umu.sePublications
Change search
Refine search result
4567 301 - 337 of 337
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 301.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Persson, Per-Axel
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Jacobsson, Per
    Umeå University, Faculty of Science and Technology, Physics.
    A Raman study of polymerised C601997In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 64, no 3, p. 223-226Article in journal (Refereed)
    Abstract [en]

    Results of Raman scattering studies on high pressure polymerized and photo polymerized C60 are reported. Although prepared according to different routes the Raman spectra of the two polymeric phases of C60 show a quantitative agreement with respect to mode positions and intensity. We conclude from this that both materials have the same structure at least in the short range order, i.e. the same type of bonding and co-ordination between neighbouring C60 molecules. An investigation of the time dependence of the thermal decomposition of high pressure polymerised C60 is also presented. The rate of decomposition of the polymeric phase is found to be multi-exponential at all temperatures investigated. From an Arrhenius-type analysis of the short time data and the long time data, respectively, the activation energy for thermal dissociation of polymeric bonds was found to increase with time.

  • 302.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Persson, Per-Axel
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Jacobsson, Per
    Umeå University, Faculty of Science and Technology, Physics.
    Polymeric phases of C601997In: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, vol. 5: Proceedings of the 192nd Meeting of the Electrochemical Society, Paris 1997; Symposium Fullerenes: Chemistry, Physics, and New Directions, Pennington, NJ: The Electrochemical Society , 1997, p. 674-679Conference paper (Refereed)
    Abstract [en]

    We have investigated the "low" pressure region where C60 can be transformed into polymeric chains or clusters. To learn more about the polymerization process we have treated pristine C60 at several different temperatures under hydrostatic pressures in silicone oil. We found that the reaction rate varied with temperature. Above 520 K at 1.0 GPa similar and high polymer fractions were obtained in all samples, but at 497 K the polymer fraction was only 10% after three hours, as indicated by the shift of the intensity of the pentagonal pinch mode in the Raman spectrum. Also, samples treated at the same pressure and temperature but with different thermal pre-history showed different degrees of polymerization. We have also found a correlation between the shift of the pentagonal pinch mode in the Raman spectrum to 1463 /cm and the intermolecular vibrational mode at 97 /cm. We therefore make the conclusion that the shift of the pentagonal pinch mode to 1463 /cm corresponds to the presence of dimers in the sample.

  • 303.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Soldatov, Alexander
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Spectroscopic study of phase transformations between orthorhombic and tetragonal C60 polymers2006In: The European Physical Journal B: Condensed Matter and Complex Systems, ISSN 1434-6028, Vol. 49, no 1, p. 59-65Article in journal (Refereed)
    Abstract [en]

    We present a detailed study of transformations between the orthorhombic and tetragonal polymeric states of C60. The transformations are characterised by Raman spectroscopy and X-ray diffraction. We show that the transformation from the orthorhombic (O) phase to the tetragonal (T) phase is very fast and our results indicate that the transformation goes via an intermediate dimer (D) state in a two-stage process, O↦D and, D↦T transformations, where the second process is slower than the first. On the other hand, the transformation from the tetragonal to the orthorhombic phase is significantly slower, indicating a high-energy threshold to break the polymer bonds at the temperatures used. The results also support earlier suggestions that the tetragonal phase contains disordered dimers that can be viewed as lattice defects in the formation of higher polymers.

  • 304.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Stenmark, Patrik
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Structural aspects of two-dimensional polymers: Li4C60, Na4C60 and tetragonal C60. Raman spectroscopy and X-ray diffraction.2004In: Journal of Physics and Chemistry of Solids vol. 65, issue no. 2-3: Proceedings of the 12th International Symposium on Intercalation Compounds, ISIC-12, Poznan, Poland 2003, Amsterdam: Elsevier B.V. , 2004, p. 317-320Conference paper (Refereed)
    Abstract [en]

    We present an analysis of three different two-dimensional polymers, tetragonal C60, Li4C60, and Na4C60. Based on X-ray diffraction and Raman spectroscopy, we conclude that Li4C60 forms a tetragonal structure with intermolecular bonds formed by 2 plus 2 cycloaddition, in the same way as for tetragonal C60. Na4C60, on the other hand, forms a monoclinic structure with single C–C bonds between the molecules. Our Raman spectroscopy results can be interpreted in two ways: either the charge transfer to the C60 molecules is the same in both doped compounds with four electrons/molecule or the electron charge transfer is smaller from the Li ions than from the Na ions.

