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  • 1. Benyattou, T.
    et al.
    Martin, M.
    Orobtchouk, R.
    Talneau, A.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Mulot, Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Optical Bloch waves studied by near optical field microscopy2005In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 47, p. S72-S75Article in journal (Refereed)
    Abstract [en]

    Photonic bandgap structures are very promising for the integration of optical function at the nanoscale level and particularly 2D structures perforated on a slab waveguide. In this context, photonic crystal waveguides obtained by removing rows of holes in the periodic structure are very interesting. We will present here, results of near field optical microscopy conducted on PCW. With a Fourier transform analysis of the image, we can image the Bloch waves propagating in the waveguide. The results are compared to FDTD simulations and we will show that the images obtained correspond to the electric field. Such result allows us to study the interaction of the optical tip with the electromagnetic field. 2D FDTD simulations of 1D photonic crystal interaction with a SNOM tip is presented. The results obtained confirm that the SNOM signal is mainly related to the electric field.

  • 2. Bevilacqua, R.
    et al.
    Pomp, S.
    Simutkin, V. D.
    Tippawan, U.
    Hayashi, M.
    Hirayama, S.
    Naitou, Y.
    Watanabe, Y.
    Prokofiev, A. V.
    Hjalmarsson, A.
    Andersson, P.
    Blomgren, J.
    Osterlund, M.
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Lecolley, F. -R
    Marie, N.
    Kolozhvari, A.
    Light-Ion Production in the Interaction of 175 MeV Neutrons with Iron and Bismuth2011In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 59, no 2, p. 1701-1704Article in journal (Refereed)
    Abstract [en]

    We have measured double-differential (angle and energy) cross sections for light-ion (p, d, t, (3)He, and a) production in the interaction of quasi-monoenergetic 175 MeV neutrons with iron and bismuth. Measurements have been performed at the The Svedberg Laboratory, Uppsala (Sweden), using the Medley setup which allows low-energy thresholds and wide energy and angular ranges. Medley is a spectrometer system consisting of eight three-element telescopes placed at angles from 20 degrees to 160 degrees, in steps of 20 degrees. Each telescope is composed of two silicon surface barrier detectors and a CsI(Tl) scintillator, to perform particle identification, fully stop the produced light-ions and measure their kinetic energy. The time-of-flight was used to reduce the contribution from the low energy tail in the accepted incident neutron spectrum. We report double-differential production cross sections for protons, deuterons, tritons, (3)He and alpha particles and compare them with model calculations with TALYS-1.2.

  • 3. Choi, Y. W.
    et al.
    Koo, Y. M.
    Kwon, S. K.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Department of Physics and Astronomy, Division of Materials Theory Uppsala University Uppsala Sweden; Wigner Research Center for Physics Institute for Solid State Physics and Optics Budapest Hungary.
    Ordered Phases in Fe-Si Alloys: A First-Principles Study2018In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 72, no 6, p. 737-740Article in journal (Refereed)
    Abstract [en]

    It is known that the formation of ordered phases causes the brittleness of electrical steels. We employed first-principles method in order to examine the possibility of the ordered-phases formation in Fe-Si alloys. It is found that the D03-like ordered configuration is most stable among other atomic configurations in the ferromagnetic state. In the paramagnetic state, for low Si concentration, the stability of the ordered configurations is comparable to that of disordered ones. However, as Si content increases, the B2 ordered phase as well as the D03 phase becomes more stable than the disordered ones. 

  • 4. Hirayama, S.
    et al.
    Watanabe, Y.
    Naitou, Y.
    Andersson, P.
    Bevilacqua, R.
    Gustavsson, C.
    Osterlund, M.
    Pomp, S.
    Simutkin, V.
    Sjostrand, H.
    Hjalmarsson, A.
    Prokofiev, A.
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Tippawan, U.
    Light-ion Production from a Thin Silicon Target Bombarded by 175 MeV Quasi Mono-energetic Neutrons2011In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 59, no 2, p. 1447-1450Article in journal (Refereed)
    Abstract [en]

