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  • 151.
    Yao, Mingguang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Iwasiewicz-Wabnig, Agnieszka
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Makarova, Tatiana L
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Reversible nano-scale phase separation of Rb4C60 under pressure2010In: Journal of physics: conference series: proceedings of the International Conference on High Pressure Science and Technology, Joint AIRAPT-22 & HPCJ-50, 26–31 July 2009, Tokyo, Japan / [ed] K. Takemura, editor in chief, Bristol: Institute of Physics (IOP), 2010, Vol. 215:1, p. 012020-Conference paper (Refereed)
    Abstract [en]

    The alkali fulleride Rb4C60 has been investigated by studies of the resistance and by Raman spectroscopy under pressures up to 2 GPa and 13 GPa, respectively. Our data show a reversible phase separation into metallic Rb3C60 and Rb6C60 at pressures above 1 GPa. The reversibility indicates that the phase separation primarily occurs on the nanometer length scale. The data explain several puzzling results reported in the recent literature.

  • 152.
    Yao, Mingguang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Effect of high pressure on electrical transport in the Li4C60 fulleride polymer from 100 to 400 K2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 15, p. 155441-155448Article in journal (Refereed)
    Abstract [en]

    In situ resistance measurements have been carried out on Li4C60 under pressures up to 2 GPa at temperatures from below 100 to 400 K. In agreement with recent reports we find an Arrhenius law behavior for the conductivity, which can be interpreted in terms of Li+ ionic conduction with an activation energy near 225 meV. The activation energy decreases with increasing pressure at an initial rate of about −11%/GPa and the room-temperature conductivity increases by a factor of about 6 from 0.1 to 2 GPa. We also observe conductivity terms with a lower excitation energy, most probably associated with conduction by electrons excited from defect-induced states in the main band gap. We discuss this conduction behavior in the context of recent measurements on both Li4C60 and other alkali-metal intercalated phases such as Rb4C60, Na2C60, and Na4C60. After heating to 400 K at 2 GPa the conduction behavior changes drastically, manifested by a change in the slopes of R versus T curves signifying newly created gap states. Postexperimental characterization by Raman spectroscopy and x-ray diffraction indicate the loss of Li especially from the grain surfaces. Finally, high-pressure Raman studies suggest a possible metallization transition above 9 GPa.

  • 153.
    Yao, Mingguang
    et al.
    Université de Lyon, Lab. de Phys. Matière Condenseé et Nanostructures, 69622 Villeurbanne, Lyon, France.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Electrical transport properties of Na2C60 under high pressure2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 11, p. 115405-Article in journal (Refereed)
    Abstract [en]

    We present direct resistance measurements on Na2C60 under high pressure up to 2 GPa in the temperature range ~90–500 K. We show that fresh, nominally pure Na2C60 exhibits a semiconductor-type conduction behavior at all experimental conditions, with a 1.2 eV band gap and a conduction strongly influenced by defect gap states. Contrary to Rb4C60 and Na4C60, both band gap and gap states have large pressure dependences. In contrast, a Na2C60 sample preserved in an oxygen-free environment for several months shows conduction by another mechanism, variable range 3D hopping. This is consistent with recent findings of nanoscale phase segregation in Na2C60 and can be understood in terms of conduction by intergrain hopping. Heating the sample at 2 GPa leads to a significant change in the resistivity, suggesting a structural transition. By characterizing the sample after the phase transformation with Raman spectroscopy and x-ray diffraction we identify a phase separation of the material into two main structures, linearly polymerized orthorhombic C60 and two-dimensionally polymerized Na4C60.

  • 154. Zhan, Xuejia
    et al.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi, People’s Republic of China .
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhan, Shenshan
    Xu, Hanchu
    Zhou, Pei
    Electrochemical aptasensor for tetracycline using a screen-printed carbon electrode modified with an alginate film containing reduced graphene oxide and magnetite (Fe3O4) nanoparticles2016In: Microchimica Acta, ISSN 0026-3672, E-ISSN 1436-5073, Vol. 183, no 2, p. 723-729Article in journal (Refereed)
    Abstract [en]

    The authors describe a label-free electrochemical aptasensor for tetracycline (TET). The TET-binding aptamer was immobilized on a composite consisting of reduced graphene oxide, magnetite (Fe3O4) and sodium alginate, and this material was used to modify the surface of a screen-printed carbon electrode (SPCE). Cyclic voltammetry was carried out to characterize the single steps in the preparation of the modified electrode and to optimize the conditions for detection. Differential pulse voltammetry (DPV) was then used to monitor the interaction between aptamer and TET by applying the electrochemical probe thionine. Under optimal conditions, TET can be quantified by DPV in the 1 nM to 5 mu M concentration range, with a detection limit as low as 0.6 nM (at an S/N ratio of 3). The method is rapid, cost-efficient, highly sensitive and specific, and therefore is considered to be a viable platform for TET analysis in food, environmental, and clinical samples.

