| 1. |
- Cui, Wen, et al.
(författare)
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Synthesis of alkali-metal-doped C60 nanotubes
- 2011
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Ingår i: Diamond and Related Materials. - : Elsevier BV. ; , s. 93-96
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Konferensbidrag (refereegranskat)abstract
- C60 nanotubes have been synthesized by a solution–solution method. After degassing in a dynamic vacuum, the C60 nanotubes were doped with alkali metals by means of vapor evaporation method. Different temperatures have been studied to evaporate the alkali metals for the doping experiments. Raman spectrum was further employed to analyze the doping concentration of the obtained samples. It was found that all three alkali metals (Li, Na and K) used can be efficiently doped into the C60 nanotubes, forming AxC60 nanotubes. The doping concentration of Li, Na changed from low to high level, depending on the experiment temperatures, while K doping always gave saturated doping. The melt points, the ionic sizes and vapor pressures of alkali metals were thought to affect the final doping results.
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| 2. |
- Liu, Dedi, et al.
(författare)
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High pressure and high temperature induced polymerization of C60 nanotubes
- 2011
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Ingår i: CrystEngComm. - : Royal Society of Chemistry. - 1466-8033 .- 1466-8033. ; 13:10, s. 3600-3605
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Tidskriftsartikel (refereegranskat)abstract
- C60 nanotubes with outer diameters ranging from 400–800 nm were polymerized at 1.5 GPa, 573 K and 2.0 GPa, 700 K, respectively. Raman and photoluminescence spectroscopy were employed to characterize the polymeric phases of the treated samples. Both Raman and photoluminescence spectra showed that the C60 nanotubes transformed into the dimer and orthorhombic phases under the two different conditions, respectively. The photoluminescence peaks were tuned from visible to near infrared range. Comparative studies indicated that C60 nanotubes were more difficult to polymerize than bulk C60 material under the same conditions due to the nanoscale size effect in the C60 nanotubes.
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| 3. |
- Liu, Dedi, et al.
(författare)
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Pressure-induced phase transitions of C70 nanotubes
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 115:18, s. 8918-8922
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Tidskriftsartikel (refereegranskat)abstract
- Single crystalline C70 nanotubes having a face-centered-cubic (fcc) structure with diameters on a nanometer scale were synthesized by a facile solution method. In situ high pressure Raman spectroscopy and X-ray diffraction have been employed to study the structural stability and phase transitions of the pristine sample. We show that the molecular orientation-related phase transition from the fcc structure to a rhombohedral structure occurs at about 1.5 GPa, which is 1 GPa higher than in bulk C70. Also, the C70 molecules themselves are more stable in the nanotubes than in bulk crystals, manifested by a partial amorphization at 20 GPa. The crystal structure of C70 nanotubes could partially return to the initial structure after a pressure cycle above 30.8 GPa, and the C70 molecules were intact up to 43 GPa. The bulk modulus of C70 nanotubes is measured to be 50 GPa, which is twice larger than that of bulk C70.
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| 4. |
- Liu, Dedi, et al.
(författare)
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Synthesis and solid-state studies of self-assembled C60 microtubes
- 2011
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Ingår i: Diamond and Related Materials, vol. 20 issue 2. - : Elsevier BV. ; , s. 178-182
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Konferensbidrag (refereegranskat)abstract
- C60 microtubes were fabricated by a modified solution evaporation method, evaporating a solution of C60 in toluene in an atmosphere of m-xylene at room temperature. The C60 microtubes have outer diameters ranging from 2 to 8 μm. IR spectra, TG analysis and X-ray diffraction showed a solvated structure for the as-grown C60 microtubes. Through a gentle heat-treatment in vacuum, pure C60 microtubes with single crystalline fcc structure were obtained after the elimination of solvents. It is suggested that the C60 microtubes form through self-assembly from several individual C60 nanorods.
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| 5. |
- Sundqvist, Bertil, et al.
(författare)
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High pressure studies of alkali metal doped fullerides A4C60
- 2011
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Ingår i: Diamond and Related Materials, Volume 20, issue 4. - : Elsevier. ; , s. 600-603
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Konferensbidrag (refereegranskat)abstract
- The electrical resistance R of K4C60 and Li4C60 has been measured between 100 and 300 K under pressures up to 1 and 2 GPa, respectively. For both materials, the temperature coefficient of R is negative at all pressures and temperatures in this range. The transport properties of Li4C60 at low pressure are compatible with a recent observation of high ionic conductivity, but surprisingly, this conductivity term increases strongly with increasing pressure, contradicting an intuitive model. For K4C60 we see no sign of a recently suggested structural phase transformation at low temperature, nor can we find any convincing evidence for a lattice disproportionation as recently observed for Rb4C60.
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| 6. |
- Yao, Mingguang, et al.
(författare)
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Confined adamantane molecules assembled to one dimension in carbon nanotubes
- 2011
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 49:4, s. 1159-1166
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Tidskriftsartikel (refereegranskat)abstract
- We have encapsulated adamantane (C10H16) in single- and multi-walled carbon nanotubes. Adamantane is a high symmetry cage like molecule with point group symmetry T-d and can be considered as a hydrogen-terminated diamond fragment. We confirmed and identified the successful filling by high resolution transmission electron microscopy, C-13 nuclear magnetic resonance, infrared and Raman spectroscopy. C-13 nuclear magnetic resonance of the adamantane filled nanotubes reveals that the adamantane molecules stop rotating after encapsulation. A blue-shift of the Raman active radial breathing modes of the carbon nanotubes supports this and suggests a significant interaction between encapsulated adamantane molecules and the single wall nanotubes. The encapsulated adamantane molecules exhibit red shifted infrared C-H vibration modes which we assign to a slight elongation of the C-H bonds. We observe both a nanotube diameter dependence of the adamantane filling ratio and a release rate of adamantane from the CNTs that depends on the CNT diameters.
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| 7. |
- Yao, Mingguang, et al.
(författare)
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Pressure-induced transformation in Na4C60 polymer: X-ray diffraction and Raman scattering experiments
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:14, s. 144106-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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