDs are more stable than {111} RLDs but this reverses for larger defects. We attribute the electrical activity of {113} RLDs found in deep level transient spectroscopy studies with the bounding dislocations and the 0.903 eV photoluminescence to vacancy point defects lying on the habit plane.

  • 102.
    Goss, J.P.
    et al.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    The lattice location of Ni in diamond: a theoretical study2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 25, p. 4567-4578Article in journal (Refereed)
    Abstract [en]

    Experiment unambiguously shows substitutional nickel is present in as-grown synthetic diamond where Ni is present in the solvent-catalyst. There is less convincing evidence for the presence of an interstitial species. We present the results of first-principles calculations of the properties of substitutional and interstitial Ni in diamond. The formation energy and mobility of the interstitial species suggest that nickel will be predominantly of the substitutional form. We also present possible models for the trigonal 1.404 eV optical centre correlated with the NIRIM-2 paramagnetic defect.

  • 103.
    Goss, J.P.
    et al.
    School of Physics, University of Exeter.
    Coomer, B.J.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Fall, C.J.
    School of Physics, University of Exeter.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Extended defects in diamond: the interstitial platelet2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 16, p. 165208-1Article in journal (Refereed)
    Abstract [en]

    The structure and properties of the {001} planar platelet in diamond are investigated using ab initio theory. We find that a carbonaceous model, based on a layer of self-interstitials, satisfies the requirements of transmission electron microscopy, infrared absorption data, and energetic considerations. The energetics of self-interstitial production during nitrogen aggregation are considered. It is found that the growth mechanism of the platelet involves a thermally activated release of vacancies from platelets. The role of vacant sites and platelet nitrogen are also investigated and it is shown that these defects embedded within the platelet could account for the observed optical activity.

  • 104.
    Goss, J.P.
    et al.
    University of Exeter.
    Coomer, B.J.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Fall, C.J.
    University of Exeter.
    Latham, Chris
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Small aggregates of interstitials and models for platelets in diamond2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, no 49, p. 10257-10261Article in journal (Refereed)
    Abstract [en]

    By examining the structure of small clusters of self-interstitials in diamond using local-density-functional techniques, we have developed models for the planar defects called platelets. We present the structures, energies and vibrational properties

  • 105.
    Goss, J.P.
    et al.
    School of Physics, University of Exeter.
    Coomer, B.J.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Shaw, T.D.
    Department of Physics, University of Newcastle.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Rayson, Mark
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Self-interstitial aggregation in diamond2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 63, no 19, p. 195208-Article in journal (Refereed)
    Abstract [en]

    First-principles methods are used to investigate the self-interstitial and its aggregates in diamond. The experimental assignment of the spin-1 R2 EPR center to the single interstitial has been questioned because of the small fine-structure term observed. We calculate the spin-spin interaction tensor for the three interstitial defects I1〈001〉, I2NN, and I3 and compare with the experimental D tensors. The results give support for the assignments of the single and di-interstitials to microscopic models and allow us to conclusively identify a recently observed EPR center, O3, with I3. This identification, in turn, suggests a low-energy structure for I4 and a generic model for an extended defect called the platelet. We also determine the optical properties of I1〈001〉 as well as its piezospectroscopic or stress tensor and find these to be in agreement with experiment. Several multi-interstitial defects are found to possess different structural forms which may coexist. We propose that a different form of the charged I2 defect gives rise to the 3H optical peak. Several structures of the platelet are considered, and we find that the lowest-energy model is consistent with microscopic and infrared studies.

  • 106.
    Goss, J.P.
    et al.
    School of Physics, University of Exeter.
    Coomer, B.J.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Shaw, T.D.
    Department of Physics, University of Newcastle.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Interstitial aggregates in diamond2001In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 10, no 3, p. 434-438Article in journal (Refereed)
    Abstract [en]

    Theoretical modelling of magnetic resonance signals lead to convincing models for the first three self-interstitial aggregates in diamond. These in turn suggest the manner in which larger more stable aggregates including the platelet, observed in annealed type I diamonds, are formed.

  • 107.
    Goss, J.P.
    et al.
    School of Physics, University of Exeter.
    Eberlein, T.A.G.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Pinho, N.
    School of Physics, University of Exeter.
    Blumenau, A.T.
    Theoretische Physik, Universität Paderborn.
    Frauenheim, T.
    Theoretische Physik, Universität Paderborn.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Planar interstitial aggregates in Si2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 48, p. 12843-12853Article in journal (Refereed)
    Abstract [en]

    Self-interstitials in silicon aggregate to form rod-like defects aligned along [110] directions and inhabiting either {111} or {113} crystallographic planes. These systems are known to be electrically and optically active. We present the results of first-principles calculations on the structure and energetics for candidate structures contained within the {113}, {111} and {001} planes and compare the results with experiment.

  • 108.
    Goss, J.P.
    et al.
    School of Physics, University of Exeter.
    Hahn, I.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Vibrational modes and electronic properties of nitrogen defects in silicon2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 4, p. 45206-1Article in journal (Refereed)
    Abstract [en]

    Nitrogen impurities form complexes with native defects such as vacancies and self-interstitials in silicon which are stable to high temperatures. These complexes can then suppress the formation of large vacancy and self-interstitial clusters. However, there is little known about their properties. We use first-principles density-functional theory to the determine the local vibrational modes, electrical levels and stability of a range of nitrogen-interstitial and vacancy complexes. Tentative assignments of the ABC photoluminescence line and the trigonal SL6 EPR center are made to substitutional-nitrogen pair and the substitutional-nitrogen-vacancy complex.

  • 109.
    Goss, J.P.
    et al.
    School of Physical Sciences, Dublin City University.
    Jones, R.
    Department of Physics, University of Exeter.
    Breuer, S.J.
    Edinburgh Parallel Computing Centre, University of Edinburgh.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    A first principles study of interstitial Si in diamond1997In: Defects in Semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, p. 781-786Conference paper (Other academic)
    Abstract [en]

    The results of first principles calculations using AIMPRO (a local-density-functional code) are presented to describe the stability of interstitial Si in diamond. It is found that the 〈100〉 and 〈110〉 split-interstitial configurations are only local minima in the total energy surface. Td interstitial Si reconstructs to form a substitutional Si site close to a self-interstitial. The difference in total energy between the split configuration and the substitutional-Si-self-interstitial complex is more than 6 eV. It is concluded that Si would not adopt an interstitial location in diamond as has been previously suggested from experimental evidence. Interestingly the self-interstitial remains bound to the substitutional Si with a binding energy around 1 eV.

