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

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

  • 2. Abou-Hamad, E.
    et al.
    Kim, Y.
    Bouhrara, M.
    Saih, Y.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Luzzi, D. E.
    Goze-Bac, C.
    NMR strategies to study the local magnetic properties of carbon nanotubes2012Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 407, nr 4, s. 740-742Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 3.
    Abou-Hamad, Edy
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Goze-Bac, Christophe
    Université Montpellier II, France.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schmid, Michael
    Physikalisches Institut, Universität Stuttgart, Germany.
    Aznar, Robert
    Université Montpellier II, France.
    Mehring, Michael
    Physikalisches Institut, Universität Stuttgart, Germany.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Electronic properties of Cs-intercalated single-walled carbon nanotubes derived from nuclear magnetic resonance2011Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, s. 053045 (1)-(9)Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the electronic properties of Cs-intercalated singlewalled carbon nanotubes (SWNTs). A detailed analysis of the 13C and133Cs nuclear magnetic resonance (NMR) spectra reveals an increased metallization of the pristine SWNTs under Cs intercalation. The ‘metallization’ of CsxC materials where x =0–0.144 is evidenced from the increased local electronic density of states (DOS) n(EF)at the Fermi level of the SWNTs as determined from spin–lattice relaxation measurements. In particular, there are two distinct electronic phases called α and β and the transition between these occurs around x = 0.05. The electronic DOS at the Fermi level increases monotonically at low intercalation levels x <0.05 (α-phase), whereas it reaches a plateau in the range 0.05 < x < 0.143 at high intercalation levels (β-phase). The new β-phase is accompanied by a hybridization of Cs(6s) orbitals with C(sp2)orbitals of the SWNTs. In both phases, two types of metallic nanotubes are found with a low and a high local n(EF), corresponding to different local electronic band structures of the SWNTs.

  • 4.
    Abou-Hamad, Edy
    et al.
    Universite Montpellier II.
    Kim, Y
    University of Pennsylvania.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Goze-Bac, Christophe
    Universite Montpellier II.
    Luzzi, David
    University of Pennsylvania.
    Rubio, Angelo
    University of Basque Country.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Hydrogenation of C-60 in Peapods: Physical Chemistry in Nano Vessels2009Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 20, s. 8583-8587Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 5.
    Abou-Hamad, Edy
    et al.
    Universite Montpellier 2, France.
    Kim, Y.
    University of Pennsylvania, Philadelphia.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boesch, D.
    University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Aloni, S.
    University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Zettl, Alex
    University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Rubio, Angelo
    Universidad del Pas Vasco UPV/EHU.
    Luzzi, David E.
    University of Pennsylvania, Philadelphia.
    Goze-Bac, Christophe
    CNRS Universit Montpellier 2.
    Molecular dynamics and phase transition in one-dimensional crystal of C60 encapsulated inside single wall carbon nanotubes2009Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 3, nr 12, s. 3878-3883Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 6.
    Andersson, Ove
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    In situ, high pressure differential thermal analysis and ionic conductance of PMMA-based gels with and without TiO2 nano-particle filler2006Inngår i: Electrochimica Acta, Vol. 51, s. 4537-Artikkel i tidsskrift (Fagfellevurdert)
  • 7.
    Annamalai, Alagappan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sandström, Robin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Muehlbacher, Inge
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Double donor Sb5+doped hematite (Fe3+) photoanodes for surface-enhanced PEC water splitting2018Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 256Artikkel i tidsskrift (Annet vitenskapelig)
  • 8.
    Annamalai, Alagappan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sandström, Robin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Mühlbacher, Inge
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Influence of Sb5+ as a Double Donor on Hematite (Fe3+) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation2018Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, nr 19, s. 16467-16473Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To exploit the full potential of hematite (α-Fe2O3) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe2O3/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb5+) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb5+ states in Sb-doped Fe2O3 photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 1020 vs 1.3 × 1019 cm–3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb5+ can activate multiple Fe3+ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb5+- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.

  • 9.
    Barzegar, Hamid R.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ramstedt, Madeleine
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Tai, Cheuk W.
    Malolepszy, Artur
    Stobinski, Leszek
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon Nanotubes-Effect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter2012Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 22, s. 12232-12239Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solution's concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition on the substrates with the prepared catalyst particles. By decreasing the catalyst particle size to below 10 nm, the growth of carbon nanotubes can be tuned from few-walled carbon nanotubes, with homogeneous diameter, to highly pure single-walled carbon nanotubes. Analysis of the Raman radial breathing modes, using three different Raman excitation wavelengths (488, 633, and 785 nm), showed a relatively broad diameter distribution (0.8-1.4 nm) of single-walled carbon nanotubes with different chiralities. However, by changing the composition of the catalyst particles while maintaining the growth parameters, the chiralities of single-walled carbon nanotubes were reduced to mainly four different types, (12, 1), (12, 0), (8, 5), and (7, 5), accounting for about 70% of all nanotubes.

  • 10.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA.
    Gracia Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    C60/Collapsed Carbon Nanotube Hybrids: A Variant of Peapods2015Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, nr 2, s. 829-834Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine a variant of so-called carbon nanotube peapods by packing C60 molecules inside the open edge ducts of collapsed carbon nanotubes. C60 insertion is accomplished through a facile single-step solution-based process. Theoretical modeling is used to evaluate favorable low-energy structural configurations. Overfilling of the collapsed tubes allows infiltration of C60 over the full cross-section of the tubes and consequent partial or complete reinflation, yielding few-wall, large diameter cylindrical nanotubes packed with crystalline C60 solid cores.

  • 11.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitrogen Doping Mechanism in Small Diameter Single-Walled Carbon Nanotubes: Impact on Electronic Properties and Growth Selectivity2013Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 48, s. 25805-25816Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nitrogen doping in carbon nanostructures has attracted interest for more than a decade, and recent implementation of such structures in energy conversion systems has boosted the interest even more. Despite numerous studies, the structural conformation and stability of nitrogen functionalities in small diameter single-walled carbon nanotubes (SWNTs), and the impact of these functionalities on the electronic and mechanical properties of the SWNTs, are incomplete. Here we report a detailed study on nitrogen doping in SWNTs with diameters in the range of 0.8?1.0 nm, with well-defined chirality. We show that the introduction of nitrogen in the carbon framework significantly alters the stability of certain tubes, opening for the possibility to selectively grow nitrogen-doped SWNTs with certain chirality and diameter. At low nitrogen concentration, pyridinic functionalities are readily incorporated and the tubular structure is well pertained. At higher concentrations, pyrrolic functionalities are formed, which leads to significant structural deformation of the nanotubes and hence a stop in growth of crystalline SWNTs. Raman spectroscopy is an important tool to understand guest atom doping and electronic charge transfer in SWNTs. By correlating the influence of defined nitrogen functionalities on the electronic properties of SWNTs with different chirality, we make precise interpretation of experimental Raman data. We show that the previous interpretation of the double-resonance G?-peak in many aspects is wrong and instead can be well-correlated to the type of nitrogen doping of SWNTs originating from the p- or n-doping nature of the nitrogen incorporation. Our results are supported by experimental and theoretical data.