  • 305.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Can two-dimensional fullerene polymers be intercalated?2000In: Molecular Crystals and Liquid Crystals vol. 340: Proceedings of the 10th International Symposium on Intercalation Compounds (ISIC 10), Okazaki 1999, Overseas Publishing Association, B.V. , 2000, p. 677-682Conference paper (Refereed)
    Abstract [en]

    Two-dimensional C60 polymers can be produced by treatment at high T and high p. Attempts have previously been made to intercalate these layered materials by alkali metals using the gas phase method but the polymers have always decomposed. We investigate here whether intercalated 2D polymers can be formed by other methods, such as by polymerization in the presence of alkali metals. Preliminary x-ray and Raman data can be interpreted to indicate the presence of an alkali metal intercalated tetragonal fullerene polymeric structure.

  • 306.
    Wågberg, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Raman study of the two-dimensional polymers Na4C60 and tetragonal C60.2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 15, p. 155421-Article in journal (Refereed)
    Abstract [en]

    We present a Raman investigation of the monoclinic two-dimensionally polymerized phase Na4C60 and a comparison with the pure tetragonal C60 polymer and the doped K3C60 structure. The Raman spectrum of Na4C60 depends on the probing laser wavelength, and high wave-number modes are hard to observe with a low-energy laser excitation. The spectrum for Na4C60 is very rich with a pronounced splitting of the original Hg modes and a large number of new modes. Several modes at low wave numbers support the presence of intermolecular bonds and the line broadening observed for low-frequency Hg modes is typical for electron-phonon coupling in metallic fullerene systems. From the shift of the pentagonal pinch mode we deduce an unexpectedly low charge transfer of approximately three electrons per C60 molecule. The presence of a distinct mode around 980 cm-1 throws doubts on earlier assumptions that modes in this range are connected to vibrations in the intermolecular cyclobutane rings found in C60 polymers. No superconductivity is observed in Na4C60, although the electron-phonon interaction derived from the Raman spectrum is similar to that in K3C60.

  • 307. Xie, Z.L.
    et al.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Hänninen, H.
    Pietikäinen, Juha
    Isothermal martensitic transformation under hydrostatic pressure in an Fe-Ni-C alloy at low temperatures1993In: Acta Metallurgica Et Materialia, ISSN 0956-7151, Vol. 41, no 8, p. 2283-2290Article in journal (Refereed)
    Abstract [en]

    The isothermal martensitic tranformation under applied hydrostatic pressure has been investigated with an Fe-21.5Ni-0.95C alloy single crystal by electrical resistivity, magnetic susceptibility, X-ray diffraction and optical microscopy. The martensitic transformation starting temperature, M(s), is lowered by applied hydrostatic pressure. The isothermal martensitic transformation occurs first as a burst under a critical pressure and it is continued by further transformation with decreasing hydrostatic pressure The critical pressure under which the isothermal martensitic transformation starts changes curvilinearly with decreasing temperature. The morphology of the isothermal martensite formed under hydrostatic pressure is similar to that of athermal martensite. The temperature dependence of the critical pressure under which martensitic transformation starts has been calculated based on the homogeneous nucleation model and the heterogeneous nucleation model.

  • 308. Yang, Xigui
    et al.
    Yao, Mingguang
    Lu, Weibang
    Chen, Shuanglong
    Du, Mingrun
    Zhu, Luyao
    Li, Haiyan
    Liu, Ran
    Cui, Tian
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, P. R. China.
    Liu, Bingbing
    Polarized Raman study of aligned multiwalled carbon nanotubes arrays under high pressure2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 49, p. 27759-27767Article in journal (Refereed)
    Abstract [en]

    Tuning the intertube interaction and the topological structure of carbon nanotubes by the application of pressure may obviously affect their properties such as optical and electronic properties. However, characterizing such changes is still challenging. Here, we performed polarized Raman scattering studies on aligned multiwalled carbon nanotube arrays (MWNTAs). Unlike researchers from the previous literature, we found that the MWNTAs exhibit a polarization dependence similar to that of isolated single walled carbon nanotubes at ambient conditions. Upon compression, the polarization dependence weakens gradually with increasing pressure up to ∼20 GPa, which has been discussed in terms of pressure-induced enhancement of intertube interactions. At around 20 GPa, the depolarization effect vanishes, which can be explained by the formation of interlinked sp3 bonding in the MWNTAs. Our results show that polarized Raman spectroscopy is an efficient method to explore not only intertube interaction but also structural transition changes in MWNTs, which overcome the difficulty that MWNTs have no obvious fingerprints like those of single-walled carbon nanotubes in the study of structural transformations.