  • 110.
    Goss, J.P.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Heggie, M.I.
    CPES, University of Sussex, Falmer, Brighton.
    Ewels, C.P.
    CPES, University of Sussex, Falmer, Brighton.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    First principles studies of H in diamond2001In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 186, no 2, p. 263-8Article in journal (Refereed)
    Abstract [en]

    Ab initio methods are used to investigate hydrogen defects in diamond. For the isolated impurity, the bond-centered site is found lowest in energy and posses both donor and acceptor levels. The neutral defect possesses a single local mode with very small infrared effective charge, but the effective charge for the negative charge state is much larger. H+ is calculated to be very mobile with a low activation barrier. Hydrogen dimers are stable as H*2 defects which are also found to be almost IR-inactive. The complex between B and H is investigated and the activation energy for the reaction B-H → B - + H+ found to be in rasonable agreement with experiment. Hydrogen is strongly bound to dislocations which, together with H*2, may form part of the hydrogen accumulation layer detected in some plasma studies.

  • 111.
    Goss, J.P.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Heggie, M.I.
    CPES, University of Sussex, Falmer, Brighton.
    Ewels, C.P.
    CPES, University of Sussex, Falmer, Brighton.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Theory of hydrogen in diamond2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 11, p. 115207-Article in journal (Refereed)
    Abstract [en]

    Ab initio cluster and supercell methods are used to investigate the local geometry and optical properties of hydrogen defects in diamond. For an isolated impurity, the bond-centered site is found to be lowest in energy, and to possess both donor and acceptor levels. The neutral defect possesses a single local mode with a very small infrared effective charge, but the effective charge for the negative charge state is much larger. H+ is calculated to be very mobile with a low activation barrier. Hydrogen dimers are stable as H2* defects, which are also found to be almost IR inactive. The complex between B and H is investigated and the activation energy for the reaction B-H→B-+H+ found to be around 1.8 eV in agreement with experiment. We also investigate complexes of hydrogen with phosphorus and nitrogen. The binding energy of H with P is too low to lead to a significant codoping effect. A hydrogen-related vibrational mode of the N-H defect, and its isotopic shifts, are close to the commonly observed 3107-cm-1 line, and we tentatively assign this center to the defect. Hydrogen is strongly bound to dislocations which, together with H2*, may form part of the hydrogen accumulation layer detected in some plasma studies.

  • 112.
    Goss, J.P.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    (CAs)2-hydrogen defects in GaAs: a first-principles study1997In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 55, no 23, p. 15576-15580Article in journal (Refereed)
    Abstract [en]

    Hydrogen-related local vibrational modes at 2643, 2651, 2688, 2725, 2729, and 2775 cm-1 are thought to arise from C-H stretch modes from defects similar to the hydrogen-passivated carbon acceptor complex CAsH. These lines appear in samples that are grown using trimethylgallium metalorganic precursors, and it has been suggested that the 2688-, 2725-, 2729-, and 2775-cm-1 bands may be due to CAs dimers decorated with one or more H atoms. We present here the structures, energies, and vibrational modes of (CAs)2, (CAs)2H, and (CAs)2H2 complexes obtained from ab initio local-density-functional cluster calculations to investigate these assignments.

  • 113.
    Gowda, Vasantha
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Larsson, Anna-Carin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Lantto, P.
    University of Oulu.
    Telkki, V-V
    University of Oulu.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Structural investigations of rare earth dialkyl dithiocarbamate complexes: solid-state NMR, X-ray diffraction and DFT calculation studies2013Conference paper (Other academic)
    Abstract [en]

    In this study, we made an attempt to qualitatively study the structures of few rare earth metal complexes by employing solid state NMR, X-Ray Diffraction, and preliminary DFT calculations. High resolution 13C and 15N solid state CP/MAS NMR spectra were recorded for six diamagnetic polycrystalline rare earth dialkyldithiocarbamates of the general formula [(RE2S2CNR2)3 PHEN] (where RE=La or Y, R=C2H5, C3H7, and i-C3H7) [1]. Different isotropic 13C and 15N chemical shifts for the three dialkyldithiocarbamato groups were observed. Regulacio et al. (2005) inferred that irrespective of the alkyl chains, rare earth complexes of dialkyldithiocarbamates and phenanthroline (3:1) ligands always crystallize in a monoclinic system with a space P21/c group. However, comparative analysis of solid state 13C/15N CPMAS spectra of polycrystalline yttrium and lanthanum diethyldithiocarbamate complexes shows the presence of significant differences, indicating structural variations of these complexes. Also, quite different X-Ray diffraction powder pattern was observed for the above two complexes. Finally, the computational geometry optimization of Y and La complexes, followed by the preliminary calculation of 13C and 15N chemical shifts and shielding contributions with the ADF program [2], found to be very near to the experimental results.

  • 114.
    Gowda, Vasantha
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Sarma, Bipul
    Department of Chemical Sciences, Division of Chemical Engineering, Tezpur University, Tezpur, Assam.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Telkki, Ville-Veikko
    University of Oulu, NMR Research Group, Division of Chemical Engineering, Faculty of Science, University of Oulu.
    Larsson, Anna-Carin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Lantto, Perttu
    University of Oulu, NMR Research Group, Division of Chemical Engineering, Faculty of Science, University of Oulu.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Structure Elucidation of an Yttrium Diethyldithiocarbamato-Phenanthroline Complex by X-ray Crystallography, Solid-State NMR, and ab-initio Quantum Chemical Calculations2016In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, Vol. 20, p. 3278-3291Article in journal (Refereed)
    Abstract [en]

