| 1. |
- Asanou, I. P., et al.
(författare)
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Graphene nanochains and nanoislands in the layers of room-temperature fluorinated graphite
- 2013
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 59, s. 518-529
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Tidskriftsartikel (refereegranskat)abstract
- Intercalated compound of graphite fluoride with n-heptane has been synthesized at room temperature using a multi-stage process including fluorination by a gaseous BrF3 and a set of intercalant exchange reactions. It was found that composition of the compound is CF0.40(C7H16)(0.04) and the guest molecules interact with the graphite fluoride layers through the van der Waals forces. Since the distance between the filled layers is 1.04 nm and the unfilled layers are separated by similar to 0.60 nm, the obtained compound can be considered as a stack of the fluorinated graphenes. These fluorinated graphenes are large in area making it possible to study local destruction of the a conjugated system on the basal plane. It was shown that fluorine atoms form short chains, while non-fluorinated sp(2) carbon atoms are organized in very narrow ribbons and aromatic areas with a size smaller than 3 nm. These pi electron nanochains and nanoislands preserved after the fluorination process are likely responsible for the value of the energy gap of the compound of similar to 2.5 eV. Variation in the size and the shape of pi electron regions within the fluorinated graphene layers could be a way for tuning the electronic and optical characteristics of the graphene-based materials.
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| 2. |
- Kvyatkovskii, Oleg E, et al.
(författare)
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Magnetic properties of polymerized fullerene doped with hydrogen, fluorine and oxygen
- 2006
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Ingår i: Fullerenes, nanotubes, and carbon nanostructures. - Philadelphia : Taylor & Francis. - 1536-383X .- 1536-4046. ; 14:2-3, s. 385-389
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Tidskriftsartikel (refereegranskat)abstract
- We have presented recently a mechanism of ferromagnetism in polymeric fullerene phases based on spin and charge transfer from nonmagnetic donor or acceptor centers into fullerene molecules. In this work, the interaction between magnetic moments of the paramagnetic C60R radical adducts (R = H, F, OH) dispersed in the 2D polymeric network is examined by using UB3LYP hybrid density functional method at 3-21G level. The results show that the interaction is ferromagnetic, strong and long-range.
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| 3. |
- Makarova, Tatiana. L., 1959-, et al.
(författare)
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Anisotropic magnetism of graphite irradiated with medium-energy hydrogen and helium ions
- 2011
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Ingår i: Physical Review B Condensed Matter. - : APS Physics. - 0163-1829 .- 1095-3795. ; 83:8, s. 085417-8 pages
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the changes in the magnetic behavior of highly oriented pyrolytic graphite (HOPG) samples subjected to medium-energy proton and helium irradiation. The variations of the ferromagneticlike magnetization curves with the irradiation dose have been studied for two configurations: magnetic fields parallel and perpendicular to graphitic planes. For high irradiation doses, the values of magnetization at saturation are close for both geometries. At low irradiation fluences an orientationally dependent magnetic response is obtained. Directional dependence of magnetization indicates that the magnetism in irradiated graphite is triggered by vertically aligned intrinsic carbon defects induced by irradiation. This physical picture has been verified by the observation of a local stray field near linear defects by means of magnetic force microscopy. Similar results obtained with hydrogen and helium ions confirm that the chemical nature of projectiles is not crucial for formation of ferromagnetic order in oriented graphite. The dependence of induced magnetic moment versus irradiation dose shows a maximum; the optimal dose is an order of magnitude less for helium ions than for protons, being in line with simulations showing that He+ generates 8 times more defects than H+. Raman studies indicate that the degradation of magnetic ordering at large irradiation doses occurs much earlier than graphite amorphization but coincides with the destruction of graphene sheet stacking.
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| 4. |
- Makarova, Tatiana L, et al.
(författare)
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Anisotropic metallic properties of highly-oriented rhombohedral C60 polymer.
- 2001
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Ingår i: Synthetic Metals vol. 121. - Amsterdam : Elsevier B.V.. ; , s. 1099-1100
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Konferensbidrag (refereegranskat)abstract
- The pure rhombohedral phase of C60 polymer displays highly anisotropic electrical properties. Conductivity in the polymerized (001) planes exhibits a metal-insulator transition and shows the features of 2D weak localization. Anisotropy ratio is temperature-dependent and reaches 10_6. Dysonian ESR lineshape is consistent with the metallic nature of the samples.
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| 5. |
- Makarova, Tatiana L, et al.
