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  • 1.
    Andersson, Göran
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    A high-pressure cell for electrical resistance measurements at hydrostatic pressures up to 8 GPa: Results for Bi, Ba, Ni, and Si1989In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 65, no 10, p. 3943-3950Article in journal (Refereed)
    Abstract [en]

    A modified Bridgman anvil high-pressure device, capable of producing hydrostatic pressures up to 8 GPa (80 kbar), was designed and built. The size of the pressure chamber (10 mm in diameter) allows the use of large specimens and simple experimental procedures. Experimental results show that hydrostatic conditions are necessary if accurate quantitative information is desired about the electrical properties of materials under pressure. Accurate data on resistance (and resistivity) versus pressure at 294 K are given for Bi, Ba, Ni, and Si. The initial pressure coefficients of R were d(ln R)dP=0.13, −7.6×10−2, −2.0×10−2, and −0.26 GPa−1, respectively. Barium has a resistance minimum near 0.9 GPa. For Bi we observe sharp transitions at 2.55, 2.7, and 7.7 GPa, and for Ba at 5.55 GPa, but we cannot verify the existence of a transition in Ba near 7 GPa. Neither do we confirm the phase transformation in Ni recently reported to occur above 2.5 GPa. For Si, R(P) agrees very well with a theoretical function calculated from the change in band gap and electron mobility with pressure.

  • 2. Berge, John
    et al.
    Norling, Martin
    Vorobiev, Andrei
    Gevorgian, Spartak
    Field and temperature dependent parameters of the dc field induced resonances in BaxSr1-xTiO3-based tunable thin film bulk acoustic resonators2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 6Article in journal (Refereed)
  • 3. Bouhrara, M.
    et al.
    Saih, Y.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Goze-Bac, C.
    Abou-Hamad, E.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-resolution (13)C nuclear magnetic resonance evidence of phase transition of Rb,Cs-intercalated single-walled nanotubes2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 5, p. 054306-Article in journal (Refereed)
    Abstract [en]

    We present 13 C high-resolution magic-angle-turning (MAT) and magic angle spinning nuclear magnetic resonance data of Cs and Rb intercalated single walled carbon nanotubes. We find two distinct phases at different intercalation levels. A simple charge transfer is applicable at low intercalation level. The new phase at high intercalation level is accompanied by a hybridization of alkali (s) orbitals with the carbon (sp2) orbitals of the single walled nanotubes, which indicate bundle surface sites is the most probable alkali site.

  • 4.
    Castelain, Mickael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rouxhet, Paul G.
    Pignon, Frederic
    Magnin, Albert
    Piau, Jean-Michel
    Single-cell adhesion probed in-situ using optical tweezers: A case study with Saccharomyces cerevisiae2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 11, p. 114701-Article in journal (Refereed)
    Abstract [en]

    A facile method of using optical trapping to measure cell adhesion forces is presented and applied to the adhesion of Saccharomyces cerevisiae on glass, in contact with solutions of different compositions. Trapping yeast cells with optical tweezers (OT) is not perturbed by cell wall deformation or cell deviation from a spherical shape. The trapping force calibration requires correction not only for the hydrodynamic effect of the neighboring wall but also for spherical aberrations affecting the focal volume and the trap stiffness. Yeast cells trapped for up to 5 h were still able to undergo budding but showed an increase of doubling time. The proportion of adhering cells showed the expected variation according to the solution composition. The detachment force varied in the same way. This observation and the fact that the detachment stress was exerted parallel to the substrate surface point to the role of interactions involving solvated macromolecules. Both the proportion of adhering cells and the removal force showed a distribution which, in our experimental conditions, must be attributed to a heterogeneity of surface properties at the cell level or at the subcellular scale. As compared with magnetic tweezers, atomic force microscopy, and more conventional ways of studying cell adhesion (shear-flow cells), OT present several advantages that are emphasized in this paper. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4723566]

  • 5. Celzard, Alain
    et al.
    McRae, Edward
    Marêché, Jean-Francois
    Furdin, Guy
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Conduction mechanisms in some graphite-polymer composites: effects of temperature and pressure1998In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 83, no 3, p. 1410-1419Article in journal (Refereed)
    Abstract [en]

    This article is devoted to the conduction mechanisms involved in some highly electrically anisotropic resin–graphite particle composites. These materials are known to show a percolation phenomenon as the filler content is varied; they are epoxy or polyurethane based, the conducting particles are oriented single-crystal platelets, and samples are in the form of thick films. Because of their strong anisotropy, two types of measurements were made, i.e., parallel to and perpendicular to the plane of the films. Study of the resistivity variations of samples containing various concentrations in conducting particles was carried out first as a function of temperature from 4.2 to 300 K at ambient pressure, and second as a function of hydrostatic pressure up to 1.2 GPa, at room temperature. As the temperature is varied, the changes in resistivity of all the samples studied (i.e., above percolation threshold) are weak; analysis leads to the conclusion that thermally activated tunneling plays a dominant role above but close to the percolation threshold phic. As a function of pressure, more samples were studied: when the filler content is above phic, resistivity changes are quantitatively in agreement with what is expected from both percolation theory and tunneling; below threshold, the observed behavior is partially attributable to an ionic conduction mechanism throughout the polymer.