    We present a structural analysis method for molecular and electronic structure of yttrium diethyldithiocarbamato-phenanthroline complex {[Y(S2CNR2)3PHEN] with R = C2H5 and PHEN = 1,10-phenanthroline} combining solid-state NMR spectroscopy, XRD, and first principles DFT calculations. Replacing the Nd3+ ion with Y3+ in the reported crystal structure of [Nd(S2CNR2)3PHEN] complex generated an approximate 3D structure of the title complex. The structure was then subjected to first principles quantum chemical geometry optimisation using periodic DFT method. The quality of the method is discussed by comparing predicted and experimental powder XRD patterns. Full assignment of 13C and 15N solid-state CP-MAS NMR spectra as well as analyses of the principal values of the chemical shift tensors were carried out using periodic scalar relativistic DFT modelling. Spin-orbit relativistic effects, estimated by SO-ZORA formalism for one molecular unit, were evaluated. Finally, the X-ray structure of the title complex was determined, which proved that the former procedure is appropriate. The most important orbital interactions were investigated by Natural Bond Orbital analysis. The isotropic shielding values for S2CN-carbons were analysed by Natural Localised Molecular Orbital analysis. The present approach can be further extended to study other rare earth metal complexes, particularly those having similar but not yet solved crystal structures

  • 115.
    Gutiérrez, R.
    et al.
    Technische Universität, Theoretische Physik III, D-09107 Chemnitz.
    Haugk, M.
    Technische Universität, Theoretische Physik III, D-09107 Chemnitz.
    Frauenheim, Th.
    Technische Universität, Theoretische Physik III, D-09107 Chemnitz.
    Elsner, J.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Heggie, M.I.
    CPES, University of Sussex, Falmer, Brighton.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    The formation of nanopipes caused by donor impurities in GaN1999In: Philosophical Magazine Letters, ISSN 0950-0839, E-ISSN 1362-3036, Vol. 79, no 2-3, p. 147-152Article in journal (Refereed)
    Abstract [en]

    Local density-functional methods are used to examine the behaviour of O and O-related defect complexes at {1010}-type surfaces in GaN. We find that O has a tendency to segregate to the (1010) surface and we identify the gallium vacancy surrounded by three oxygen impurities (VGa-(ON)3) to be a particularly stable and electrically inert complex. We suggest that these complexes impede growth at the walls of the nanopipes preventing them from growing in. Also, other donor-related defect complexes, in particular gallium vacancies surrounded by three silicon atoms as second nearest neighbours, are expected to have the same effect.

  • 116.
    Hedlund, Jonas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Korelskiy, Danil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Rayson, Mark
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, Patrick R.
    School of Electrical, Electronic and Computer Engineering, University of Newcastle upon Tyne.
    Mass transport in porous media from first principles: an experimental and theoretical study2012In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 415-416, p. 271-277Article in journal (Refereed)
    Abstract [en]

    In the present work, the mass transport of helium through zeolite is experimentally determined by measuring the flow of helium through a zeolite membrane. By using a mathematical model, the mass transport through defects was accounted for to arrive at mass transport through zeolite pores. For the first time, we could thereby experimentally show that the mass transport of helium in zeolite pores is strongly controlled by the amount and location of hydrocarbons in the zeolite pores and varies several orders of magnitude. The mass transport of helium in ZSM-5 zeolite pores is first reduced gradually more than one order of magnitude when the loading of n-hexane is increased from 0 to 47% of saturation. As the loading of n-hexane is further increased to 54% of saturation, the mass transport of helium in the zeolite pores is further reduced abruptly by more than two orders of magnitude. This gradual decrease followed by an abrupt decrease of mass transport is caused by adsorption of n-hexane in the zeolite pores. In a similar yet different fashion, the mass transport of helium in the zeolite pores is reduced abruptly by almost two orders of magnitude when the loading of benzene is increased from 0 to 19% of saturation due to adsorption of benzene in the pore intersections. Effective medium approximation percolation models with parameters estimated using density functional theory employing the local density approximation, i.e. models with no adjustable parameters and the most sophisticated theory yet applied to this system, can adequately describe the experimental observations.

  • 117.
    Heikkinen, Olli
    et al.
    Department of Applied Physics, Aalto University School of Science.
    Pinto, H.
    School of Physics, University of Exeter, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Department of Physics, University of Minho, Campus de Gualtar, 4710-553 Braga, Hungarian Academy of Sciences, Wigner Research Centre for Physics, Institute for Solid State Physics and Optics, COMP Centre of Excellence, Department of Applied Physics, Aalto University School of Science.
    Sinha, Godhuli
    Department of Applied Physics, Aalto University School of Science.
    Hämäläinen, Sampsa K.
    Department of Applied Physics, Aalto University School of Science.
    Sainio, Jani P.
    Department of Applied Physics, Aalto University School of Science.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Briddon, Patrick R.
    Department of Physics, University of Newcastle, School of Electrical, Electronic and Computer Engineering, University of Newcastle upon Tyne, School of Natural Science, University of Newcastle upon Tyne.
    Foster, Adam S.
    COMP Centre of Excellence, Department of Applied Physics, Aalto University School of Science.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science.
    Characterization of a Hexagonal Phosphorus Adlayer on Platinum (111)2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 22, p. 12291-12297Article in journal (Refereed)
    Abstract [en]

    Platinum is a well-known catalytic metal whose efficiency can be degraded by the adsorption of impurities. Using different characterization techniques, such as scanning tunnelling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy, we present a study of phosphorus adsorption on a platinum (111) surface. Under saturation and after annealing at 750 °C, phosphorus was observed to form an ordered hexagonal adlayer with a (4√3 × 4√3)-R30° symmetry. On the basis of density functional theory calculations, we propose a model for the phosphorus adlayer, consisting of either P13 or P14 clusters. In addition, carbon monoxide adsorption as a function of the phosphorus coverage was also investigated. We found that the phosphorus adlayer prevents carbon monoxide adsorption on Pt(111) reducing its catalytic efficiency. (Figure Presented

  • 118. Hellström, Pär
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    An ab initio study of ethyl xanthate adsorbed on Ge(111) surfaces2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 45, p. 16920-16926Article in journal (Refereed)
    Abstract [en]

    The interaction between adsorbed ethyl xanthate on a clean Ge(111) surface and a hydroxylated surface was studied, using first-principle density functional theory. Geometrically optimized structures are presented and discussed. Results suggest a bidentate bridging conformation on a clean Ge(111) surface, whereas a monodentate bonding is preferred when the surface is saturated by hydrogen atoms. Then the interaction with a hydroxylated surface was considered. The lowest energy configuration was obtained when xanthate binds with one sulfur to the surface and with the other to an OH group adsorbed on the surface. A marker for this configuration was found in the vibrational spectra at 3200 cm-1. Vibrational frequencies down to 250 cm-1 were calculated and assigned to vibrational modes and presented together with the calculated infrared spectra. The tilt angle of the hydrocarbon chain was also investigated.