  • 309. Yang, Xigui
    et al.
    Yao, Mingguang
    Wu, Xiangying
    Liu, Shijie
    Chen, Shuanglong
    Yang, Ke
    Liu, Ran
    Cui, Tian
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Lab of Superhard Materials, Jilin University, Changchun, China.
    Liu, Bingbing
    Novel Superhard sp3 Carbon Allotrope from Cold-Compressed C70 Peapods2017In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 118, no 24, article id 245701Article in journal (Refereed)
    Abstract [en]

    Design and synthesis of new carbon allotropes have always been important topics in condensed matter physics and materials science. Here we report a new carbon allotrope, formed from cold-compressed C70 peapods, which most likely can be identified with a fully sp3-bonded monoclinic structure, here named V carbon, predicted from our simulation. The simulated x-ray diffraction pattern, near K-edge spectroscopy, and phonon spectrum agree well with our experimental data. Theoretical calculations reveal that V carbon has a Vickers hardness of 90 GPa and a bulk modulus ∼400  GPa, which well explains the "ring crack" left on the diamond anvils by the transformed phase in our experiments. The V carbon is thermodynamically stable over a wide pressure range up to 100 GPa, suggesting that once V carbon forms, it is stable and can be recovered to ambient conditions. A transition pathway from peapod to V carbon has also been suggested. These findings suggest a new strategy for creating new sp3-hybridized carbon structures by using fullerene@nanotubes carbon precursor containing odd-numbered rings in the structures.

  • 310. Yang, Zhenxing
    et al.
    Hu, Kuo
    Meng, Xianwei
    Tao, Qiang
    Dong, Jiajun
    Liu, Bo
    Lu, Qian
    Zhang, Hua
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Superhard Materials, College of Physics, Jilin University, People's Republic of China.
    Zhu, Pinwen
    Yao, Mingguang
    Liu, Bing bing
    Tuning the band gap and the nitrogen content in carbon nitride materials by high temperature treatment at high pressure2018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 130, p. 170-177Article in journal (Refereed)
    Abstract [en]

    Carbon nitride (C-N) materials have been attracting great interest because of their extraordinary performance in photocatalysis and energy conversion. However, developing an effective strategy for achieving band-gap engineering of C-N materials to satisfy practical applications remains highly desired. Here we report an efficient way to tune the band gap and control the nitrogen stoichiometry in carbon nitride compounds by using high pressure and high temperature (HPHT) treatment. It is found that treating a g-C3N4 precursor at relatively low temperature (630oC and below) under pressure can efficiently narrow the band gap even down to the red light region (~600 nm), increase the crystallinity, and significantly improve the charge carrier separation efficiency (by two orders of magnitude), almost without changing their stoichiometry. When increasing the treatment temperature under pressure, nitrogen-doped graphene/graphite materials with weak ferromagnetism were obtained. We thus obtained C-N materials with tunable band gaps, ranging from semiconducting to metallic states. XPS measurements show that pyridinic nitrogen is preferentially eliminated under such HPHT conditions while graphitic nitrogen is preserved in the C-N network. Our results thus provide an efficient strategy for tuning the structure and physical properties of C-N materials for applications.

    The full text will be freely available from 2019-12-29 00:00
  • 311.
    Yao, Mingguang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Britt M
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Stenmark, Patrik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Liu, Bingbing
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Synthesis and growth mechanism of differently shaped C60 nano/microcrystals produced by evaporation of various aromatic C60 solutions2009In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 47, no 4, p. 1181-1188Article in journal (Refereed)
    Abstract [en]

    We present a detailed study of the synthesis of C60 nano- and microrods as well as crystals with normal shapes by the evaporation of C60 solutions based on different aromatic solvents. C60 nano- and microrods are grown with high yield by vaporizing C60 solutions in meta-isomers of aromatic solvents on different substrates while para-isomers give a different type of growth leading to highly crystalline two- and three-dimensional nano- and microcrystals with fcc structure. The role of solvent properties was investigated by using positional isomers containing different halogen radicals. The as-grown crystal rods formhexagonal structures but transform into fcc structure on annealing in vacuum. IR and EDX analysis indicate that solvents remain in the hexagonal nano- and microrods, while it is hard to detect any trace of solvents in the two- or three-dimensional nano- and microcrystals. Furthermore, we present direct proof of the nucleation-growth mechanism for C60 rods. By the vaporization method, the solubility of C60 in the studied halogen aromatic solvents is found to correlate with the diameter distribution of the C60 rods and we suggest that the chemical affinity of the aromatic solvent molecules to C60 may determine its ability to force C60 to form rod-shaped crystals.