  • 12.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hu, Guangzhi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Larsen, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Jia, Xueen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Palladium nanocrystals supported on photo-transformed C-60 nanorods: effect of crystal morphology and electron mobility on the electrocatalytic activity towards ethanol oxidation2014Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 73, s. 34-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the synthesis and decoration of high-aspect-ratio crystalline C-60 nanorods (NRs) by functionalized palladium nanoparticles with an average size of 4.78 +/- 0.66 nm. In their pristine form, C-60 NRs suffer from partial damage in the solution-based decoration process resulting in poor crystallinity. However, by modifying the NR surface via in situ photochemical transformation in the liquid state, we are able to prepare highly stable NRs that retain their crystalline structure during the decoration process. Our method thus opens up for the synthesis of highly crystalline nanocomposite hybrids comprising Pd nanoparticles and C-60 NRs. Bys measuring the electron mobility of different C-60 NRs, we relate both the effect of electron mobility and crystallinity to the final electrocatalytic performance of the synthesized hybrid structures. We show that the photo-transformed C-60 NRs exhibit highly advantageous properties for ethanol oxidation based on both a better crystallinity and a higher bulk conductivity. These findings give important information in the search for efficient catalyst support.

  • 13.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Physics, University of California, Berkeley, California 94720, United States ‡ Department of Physics, Umeå University, SE-901 87 Umeå, Sweden § Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States ∥ Kavli Energy NanoSciences Institute at the University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
    Larsen, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zettl, Alex
    Department of Physics, University of California, Berkeley, California 94720, United States.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Self-assembled PCBM nanosheets: a facile route to electronic layer-on-Layer heterostructures2018Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, nr 2, s. 1442-1447Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the self-assembly of semicrystalline [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanosheets at the interface between a hydrophobic solvent and water, and utilize this opportunity for the realization of electronically active organic/organic molecular heterostructures. The self-assembled PCBM nanosheets can feature a lateral size of >1 cm2 and be transferred from the water surface to both hydrophobic and hydrophilic surfaces using facile transfer techniques. We employ a transferred single PCBM nanosheet as the active material in a field-effect transistor (FET) and verify semiconductor function by a measured electron mobility of 1.2 × 10–2 cm2 V–1 s–1 and an on–off ratio of ∼1 × 104. We further fabricate a planar organic/organic heterostructure with the p-type organic semiconductor poly(3-hexylthiophene-2,5-diyl) as the bottom layer and the n-type PCBM nanosheet as the top layer and demonstrate ambipolar FET operation with an electron mobility of 8.7 × 10–4 cm2 V–1 s–1 and a hole mobility of 3.1 × 10–4 cm2V–1 s–1.

  • 14.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Larsen, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Solution-Based Phototransformation of C-60 Nanorods: Towards Improved Electronic Devices2013Inngår i: Particle & particle systems characterization, ISSN 0934-0866, E-ISSN 1521-4117, Vol. 30, nr 8, s. 715-720Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A modified liquid-liquid interface precipitation synthesis of C-60 nanorods, effects and opportunities following an in situ photochemical transformation in the liquid state, and an electronic characterization using a field-effect transistor (FET) geometry are reported. The nanorods feature a high aspect ratio of approximate to 10(3) and a notably small average diameter of 172 nm. Interestingly, it is found that a decreased nanorod diameter appears to correlate with distinctly improved electronic properties, and an average electron mobility of 0.30 cm(2) V-1 s(-1), as measured in a FET geometry, is reported for as-grown nanorods, with the peak value being an impressive 1.0 cm(2) V-1 s(-1). A photoexposure using green laser light ( = 532 nm) is demonstrated to result in the formation of a polymer-C-60 shell encapsulating a monomer-C-60 bulk; such photo-transformed nanorods exhibit an electron mobility of 4.7 x 10(-3) cm(2) V-1 s(-1). It is notable that the utilized FET geometry only probes the polymer-C-60 nanorod surface shell, and that the monomer-C-60 bulk is anticipated to exhibit a higher mobility. Importantly, photoexposed nanorods can be conveniently processed as a stabile dispersion in common hydrophobic solvents, and this finding is attributed to the insoluble character of the polymer-C-60 shell.

  • 15.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Malolepszy, Artur
    Stobinski, Leszek
    Tai, Cheuk-Wai
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Water assisted growth of C-60 rods and tubes by liquid-liquid interfacial precipitation method2012Inngår i: Molecules, ISSN 1420-3049, E-ISSN 1420-3049, Vol. 17, nr 6, s. 6840-6853Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    C-60 nanorods with hexagonal cross sections are grown using a static liquid-liquid interfacial precipitation method in a system of C-60/m-dichlorobenzene solution and ethanol. Adding water to the ethanol phase leads instead to C-60 tubes where both length and diameter of the C-60 tubes can be controlled by the water content in the ethanol. Based on our observations we find that the diameter of the rods/tubes strongly depends on the nucleation step. We propose a liquid-liquid interface growth model of C-60 rods and tubes based on the diffusion rate of the good C-60 containing solvent into the poor solvent as well as on the size of the crystal seeds formed at the interface between the two solvents. The grown rods and tubes exhibit a hexagonal solvate crystal structure with m-dichlorobenzene solvent molecules incorporated into the crystal structure, independent of the water content. An annealing step at 200 degrees C at a pressure <1 kPa transforms the grown structures into a solvent-free face centered cubic structure. Both the hexagonal and the face centered cubic structures are very stable and neither morphology nor structure shows any signs of degradation after three months of storage.