  • 119. Hellström, Pär
    et al.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Fredriksson, Andreas
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A theoretical and experimental study of vibrational properties of alkyl xanthates2006In: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy, ISSN 1386-1425, E-ISSN 1873-3557, Vol. 65, no 3-4, p. 887-895Article in journal (Refereed)
    Abstract [en]

    Geometrical structure and vibrational modes of potassium and sodium ethyl/heptyl xanthates were studied, using both theoretical and experimental methods. Both Hartree-Fock and density functional theory were used. The experimental method used was infrared absorption spectroscopy (FTIR). Our work showed that vibrational frequencies calculated with density functional theory, using the local density approximation, are in very good agreement with experiments. The results were not improved by using the more sophisticated and computationally demanding B3LYP functional.

  • 120. Hoffmann, L
    et al.
    Bach, J C
    Nielsen, B Bech
    Leary, P
    Jones, R
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Erratum: Substitutional carbon in germanium [Phys. Rev. B 55, 11 167 (1997)]1997In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 56, no 13, p. 8434-8434Article in journal (Other academic)
  • 121.
    Hoffmann, L
    et al.
    Aarhus University.
    Bach, J C
    Aarhus University.
    Nielsen, B Bech
    Aarhus University.
    Leary, P
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Substitutional carbon in germanium1997In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 55, no 17, p. 11167-11173Article in journal (Refereed)
    Abstract [en]

    Carbon impurities implanted into single-crystalline germanium are studied with infrared absorption spectroscopy and ion channeling. After implantation of 12C+ at room temperature and subsequent annealing at 350 °C, a sharp infrared absorption line is observed at 531 cm-1. When 12C+ is substituted by 13C+, the line shifts down in frequency to 512 cm-1 and co-implantation of 12C+ and 13C+ does not give rise to additional lines. Therefore, the 531-cm-1 line represents a local vibrational mode of a defect containing a single carbon atom. Channeling measurements are carried out around the 〈100〉, 〈110〉, and 〈111〉 axes in 12C+-implanted samples annealed at 450 °C. The analysis of the data shows that 31±3 % of the carbon atoms are located at substitutional sites, while the remaining carbon atoms appear to be located randomly. The population of the substitutional site and the intensity of the 531-cm-1 mode have identical temperature dependencies. It is concluded that the 531-cm-1 mode is the three-dimensional T2 stretch mode of substitutional carbon. The effective charge of the mode is determined to be (3.4±0.5)e.mAb initio local density functional cluster theory is applied to calculate the structure and the local vibrational modes of substitutional carbon in germanium. The calculated frequencies and isotope shifts for the T2 stretch mode are in good agreement with the observations.

  • 122.
    Hoffmann, L.
    et al.
    Institute of Physics and Astronomy, University of Aarhus.
    Bach, J.C.
    Institute of Physics and Astronomy, University of Aarhus.
    Hansen, J. Lundsgaard
    Institute of Physics and Astronomy, University of Aarhus.
    Larsen, A. Nylandsted
    Institute of Physics and Astronomy, University of Aarhus.
    Nielsen, B. Bech
    Institute of Physics and Astronomy, University of Aarhus.
    Leary, P.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Substitutional carbon in Ge and Si1-xGex1997In: Defects in semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, p. 97-102Conference paper (Refereed)
    Abstract [en]

    In the present work, carbon is implanted into monocrystalline Ge and into relaxed epitaxial MBE-grown Si1-xGex. The samples are studied with infrared absorption spectroscopy along with ion-channeling studies on the Ge samples. Finally, ab-initio local density functional cluster theory is applied to calculate the structure and the local vibrational modes of substitutional carbon, Cs, in Ge. After implantation of 12C+ in Ge at room temperature and subsequent annealing at 350°C, a sharp absorption line is observed at 531 cm-1. By isotope substitution, it is concluded that the 531 cm-1 line represents a local vibrational mode of a single carbon atom. From ion-channeling measurements on samples annealed at 450°C, it is found that 31±3 % of the carbon atoms are located at substitutional sites. The population of the substitutional site and the intensity of the 531 cm-1 mode have identical annealing behavior and it is concluded that the 531 cm-1 mode is the three-dimensional T2 stretch mode of Cs in Ge. The calculated frequency and isotope shift for this mode are in good agreement with the observations. In Si0.65Ge0.35, two broad absorption lines are observed at ∼551 and ∼592 cm-1 after implantation of 12C+ and subsequent annealing at 550°C. From measurements on samples implanted with 13C+ and coimplanted with 12C+ and 13C+ we conclude that these lines represent local vibrational modes of defects containing a single carbon atom. In 13C+ implanted Si1-xGex samples that contain 15 to 50 % Ge a number of modes are observed in a frequency range from ∼510 to ∼610 cm-1, i.e., in the range of Cs in Ge and in Si. From the experimental findings it is concluded that substitutional carbon in Si1-xGex binds to both Si and Ge.

  • 123.
    Hoffmann, L
    et al.
    Aarhus University.
    Lavrov, E V
    Aarhus University.
    Nielsen, B Bech
    Aarhus University.
    Hourahine, B
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Weakly bound carbon-hydrogen complex in silicon2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 24, p. 16659-16666Article in journal (Refereed)
    Abstract [en]

    Local vibrational modes of a weakly bound carbon-hydrogen complex in silicon have been identified with infrared-absorption spectroscopy. After implantation of protons at ∼20 K and subsequent annealing at 180 K, two carbon modes at 596 and 661 cm-1, and one hydrogen mode at 1885 cm-1 are observed. The three modes originate from the same complex, which is identified as bond-centered hydrogen in the vicinity of a nearby substitutional carbon atom. Ab initio theory has been applied to calculate the structure and local modes of carbon-hydrogen complexes with hydrogen located at the first, second, and third nearest bond-center site to substitutional carbon. The results support our assignment.