  • 312.
    Yao, Mingguang
    et al.
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Cui, Wen
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Du, Mingrun
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Xiao, Junping
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Yang, Xigui
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Liu, Shijie
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Liu, Ran
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Wang, Fei
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Cui, Tian
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Liu, Bingbing
    State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
    Tailoring Building Blocks and Their Boundary Interactionfor the Creation of New, Potentially Superhard, Carbon Materials2015In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 27, no 26, p. 3962-3968Article in journal (Refereed)
    Abstract [en]

    A strategy for preparing hybrid carbon structures with amorphous carbon clusters as hard building blocks by compressing a series of predesigned two-component fullerides is presented. In such constructed structures the building blocks and their boundaries can be tuned by changing the starting components, providing a way for the creation of new hard/superhard materials with desirable properties.

  • 313. Yao, Mingguang
    et al.
    Cui, Wen
    Xiao, Junping
    Chen, Shuanglong
    Cui, Jinxing
    Liu, Ran
    Cui, Tian
    Zou, Bo
    Liu, Bingbing
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Pressure-induced transformation and superhard phase in fullerenes: the effect of solvent intercalation2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 7, p. 071913-Article in journal (Refereed)
    Abstract [en]

    We studied the behavior of solvated and desolvated C-60 crystals under pressure by in situ Raman spectroscopy. The pressure-induced bonding change and structural transformation of C60s are similar in the two samples, both undergoing deformation and amorphization. Nevertheless, the high pressure phases of solvated C-60 can indent diamond anvils while that of desolvated C(60)s cannot. Further experiments suggest that the solvents in the solvated C-60 act as both spacers and bridges by forming covalent bonds with neighbors in 3D network at high pressure, and thus, a fraction of fullerenes may preserve the periodic arrangement in spite of their amorphization.

  • 314. Yao, Mingguang
    et al.
    Fan, Xianhong
    Zhang, Weiwei
    Bao, Yongjun
    Liu, Ran
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
    Liu, Bingbing
    Uniaxial-stress-driven transformation in cold compressed glassy carbon2017In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 111, no 10, article id 101901Article in journal (Refereed)
    Abstract [en]

    We show that transformation of glassy carbon (GC) into a translucent superhard carbon phase by cold-compression is obtained in the presence of a uniaxial stress field. This transition accompanies with sp(2) to sp(3) bonding change in GC, and it is found that the uniaxial stress strongly favors this bonding transition. The transformation of GC causes photoluminescence and significantly increases light transmissivity. Upon decompression, the high pressure phase can be maintained under large uniaxial stress at a chamber pressure even down to similar to 10GPa. We discuss possible mechanisms of these transitions by a distinct bonding process that occurs in noncrystalline carbon.

  • 315. Yao, Mingguang
    et al.
    Liu, Bingbing
    Zou, Y.G.
    Wang, Lin
    Li, D.M.
    Zou, Guangtian
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Synthesis of single-wall carbon nanotubes and long nanotube ribbons with Ho/Ni as catalyst by arc discharge2005In: Carbon, ISSN 0008-6223, Vol. 43, no 14, p. 2894-2901Article in journal (Refereed)
    Abstract [en]

    The effect of a new bimetallic catalyst Ho/Ni for synthesis of single-walled carbon nanotubes (SWNTs) by arc discharge has been studied. Long ribbons consisting of roughly-aligned SWNT bundles were obtained by a modified arc discharge apparatus. Ribbon lengths can reach as much as 20 cm. Both elements Ho and Ni play important roles in the synthesis of SWNTs with high yield and purity. Changes in the Ho and Ni concentration in the catalyst hardly affect the diameter distribution of SWNTs, but the yield and purity of SWNTs are very sensitive to the concentration. An optimal range of Ho/Ni compositions for synthesis of SWNTs with relatively high purity and yield is given.