(författare)
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Conductivity of two-dimensional C60 polymers
- 2000
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Ingår i: Proceedings of the 4th International Workshop on Fullerenes and Atomic Clusters (IWFAC'99), St. Petersburg 1999. - : Overseas Publishers Association N.V.. ; , s. 151-156
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Konferensbidrag (refereegranskat)abstract
- The general trend in the shift of electronic properties as the result of polymerization has been studied with the aid of temperature dependences of conductivity. Samples representing the pure rhombohedral phase exhibit great anisotropy in their electrical properties. The main features of the behaviour of these samples are: (i) in the z-direction the resistivity is of the order of several kOhm cm and decreases with temperature; (ii) in the x-y direction resistivity is less than 1 Ohm cm and shows a minimum at a certain temperature.
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| 6. |
- Makarova, Tatiana L, et al.
(författare)
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Electrical properties of the rhombohedral C60 polymers
- 1999
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Ingår i: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, vol. 7. - Pennington, NJ : The Electrochemical Society. - 1566772346 ; , s. 628-639
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Konferensbidrag (refereegranskat)abstract
- Electrical properties of polymerized fullerenes C60 are governed by the type of polymerization which is in turn determined by the initial (P or H) orientation of molecules, the pressure and the temperature of polymerization. The mixed tetragonal - rhombohedral polymerized structure shows a semiconductor-like behavior. An increase in the polymerization temperature results in a decrease in the activation energy and an increase in conductivity. The conductivity prefactor and the activation energy are interconnected by the Meyer-Neldel rule. The pure rhombohedral phase shows highly anisotropic electrical properties. The conductivity in the polymerized (111) planes exhibits a metal-insulator transition and shows the features of 2D weak localization.
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| 7. |
- Makarova, Tatiana L, et al.
(författare)
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Electrical properties of two-dimensional fullerene matrices
- 2001
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Ingår i: Carbon. - : Elsevier B.V.. - 0008-6223 .- 1873-3891. ; 39:14, s. 2203-2209
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Tidskriftsartikel (refereegranskat)abstract
- The electrical properties of two-dimensionally polymerized C60 fullerenes were studied. Fullerene matrices consisting of randomly oriented domains are compared to the highly-oriented rhombohedral phase. The conductivity of the randomly oriented polymers obeys the Arrhenius law and can be described in a multiple trapping model. The oriented phase of polymeric C60 shows a distinct anisotropy in the electrical properties with a metallic-like in-plane conductivity at high temperatures.
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| 8. |
- Makarova, Tatiana L., et al.
(författare)
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Experimental realization of high spin states in dilutely hydrogenated fullerenes
- 2009
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Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 246:11-12, s. 2778-2781
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Tidskriftsartikel (refereegranskat)abstract
- A novel method for preparing dilutely hydrogenated fullerenes H:C60 is presented. DFT calculations of the Raman spectra at the B3LYP/3-21G level are compared with the experimental data. Under the laser treatment these phases form a rich variety of dimeric and polymeric structures, quite in contrast to pristine C60 which forms dimers and polymers bonded through the [2 + 2] addition, and in contrast to heavily hydrogenated fullerenes which do not polymerize at all. Dilutely hydrogenated fullerenes polymerize differently, forming both double bonded structures and single bonded dimers. We have shown that dilute hydrogenation of C60 creates large amount of unpaired spins which disappear due to the formation of diamagnetic single bonded dimers.
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| 9. |
- Makarova, Tatiana L., 1959-, et al.
(författare)
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Induced Ferromagnetism in Helium-Bombarded Graphite
- 2012
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 12:6, s. 5051-5053
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Tidskriftsartikel (refereegranskat)abstract
- Irradiation with helium ions is an effective method for triggering ferromagnetism in graphite. Chemical inertness of helium suggests that local magnetic moment formation is determined solely by the intrinsic carbon defects created during the target damage. Interacting moments are located in two places: in the vicinity of the sample surface and near the point of maximum defect generation.
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| 10. |
- Makarova, Tatiana L., 1959-, et al.
(författare)
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Laser controlled magnetism in hydrogenated fullerene films
- 2011
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Ingår i: Journal of Applied Physics. - : AIP. - 0021-8979 .- 1089-7550. ; 109:8, s. 083941-7
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Tidskriftsartikel (refereegranskat)abstract
- Room temperature ferromagnetic-like behavior in fullerene photopolymerized films treated with monatomic hydrogen is reported. The hydrogen treatment controllably varies the paramagnetic spin concentration and laser induced polymerization transforms the paramagnetic phase to a ferromagnetic-like one. Excess laser irradiation destroys magnetic ordering, presumably due to structural changes, which was continuously monitored by Raman spectroscopy. We suggest an interpretation of the data based on first-principles density-functional spin-unrestricted calculations which show that the excess spin from mono-atomic hydrogen is delocalized within the host fullerene and the laser-induced polymerization promotes spin exchange interaction and spin alignment in the polymerized phase.
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