  • 16.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA; Lawrence Berkeley Natl Lab, Div Mat Sci, Berkeley, CA 94720 USA; Univ Calif Berkeley, Kavli Energy NanoSci Inst, Berkeley, CA 94720 USA; Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA.
    Yan, Aiming
    Coh, Sinisa
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Dunn, Gabriel
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Louie, Steven G.
    Cohen, Marvin L.
    Zettl, Alex
    Electrostatically Driven Nanoballoon Actuator2016Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, nr 11, s. 6787-6791Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate an inflatable nanoballoon actuator based on geometrical transitions between the inflated (cylindrical) and collapsed (flattened) forms of a carbon nanotube. In situ transmission electron microscopy experiments employing a nanoelectromechanical manipulator show that a collapsed carbon nanotube can be reinflated by electrically charging the nanotube, thus realizing an electrostatically driven nanoballoon actuator. We find that the tube actuator can be reliably cycled with only modest control voltages (few volts) with no apparent wear or fatigue. A complementary theoretical analysis identifies critical parameters for nanotube nanoballoon actuation.

  • 17.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Physics, University of California, Berkeley, CA 94720, USA; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Kavli Energy NanoSciences Institute at the University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
    Yan, Aiming
    Coh, Sinisa
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ojeda-Aristizabal, Claudia
    Dunn, Gabriel
    Cohen, Marvin L.
    Louie, Steven G.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zettl, Alex
    Spontaneous twisting of a collapsed carbon nanotube2017Inngår i: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 10, nr 6, s. 1942-1949Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the collapsing and subsequent spontaneous twisting of a carbon nanotube by in situ transmission electron microscopy (TEM). A custom-sized nanotube is first created in the microscope by selectively extracting shells from a parent multi-walled tube. The few-walled, large-diameter daughter nanotube is driven to collapse via mechanical stimulation, after which the ribbon-like collapsed tube spontaneously twists along its long axis. In situ diffraction experiments fully characterize the uncollapsed and collapsed tubes. The experimental observations and associated theoretical analysis indicate that the origin of the twisting is compressive strain.

  • 18. Bouhrara, M.
    et al.
    Abou-Hamad, E.
    Alabedi, G.
    Al-Taie, I.
    Kim, Y.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Goze-Bac, C.
    Electromagnetic Properties of Inner Double Walled Carbon Nanotubes Investigated by Nuclear Magnetic Resonance2013Inngår i: Journal of Nanomaterials, ISSN 1687-4110, E-ISSN 1687-4129, Vol. 2013, s. 713475-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The nuclear magnetic resonance (NMR) analytical technique was used to investigate the double walled carbon nanotubes (DWNTs) electromagnetic properties of inner walls. The local magnetic and electronic properties of inner nanotubes in DWNTs were analyzed using 25% (13) C enriched C-60 by which the effect of dipolar coupling could be minimized. The diamagnetic shielding was determined due to the ring currents on outer nanotubes in DWNTs. The NMR chemical shift anisotropy (CSA) spectra and spin-lattice relaxation studies reveal the metallic properties of the inner nanotubes with a signature of the spin-gap opening below 70 K.

  • 19. Bouhrara, M.
    et al.
    Saih, Y.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Goze-Bac, C.
    Abou-Hamad, E.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    High-resolution (13)C nuclear magnetic resonance evidence of phase transition of Rb,Cs-intercalated single-walled nanotubes2011Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, nr 5, s. 054306-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 20. Buga, Sergei G.
    et al.
    Blank, Vladimir D.
    Dubitsky, Gennadii A.
    Serebryanaya, Nadejda R.
    Fransson, Åke
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Tillämpad fysik och elektronik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Synthesis of superhard 3D-polymeric C60 fullerites from rhombohedral 2D-polymer by high-pressure-high-temperature treatment.2003Inngår i: High Pressure Research vol. 23, issue 3: Proceedings of the 40th European High Pressure Research Group Meeting on Advances in High Pressure Research (EHPRG'40), London: Taylor & Francis , 2003, s. 259-264Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Rhombohedral C60 polymer was subjected to high-pressure-high-temperature treatment at P =13 GPa, T =620-1620 K. After quenching, crystalline and disordered structures with densities in the range of 2.1-2.9 g cm-1 were obtained. The structures of the samples have been investigated by powder X-ray diffraction and Raman scattering. DSC analysis showed a transformation of the polymeric structure into monomeric on annealing in the range 400-640 K. The temperature dependence of the electrical resistance of samples with disordered structure was measured in the range 2.5-300K. For different samples, the conductivity was proportional to T1/2, T3/2, T4 and exp(-1/T1/4).

  • 21.
    Dzwilewski, Andrzej
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Matyba, Piotr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Moons, Ellen
    Karlstad universitet, Fysik.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Facile fabrication of organic CMOS circuits: understanding and optimization of the processManuskript (Annet vitenskapelig)
  • 22.
    Dzwilewski, Andrzej
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    C60 Field-Effect Transistors: Effects of Polymerization on Electronic Properties and Device Performance.2007Inngår i: Extended abstracts – 9th European Conference on Molecular Electronics, 2007Konferansepaper (Annet vitenskapelig)
  • 23.
    Dzwilewski, Andrzej
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    C60 Field-Effect Transistors: Effects of Polymerization on electronic Properties and Device Performance.2007Inngår i: Physical Review B, Vol. 75, nr 7, s. 075203-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated thin-film field-effect transistors (TFTs) with C60 as the active material, and we report the effects of photo-induced polymerization of the C60 film. We find that the effects of a complete polymerization for a typical top-contact C60 TFT is as follows: the electron mobility (μn) at room temperature drops slightly from 0.074 to 0.068 cm2/Vs, the activation energy of μn decreases from 0.10 meV to 0.09 meV, and the threshold voltage for TFT operation decreases markedly by ~15 %. The latter observation suggests that the effective number of electron traps in the C60 film decreases following polymerization. Considering that the polymerization was achieved with a low-energy HeNe laser, it is conceivable that the polymerization approach could be of interest for applications, e.g., organic bulk-heterojunction solar cells, where a stabilized C60 morphology attained with benign means is desired

  • 24.
    Dzwilewski, Andrzej
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Photo-induced and resist-free imprint patterning of fullerene materials for use in functional electronics2009Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, nr 11, s. 4006-4011Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a novel and potentially generic method for the efficient patterning of films of organic semiconductors and demonstrate the merit of the method on the high-solubility fullerene [6,6]-phenyl C61- butyric acid methyl ester (PCBM). The patterning technique is notably straightforward as it requires no photoresist material and encompasses only two steps: (i) exposure of select film areas to visible laser light during which the PCBM mononer is photochemically converted into a dimeric state, and (ii) development via solvent washing after which the nonexposed portions of the PCBM film are selectively removed. Importantly, the method is highly benign in that it leaves the electronic properties of the remaining patterned material intact, which is directly evidenced by the fact that we fabricate fully functional arrays of micrometersized field-effect transistors with patterned PCBM as the active material.

