| 51. |
- Mattsson, M, et al.
(författare)
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Dielectrophoresis-induced separation of metallic and semiconducting SWNT in a continuous flow microfluidic system
- 2007
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Ingår i: Journal of Nanotechnology and Nanoscience. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 7, s. 3431-3435
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Tidskriftsartikel (refereegranskat)abstract
- The AC dielectrophoresis-induced separation of metallic and semiconducting single-wall carbon nanotubes has been carried out in a continuous flow microfluidic system with isolated electrodes. The separation has been studied for single-wall carbon nanotube aqueous suspensions with ionic (sodium dodecylsulphate) and non-ionic (TritonX-100) surfactants. The efficiency of separation has been determined with the help of resonant Raman spectroscopy using various excitation energies. The prototype microfluidic cell presently shows somewhat inferior separation efficiency with respect to static dielectrophoretic filtering on arrays of microelectrodes but has potential for improvements. Factors influencing the separation efficiency and scaling up of the process are discussed.
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| 52. |
- Mehlig, Kirsten, 1964, et al.
(författare)
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Energy distributions in multiple photon absorption experiments
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120, s. 4281-4288
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation experiments on molecules and clusters often involve multiple photon absorption. The distributions of the absorbed number of photons are frequently approximated by Poisson distributions. For realistic laser beam profiles, this approximation fails seriously due to the spatial variation of the mean number of absorbed photons across the laser beam. We calculate the distribution of absorbed energy for various laser and molecular-beam parameters. For a Gaussian laser beam, the spatially averaged distributions have a power-law behavior for low energy with a cutoff at an energy which is proportional to fluence. The power varies between –1 for an almost parallel laser beam and –5/2 for a divergent beam (on the scale of the molecular beam). We show that the experimental abundance spectra of fullerenes and small carbon clusters can be used to reconstruct the distribution of internal energy in the excited C60 molecule prior to fragmentation and find good agreement with the calculated curves
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| 53. |
- Morjan, Raluca Elena, 1976, et al.
(författare)
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High growth rates and wall decoration of carbon nanotubes grown by plasma-enhanced chemical vapour deposition
- 2004
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 383/4, s. 385-390
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- DC plasma-enhanced chemical vapour deposition (PECVD) was used to grow films of aligned carbon nanotubes on a silicon wafer using Fe as catalyst and a C2H2/H2 gas mixture. The films were of high quality and showed an exceptionally high growth rate compared with other plasma growth techniques. For long growth times, the upper parts of the nanotubes developed additional outer graphite flakes. The onset of the ‘tube decoration’ correlates with a decrease in linear growth rate and can be related to the gradient of plasma parameters in the cathode sheath.
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| 54. |
- Morjan, Raluca Elena, 1976, et al.
(författare)
-
Selective growth of individual multiwalled carbon nanotubes
- 2004
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Ingår i: Current Applied Physics. - : Elsevier BV. - 1567-1739. ; 4:6, s. 591-594
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Tidskriftsartikel (refereegranskat)abstract
- Growth of individual, vertically aligned multiwalled carbon nanotubes (VACNT) on patterned Si wafers using dc plasma-enhanced CVD is described. The selective growth of individual VACNT within larger holes etched in Si is demonstrated for the first time.
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| 55. |
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| 56. |
- Podenok, S., et al.
(författare)
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Electric field enhancement factors around a metallic, end-capped cylinder
- 2006
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Ingår i: Nano. - 1793-2920. ; 1, s. 87-93
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Tidskriftsartikel (refereegranskat)abstract
- We have calculated the electric field enhancement factor for a metallic cylinder with a hemispherical end-cap in a plane capacitor geometry paying particular attention to the dependence of the field enhancement factor on the anode distance. In addition, we have investigated the angular dependence of the local field at the end-cap. The numerical results, which cover a range of different ratios of cylinder lengths and anode distances, can be fitted with simple functional expressions which provide a useful scaling for calculations of field emission currents from closed cap carbon nanotubes or nanowires.