  • 6.
    Hagman, Henning
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sjölund, Peder
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Petra, Stefan J. H.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nylén, Mats
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kastberg, Anders
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ellmann, Harald
    Department of Physics, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden.
    Jersblad, Johan
    Department of Physics, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden.
    Assessment of a time-of-flight detection technique for measuring small velocities of cold atoms2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 8, p. 083109-Article in journal (Refereed)
    Abstract [en]

    A low noise time-of-flight detection system for laser cooled atoms has been constructed and incrementally optimized. Here, a thorough description of the construction is presented along with an analysis of the capabilities of the system. The quality of the detection (the resolution, the reproducibility, the sensitivity, etc.) is crucial for, e.g., the ability to see details in the velocity distribution profile, which is of interest for fundamental studies of statistical physics and of the laser cooling processes, and for detection of small initial velocities of an atomic cloud, important, e.g., when studying small drifts induced by Brownian motors and ratchets. We estimate the signal-to-noise ratio of our signal to be better than 1000:1 for a typical single shot, and we discuss the effect of the initial atomic cloud size, the probe size, and the effects of the wave packet spread during the fall time on the measured quantities. We show that the shape of the velocity distribution is well conserved during the mapping done in the detection, i.e., in the convolution with the probe beam, and that velocities as small as a few percent of the single photon recoil velocity can be resolved.

  • 7.
    Lundberg, Bo
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Resistivity of a composite conducting polymer as a function of temperature, pressure, and environment: Applications as a pressure and gas concentration transducer1986In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 60, no 3, p. 1074-1079Article in journal (Refereed)
    Abstract [en]

    The resistivity of a commercial carbon-filled composite conducting polymer (ET-Semicon[large-closed-square]) has been measured as a function of temperature between 80 and 400 K and under pressure up to 1.5 GPa (15 kbar). Large changes in resistivity were observed. The resistivity was also very sensitive to the presence of certain solvents and hydrocarbons. The results are explained as percolation effects caused by changes in volume due to pressure, thermal expansion, or dissolved solvents. The material studied is found to have a wide range of potential applications for pressure measurements and as a transducer for gas or liquid concentration.

  • 8. Mahfouz, R.
    et al.
    Bouhrara, M.
    Kim, Y.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Goze-Bac, C.
    Abou-Hamad, E.
    Properties of K,Rb-intercalated C60 encapsulated inside carbon nanotubes called peapods derived from nuclear magnetic resonance2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 11, article id 114305Article in journal (Refereed)
    Abstract [en]

    We present a detailed experimental study on how magnetic and electronic properties of Rb, K-intercalated C-60 encapsulated inside carbon nanotubes called peapods can be derived from C-13 nuclear magnetic resonance investigations. Ring currents do play a basic role in those systems; in particular, the inner cavities of nanotubes offer an ideal environment to investigate the magnetism at the nanoscale. We report the largest diamagnetic shifts down to -68.3 ppm ever observed in carbon allotropes, which is connected to the enhancement of the aromaticity of the nanotube envelope upon intercalation. The metallization of intercalated peapods is evidenced from the chemical shift anisotropy and spin-lattice relaxation (T-1) measurements. The observed relaxation curves signal a three-component model with two slow and one fast relaxing components. We assigned the fast component to the unpaired electrons charged C-60 that show a phase transition near 100 K. The two slow components can be rationalized by the two types of charged C-60 at two different positions with a linear regime following Korringa behavior, which is typical for metallic system and allow us to estimate the density of sate at Fermi level n(E-F).

  • 9.
    Makarova, Tatiana L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kvyatkovskii, Oleg E.
    Zakharova, Irina B.
    Buga, Sergei G.
    Voklov, Aleksandr P.
    Shelankov, Andrei L.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Laser controlled magnetism in hydrogenated fullerene films2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 8, p. 083941-7Article in journal (Refereed)
    Abstract [en]

    Room temperature ferromagnetic-like behavior in fullerene photopolymerized films treated with monatomic hydrogen is reported. The hydrogen treatment controllably varies the paramagnetic spin concentration and laser induced polymerization transforms the paramagnetic phase to a ferromagnetic-like one. Excess laser irradiation destroys magnetic ordering, presumably due to structural changes, which was continuously monitored by Raman spectroscopy. We suggest an interpretation of the data based on first-principles density-functional spin-unrestricted calculations which show that the excess spin from mono-atomic hydrogen is delocalized within the host fullerene and the laser-induced polymerization promotes spin exchange interaction and spin alignment in the polymerized phase.