  • 25.
    Edman, Ludvig
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Matyba, Piotr
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Shin, Joon Ho
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Andersson, Mats
    Light-emitting Electrochemical Cells with mm-sized Electrode Gap: Controlling Light at Low Voltage and Identification of Degradation Mechanism.2008Inngår i: SPIE Photonics Europe, 2008Konferansepaper (Annet vitenskapelig)
  • 26. Ekeroth, Sebastian
    et al.
    Münger, E. Peter
    Boyd, Robert
    Ekspong, Joakim
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brenning, Nils
    Helmersson, Ulf
    Catalytic nanotruss structures realized by magnetic self-assembly in pulsed plasma2018Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, nr 5, s. 3132-3137Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 μm thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm2.

  • 27.
    Ekspong, Joakim
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sandström, Robin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Rajukumar, Lakshmy Pulickal
    Terrones, Mauricio
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stable Sulfur‐Intercalated 1T′ MoS2 on Graphitic Nanoribbons as Hydrogen Evolution Electrocatalyst2018Inngår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 28, nr 46, artikkel-id 1802744Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The metastable 1T′ polymorph of molybdenum disulfide (MoS2) has shown excellent catalytic activity toward the hydrogen evolution reaction (HER) in water‐splitting applications. Its basal plane exhibits high catalytic activity comparable to the edges in 2H MoS2 and noble metal platinum. However, the production and application of this polymorph are limited by its lower energetic stability compared to the semiconducting 2H MoS2 phase. Here, the production of stable intercalated 1T′ MoS2 nanosheets attached on graphitic nanoribbons is reported. The intercalated 1T′ MoS2 exhibits a stoichiometric S:Mo ratio of 2.3 (±0.1):1 with an expanded interlayer distance of 10 Å caused by a sulfur‐rich intercalation agent and is stable at room temperature for several months even after drying. The composition, structure, and catalytic activity toward HER are investigated both experimentally and theoretically. It is concluded that the 1T′ MoS2 phase is stabilized by the intercalated agents, which further improves the basal planes′ catalytic activity toward HER.

  • 28.
    Ekspong, Joakim
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Klechikov, Alexey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stabilizing Active Edge Sites in Semicrystalline Molybdenum Sulfide by Anchorage on Nitrogen-Doped Carbon Nanotubes for Hydrogen Evolution Reaction2016Inngår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 26, nr 37, s. 6766-6776Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Finding an abundant and cost-effective electrocatalyst for the hydrogen evolu-tion reaction (HER) is crucial for a global production of hydrogen from water electrolysis. This work reports an exceptionally large surface area hybrid catalyst electrode comprising semicrystalline molybdenum sulfi de (MoS 2+ x) catalystattached on a substrate based on nitrogen-doped carbon nanotubes (N-CNTs), which are directly grown on carbon fiber paper (CP). It is shown here that nitrogen-doping of the carbon nanotubes improves the anchoring of MoS 2+ xcatalyst compared to undoped carbon nanotubes and concurrently stabilizes a semicrystalline structure of MoS 2+ x with a high exposure of active sites for HER. The well-connected constituents of the hybrid catalyst are shown to facilitate electron transport and as a result of the good attributes, the MoS 2+ x/N-CNT/CPelectrode exhibits an onset potential of −135 mV for HER in 0.5 M H2SO4, a Tafel slope of 36 mV dec −1, and high stability at a current density of −10 mA cm −2.

  • 29.
    Ekspong, Joakim
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stainless Steel as A Bi-Functional Electrocatalyst – A Top-Down Approach2019Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, nr 13, artikkel-id 2128Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For a hydrogen economy to be viable, clean and economical hydrogen production methods are vital. Electrolysis of water is a promising hydrogen production technique with zero emissions, but suffer from relatively high production costs. In order to make electrolysis of water sustainable, abundant, and efficient materials has to replace expensive and scarce noble metals as electrocatalysts in the reaction cells. Herein, we study activated stainless steel as a bi-functional electrocatalyst for the full water splitting reaction by taking advantage of nickel and iron suppressed within the bulk. The final electrocatalyst consists of a stainless steel mesh with a modified surface of layered NiFe nanosheets. By using a top down approach, the nanosheets stay well anchored to the surface and maintain an excellent electrical connection to the bulk structure. At ambient temperature, the activated stainless steel electrodes produce 10 mA/cm(2) at a cell voltage of 1.78 V and display an onset for water splitting at 1.68 V in 1M KOH, which is close to benchmarking nanosized catalysts. Furthermore, we use a scalable activation method using no externally added electrocatalyst, which could be a practical and cheap alternative to traditionally catalyst-coated electrodes.

  • 30. Gao, Sanshuang
    et al.
    Liu, Jing
    Luo, Jun
    Mamat, Xamxikamar
    Sambasivam, Sangaraju
    Li, Yongtao
    Hu, Xun
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hu, Guangzhi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi, China.
    Selective voltammetric determination of Cd(II) by using N,S-codoped porous carbon nanofibers2018Inngår i: Microchimica Acta, ISSN 0026-3672, E-ISSN 1436-5073, Vol. 185, artikkel-id 282Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Porous carbon nanofibers codoped with nitrogen and sulfur (NFs) were prepared by pyrolysis of trithiocyanuric acid, silica nanospheres and polyacrylonitrile (PAN) followed by electrospinning. The NFs were used to modify a glassy carbon electrode (GCE) which then displayed highly sensitive response to traces of Cd(II). Compared to a bare GCE and a Nafion modified GCE, the GCE modified with codoped NFs shows improved sensitivity for Cd(II) in differential pulse anodic sweep voltammetry. The stripping peak current (typically measured at 0.81 V vs. Ag/AgCl) increases linearly in the 2.0–500 μg·L−1 Cd(II) concentration range. This is attributed to the large surface area (109 m2·g−1), porous structure, and high fraction of heteroatoms (19 at.% of N and 0.75 at.% of S). The method was applied to the determination of Cd(II) in (spiked) tap water where it gave recoveries that ranged between 96% and 103%.

  • 31. Gao, Sanshuang
    et al.
    Xu, Chuyang
    Yalikun, Nuerbiya
    Mamat, Xamxikamar
    Li, Yongtao
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hu, Xun
    Liu, Jing
    Luo, Jun
    Hu, Guangzhi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Science, Urumqi 830011, People's Republic of China.
    Sensitive and Selective Differential Pulse Voltammetry Detection of Cd(II) and Pb(II) Using Nitrogen-Doped Porous Carbon Nanofiber Film Electrode2017Inngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 164, nr 13, s. H967-H974Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Carbon matrix materials are regarded as one of the most important electrode materials for heavy metal detection. But even so, optimization procedures of carbon nanofibers (CNFs) for tracing Cd(II) and Pb(II) remains challenging. Here, zeolitic imidazolate framework (ZIF-8)/polyacrylonitrile (PAN)-derived nitrogen-doped porous carbon nanofibers (N-PCNFs) were investigated as a new electrode material for determining the concentration of Cd(II) and Pb(II). By optimizing electrochemical conditions such as deposition potential, deposition time, pH of buffer solution, and quantity of N-PCNFs loaded on a glassy carbon electrode (GCE), the linear response curves of Cd(II) and Pb(II) could be obtained. Due to the unique structural feature and N content, the N-PCNFs possess excellent detection limits of 0.8 mu g L-1 for Cd(II) and 0.3 mu g L-1 for Pb(II) (S/N = 3). To manifest the practical use of the sensor platform the concentration of Cd(II) and Pb(II) in normal tap and waste water were monitored. According to the ICP-MS results, the calculated recovery (97.0-107%) indicates that N-PCNFs have potential as a candidate material to monitor the concentration of Cd(II) and Pb(II) in practical samples.

  • 32.
    Gracia-Espino, Eduardo
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Yan, Aiming
    Zettl, Alex
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Fabrication of One-Dimensional Zigzag [6,6]-Phenyl-C-61-Butyric Acid Methyl Ester Nanoribbons from Two-Dimensional Nanosheets2015Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, nr 10, s. 10516-10522Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One-dimensional (10) zigzag [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanoribbons are produced by folding two-dimensional ultrathin PCBM nanosheets in a simple solvent process. The unique 1D PCBM nanostructures exhibit uniform width of 3.8 +/- 0.3 nm, equivalent to four PCBM molecules, and lengths of 20-400 nm. These nanoribbons show well-defined crystalline structure, comprising PCBM molecules in a hexagonal arrangement without trapped solvent molecules. First-principle calculations and detailed experimental characterization provide an insight into the structure and formation mechanism of the 1D PCBM nanoribbons. Given their dimensions and physical properties, we foresee that these nanostructures should be ideal as acceptor material in organic solar cells.

  • 33.
    Gracia-Espino, Eduardo
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Hu, Guangzhi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Understanding the Interface of Six-Shell Cuboctahedral and Icosahedral Palladium Clusters on Reduced Graphene Oxide: Experimental and Theoretical Study2014Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, nr 18, s. 6626-6633Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Studies on noble-metal-decorated carbon nanostructures are reported almost on a daily basis, but detailed studies on the nanoscale interactions for well-defined systems are very rare. Here we report a study of reduced graphene oxide (rGOx) homogeneously decorated with palladium (Pd) nanoclusters with well-defined shape and size (2.3 +/- 0.3 nm). The rGOx was modified with benzyl mercaptan (BnSH) to improve the interaction with Pd clusters, and N,N-dimethylformamide was used as solvent and capping agent during the decoration process. The resulting Pd nanoparticles anchored to the rGOx-surface exhibit high crystallinity and are fully consistent with six-shell cuboctahedral and icosahedral clusters containing similar to 600 Pd atoms, where 45% of these are located at the surface. According to X-ray photoelectron spectroscopy analysis, the Pd clusters exhibit an oxidized surface forming a PdOx shell. Given the well-defined experimental system, as verified by electron microscopy data and theoretical simulations, we performed ab initio simulations using 10 functionalized graphenes (with vacancies or pyridine, amine, hydroxyl, carboxyl, or epoxy groups) to understand the adsorption process of BnSH, their further role in the Pd cluster formation, and the electronic properties of the graphene-nanoparticle hybrid system. Both the experimental and theoretical results suggest that Pd clusters interact with fiinctionalized graphene by a sulfur bridge while the remaining Pd surface is oxidized. Our study is of significant importance for all work related to anchoring of nanoparticles on nanocarbon-based supports, which are used in a variety of applications.

  • 34.
    Gracia-Espino, Eduardo
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Jia, Xueen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Improved oxygen reduction performance of Pt–Ni nanoparticles by adhesion on nitrogen-doped graphene2014Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 5, s. 2804-2811Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Graphene and its derivatives hold great potential as support for nanocatalyst in various energy applications, such as fuel cells, batteries, and capacitors. In this work, we used density functional theory to analyze substrate effect on the electrocatalytic activity of Pt–Ni bimetallic nanoparticles for oxygen reduction reaction (ORR). The dissociative mechanism is used to evaluate the ORR performance (energy barrier for O2 dissociation, free energy of intermediates, d-band center, overpotential, and electrochemical activity) for a Pt–Ni core–shell-like nanoparticle (PtNiCS) deposited on nondefective graphene (GS) or nitrogen-doped graphene (N-GS). The electronic and catalytic properties of PtNiCS on N-GS designate N-doped graphene as the best substrate to use for ORR, showing better interaction with the bimetallic cluster, improved charge transfer between constitutes, and a superior ORR performance when compared to PtNiCS on GS. The N-GS has a significant effect in reducing the energy barrier for O2 dissociation and decrease the energetic stability of HO* intermediates, resulting in enhanced ORR activity compared with the PtNiCS on GS. In addition, the strong interaction between PtNiCS cluster and N-GS substrate may lead to an improved long-term stability of the catalytic particle during ORR cycles.

  • 35. Han, Xin-Bao
    et al.
    Tang, Xing-Yan
    Lin, Yue
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Liu, San-Gui
    Liang, Hai-Wei
    Hu, Guangzhi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China.
    Zhao, Xin-Jing
    Liao, Hong-Gang
    Tan, Yuan-Zhi
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Xie, Su-Yuan
    Zheng, Lan-Sun
    Ultrasmall Abundant Metal-Based Clusters as Oxygen-Evolving Catalysts2019Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, nr 1, s. 232-239Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The oxygen evolution reaction is a crucial step in water electrolysis to develop clean and renewable energy. Although noble metal-based catalysts have demonstrated high activity for the oxygen evolution reaction, their application is limited by their high cost and low availability. Here we report the use of a molecule-to-cluster strategy for preparing ultrasmall trimetallic clusters by using the polyoxometalate molecule as a precursor. Ultrafine (0.8 nm) transition-metal clusters with controllable chemical composition are obtained. The transition-metal clusters enable highly efficient oxygen evolution through water electrolysis in alkaline media, manifested by an overpotential of 192 mV at 10 mA cm–2, a low Tafel slope of 36 mV dec–1, and long-term stability for 30 h of electrolysis. We note, however, that besides the excellent performance as an oxygen evolution catalyst, our molecule-to-cluster strategy provides a means to achieve well-defined transition-metal clusters in the subnanometer regime, which potentially can have an impact on several other applications.

  • 36.
    Hedenström, Mattias
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Johnels, Dan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Characterization of Hydrogenated Fullerenes by NMR Spectroscopy2010Inngår i: Fulleranes: The Hydrogenated Fullerenes / [ed] Franco Cataldo, Susana Iglesias-Groth, Dordrecht: Springer Netherlands, 2010, Vol. 2, s. 171-202Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    NMR spectroscopy is so far the only analytical technique that has been used to get a detailed structural characterization of hydrogenated fullerenes. A substantial amount of information derived from different NMR experiments can thus be found in the literature for a number of fullerenes hydrogenated to various degrees. These studies have benefitted from the fact that chemical shifts of H-1 and C-13 and in some cases also He-3 can be used to obtain structural information of these compounds. Such results, together with discussions about different NMR experiments and general considerations regarding sample preparations, are summarized in this chapter. The unique information, both structural and physicochemical, that can be derived from different NMR experiments ensures that this technique will continue to be of central importance in characterization of hydrogenated fullerenes.

  • 37. Hedman, Daniel
    et al.
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Physics, University of California and the Lawrence Berkeley National Laboratory, USA.
    Rosen, Arne
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Larsson, J. Andreas
    On the Stability and Abundance of Single Walled Carbon Nanotubes2015Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, artikkel-id 16850Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many nanotechnological applications, using single-walled carbon nanotubes (SWNTs), are only possible with a uniform product. Thus, direct control over the product during chemical vapor deposition (CVD) growth of SWNT is desirable, and much effort has been made towards the ultimate goal of chirality-controlled growth of SWNTs. We have used density functional theory (DFT) to compute the stability of SWNT fragments of all chiralities in the series representing the targeted products for such applications, which we compare to the chiralities of the actual CVD products from all properly analyzed experiments. From this comparison we find that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. Our analysis shows that the diameter of the SWNT product is governed by the well-known relation to size of the catalytic nanoparticles, and the specific chirality is normally determined by the product's relative stability, suggesting thermodynamic control at the early stage of product formation. Based on our findings, we discuss the effect of other experimental parameters on the chirality of the product. Furthermore, we highlight the possibility to produce any tube chirality in the context of recent published work on seeded-controlled growth.

  • 38.
    Horvath, Istvan
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Jia, Xueen
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Johansson, Per
    Wang, Chao
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Moskalenko, Roman
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik. Department of Pathology, Sumy State University, Sumy 40000, Ukraine.
    Steinau, Andreas
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Forsgren, Lars
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Svensson, Johan
    Zetterberg, Henrik
    Morozova-Roche, Ludmilla A
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Pro-inflammatory S100A9 Protein as a Robust Biomarker Differentiating Early Stages of Cognitive Impairment in Alzheimer's Disease2016Inngår i: ACS Chemical Neuroscience, ISSN 1948-7193, E-ISSN 1948-7193, Vol. 7, nr 1, s. 34-39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pro-inflammatory protein S100A9 was established as a biomarker of dementia progression and compared with others such as Aβ1-42 and tau-proteins. CSF samples from 104 stringently diagnosed individuals divided into five subgroups were analyzed, including nondemented controls, stable mild cognitive impairment (SMCI), mild cognitive impairment due to Alzheimer's disease (MCI-AD), Alzheimer's disease (AD), and vascular dementia (VaD) patients. ELISA, dot-blotting, and electrochemical impedance spectroscopy were used as research methods. The S100A9 and Aβ1-42 levels correlated with each other: their CSF content decreased already at the SMCI stage and declined further under MCI-AD, AD, and VaD conditions. Immunohistochemical analysis also revealed involvement of both Aβ1-42 and S100A9 in the amyloid-neuroinflammatory cascade already during SMCI. Tau proteins were not yet altered in SMCI; however their contents increased during MCI-AD and AD, diagnosing later dementia stages. Thus, four biomarkers together, reflecting different underlying pathological causes, can accurately differentiate dementia progression and also distinguish AD from VaD.

  • 39.
    Hu, Guangzhi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sandström, Robin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Cheng, Shaodong
    Shen, Hangjia
    Wang, Chuanyi
    Guo, Shaojun
    Yang, Guang
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Atomistic understanding of the origin of high oxygen reduction electrocatalytic activity of cuboctahedral Pt3Co-Pt core-shell nanoparticles2016Inngår i: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 6, nr 5, s. 1393-1401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    PtM-based core-shell nanoparticles are a new class of active and stable nanocatalysts for promoting oxygen reduction reaction (ORR); however, the understanding of their high electrocatalytic performance for ORR at the atomistic level is still a great challenge. Herein, we report the synthesis of highly ordered and homogeneous truncated cuboctahedral Pt3Co-Pt core-shell nanoparticles (cs-Pt3Co). By combining atomic resolution electron microscopy, X-ray photoelectron spectroscopy, extensive first-principles calculations, and many other characterization techniques, we conclude that the cs-Pt3Co nanoparticles are composed of a complete or nearly complete Pt monolayer skin, followed by a secondary shell containing 5-6 layers with similar to 78 at% of Pt, in a Pt3Co configuration, and finally a Co-rich core with 64 at% of Pt. Only this particular structure is consistent with the very high electrocatalytic activity of cs-Pt3Co nanoparticles for ORR, which is about 6 times higher than commercial 30%-Pt/Vulcan and 5 times more active than non-faceted (spherical) alloy Pt3Co nanoparticles. Our study gives an important insight into the atomistic design and understanding of advanced bimetallic nanoparticles for ORR catalysis and other important industrial catalytic applications.

  • 40.
    Hu, Guangzhi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Mikolajczuk, Ania
    Polish Acad Sci, Inst Phys Chem, PL-01224 Warsaw, Poland.
    Tai, Cheuk-Wai
    Stockholm Univ, Arrhenius Lab, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.
    Borodzinski, Andrzej
    Polish Acad Sci, Inst Phys Chem, PL-01224 Warsaw, Poland.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Palladium nanocrystals supported on helical carbon nanofibers for highly efficient electro-oxidation of formic acid, methanol and ethanol in alkaline electrolytes2012Inngår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 209, s. 236-242Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the synthesis of palladium nanocrystals self-assembled on helical carbon nanofibers functionalized with benzyl mercaptan (Pd-S-HCNFs) and their electrocatalytic activity toward the oxidation of formic acid, methanol and ethanol. Helical carbon nanofibers (HCNFs) were first functionalized with benzyl mercaptan based on the pi-pi interactions between phenyl rings and the graphitic surface of HCNFs. Palladium nano crystals (PdNC) were fixed on the surface of functionalized HCNF by Pd-S bonds in a simple self-assembly method. The as-prepared materials were characterized by high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and fuel cell tests. CV characterization of the as-prepared materials shows a very high electrocatalytic activity for oxidation of formic acid, ethanol and methanol in strong alkaline electrolyte. In comparison to commercial catalyst Vulcan XC-72 decorated with Pd nanoparticles, the proposed Pd-S-HCNFs nano composite material shows oxidation currents for formic acid, ethanol and methanol at the Pd-S-HCNF-modified electrode that are higher than that at the Pd/XC-72 modified electrode with a factor of 2.0, 1.5, and 2.3, respectively. In a formic acid fuel cell the Pd-S-HCNF modified electrode yields equal power density as commercial Pd/XC-72 catalyst. Our results show that Pd-decorated helical carbon nanofibers with diameters around 40-60 nm have very high potential as active material in fuel cells, electrocatalysts and sensors. (C) 2012 Elsevier B.V All rights reserved.

  • 41.
    Hu, Guangzhi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ma, Jingyuan
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Jia, Xueen
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lu, Lu
    Ma, Chuansheng
    Yang, Guang
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Small palladium islands embedded in palladium-tungsten bimetallic nanoparticles form catalytic hotspots for oxygen reduction2014Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, s. Article number: 5253-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The sluggish kinetics of the oxygen reduction reaction at the cathode side of proton exchange membrane fuel cells is one major technical challenge for realizing sustainable solutions for the transportation sector. Finding efficient yet cheap electrocatalysts to speed up this reaction therefore motivates researchers all over the world. Here we demonstrate an efficient synthesis of palladium-tungsten bimetallic nanoparticles supported on ordered mesoporous carbon. Despite a very low percentage of noble metal (palladium: tungsten = 1:8), the hybrid catalyst material exhibits a performance equal to commercial 60% platinum/Vulcan for the oxygen reduction process. The high catalytic efficiency is explained by the formation of small palladium islands embedded at the surface of the palladium-tungsten bimetallic nanoparticles, generating catalytic hotspots. The palladium islands are similar to 1 nm in diameter, and contain 10-20 palladium atoms that are segregated at the surface. Our results may provide insight into the formation, stabilization and performance of bimetallic nanoparticles for catalytic reactions.

  • 42.
    Hu, Guangzhi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Chalmers University of Technology.
    Jia, Xueen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Reduction free room temperature synthesis of a durable and efficient Pd/ordered mesoporous carbon composite electrocatalyst for alkaline direct alcohols fuel cell2014Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, nr 2, s. 676-682Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The development of easy and environmentally benign synthesis methods of efficient electrocatalysts for use in energy conversion applications motivates researchers all over the world. Here we report a novel and versatile method to synthesize well-dispersed palladium-functionalized ordered mesoporous carbons (Pd/OMCs) at room temperature without any reducing agent by one-pot mixing of tri(dibenzylideneacetone)palladium(0) (Pd2DBA3) and OMCs together in a common N,N-dimethylformamide (DMF) solution. The formation of Pd nanoparticles and their crystallization on the OMC is catalyzed by protons in the solution and can thus be controlled by the solution pH. The complete process and the as-prepared nanocomposite was characterized by UV-spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (HTEM), X-ray photoelectron spectrum (XPS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The electrocatalytic property of the as-decorated material was examined with cyclic voltammetry (CV). The Pd/OMC composite shows up to two times higher electrocatalytic ability with a significantly better durability towards ethanol and methanol oxidation in alkaline media compared to commercial high surface area conductive carbon black Vulcan XC-72 decorated with equivalent Pd nanoparticles. Our described method provides new insight for the development of highly efficient carbon based nanocatalysts by simple and environmentally sound methods.

  • 43.
    Hu, Guangzhi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Self-assembled palladium nanocrystals on helical carbon nanofibers as enhanced electrocatalysts for electro-oxidation of small molecules2012Inngår i: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, nr 17, s. 8541-8548Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a novel approach to prepare helical carbon nanofibers homogeneously functionalized with single crystal palladium nanoparticles via a phase-transfer method. The materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA) and electrochemical measurements. We find that homogeneous and small single-crystal Pd nanoparticles can be easily functionalized with phenyl mercaptan, transferred into the toluene phase from the dimethyl sulfoxide (DMSO) phase and then non-covalently self-assembled onto the surface of helical carbon nanofibers with a very good dispersion and homogeneous diameters of 4.5 +/- 0.6 nm. The palladium-helical carbon nanofiber composite exhibits significantly higher electrochemical active area and electrocatalytic activity towards the electrooxidation of formic acid, ethanol and methanol than the commercial electrocatalyst Pd/Vulcan XC-72. Our results show that the prepared material can be potentially used as an advanced nano-electrocatalyst in a direct alkaline fuel cell system.

  • 44.
    Hu, Guangzhi
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Tai, Cheuk-Wai
    Stockholm Univ, Dept Mat & Environm Chem, Stockholm, Sweden.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Phase-transfer synthesis of amorphous palladium nanoparticle-functionalized 3D helical carbon nanofibers and its highly catalytic performance towards hydrazine oxidation2012Inngår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 543, s. 96-100Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Amorphous palladium nanoparticles functionalized helical carbon nanofibers (ApPd-HCNFs) were synthesized using a phase-transfer method. Palladium nanoparticles (Pd-NP) were first prepared using n-dodecyl sulfide as reducing agent and stabilizing ligands in ethanol. The Pd-NPs were then modified with benzyl mercaptan and transferred into a toluene solution with HCNFs which were decorated with amorphous palladium. The materials were characterized with high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and cyclic voltammetry showing that amorphous palladium nanoparticles were uniformly anchored at the HCNFs surface and that the ApPd-HCNFs exhibit high electrocatalytic activity towards hydrazine oxidation. (C) 2012 Elsevier B.V. All rights reserved.

  • 45.
    Inaba, Akira
    et al.
    Osaka, Japan.
    Miyazaki, Yuji
    Osaka, Japan.
    Michalowski, Pawel P.
    Warsaw, Poland.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Calorimetric measurements on Li4C60 and Na4C602015Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, nr 16, artikkel-id 164706Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show specific heat data for Na4C60 and Li4C60 in the range 0.4-350 K for samples characterized by Raman spectroscopy and X-ray diffraction. At high temperatures, the two different polymer structures have very similar specific heats both in absolute values and in general trend. The specific heat data are compared with data for undoped polymeric and pristine C60. At high temperatures, a difference in specific heat between the intercalated and undoped C60 polymers of 100 J K−1 mol−1 is observed, in agreement with the Dulong-Petit law. At low temperatures, the specific heat data for Li4C60 and Na4C60 are modified by the stiffening of vibrational and librational molecular motion induced by the polymer bonds. The covalent twin bonds in Li4C60 affect these motions to a somewhat higher degree than the single intermolecular bonds in Na4C60. Below 1 K, the specific heats ofboth materials become linear in temperature, as expected from the effective dimensionality of the structure. The contribution to the total specific heat from the inserted metal ions can be well described by Einstein functions with TE = 386 K for Li4C60 and TE = 120 K for Na4C60, but for both materials we also observe a Schottky-type contribution corresponding to a first approximation to a two-level system with ΔE = 9.3 meV for Li4C60 and 3.1 meV for Na4C60, probably associated with jumps between closely spaced energy levels inside “octahedral-type” ionic sites. Static magnetic fields up to 9 T had very small effects on the specific heat below 10 K.

  • 46.
    Iqbal, Javed
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Department of Chemistry, University of Agriculture, Faisalabad 38040, Pakistan.
    Enevold, Jenny
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Larsen, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wang, Jia
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Revoju, Srikanth
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Eliasson, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Edman, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    An arylene-vinylene based donor-acceptor-donor small molecule for the donor compound in high-voltage organic solar cells2016Inngår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 155, s. 348-355Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A donor-acceptor-donor (D-A-D) molecule has been designed and synthesized for use as the electron donating material in solution-processed small-molecule organic solar cells (OSCs). The D-A-D molecule comprises a central electron-accepting (2Z,2'Z)-2,2'-(2,5-bis(octyloxy)-1,4-phenylene)bis(3-(thiophen-2-yl)acry lonitrile) (ZOPTAN) core, which is chemically connected to two peripheral and electron-donating triphenylamine (TPA) units. The ZOPTAN-TPA molecule features a low HOMO level of -5.2 eV and an optical energy gap of 2.1 eV. Champion OSCs based on a solution-processed and non-annealed active material blend of [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) and ZOPTAN-TPA in a mass ratio of 2:1 exhibits a power conversion efficiency of 1.9% and a high open-circuit voltage of 1.0 V. 

  • 47.
    Iwasiewicz-Wabnig, Agnieszka
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Makarova, Tatiana L.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    No insulator-metal transition in Rb4C60 under pressure below 2 GPaInngår i: Physical Review BArtikkel i tidsskrift (Fagfellevurdert)
  • 48.
    Iwasiewicz-Wabnig, Agnieszka
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Makarova, Tatiana
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Absence of an insulator-metal transition in Rb4C60 up to 2 GPa2008Inngår i: Physical Review B, ISSN 0163-1829, Vol. 77, nr 8, s. 085434-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the results of direct resistance measurements on Rb4C60 under pressures up to 2 GPa. At all pressures covered by this study and over the temperature range of 90–450 K Rb4C60 is a semiconductor with a weakly pressure dependent band gap near 0.7 eV. We do not observe the insulator-to-metal transition previously reported to occur below 1.2 GPa, although we cannot rule out the possibility that such a transition might occur at some significantly higher pressure. The measured resistivity is surprisingly low and is dominated by carriers excited over a 0.1 eV gap. Because the corresponding conductivity increases with deformation of the sample, we assign these states to structural or orientational defects. The known structural transformation below 0.5 GPa leads to a decrease in resistivity under high pressure, but the material remains semiconducting. A Rb6C60 control sample showed a similar behavior, also being a semiconductor under all conditions studied. At temperatures above 460 K, Rb was partially lost from our samples, resulting in metallization by a transformation into Rb3C60.

  • 49.
    Iwasiewicz-Wabnig, Agnieszka
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sundqvist, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Electrical resistance of Rb4C60 under pressure2008Inngår i: The Journal of Physics and Chemistry of Solids, vol. 69, issues 5-6: Proceedings of the 14th International Symposium on Intercalation Compounds - ISIC 14, Amsterdam: Elsevier B.V. , 2008, s. 1218-1220Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We report the results of direct in situ resistance measurements of Rb4C60 under high pressure up to 2 GPa, in the temperature range 90–400 K. The resistance changes smoothly with pressure and temperature without sharp anomalies, and all data sets can be fitted to the same theoretical semiconductor model. We find no signs of the insulator-to-metal transition previously reported in this range, but the fitted band gap decreases with pressure and such a transition may possibly take place above 5 GPa.

  • 50.
    Jia, Xueen
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hu, Guangzhi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nitze, Florian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Barzegar, Hamid Reza
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sharifi, Tiva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Tai, Cheuk-Wai
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Synthesis of Palladium/Helical Carbon Nanofiber Hybrid Nanostructures and Their Application for Hydrogen Peroxide and Glucose Detection2013Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, nr 22, s. 12017-12022Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on a novel sensing platform for H2O2 and glucose based on immobilization of palladium-helical carbon nanofiber (Pd-HCNF) hybrid nanostnictures and glucose oxidase (GOx) with Nafion on a glassy carbon electrode (GCE). HCNFs were synthesized by a chemical vapor deposition process on a C-60-supported Pd catalyst. Pd-HCNF nanocomposites were prepared by a one-step reduction free method in dimethylformamide (DMF). The prepared materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The Nafion/Pd-HCNF/GCE sensor exhibits excellent electrocatalytic sensitivity toward H2O2 (315 mA M-1 cm(-2)) as probed by cyclic voltammetry (CV) and chronoamperometry. We show that Pd-HCNF-modified electrodes significantly reduce the overpotential and enhance the electron transfer rate. A linear range from 5.0 mu M to 2.1 mM with a detection limit of 3.0 mu M (based on the S/N = 3) and good reproducibility were obtained. Furthermore, a sensing platform for glucose was prepared by immobilizing the Pd-HCNFs and glucose oxidase (GOx) with Nafion on a glassy carbon electrode. The resulting biosensor exhibits a good response to glucose with a wide linear range (0.06-6.0 mM) with a detection limit of 0.03 mM and a sensitivity of 13 mA M-1 cm(-2). We show that small size and homogeneous distribution of the Pd nanoparticles in combination with good conductivity and large surface area of the HCNFs lead to a H2O2 and glucose sensing platform that performs in the top range of the herein reported sensor platforms.

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