  • 124.
    Hoffmann, L
    et al.
    Aarhus University.
    Nielsen, B Bech
    Aarhus University.
    Larsen, A Nylandsted
    Aarhus University.
    Leary, P
    University of Exeter.
    Jones, R
    University of Exeter.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Substitutional carbon in Si1-xGex1999In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 60, no 19, p. 13573-13581Article in journal (Refereed)
    Abstract [en]

    Local vibrational modes of carbon impurities in relaxed Si1-xGex have been studied with infrared absorption spectroscopy in the composition range 0.05<~x<~0.50. Carbon modes with frequencies in the range 512-600 cm-1 are observed in 13C+-implanted Si1-xGex after annealing at 550 °C. Measurements on samples coimplanted with 12C+ and 13C+ show that these modes originate from defects containing a single carbon atom and from the variation of the mode frequencies with composition x, the modes are assigned to substitutional carbon in Si1-xGex. Based on the frequencies obtained from a simple vibrational model, the observed modes are assigned to specific combinations of the four Si and Ge neighbors to the carbon. The intensities of the modes indicate that the combination of the four neighbors deviates from a random distribution. Ab initio local-density-functional cluster theory has been applied to calculate the structure and the local mode frequencies of substitutional carbon with n Ge and 4-n Si neighbors in a Si and a Ge cluster. The calculated frequencies are ∼9% higher than those observed, but the ordering and the splitting of the mode frequencies agree with our assignments.

  • 125.
    Holbech, J D
    et al.
    University of Aarhus.
    Nielsen, B Bech
    University of Aarhus.
    Jones, R
    University of Exeter.
    Stich, S
    University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    H2* defect in crystalline silicon1993In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 71, no 6, p. 875-878Article in journal (Refereed)
    Abstract [en]

    Detailed infrared studies have been carried out on proton- and deuteron-implanted Si. A dominant trigonal defect involving a pair of inequivalent hydrogen atoms has been identified, with local modes at 2061.5, 1838.3, 1599.1, and 817.2 cm-1. The structure, the local modes, and the isotopic shifts of the H2* defect have been calculated using ab initio pseudopotential cluster theory. The structure is consistent with channeling and uniaxial stress experiments. The calculated frequencies and isotopic shifts are in close agreement with those observed.

  • 126.
    Hounsome, L.S.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Martineau, P.M.
    DTC, Maidenhead.
    Fisher, D.
    DTC, Maidenhead.
    Shaw, M.J.
    Centre, School of Natural Science, Newcastle upon Tyne.
    Briddon, P.R.
    Centre, School of Natural Science, Newcastle upon Tyne.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Origin of brown coloration in diamond2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 12, p. 125203-1Article in journal (Refereed)
    Abstract [en]

    Measurements of the absorption spectra of brown natural type IIa diamond as well as brown nitrogen-doped CVD diamond are reported. These are largely featureless and increase almost monotonically from about 1-5.5 eV. It is argued that the brown coloration is due to an extended defect and not to a point defect. First principles modeling studies demonstrate that the spectra could be attributed to vacancy disks lying on {111} planes. Such disks are unstable above about 200 vacancies and should relax to dislocation loops in natural diamond. Hydrogen is shown to passivate the optical activity of the disks.

  • 127.
    Hounsome, L.S.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Martineau, P.M.
    DTC, Maidenhead.
    Fisher, D.
    DTC, Maidenhead.
    Shaw, M.J.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Role of extended defects in brown colouration of diamond2007In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 4, no 8, p. 2950-2957Article in journal (Refereed)
    Abstract [en]

    The absorption spectrum of brown diamond is broad and featureless, in both natural type IIa and CVD-grown material. It is argued that such an absorption is due to an extended, rather than a point, defect. Ab-initio modelling studies have been conducted on dislocations and extended vacancy-related defects. While certain dislocations could potentially explain the origin of colour, their density is too low to account for experimentally observed absorption magnitudes. It is demonstrated that a vacancy disk lying in the {111} plane has an absorption spectrum similar to that seen in natural and CVD brown diamond. Such disks are unstable above about 200 vacancies and should relax to dislocation loops in natural diamond. Hydrogen is shown to passivate the optical activity of the disks.

  • 128.
    Hounsome, L.S.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Martineau, P.M.
    DTC, Maidenhead.
    Shaw, M.J.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Blumenau, A.T.
    Max-Planck-Institut für Eisenforschung GmbH.
    Fujita, N.
    School of Physics, University of Exeter.
    Optical properties of vacancy related defects in diamond2005In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 202, no 11, p. 2182-2187Article in journal (Refereed)
    Abstract [en]

    ‹110› vacancy chains, multi-vacancy clusters and vacancy discs have been modeled using density functional theory within the AIMPRO and DFTB codes. While a connection can be established between the results on vacancy chains and previous EPR experiments, no connection can be made between the point defects and the optical properties of natural type IIa brown diamonds. However, a vacancy disc consisting of a {111} double plane of vacancies is stable and possesses an absorption spectrum similar to that found in brown diamonds.

  • 129.
    Hourahine, B
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Safonov, A N
    University of Durham.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Estreicher, S K
    Texas Tech University.
    Identification of the hexavacancy in silicon with the B804 optical center2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 19, p. 12594-12597Article in journal (Refereed)
    Abstract [en]

    The ring hexavacancy (V6) has been found by previous theoretical modeling to be a particularly stable defect, but it has not been identified with any observed center to date. Here, we use ab initio calculations to derive the structure and properties of two forms of V6H2 and identify these defects with the trigonal optical centers B41 and B711, which are known to contain two hydrogen atoms in equivalent and inequivalent sites, respectively. It follows from the calculations that V6 should also be optically active and we identify it with the B804 (J line) center. This allows us to place the acceptor level of V6 at Ec-0.04 eV.