  • 316. Yao, Mingguang
    et al.
    Liu, Bingbing
    Zou, Yonggang
    Li, DongMei
    Ai, XiaoLei
    Wang, Lin
    Yu, Shidan
    Zou, Guangtian
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Synthesis and characterization of SWCNTs with Ho/Ni as catalyst2006In: New Carbon Materials, ISSN 1007-8827, Vol. 21, no 1, p. 70-74Article in journal (Refereed)
    Abstract [en]

    SWCNTs were synthesized with high yield by DC arc discharge using Ho/Ni as catalysts. The morphologies, diameter distribution and the content of SWCNTs in the products were characterized by SEM, Raman scattering and TGA. Results indicate that SWCNTs can be efficiently synthesized with Ho/Ni as catalysts. The volume content of SWCNTs in a "web-like" form is as high as 80% in the product. Furthermore, the diameter distribution of SWCNTs, estimated by analyzing the resonance Raman scattering using excitation wavelengths of 632 and 488nm, varies from 1.35 to 1.69nm with a dominant diameter of 1.5nm, which is different from that of the SWCNTs synthesized with Ce/Ni as catalyst, proving that the diameter distribution of SWCNTs is dependent on the properties of the metal catalysts.

  • 317. Yao, Mingguang
    et al.
    Liu, Bingbing
    Zou, Yonggang
    Wang, Lin
    Cui, Tian
    Zou, Guangtian
    Li, Jixue
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Effect of rare-earth component of the RE/Ni catalyst on the formation and nanostructure of single-walled carbon nanotubes2006In: Journal of Physical Chemistry B, ISSN 1520-6106, Vol. 110, no 31, p. 15284-15290Article in journal (Refereed)
    Abstract [en]

    A systematic experimental study has been carried out on the efficiency of bimetallic catalysts based on Ni and the rare-earth elements Y, La, Ce, Nd, Gd, Tb, Dy, Ho, Er, and Lu ( group A) and Eu, Sm, Yb, and Tm ( group B) in the synthesis of single-walled carbon nanotubes (SWNTs). The two groups give quite different results when analyzed by a combination of SEM/TEM and Raman and UV-NIR spectroscopies. The elements in group A have an obvious catalytic effect and increase the yield of SWNTs dramatically, whereas those in group B are not efficient catalysts. The diameter distribution of the synthesized SWNTs was also affected by the rare-earth element used. For group A metals, there is a tendency that the fraction of small-diameter tubes decreases with decreasing ionic radius of the rare-earth element used. EDX and X-ray analyses indicate that group A metals deposit on the cathode deposits and form rare-earth carbides, whereas no group B metals are found in cathode deposits, except for a small amount of Tm present in the form of thulium carbide. Further analysis indicates that there is a very strong correlation between the ability to form rare-earth carbides and the catalytic efficiency for the formation of SWNTs.

  • 318. Yao, Mingguang
    et al.
    Pischedda, Vittoria
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mezouar, Mohamed
    Debord, Régis
    San Miguel, Alfonso
    Pressure-induced transformation in Na4C60 polymer: X-ray diffraction and Raman scattering experiments2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 14, p. 144106-Article in journal (Refereed)
    Abstract [en]

    In this article the alkali metal-intercalated two-dimensional (2D) polymer Na4C60 is studied under pressure up to 41 GPa at room temperature by Raman spectroscopy and x-ray diffraction (XRD) measurements. Two transitions are identified in the studied pressure range. The first one is observed at ∼3 GPa by both diffraction and Raman scattering. A kink in the pressure slope of the cell parameters (especially along the c axis) shows the appearance of a less compressible phase. The decrease in the C60-C60 distance and the Na-C distance, combined with the frequency softening of the Raman modes, leads to a picture of higher electron hopping. The second transition occurs at around 15 GPa, where the distinct Raman peaks of 2D-Na4C60 disappear and become very broad and diffuse. New bands at 200–800 cm−1, 1590 cm−1, and ∼1800 cm−1, exhibit similar features to those of a reported 3D-C60 polymeric structure. The XRD data show that the cell parameters a, b, and c deviate from their early pressure evolution and become almost pressure independent, accompanied by the formation of amorphous material. Both the evolution of the Raman features of Na4C60 at pressures above 15 GPa and the Raman measurements of the samples on decompression indicate that most C60 molecules in the material are preserved after such a high pressure cycle. Our findings are discussed in terms of the formation of the first high-pressure intercalated C60 3D-polymer structure through the random creation of new polymeric bonds between fullerene molecules.