    Double-differential production yields of light ions (p, d, t, (3)He, and alpha) from a thin silicon target induced by 175 MeV quasi mono-energetic neutrons were measured using the MEDLEY setup at the The Svedberg Laboratory (TSL) in Uppsala in order to benchmark evaluated nuclear data and nuclear reaction models. The MEDLEY is a conventional spectrometer system which consists of eight counter telescopes. Each telescope is composed of two silicon surface barrier detectors as the Delta E detectors and a CsI(Tl) scintillator as the E detector for particle identification. The telescopes are placed at angles from 20 degrees to 160 degrees in steps of 20 degrees. The measured double-differential yields of light ions are compared with PHITS calculations using the following nuclear reaction options: the high-energy nuclear data library (JENDL/HE-2007), the quantum molecular dynamics (QMD) model, and the intra-nuclear cascade (INC) model.

  • 5. Holme, Petter
    Local symmetries in complex networks2007In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 50, no 1, p. 300-303Article in journal (Refereed)
    Abstract [en]

    Symmetry-invariance to certain operators-is a fundamental concept in many branches of physics. We propose ways to measure symmetric properties of vertices, and their surroundings, in networks. To be stable to the randomness inherent in many complex networks, we consider measures that are continuous rather than dichotomous. The main operator we suggest is permutations of paths of a certain length leading out from a vertex. If these paths are more similar (in some sense) than expected, the vertex is a local center of symmetry in the network. We discuss different precise definitions based on this idea and give examples how different symmetry coefficients can be applied to protein interaction networks.

  • 6. Kim, H.
    et al.
    Lee, H.
    Chung, S. J.
    Department of Physics, Korea University.
    Lee, S.
    Cho, Y. J.
    Liu, X.
    Furdyna, J. K.
    Magneto-transport properties of GaMnAs:Si ferromagnetic semiconductors2009In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 55, no 1, p. 304-308Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of a series of GaMnAs:Si ferromagnetic semiconductor films, in which the Mn concentration ranges from 7% to 10%, were investigated by using magneto-transport measurements. The temperature dependence of the resistivity revealed a systematic increase in the Curie temperature (T c) with increasing Mn concentration in the series. Since the T0 of the undoped GaMnAs ferromagnetic semiconductor decreases with increasing Mn concentration above 6%, the observation of a systematic increase of T c with increasing Mn concentration in our GaMnAs:Si series indicates the effectiveness of our counter doping for the incorporation of a a large amount of 7% Mn in the system. The field scan of the planar Hall effect (PHE) showed a typical two-step switching behavior at low temperatures, indicating the presence of a strong cubic anisotropy. The switching fields, however, systematically decreased with increasing Mn concentration in the series. The angular dependences of the switching fields were fitted by using the magnetic free energy and Cowburn's model to obtained the domain pinning energy, which showed systematically smaller values as the Mn concentration of the sample was increased. The temperature dependences of the pinning energies indicated a change in the uniaxial anisotropy from the [110] to the [110] direction with increasing Mn concentration in the series.

  • 7. Kim, T.
    et al.
    Chung, S. J.
    Shin, D. Y.
    Choi, I. S.
    Lee, S.
    Liu, X.
    Furdyna, J. K.
    Strain-engineered magnetic anisotropy of GaMnAs ferromagnetic semiconductors2007In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 50, no 3, p. 829-833Article in journal (Refereed)
    Abstract [en]

    A series of GaMnAs epilayers grown on GaInAs buffer layers have been investigated. The concentrations of Mn in the GaMnAs layer and In in the GaInAs layer were varied in the series, for which the tensile strain condition for the GaMnAs layer are systematically changed. The X-ray measurement provided the lattice constants of the layers, from which the stain of the GaMnAs layer was determined. The magneto-transport data revealed in-plane anisotropy in the GaMnAs sample grown on a GaInAs buffer with a low concentration of In. Such in-plan magnetic anisotropy of the GaMnAs layer continuously changed to a vertical magnetic anisotropy when the tensile strain was increased in the sample grown on the GaInAs buffer with a higher In concentration. This experiment clearly demonstrated that the magnetic anisotropy of GaMnAs could be continuously engineered by using the strain introduced by the GaInAs buffer layers.

  • 8.
    Lee, S.
    et al.
    Department of Physics, Korea University.
    Chung, S. J.
    Department of Physics, Korea University.
    Liu, X.
    Furdyna, J. K.
    Doping effect on the properties of III-V ferromagnetic semiconductor GaMnAs epilayers and their superlattices2005In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 47, no 3, p. 444-447Article in journal (Refereed)
    Abstract [en]

    We present a systematic study on the properties of the ferromagnetic (FM) III-V-based semiconductor GaMnAs, including extrinsically doped GaMnAs: Be and its heterostructures in the form of superlattices. In an attempt to further improve the Curie temperature T c of GaMnAs, we have undertaken a systematic program of extrinsic p-doping of this material. In GaMnAs with low x (x = 0.03), T c is, indeed, seen to increase monotonically with increasing Be doping. We also studied the effect of p-doping of non-magnetic spacer layers on the magnetic properties of GaMnAs/GaAs superlattices (SLs). While Be-doped SLs exhibited relatively robust remanent magnetization and a larger coercivity over a broad temperature range, undoped SLs showed a fast decrease in the remanent magnetization with temperature, and a rather small coercivity. We propose that the observed hardness of the magnetization in SLs with Be-doped GaAs layers is related to the interlayer coupling introduced by the doping of the non-magnetic layers.

  • 9. Lee, S. K.
    et al.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Moon, B. M.
    Electrical characterization of titanium-based ohmic contacts to 4H-Silicon carbide for high-power and high-temperature operation2002In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 40, no 4, p. 572-576Article in journal (Refereed)
    Abstract [en]

    We report on titanium-based ohmic contacts (titanium carbide. titanium tungsten, and titanium) on both highly doped epilayers (n(+) and p(+)) and Al-ion-implanted layers. The TiC contact layer was epitaxially grown on epilayers as well as an Al-ion-implanted layers of 4H-SiC by co-evaporation Ti and C-60 under an ultra-high vacuum condition at low temperature (<500 degreesC). For comparison and long-term stability test, we also deposited TiW (weight ratio 30 : 710) ohmic contacts to p and n-type epilayers of 4H-SiC. The specific contact resistances (p(c)) were found to be as low as p- 5X10(-6), 2x10(-5), 2x10(-5), 3x10(-4), 4x10(-5), and 1X10(-4) Omegacm(2) for TiC contacts to n(+) epilayers, p(+) epilayers, and Al-ion-implanted layers, Ti contacts to p(+) epilayers, and TiW contacts to p(+) and to n(+) epilayers, respectively, by using linear transmission line method (TLM) measurements. During the long-term reliability tests in a vacuum chamber, we found that evaporated Au capping layers helped to keep the contacts from degrading.

  • 10. Naitou, Y.
    et al.
    Watanabe, Y.
    Hirayama, S.
    Hayashi, M.
    Prokofiev, A.
    Hjalmarsson, A.
    Pomp, S.
    Andersson, P.
    Bevilacqua, R.
    Gustavsson, C.
    Österlund, M.
    Simutkin, V.
    Sjöstrand, H.
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Tippawan, U.
    Characterization of ANITA and QMN Neutron Beams at TSL Using Proton Recoil Techniques2011In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 59, no 2, p. 1439-1442Article in journal (Refereed)
    Abstract [en]

    Neutron beam characterization measurements have been carried out in both the AN:ITA and QMN modes using the incident proton beam of 180 MeV at the The Svedverg Laboratory (TSL) in Uppsala. The spectral neutron flux data have been obtained by measuring elastic np-scattering with the Medley setup. The experimental results in the ANITA and QMN modes are compared with an MCNPX simulation and with the systematics of QMN spectra, respectively.

  • 11.
    Tesinsky, Milan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Andersson, P.
    Gustavsson, C.
    Pomp, S.
    Osterlund, M.
    Blomgren, J.
    Simutkin, V.
    Bevilacqua, R.
    Hjalmarsson, A.
    Pokofiev, A.
    Tippawan, U.
    Lecolley, F. -R
    Marie, N.
    Kolozhvari, A.
    Neutron Elastic Scattering Cross-Section Measurements at 175 MeV2011In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 59, no 2, p. 1797-1800Article in journal (Refereed)
    Abstract [en]

    An off-line data analysis of an experimental campaign on elastic neutron cross-section measurements at 175 MeV for iron and bismuth performed by the SCANDAL set-up has started. Energy calibration has shown expected values of energy resolution and MCNPX simulations have provided suggestions for further analysis.

  • 12. Tippawan, U.
    et al.
    Vilaithong, T.
    Pomp, S.
    Andersson, P.
    Bevilacqua, R.
    Blomgren, J.
    Gustavsson, C.
    Nilsson, L.
    Osterlund, M.
    Simutkin, V.
    Sjostrand, H.
    Hayashi, M.
    Hirayama, S.
    Naitou, Y.
    Watanabe, Y.
    Hjalmarsson, A.
    Prokofiev, A.
    Tesinsky, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Light-ion Production in 175 MeV Neutron-induced Reactions on Oxygen2011In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 59, no 2, p. 1979-1982Article in journal (Refereed)
    Abstract [en]

    Data on light-ion production in light nuclei such as carbon, nitrogen and oxygen are particularly important in calculations of dose distributions in human tissue for radiation therapy at neutron beams, and for dosimetry of high energy neutrons produced by high-energy cosmic radiation interacting with nuclei (nitrogen and oxygen) in the atmosphere. When studying neutron dose effects, special consideration on carbon and oxygen is needed since they are, by weight, the most abundant elements in human tissue. The MEDLEY setup at The Svedberg Laboratory (TSL), Uppsala, Sweden has been used to measure such data with double-differential cross sections (DDX) for the (n, xp), (n, xd), xt), (n,(3)He), and (n,alpha) reactions from C, 0, Si, Ca, Fe, Pb, and U around 96 MeV. At the new Uppsala neutron beam facility the available energy range of quasi mono-energetic neutron beams is extended up to 175 MeV. The detector setup used in MEDLEY consists of eight so-called telescopes mounted at different angles inside all evacuated reaction chamber. Each of the telescopes consists of two fully depleted Delta E silicon surface barrier detectors (SSBD) and a CsI(Tl) crystal. In order to make measurements at this higher neutron energy possible some changes in the detector setup compared to the campaign at 96 MeV were applied Accordingly, the second Delta E detectors have been replaced by 1000 mu m thick SSBDs as well as the size of the crystals used as E detectors was increased to a total length of 100 mm and a diameter of 50 mm. The Delta E - E technique is used to identify the light ions, and cutoff energies as low as 2.5 MeV for protons and 4.0 MeV for alpha particles are achieved. The data are normalised relative to elastic up scattering measured in one of the telescopes at 20 degrees. Preliminary DDXs for oxygen are presented and compared with theoretical calculations.

  • 13. Yoon, Y. J.
    et al.
    Chung, S. J.
    Lee, H. J.
    Lee, S.
    An, S. Y.
    Liu, X.
    Furdyna, J. K.
    Effect of p-type buffer layer on the properties of GaMnAs ferromagnetic semiconductors2004In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 45, no SUPPL., p. S720-S723Article in journal (Refereed)
    Abstract [en]

    We have studied the magnetic and transport properties of Ga 1-xMn xAs epilayers grown either on undoped or on p-type doped GaAs buffer layer. The temperature dependence of the resistivity at zero magnetic field reveals that the Curie temperature (T C) in the Ga 1-xMn xAs layer grown on p-type doped GaAs buffer is slightly higher than that observed in the layer grown on undoped GaAs buffer. The magnetic and transport properties of the two samples show significant differences when they are placed in a magnetic field. In SQUID measurements, the Ga 1-xMn xAs layer grown on p-type buffer shows a larger coercive field and much slower decay of remanent magnetization than the layer grown on undoped buffer. This robust magnetic behavior observed in the doped sample is discussed in terms of the increase of free carrier concentration in the system arising from p-type doping in the buffer layer.

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