  • 130.
    Hourahine, B.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Safonov, A.N.
    Department of Physics, University of Durham.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Estreicher, S.K.
    Department of Physics, Texas Tech University, Lubbock.
    Optically active hydrogen dimers in silicon1999In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 273-274, p. 176-179Article in journal (Refereed)
    Abstract [en]

    First-principles calculations are used to explore the structure and properties of several defects which are prominent luminescent centers in Si. The trigonal defects B41 and B711, which are known to contain two hydrogen atoms in equivalent and inequivalent sites, respectively, are attributed to a hexavacancy containing two H atoms in different configurations. It is suggested that the J luminescence centers arises from a stable hexavacancy without hydrogen atoms

  • 131.
    Hourahine, B.
    et al.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Anomalous shift of the 1075 cm-1 oxygen-hydrogen defect in silicon1997In: Defects in semiconductors: : proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, p. 277-282Conference paper (Refereed)
    Abstract [en]

    First principles calculations are carried out on i) hydrogen and ii) water molecules trapped near an interstitial oxygen atom in Si. We find that it is possible for these molecules to cause an upward shift in the antisymmetric stretch mode of Oi when H is replaced by D, which could explain the anomalous shift in the 1075 cm-1 O-H related local vibrational mode. Both these molecules lead to modes in the 3500-4000 cm-1 region but those of the H2 lie close to those recently detected using Fourier transform infra-red spectroscopy.

  • 132.
    Hourahine, B
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Self-interstitial-hydrogen complexes in silicon1999In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 59, no 24, p. 15729-15732Article in journal (Refereed)
    Abstract [en]

    The vibrational properties of interstitial silane (SiH4)i and silyl (SiH3)i molecules in crystalline silicon are calculated using a first-principle, cluster-based, spin-polarized local-density method. The Si-H stretch modes are found to be redshifted by ∼300 cm-1 from those of the isolated molecule, which lie around 2200 cm-1. These results refute recent suggestions that modes observed around 2200 cm-1, and previously assigned to hydrogenated vacancy defects, are due to these interstitial molecules.

  • 133.
    Hourahine, B.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Molecular hydrogen traps within silicon1998In: E-MRS Meeting, European Materials Research Society , 1998Conference paper (Refereed)
    Abstract [en]

    We present the results of rst principle calculations on the behaviour of molecular hydrogen within crystalline silicon, both as an isolated species, and within defects in the material. These results are compared with recent experimental infra-red and Raman data obtained for silicon treated by either hydrogen plasma or soaked in hydrogen gas. The effect of Fermi level position on the diffusion barrier of molecular hydrogen within silicon is also discussed.

  • 134.
    Hourahine, B.
    et al.
    Department of Physics, University of Exeter.
    Jones, r.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Molecular hydrogen traps within silicon1999In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 58, no 1-2, p. 24-25Article in journal (Refereed)
    Abstract [en]

    We present the results of first principle calculations on the behaviour of molecular hydrogen within crystalline silicon, both as an isolated species, and within defects in the material. These results are compared with recent experimental infra-red and Raman data obtained for silicon treated by either hydrogen plasma or soaked in hydrogen gas. The effect of Fermi-level position on the diffusion barrier of molecular hydrogen within silicon is also discussed

  • 135.
    Hourahine, B.
    et al.
    Department of Physics, Universität Paderborn.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Frauenheim, T.
    Department of Physics, Universität Paderborn.
    Germanium-hydrogen pairs in silicon2003In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 15, no 39, p. S2803-S2807Article in journal (Refereed)
    Abstract [en]

    Hydrogen in a dilute SiGe alloy is considered theoretically in comparison with hydrogen in Si and Ge. Structural, vibrational and electronic properties of crystalline alloys containing ~1.6 at.% Ge complexed with single hydrogen atoms are considered. The behaviour of bond-centred hydrogen is found to be weakly perturbed, when compared to hydrogen in pure Si.

  • 136.
    Hourahine, B.
    et al.
    Theoretische Physik, Universität Paderborn.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Frauenheim, T.
    Theoretische Physik, Universität Paderborn.
    Platinum and gold dihydrides in silicon2003In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 340, p. 668-72Article in journal (Refereed)
    Abstract [en]

    The structural, electronic and vibrational properties of single substitutional platinum or gold atoms complexed with two hydrogen atoms in silicon are considered on the basis of local density functional theory. The calculated behaviour of these centres is compared with experimental results from infrared absorption and deep-level transient spectroscopy. In contrast with suggestions in the literature, based on hyperfine parameters of electron-paramagnetic resonance, we suggest that such complexes possess direct metal-H bonding.

  • 137.
    Hourahine, B.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Markevich, V.P.
    Centre for Electronic Materials, University of Manchester.
    Newman, R.C.
    Blacket Laboratory, Department of Physics, Imperial College, London.
    Hermansson, J.
    Department of Physics, University of Lund.
    Kleverman, M.
    Department of Physics, University of Lund.
    Lindström, J.L.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Murin, L.I.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Fukata, N.
    Institute of Materials Research, Tohoku University, Sendai.
    Suezawa, M.
    Institute of Materials Research, Tohoku University, Sendai.
    Evidence for H2* trapped by carbon impurities in silicon2001In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 308, p. 197-201Article in journal (Refereed)
    Abstract [en]

    Local mode spectroscopy and ab initio modelling are used to investigate two trigonal defects found in carbon-rich Si into which H had been in-diffused. Isotopic shifts with D and 13C are reported along with the effect of uniaxial stress. Ab initio modelling studies suggest that the two defects are two forms of the CH2* complex where one of the two hydrogen atoms lies at an anti-bonding site attached to C or Si, respectively. The two structures are nearly degenerate and possess vibrational modes in good agreement with those observed.

  • 138.
    Hourahine, B
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Newman, R C
    Imperial College London.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Roduner, E
    Institut für Physikalische Chemie, Stuttgart.
    Hydrogen molecules in silicon located at interstitial sites and trapped in voids1998In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 57, no 20, p. 12666-12669Article in journal (Refereed)
    Abstract [en]

    The vibrational modes of H2 molecules in Si are found using a first-principles method and compared with recent experimental investigations. The isolated molecule is found to lie at a Td interstitial site, oriented along [011] and is infrared active. The rotational barrier is at least 0.17 eV. The molecular frequency is a sensitive function of cage size and increases to lie close to the gas value for cages about 50% larger than the Td site. It is suggested that Raman-active modes around 4158 cm-1 are due to molecules within voids.