  • 319. Yao, Mingguang
    et al.
    Pischedda, Vittoria
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Le Floch, Sylvie
    San Miguel, Alfonso
    Laser-induced transformation of Li4C60 and Na4C60 polymers into metallic monomeric fulleride phases2010In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 489, no 1-3, p. 64-68Article in journal (Refereed)
    Abstract [en]

    We demonstrate that laser irradiation on the narrow-gap insulator Li4C60 and Na4C60 polymers results in metallic monomeric structures, having the same Raman features as metallic fcc K3C60 and Rb3C60, with orientationally disordered C3-60  anions stable at ambient conditions. The Raman Ag(2) mode indicates that a single phase was obtained. Additionally, a monomeric A4C60-type phase (A = K, Rb) is observed in Na4C60 after irradiation. The electron–phonon coupling constants derived from Raman modes of C3-60 fullerides is found to be higher than that of C3-60 fullerides, agreeing with the trend found in heavy alkali fullerides. We propose possible structures of the metallic phases.

  • 320.
    Yao, Mingguang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Reversible pressure-driven nanoscale phase separation in Rb4C602009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 8, p. 081403-Article in journal (Refereed)
    Abstract [en]

    Wepresent Raman spectra for Rb4C60 at pressures up to 13GPa. Above 1 GPa we observe a phase separation ofRb4C60 into Rb6C60 and Rb3C60, identified by a splitting ofthe Ag(2) mode and the appearance of characteristic Raman modesof the daughter phases. Remarkably, the phase separation is completelyreversible and the sample returns to a homogeneous Rb4C60 phaseafter pressure release. The reversibility of the phase separation suggeststhat the structural change is associated with small displacements ofRb ions in the unit cell, giving local differences inthe charge state of the C60 molecules. The pressure dependenceof the Raman shifts agrees well with earlier measurements. Ourobservation of a reversible phase separation explains several peculiar resultsreported earlier for Rb4C60.

  • 321.
    Yao, Mingguang
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Wang, Zhigang
    Liu, Bingbing
    Zou, Yonggang
    Yu, Shidan
    Lin, Wang
    Hou, Yuanyuan
    Pan, Shoufu
    Jin, Mingxing
    Zou, Bo
    Cui, Tian
    Zou, Guangtian
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Raman signature to identify the structural transition of single-wall carbon nanotubes under high pressure2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 20, p. 205411-Article in journal (Refereed)
    Abstract [en]

    Raman spectra of single-walled carbon nanotubes (SWNTs) with diameters of 0.6–1.3 nm have been studied under high pressure. A “plateau” in the pressure dependence of the G-band frequencies was observed in all experiments, both with and without pressure transmission medium. Near the onset of the G-band plateau, the corresponding radial breathing mode (RBM) lines become very weak. A strong broadening of the full width at half maximum of the RBMs just before the onset of the G-band plateau suggests that a structural transition starts in the SWNTs. Raman spectra from SWNTs released from different pressures also indicate that a significant structural transition occurs during the G-band plateau process. Simulations of the structural changes and the corresponding Raman modes of a nanotube under compression show a behavior similar to the experimental observations. Based on the experimental results and the theoretical simulation, a detailed model is suggested for the structural transition of SWNTs, corresponding to the experimentally obtained Raman results in the high-pressure domain.

  • 322.
    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.

  • 323.
    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.

  • 324.
    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.

  • 325.
    You, Shujie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Luzan, Serhiy
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr V
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Phase transitions in graphite oxide solvates at temperatures near ambient2012In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 3, no 7, p. 812-817Article in journal (Refereed)
    Abstract [en]

    It is demonstrated that solvent-saturated graphite oxide can be considered to be solid solvate, and two phases with distinctly different solvent composition are found near room temperature. Phase transitions between these two solvated phases were observed using synchrotron powder X-ray diffraction and DSC for methanol, ethanol, acetone, and dimethylformamide (DMF) solvents. Solvate A, formed at room temperature, undergoes a reversible phase transition into expanded Solvate L at temperatures slightly below ambient due to insertion of one monolayer of solvent molecules between the GO planes. The phase transition is reversible upon heating, whereas the low-temperature expanded phase L can be quenched to room temperature for ethanol and DMF solvates.