  • 155. Zhan, Xuejia
    et al.
    Hu, Guangzhi
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhang, Dongwei
    Zhou, Pei
    A Label-Free Electrochemical Aptasensor for the Rapid Detection of Tetracycline Based on Ordered Mesoporous Carbon-Fe3O42018In: Australian journal of chemistry (Print), ISSN 0004-9425, E-ISSN 1445-0038, Vol. 71, no 2-3, p. 170-176Article in journal (Refereed)
    Abstract [en]

    A novel aptasensor based on a tetracycline (TET) aptamer immobilized by physical adsorption on an ordered mesoporous carbon-Fe3O4 (OMC-Fe3O4)-modified screen-printed electrode surface was successfully fabricated. OMC-Fe3O4 was characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The modification procedure of the aptasensor was characterized by cyclic voltammetry. Interaction between the TET aptamer and target was determined by differential pulse voltammetry. Under optimal conditions, the proposed aptasensor exhibited good electrochemical sensitivity to TET in a concentration range of 5 nM to 10 μM, with a detection limit of 0.8 nM (S/N =3D 3). This aptasensor exhibited satisfactory specificity, reproducibility, and stability.

  • 156. Zou, Yonggang
    et al.
    Liu, Bingbing
    Wang, Liancheng
    Liu, Dedi
    Yu, Shidan
    Wang, Peng
    Wang, Tianyi
    Yao, Mingguang
    Li, Quanjun
    Zou, Bo
    Cui, Tian
    Zou, Guangtian
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mao, Ho-Kwang
    Rotational dynamics of confined C60 from near-infrared Raman studies under high pressure2009In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, no 52, p. 22135-22138Article in journal (Refereed)
    Abstract [en]

    Peapods present a model system for studying the properties of dimensionally constrained crystal structures, whose dynamical properties are very important. We have recently studied the rotational dynamics of C60 molecules confined inside single walled carbon nanotube (SWNT) by analyzing the intermediate frequency mode lattice vibrations using near-infrared Raman spectroscopy. The rotation of C60 was tuned to a known state by applying high pressure, at which condition C60 first forms dimers at low pressure and then forms a single-chain, nonrotating, polymer structure at high pressure. In the latter state the molecules form chains with a 2-fold symmetry. We propose that the C60 molecules in SWNT exhibit an unusual type of ratcheted rotation due to the interaction between C60 and SWNT in the “hexagon orientation,” and the characteristic vibrations of ratcheted rotation becomes more obvious with decreasing temperature.

  • 157. Zou, Yonggang
    et al.
    Liu, Bingbing
    Yao, Mingguang
    Hou, Yuanyuan
    Wang, Lin
    Yu, Shidan
    Wang, Peng
    Li, Bing
    Zou, Bo
    Cui, Tian
    Zou, Guangtian
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Raman spectroscopy study of carbon nanotube peapods excited by near-IR laser under high pressure2007In: Physical Review B, ISSN 0163-1829, Vol. 76, no 19, p. 195417-Article in journal (Refereed)
    Abstract [sv]

    A resonant Raman spectroscopy study has been carried out under high pressure, using a diamond anvil cell,

    on carbon nanotube peapods (C60@SWNT) synthesized in high yield in our laboratory. The Raman signal was

    excited by a near IR laser (830 nm) to avoid photopolymerization of C60 and thus obtain the intrinsic vibrational

    information on the C60 molecules in the nanotubes. It is found that the surrounding tubes create an

    effective pressure on the encapsulated C60 due to tube-fullerene interactions, resulting in a shift of the intrinsic

    Ag(2) vibrational mode to 1474 cm−1 at ambient pressure. High pressure Raman spectroscopy indicates that

    (C60)2 dimers form near 1 GPa, and that a further polymerization of C60 occurs near 23 GPa, creating linear

    chains of covalently linked C60 molecules in the tubes.

  • 158.
    Zäll, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nordenström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mossegård, Jonatan
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Electroplating of selective surfaces for concentrating solar collectors2018In: PROCEEDINGS OF THE ISES EUROSUN 2018 CONFERENCE - 12TH INTERNATIONAL CONFERENCE ON SOLAR ENERGY FOR BUILDINGS AND INDUSTRY / [ed] Haberle, A, International Solar Energy Society, 2018, p. 1086-1095Conference paper (Refereed)
    Abstract [en]

    A spectrally selective surface is produced by electrodeposition of a Co-Cr coating on a stainless steel substrate. The plating bath consisted of CrCl3 center dot 6H(2)O and CoCl2 center dot 6H(2)O dissolved in a deep eutectic solvent (DES) of choline chloride and ethylene glycol. This DES enables the use of trivalent (Cr(III)) instead of hexavalent chromium (Cr(XI)) which significantly reduces health risks associated with chromium electroplating. The selective surface exhibits an absorptance (alpha) of 0.96 and an emittance (epsilon) of 0.13 at 100 degrees C making it well adapted for mid- to lowtemperature concentrating solar collectors. The 1.8 mu m thick coating exhibits a porous structure on the surface as well as throughout the entire coating. The surface of the coating comprises of Co oxides and hydroxides, while the bulk consists of metallic and oxidized Co and only small fractions of Cr compounds. Initial tests of the thermal stability indicate that the coating does not maintain optical properties at an acceptable level over a lifetime of 25 years. At approximately 438 degrees C significant parts of the coating is oxidized in an oxygen rich environment.

1234 151 - 158 of 158
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