  • 10.
    Makarova, Tatiana L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kvyatkovskii, Oleg E.
    Zakharova, Irina B.
    Buga, Sergei G.
    Volkov, Aleksandr P.
    Shelankov, Andrei L.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Response to "Comment on 'Laser controlled magnetism in hydrogenated fullerene films'" [J. Appl. Phys. 113, 036101 (2013)]2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 3, p. 036102-Article in journal (Other academic)
  • 11.
    Sandberg, Olov
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Thermal properties of two low viscosity silicone oils as functions of temperature and pressure1982In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 53, no 12, p. 8751-8755Article in journal (Refereed)
    Abstract [en]

    The thermal conductivity and the specific heat capacity per unit volume have been measured for two low viscosity grades of Dow Corning 200 fluid (polydimethyl siloxane) in the range 110 to 350 K and under pressures up to 2.0 GPa (20 kbar). Both the quantities studied are found to increase with increasing pressure in the liquid phase. From the measured data the phase diagrams are obtained. The 5 mm2/s (5 cSt) grade fluid does not crystallize, but undergoes a glass transition at 1.0 GPa at room temperature. The 1 mm2/s (1 cSt) grade has a more complicated phase diagram with a partly crystalline phase at low temperatures and pressures and two glass transitions at high temperatures and pressures.

  • 12.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Thermal diffusivity and thermal conductivity of Chromel, Alumel, and Constantan in the range 100-450 K1992In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 72, no 2, p. 539-545Article in journal (Refereed)
    Abstract [en]

    Data are presented for the thermal diffusivity and the thermal conductivity of commercially available Chromel, Alumel, and Constantan alloys, and the specific heat capacity of Alumel, over the temperature range 100 to 450 K. Over this range, the thermal conductivity of all materials increases by more than 50%; room-temperature values are 17, 29, and 23 W m−1 K−1, respectively. The thermal conductivity data are discussed in terms of simple theory.

  • 13.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Comment on "Laser controlled magnetism in hydrogenated fullerene films": [J. Appl. Phys. 109, 083941 (2011)]2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 3, p. 036101-Article in journal (Other academic)
    Abstract [en]

    Hydrogenation of C-60 films with formation of single hydrogen adduct reported by Makarova et al. [J. Appl. Phys. 109, 083941 (2011); Phys. Status Solidi B 246, 2778 (2009)] was supported only by several features found in Raman spectra of treated samples. However, no spectra were shown for untreated samples. Data shown in this comment prove that all Raman peaks assigned by Makarova et al. [J. Appl. Phys. 109, 083941 (2011); Phys. Status Solidi B 246, 2778 (2009)] to effects of hydrogenation can be found in spectra of pristine untreated commercial C-60 powder. These peaks represent some second order vibrations of C-60 as well as some possible solvent impurities. Therefore, all magnetic effects reported in this study should be assigned to unknown effects but not necessarily to hydrogenation. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775821]

  • 14. Vendik, Irina
    et al.
    Turalchuk, Pavel
    Vendik, Orest
    Berge, John
    Modeling tunable bulk acoustic resonators based on induced piezoelectric effect in BaTiO[sub 3] and Ba[sub 0.25]Sr[sub 0.75]TiO[sub 3] films2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 1, p. 014107-1Article in journal (Refereed)
  • 15. Vorobiev, Andrei
    et al.
    Berge, John
    Gevorgian, Spartak
    Löffler, Markus
    Olsson, Eva
    Effect of interface roughness on acoustic loss in tunable thin film bulk acoustic wave resonators2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 2Article in journal (Refereed)
    Abstract [en]

    Tunable 5.2 GHz bulk acoustic wave resonators utilizing Ba(x)Sr(1-x)TiO(3) ferroelectric films with similar intrinsic properties but different interface roughness are fabricated and characterized. Increase in roughness from 3.2 nm up to 6.9 nm results in reduction in Q-factor from 350 down to 150 due to extrinsic acoustic losses caused by wave scattering at reflections from rough interfaces and other mechanisms associated with roughness. The increased roughness is a result of distortion of Pt bottom electrode caused by formation of heterogeneous enclosures of TiO(2-x) in the Pt layer. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3610513]

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