  • 326.
    You, Shujie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Enormous lattice expansion of hummers graphite oxide in alcohols at low temperatures2013In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 7, no 2, p. 1395-1399Article in journal (Refereed)
    Abstract [en]

    A structural study of swelling of Hummers graphite oxide (H-GO) in excess of liquid alcohols was performed as a function of temperature using synchrotron X-ray diffraction and revealed a strong “negative thermal expansion” effect. The increase of the distance between graphene oxide layers is explained by insertion of additional solvent upon cooling of the H-GO/solvent system. The interlayer distance of H-GO is found to increase gradually upon temperature decrease, reaching 19.4 and 20.6 Å at 140 K for methanol and ethanol, respectively. The gradual expansion of the H-GO lattice upon cooling corresponds to insertion of at least two additional solvent monolayers and can be described as osmotic swelling. This phenomenon is distinctly different from the solvation of Brodie graphite oxide (B-GO), which was found earlier to exhibit crystalline swelling: single-step insertion of an additional solvent monolayer at low temperatures. The enormous structural expansion of H-GO at low temperatures is suggested to be useful for solution-based intercalation of graphite oxide with relatively large molecules and the synthesis of various composite materials.

  • 327.
    You, Shujie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Belyaeva, L. A.
    Avramenko, Natalya V.
    Korobov, Mikhail V.
    Talyzin, Alexandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Selective Intercalation of Graphite Oxide by Methanol in Water/Methanol Mixtures2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 4, p. 1963-1968Article in journal (Refereed)
    Abstract [en]

    Graphite oxide is selectively intercalated by methanol when exposed to liquid water/methanol mixtures with methanol fraction in the range 20-100%. Insertion of water into the GO structure occurs only when the content of water in the mixture with methanol is increased up to 90%. This conclusion is confirmed by both ambient temperature XRD data and specific temperature variations of the GO structure due to insertion/deinsertion of an additional methanol monolayer observed upon cooling/heating. The composition of GO-methanol solvate phases was determined for both low temperature and ambient temperature phases. Understanding of graphite oxide structural properties in binary water/methanol mixtures is important for the unusual permeation properties of graphene oxide membranes for water and alcohols. It is suggested that graphite oxide prepared by Brodie's method can be used for purification of water using selective extraction of methanol from water/alcohol mixtures.

  • 328.
    You, Shujie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Solvation of graphite oxide in water-methanol binary polar solvents2012In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 249, no 12, p. 2568-2571Article in journal (Refereed)
    Abstract [en]

    The phase transition between two solvated phases was studied by DSC for graphite oxide (GO) powders immersed in water–methanol mixtures of various compositions. GO forms solid solvates with two different compositions when immersed in methanol. Reversible phase transition between two solvate states due to insertion/desertion of methanol monolayer occurs upon temperature variations. The temperature point and the enthalpy (DH) of the phase transition are maximal for pure methanol and decrease linearly with increase of water fraction up to 30%.

     

  • 329.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermal conductivity of highly crystallized polyethylene2014In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 55, no 1, p. 195-200Article in journal (Refereed)
    Abstract [en]

    We report thermal conductivity (kappa) of low-density, high-density and ultra-high density polyethylene (PE) with different crystallinity and microstructures. PE was crystallized under high-pressure and high-temperature conditions which produce extended chain crystals. By applying a two-phase model, we estimate kappa of 100% crystallized PE as a function of pressure and temperature. The increased crystallinity and lamellar thickness (fold length) reduce the thermal resistance, which is reflected not only in the absolute value of kappa but also in more pronounced pressure and temperature dependencies approaching those of polycrystalline low-molecular weight materials. The results suggest that it is crucial to increase the lamellar thickness to significantly improve kappa of PE with randomly oriented lamellae.

  • 330.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yao, Mingguang
    Gröbner, Gerhard
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Liu, Bingbing
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Buckminsterfullerene: A Strong, Covalently Bonded, Reinforcing Filler and Reversible Cross-Linker in the Form of Clusters in a Polymer2013In: ACS Macro Letters, ISSN 2161-1653, Vol. 2, no 6, p. 511-517Article in journal (Refereed)
    Abstract [en]

    A Buckminsterfullerene/polyisoprene (C60/PI) composite was synthesized at high-temperature, high-pressure (HP&HT) conditions. The composite has significantly improved tensile strength and Young’s modulus, by up to 49% and 88% per wt % C60, respectively, which is much higher than for corresponding composites with carbon nanotube (CNT) fillers. The reinforcing action of C60 fillers is different from that of CNTs as C60 becomes covalently bonded to PI chains, and C60 clusters in PI form C60–C60 covalent bonds. The latter are reversible and break by heating at 1 bar, which suggests improved recyclability of the material and indicates that carbon nanostructures can be used as strong reversible cross-linkers (“vulcanizers”) in elastomers.