  • 139.
    Iwata, H.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    A new type of quantum wells: stacking faults in silicon carbide2003In: Microelectronics Journal, ISSN 0959-8324, Vol. 34, no 5, p. 371-374Article in journal (Refereed)
    Abstract [en]

    We report on a new type of quantum wells with the width as thin as 10 Å, which are composed of SiC only, and consequently have ideal interfaces. These quantum wells are actually stacking faults in SiC. Certain types of stacking faults in SiC polytypes create small 3C-like regions, where the stacking sequences along the c-axis become locally cubic in the hexagonal host crystals. Since the conduction band offsets between the cubic and hexagonal polytypes are very large with the conduction band minima of 3C-SiC lower than that of the other polytypes, such thin 3C inclusions can introduce locally lower conduction bands, thus acting as quantum films perpendicular to the c-axis. One mechanism for the occurrence of stacking faults in the perfect SiC single crystals is the motion of partial dislocations in the basal planes, the partial dislocations leaving behind stacking fault regions.

  • 140.
    Iwata, H.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Cubic polytype inclusions in 4H-SiC2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, no 3, p. 1577-1585Article in journal (Refereed)
    Abstract [en]

    Multiple stacking faults in 4H-SiC, leading to narrow 3C polytype inclusions along the hexagonal c direction, have been studied using an ab initio supercell approach with 96 atoms per supercell. The number of neighboring stacking faults considered is two, three, and four. The wave functions and the two-dimensional energy bands, located in the band gap and associated with the narrow inclusions, can be reconciled with a planar quantum-well model with quantum-well depth equal to the conduction band offset between 3C- and 4H-SiC. We show that the existence of the electronic dipole moment due to the spontaneous polarization leads to a clear asymmetry of the bound wave functions inside the quantum well, and that the perturbation associated with the change in the dipole moment caused by the 3C-like inclusion accounts for the appearance of very shallow localized states at the valence band edge. We have also calculated the stacking fault energies for successive stacking faults. It is found that the stacking fault energy for two stacking faults in adjacent basal planes is reduced by approximately a factor of 4 relative to that of one isolated stacking fault, indicating that double stacking faults in 4H-SiC could be quite common.

  • 141.
    Iwata, H.
    et al.
    Department of Physics & Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Effective mass of electrons in quantum-well-like stacking-fault gap states in silicon carbide2003In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 433-436, p. 519-522Article in journal (Refereed)
    Abstract [en]

    A first-principles calculation of the effective mass of electrons in quantum-well-like gap states induced by stacking faults and cubic inclusions in 4H- and 6H-SiC is performed, based on the density functional theory in the local density approximation. Our calculated effective electron masses for perfect crystals are in very good agreement with those previously determined both theoretically and experimentally. It has been found that electrons confined in the thin 3C-like regions have clearly heavier effective masses than that in perfect 3C-SiC.

  • 142.
    Iwata, H.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Electronic localization around stacking faults in silicon carbide2002In: Silicon carbide and related materials: ICSCRM2001 : proceedings of the International Conference on Silicon Carbide and Related Materials, Tsukuba, Japan, October 28 - November 2, 2001 / [ed] S. Yoshida, Zürich-Uetikon: Trans Tech Publications Inc., 2002, Vol. 1, p. 529-532Conference paper (Refereed)
    Abstract [en]

    First-principles band structure calculations of all the structurally different stacking faults that can be introduced by glide along the (0001) basal plane in 3C-, 4H-, and 6H-SiC are performed, based on the local-density approximation within the density-functional theory. Our calculations, using supercells containing 96 atoms, have revealed that both types of stacking faults in 4H-SiC and two of the three different SFs in 6H-SiC give rise to quasi-2D energy band states in the band gap at around 0.2 eV below the lowest conduction band, and are electrically active. The corresponding wave functions are strongly localized around the stacking fault plane. These results imply that stacking faults in these SiC polytypes are efficient planar traps for electron capture and responsible for subsequent electron-hole recombination. This can therefore have a profound influence on bipolar SiC technology

  • 143.
    Iwata, H.
    et al.
    Department of Physics, Linköping University.
    Lindefelt, U.
    Department of Physics, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Electronic properties of stacking faults in 15R-SiC2003In: Silicon carbide and related materials: ECSCRM 2002 : proceedings of the 4th European Conference on Silicon Carbide and Related Materials, September 2-5, 2002, Linköping, Sweden, Uetikon-Zuerich: Trans Tech Publications Inc., 2003, p. 531-534Conference paper (Refereed)
    Abstract [en]

    A first-principles calculation of stacking faults in 15R-SiC is reported. All the geometrically distinguishable stacking faults which can be introduced by the glide of partial dislocations in (0001)-basal planes are investigated: there exist as many as five different stacking faults in 15R-SiC. Electronic properties and stacking fault energies of these extended defects are studied based on the density functional theory in the local density approximation. Stacking fault energies are also calculated using the axial next nearest neighbor Ising (ANNNI) model.

  • 144.
    Iwata, H.
    et al.
    Department of Physics & Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Electronic structure of twin boundaries in 3C-SiC, Si and diamond2003In: Silicon carbide and related materials 2002: ECSCRM 2002 ; proceedings of the 4th European Conference on Silicon Carbide and Related Materials, September 2 - 5, 2002, Linköping, Sweden / [ed] Peder Bergman; Erik Janzén, Uetikon-Zuerich: Trans Tech Publications Inc., 2003, p. 527-30Conference paper (Refereed)
    Abstract [en]

    We report on a first-principles band structure calculation of twin boundaries in 3C-SiC, Si, and diamond, based on the density functional theory in the local density approximation. It is found that the electron wave functions belonging to the conduction and valence band edge states in 3C-SiC tend to be localized almost exclusively on different sides of the boundaries, while there is no such feature in Si and diamond. We have interpreted these localization and segregation phenomena as a consequence of the electrostatic field caused by the spontaneous polarization due to the hexagonal symmetry around twin boundaries. A mechanism for the creation of twin boundaries, i.e., propagation of partial dislocations in neighboring basal planes, has been investigated using total energy calculations, and it has been realized that the double-intrinsic-stacking-fault structure in 3C-SiC, coinciding with the extrinsic stacking faults, is much energetically favored.

  • 145.
    Iwata, H.
    et al.
    Department of Physics, Linköping University.
    Lindefelt, U.
    Department of Physics, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Stacking fault - stacking fault interactions and cubic inclusions in 6H-SiC: an ab initio study2003In: Silicon carbide and related materials: ECSCRM 2002 : proceedings of the 4th European Conference on Silicon Carbide and Related Materials, September 2-5, 2002, Linköping, Sweden / [ed] Peder Bergman; Erik Janzén, Uetikon-Zuerich: Trans Tech Publications Inc., 2003, p. 921-924Conference paper (Refereed)
    Abstract [en]

    We report on a first-principles supercell calculation of cubic inclusions in 6H-SiC. Motions of successive partial dislocations having the same Burgers vector in the basal planes can lead to a 3C-like region in the perfect 6H-SiC crystal, which corresponds to multiple stacking faults. We have calculated the electronic structures and the total energies of 6H-SiC crystals containing m stacking faults (m=l-4) in the adjacent basal planes, based on the density functional theory in the local density approximation. It has been found that 3C-like sequences in the 6H-host crystals can act as planar quantum wells, in which conduction band electrons can be confined. The total energy calculations using both the supercell method and the axial next nearest neighbor Ising model (ANNNI) have revealed that the 2nd stacking fault energy in 6H-SiC is about 6 times larger than that of an isolated stacking fault.

  • 146.
    Iwata, H.
    et al.
    Department of Physics & Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Theoretical calculation of stacking fault energies in silicon carbide2002In: Silicon carbide and related materials: ICSCRM2001 : proceedings of the International Conference on Silicon Carbide and Related Materials, Tsukuba, Japan, October 28 - November 2, 2001 / [ed] S. Yoshida, Zürich-Uetikon: Trans Tech Publications Inc., 2002, Vol. 1, p. 439-42Conference paper (Refereed)
    Abstract [en]

    A first-principles calculation of stacking fault energies in 3C-, 4H-, and 6H-SiC, based on the local-density approximation within the density-functional theory, is reported. All the structurally different stacking faults -which can be introduced by glide along the (0001) basal plane are considered. The number of such stacking faults in these polytypes is one, two, and three, respectively. The stacking fault energies are also calculated using the simpler generalized axial next-nearest-neighbor Ising (ANNNI) model. Our calculations confirm that the stacking fault energy of 3C-SiC is negative, and we also find that one of the three types of stacking faults in 6H-SiC has a considerably higher stacking fault energy than the other two types

  • 147.
    Iwata, H.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Theoretical study of cubic polytype inclusions in 4H-SiC2002In: Silicon carbide and related materials: ICSCRM2001 : proceedings of the International Conference on Silicon Carbide and Related Materials 2001, Tsukuba, Japan, October 28 - November 2, 2001 / [ed] S. Yoshida, Zürich-Uetikon: Trans Tech Publications Inc., 2002, Vol. 1, p. 533-6Conference paper (Refereed)
    Abstract [en]

    First-principles density-functional calculations of the band structure and wave functions around narrow 3C-like inclusions in 4H-SiC have been performed. 3C-like inclusions of various thicknesses, corresponding to two, three, and four stacking faults in neighbouring basal planes, have been investigated. The results for the number of bound states in the inclusion, their energies, and wave functions are well described by a simple one-dimensional quantum-well square potential. The quantum-well property of these inclusions suggests that 3C-like regions in 4H-SiC are efficient planar traps for conduction band electrons

  • 148.
    Iwata, H.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Theoretical study of planar defects in silicon carbide2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 48, p. 12733-12740Article in journal (Refereed)
    Abstract [en]

    We report on a theoretical investigation of extended planar defects in 3C-, 4H-, 6H-, and 15R-SiC which can be formed without breaking any bonds, covering a wide range of planar defects: twin boundaries, stacking faults, and polytype inclusions. Their electronic structures have been intensively studied using an ab initio supercell approach based on the density functional theory. Stacking fault energies are also calculated using both the supercell method and the axial next-nearest-neighbour Ising model. We discuss the electronic properties and energies of these defects in terms of the geometrical differences of stacking patterns.

  • 149.
    Iwata, Hisaomi
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, Ulf
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, Patrick R.
    Department of Physics, University of Newcastle.
    Localized electronic states around stacking faults in silicon carbide2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 3, p. 33203-Article in journal (Refereed)
    Abstract [en]

    We report on a first-principles study of all the structurally different stacking faults that can be introduced by glide along the (0001) basal plane in 3C-, 4H-, and 6H-SiC based on the local-density approximation within the density-functional theory. Our band-structure calculations have revealed that both types of stacking faults in 4H-SiC and two of the three different types of stacking faults in 6H-SiC give rise to quasi-two-dimensional energy band states in the band gap at around 0.2 eV below the lowest conduction band, thus being electrically active in n-type material. Although stacking faults, unlike point defects and surfaces, are not associated with broken or chemically perturbed bonds, we find a strong localization, within roughly 10-15 Å perpendicular to the stacking fault plane, of the stacking fault gap state wave functions. We find that this quantum-well-like feature of certain stacking faults in SiC can be understood in terms of the large conduction-band offsets between the cubic and hexagonal polytypes. Recent experimental results give qualitative support to our results.

  • 150.
    Iwata, H.P.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.H.
    Department of Physics, University of Newcastle.
    Effective masses of two-dimensional electron gases around cubic inclusions in hexagonal silicon carbide2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 24, p. 245309-1Article in journal (Refereed)
    Abstract [en]

    The main purpose of this article is to determine the two-dimensional effective mass tensors of electrons confined in thin 3C wells in hexagonal SiC, which is a first step in the understanding of in-plane electron motion in the novel quantum structures. We have performed ab initio band structure calculations, based on the density functional theory in the local density approximation, for single and multiple stacking faults leading to thin 3C-like regions in 4H- and 6H-SiC and deduced electron effective masses for two-dimensional electron gases around the cubic inclusions. We have found that electrons confined in the thin 3C-like layers have clearly heavier effective masses than in the perfect bulk 3C-SiC single crystal.

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