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| 57. |
- Popok, Vladimir, 1966, et al.
(författare)
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Complex crater formation on silicon surfaces by low-energy Ar cluster ion implantation
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 566-568, s. 1179-1184
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Tidskriftsartikel (refereegranskat)abstract
- Silicon samples were implanted by small mass-selected Ar cluster and Ar+ monomer ions with energies in the range of 1.5-18.0 keV/ion. Atomic force microscopy (AFM) shows simple and complex crater formation on the Si surface at the collision spots. A typical complex crater is surrounded by a low-height (0.5 nm) rim and it encloses a centre-positioned cone-shaped hillock with height of up to 3.5 nm depending on the implantation conditions. The morphology and dimensions of the craters and hillocks are studied as a function of the cluster size and implantation energy. A model explaining the hillock formation with relation to the thermal-transfer effect and local target melting at the collision spot is proposed.
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| 58. |
- Popok, Vladimir, 1966, et al.
(författare)
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Conductance and EPR study of the endohedral fullerene Li@C60
- 2005
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Ingår i: Solid State Communications. ; 133:8, s. 499-503
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Tidskriftsartikel (refereegranskat)abstract
- Thin films and bulk samples of endohedral fullerenes Li@C60 are studied using current-voltage (I-V) measurements and electron paramagnetic resonance (EPR). Electrical measurements show a linear behaviour for the I-V curves and give an average resistivity of ca. 1.5 kOhmcm for thin Li@C60 films deposited in vacuum, four orders of magnitude lower than C60 samples. A drastic effect on the conductance, lowering it to the values typical for C60, is observed when the Li@C60 samples are exposed to ambient atmosphere. No additional paramagnetic centres (PCs) are found for the Li@C60 compared to C60 that can be related to the formation of dimers or trimers of the endohedral fullerene molecules. However, the presence of the Li atoms in the fullerene cages contributes to a change of the spin-spin and spin-lattice relaxation times. The spin-lattice relaxation time becomes 4 orders of magnitude longer compared to the spin-spin relaxation time.
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| 59. |
- Popok, Vladimir, 1966, et al.
(författare)
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Conductance and polarisability of C60 films
- 2007
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Ingår i: Journal of Nanoscience and Nanotechnology. ; 7:4-5, s. 1434-1438
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of C60 deposited in vacuum are studied using current-voltage (I-V) measurements and atomic force microscopy (AFM). In situ electrical measurements give an average resistivity of ca. 30 MΩcm for the as-deposited films at room temperature. The I-V dependences are found to correspond to ohmic behaviour but they have a hysteresis shape attributed to remnant polarisation due to the domain structure of the films. AFM images show a grainy surface morphology for the deposited C60. Temperature dependent measurements in the range 290-365 K provide evidence for a variable range hopping mechanism of conductance with an activation energy of 0.8-1.0 eV. With further temperature increase the C60 films restructure leading to an increase in grain size and a change of the electrical properties with I-V dependences showing Schottky barrier formation. The effect of oxygen on the conductance of the C60 films under their exposure to an ambient atmosphere is considered and discussed.
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| 60. |
- Popok, Vladimir, 1966, et al.
(författare)
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Electronic Properties of thin films sublimed from La@C82 and Li@C60
- 2008
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Ingår i: Nano. ; 3:3, s. 155-160
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Tidskriftsartikel (refereegranskat)abstract
- La@C82 and Li@C60 thin films obtained by sublimation in vacuum are studied using four-probe current-voltage measurements and atomic force microscopy. In situ electrical measurements show semiconducting behavior of both films with room-temperature resistivity of 21+-8 and 1230+-50 Ohm.cm for the La@C82 and Li@C60, respectively. A variable range hopping mechanism of conductance is suggested from the temperature dependences of resistance. The activation energies for electron transport are calculated for both metallofullerenes. Irreversible changes to the Li@C60 film structure increasing the film resistivity to values typical for C60 are found at elevated temperatures. The effect of exposure to ambient atmosphere on the conductance of the films is discussed.
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