  • 331. Yu, Miao
    et al.
    Liu, Bingbing
    Li, Dongmei
    Li, Minghui
    Yao, Mingguang
    Wang, Lin
    Wang, Hui
    Zou, Guangtian
    Wang, Xu
    Zhao, Bing
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    SERS study of single-walled carbon nanotubes on silver films deposited on different substrates2003In: Chemical Journal of Chinese Universities / Gao Deng Xue Xiao Hua Xue Xue Bao, ISSN (printed): 0251-0790, Vol. 24, no 6, p. 1285-1288Article in journal (Refereed)
    Abstract [en]

    Surface-enhanced Raman scattering of single-walled carbon nanotubes (SWNTs) on silver films deposited on various substrates, including sapphire, quartz and glass, has been studied systematically. The characteristic features of G-band and D-band have been analyzed and compared with arc discharged and laser ablation samples. D-band is much more sensitive than G-band. The position and the intensity of the G-band in SERS spectra depend on substrates. The peak shift and absolute intensity of G-band on sapphire is obviously larger than that on glass. The contribution of high frequency vibrations to the D-band is also deendent on substrates. Compared to the SWNTs samples with a high semiconducting tube concentration, the sample with high metallic tube concentration has a stronger interaction with silver films.

  • 332.
    Zhu, Xiaomei
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Brändström, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Mechanical measurement of the transverse force on the moving vortices in superconductors1996In: Czechoslovak Journal of Physics volume 46, Supplement S3: Proceedings of the 21st International Conference on Low Temperature Physics (LT 21), Prague 1996, part S3: Superconductivity 2, Praha: CZECHOSLOVAK JOURNAL OF PHYSICS , 1996, p. 1727-1728Conference paper (Refereed)
    Abstract [en]

    We have designed a mechanical experiment to measure the total transverse force on moving vortices in a type II superconductor. The transverse force is measured by monitoring the motion of the superconductor while the vortices are driven into motion by a moving magnet. The advantage of this direct force measurement is that it is free from complications due to vortex interactions.

  • 333.
    Zhu, Xiaomei
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Brändström, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Observation of the transverse force on moving vortices in YBCO films1997In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 78, no 1, p. 122-125Article in journal (Refereed)
    Abstract [en]

    We have designed a mechanical experiment to measure the total transverse force on moving vortices in a type II superconductor. The vortices are driven into motion by the vibration of a magnet above a superconducting YBCO film. The transverse force is measured by monitoring the motion of the superconductor in response. The advantage of this direct force measurement is that it is free from complications due to the vortex interaction. Our results are consistent with the Ao-Thouless theory.

  • 334.
    Zhu, Xiaomei
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Brändström, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Bäckström, Gunnar
    Umeå University, Faculty of Science and Technology, Physics.
    Measurement of the total transverse force on moving vortices in YBCO films1996In: Proceedings of 10th Anniversary HTS Workshop on Physics, Materials, and Applications, Houston 1996, Singapore: World Scientific , 1996, p. 417-418Conference paper (Refereed)
    Abstract [en]

    We have designed a mechanical experiment to measure the total transverse force on moving vortices in type II superconductors. The vortices are driven into motion by the vibration of a permanent magnet above a relatively large superconductor. The transverse force is measured by monitoring the motion of the superconducting film mounted on a quartz plate.

  • 335. 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.

  • 336. Zou, Yonggang
    et al.
    Liu, Bingbing
    Yao, Mingguang
    Hou, Yuanyuan
    Wang, Lin
    Yu, Shidan
    Wang, Peng
    Cui, Tian
    Zou, Guangtian
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Guorui
    Lin, Yichun
    Effective polymerization of C60 in SWNTs under high pressure and simultaneous UV light irradiation2007In: Acta Physica Sinica (Wuli Xuebao), ISSN 1000-3290, Vol. 56, no 9, p. 5172-5175Article in journal (Refereed)
    Abstract [en]

    The C-60 @ SWNT ( peapod) samples were prepared by the vapor diffusion method. Polymerization of C60 molecules in single walled carbon nanotubes (SWNTs) under high pressure and simultaneous irradiation of UV laser (325 nm) has been carried out for the first time by using diamond anvil cell. Raman spectra of the peapod samples decompressed from high pressure indicated that C60 molecules form one-dimensional orthorhombic polymer in SWNTs under UV laser irradiation at a high pressure of 21.5 GPa, which is lower than that for the polymerization of samples induced by high pressure only. The polymerization is an irreversible phase transition in the peapod.

  • 337. 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.

4567 301 - 337 of 337
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf